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M52TU Turbo Swapped MX5 (No that's not a joke or a typo)
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Discussion Starter · #1 · (Edited by Moderator)
So I thought I'd start a Project thread before I started tearing the car apart again for the next project.

Back in February, I bought this Golden Nugget MX5 and had started buying turbo parts before I'd even bought the car because going from a 300HP WRX to a 140hp MX5 just wasn't going to cut it.

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It came with some questionable stickers, coilovers and choice of alloys but it was cheap. It did also come with stripes along the bonnet but I removed those before I took this picture (Still haven't removed the rest). So I jumped on the internet and got to ordering parts but I wanted to do this on a tight budget and do it for less than £2k as I already have another long running project car that is burning money and this was a temporary setup so didn't want to throw too much money at it.

I work as a welder/fabricator so figured I'd make my own manifold, downpipe and exhaust as I've done with most of my cars as without including labour it keeps the cost way down. Now the manifold for this car was a bit of an inside joke between my friend and I where we joked about Subaru swapping my original mx5 (which incidentally someone in the states actually did this). Instead we thought it would be funny to try and get some Subaru farty burble on an I4 so I spent some time in Fusion and designed a manifold that would just about fit in an MX5 but had runners with really unequal lengths and we came up with this piece of madness with exhuast runners 2 & 4 being double the length of runners 1 & 3.

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I didn't exactly build this to make insane power as the limits of the BP8 engine internals are well documented and I wasn't in the mode to go through another engine build so any loss/limitations due to the inefficient manifold design is not a problem. Next up was an exhaust and as with my previous mx5 I wanted to do full 3 inch all way from the turbo and as I was on a tight budget that meant no mandrel bends, so enter 3 inch pie cuts lots and lots of them.

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Unfortunately I never actually took pictures of the completed exhaust but It looked awesome, and I even threw in a cat to keep the MOT man happy. After that everything was pretty straight forward, I sourced a "New old stock" ME221 for a bargain price, got some reconditioned RX8 Yellow injectors, Intercooler, piping and fittings for a turbo. Now for the turbo, previously on my last 5 I bought a used Subaru WRX turbo and rebuilt it but I couldn't find any decent stock this time round so opted for the finest ebay China spec turbo (which is about the same price as a genuine TD04 that needs a rebuild).

Next up I threw in a wideband, boost gauge and a few other bits and got the thing running, unfortunately I didn't have access to a dyno (especially as this was in the middle of Lockdown 1.0) so I opted for some street tuning and got the fuel and ignition timing dialled in to where I was happy with it. I started to crank the boost up from 7 pounds and left it at about 12 pounds with a conservative tune. so the turbo install ended up looking like this. Looks a bit messy but it all works and that's all I need for now

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I have skipped some things that I would normally absolutely do on a turbo conversion but as I knew this was only a temporary setup I couldn't justify the money. As such, I'm still running a stock radiator and single fan, stock clutch and no re-circ or dump valve for the turbo. So far its been reliable and not had any issues except coolant temps when drifting, doing burnouts or doing doughnuts.

So all in all the turbo install came to a total of £1734 which I'm quite happy with and this included the following:

Ebay TD04 Turbo

Custom Manifold

Custom 3 inch stainless downpipe

Custom 3 inch stainless exhaust

Reconditioned Rx8 Yellow Injectors

Generic Intercooler

Intercooler Piping

AEM Wideband

Turbo Smart Boost Gauge

ME221 ECU

Air Filter

Turbo Fittings and Hoses

Spark plugs

Poly Engine Mounts

And a few other parts required for a turbo install.

After the turbo project I also pulled the ABS out as the sensors are knacked, one snapped off in the hub and both front sensor bolts sheared off in the hubs. Replaced the lot with Full Braided stainless lines and an adjustable rear bias valve. Also painted the wheels black and swapped the shredded budget tires for a set of TOYO TR1's as they are certainly better than the bald tires I pulled off. I also threw together a rollbar from some ROPT510 I had left over from a roll cage we built, so that I could throw in a bucket seat and use harnesses.

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Now if you wondering what the Exhaust sounds like then its a little like this (Ignore the terrible cutting around the exhaust, its since has a tidy bumper cut): https://video.wixstatic.com/video/07fb17_6a77ed4924994171b1886fdeb535eded/1080p/mp4/file.mp4

Starting In February the car will be back in the workshop to pull the whole driveline out for a new bigger and better setup (Better might be debatable amongst some), If all goes well the first phase of that should be done by the end of march so stay posted.
 

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M52TU Turbo Swapped MX5 (No that's not a joke or a typo)
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Discussion Starter · #2 · (Edited by Moderator)
GOOD NEWS EVERYONE... I figured its time for an update. So pretty soon after buying the car I'd planned to do something with it and eventually decided to engine swap it and I knew exactly what engine was going in as I'd looked into it before when I had my original MX5. So for starters I pulled the turbo 1.8 out of the car and sold it to a lovely chap who'd just blown his stock 1.8 up. When I purchased the car last year I'd seen that the front chassis legs had had some welding done on them, it looked shit but I assumed that it was solid... Boy was I wrong.

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So that was just the rust that broke apart once I started jabbing it with a crowbar, effectively all that the previous owners had done is weld (if you can call it that) some steel plates over the top of the rust and then paint over the top of it all. It had been noted in the most recent MOT that there was "Minor Corrosion" but it was definitely more than minor! So I took some rough measurements and worked out how big of a patch I needed, then jumped into Fusion 360, draw them out and fired up the cnc plasma to cut them out. I also designed and cut some internal reinforcements to sit inside the chassis leg where the anti roll bar mounts are. The end result looked something like this

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All of that probably took about a week of evenings to get done but I wanted to get it sorted now whilst I had easy access to everything and before the new engine went in. So onto the rest of the project, The plan is to swap in a BMW M52TU straight 6 along with the BMW gearbox and BMW Diff and then slap a turbo on the side of it. I know that a couple of people have managed to get the engine in and get it running but beyond that the details are all a bit murky. As such I thought I'd give it a crack. I got hold of a M52TUB25 (2.5L i6) along with the accompanying Getrag 5 Speed from a guy who was breaking one for about £270 delivered. Then I started putting together a plan and started gathering parts, I got hold of a e36 Diff with the ratios that I wanted, as well as a donor prop shaft and a donor BMW axle so that I can make a mock up axle to send off to manufactured. I also started learning the ins and outs of reflashing BMW ECU's so that I could run the standard ECU even with the turbo.

Now originally I had planned on initially running the engine for a while without a turbo but decided that I couldn't be bothered to pull it all back out at a later date to change the head gasket. Instead I decided to do the upgrades now and just go straight into Turbo charging it. So the bottom end on these engines is good for 600hp+ however as they are high compression you'll blow the head gasket long before you get there. The easiest and what seems like the most common fix amongst BMW guys is to install a decompression plate, this is essentially a 2.5mm stainless steel plate that replaces the middle layer of an MLS. Along with the decompression plate I also installed ARP head bolts... or at least tried to.

So these engines are notorious for the threads stripping out of the block when torqueing the head bolts and when I did the 3rd and final pass with the torque wrench 2 of the threads stripped. As I said this is a fairly common issue when reinstalling the heads on these engines and there are a couple of solutions. Option 1 is get the block and head machined to take a larger head stud, but as I'd already thrown down nearly £300 on ARP head bolts I reluctant to buy another set along with the machining costs. So I decided to go with option 2, which is to drill and time-sert the broken threads, this still ending up costing the best part of £500 to buy the time-serts and the installation tools. (So if anybody has a BMW with stripped threads in the block feel free to hit me up :lol: ) So I got the engine all back together with the new gasket set and ARP head studs.

Next up was sorting out a turbo, So I jumped on the internet and did some research to find the best turbo match to get the power and responsiveness that I'm after and settled on a GT3071R. Now this isn't some money no object project where I can throw down £2000 on a turbo so I decided id go for a cheap Chinese turbo to begin with as it had worked well for me so far and see what happens. Well I ended up getting a GT3071R "Racing Turbo" from Maxpeedingrods as they have stainless V-band exhaust housings and for less than £400 I cant complain. Then I looked into a wastegate to go with it and decided that on this cheaping out was just not worth it as I've never met a single persons that had a good experience with cheap wastegates so I order a GFB EX44 wastegate.

I also order a bunch of other crap as well; e46 Alloy Radiator, Intercooler, Poly gearbox bushings, engine mounts bushings, Chassis mount gear assembly and a load of other stuff that I cant be bothered to mention.

Anyway I've actually been working on this for a little while and getting the engine in was surprisingly easy, however getting it to sit exactly where it should was a tad more tricky. I started by trimming the back corner section that joins the chassis leg to the firewall, I had to cut that out entirely on the drivers side. Next up was the subframe, I needed to trim a fair amount of it out and due to the 30 degree lean of the engine more of the subframe has to be removed from the passenger side than the drivers side. I welded it all back to together so that it has some structural rigidity then started work on engine mounts. So this was the first attempt at sitting it on its mounts, however here the engine is sat about 30mm to far back and about 20mm to high in the engine bay.

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after that I tweaked the mounts slightly and got it far enough forward however dropping the engine 20mm is where things got tricky as at this point there was only about 5mm Clearance between the oil ban and the steering rack. So after some investigation and help from a fellow nutzer I came up with a plan. I initially cut out some 10mm spacers to drop the whole front subframe slightly and then later modified the subframe mounting points so that it sat 10mm lower. I ended up having to modify the subframe instead of using spacers as the studs just aren't long enough and its an absolute pig to change them. I also remade the engine mounts so that the engine sat about 10mm lower in the subframe and then moved the steering rack down by 5mm I had to sacrifice power steering as well but that doesn't really bother me that much. I really didn't want to have to move the rack but I had no choice if I wanted to get the engine in at the right height, we'll see how bad the bump steer is later I guess, although I may see if there is something I can do to address that at some point.

so after the engine was mounted where it needed to be, the next job was to get the gearbox mounted. I don't currently own a gearbox jack so I called in some muscle to help me fit the gearbox and got it bolted to the engine. Once again I took some measurements jumped into fusion 360 and designed a new gearbox crossmember then fired up the cnc plasma to cut it out. The crossmember bolts into the tunnel with 8 bolts and has reinforcement plates that site inside the car under the carpet. A few hours later I had this

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After the engine was in properly it became clear that that standard MX5 anti roll bar just isn't going to fit, so I did some research and took a punt on an e36 anti roll bar as the overall width and mounting point width are close enough that it should work. An MX5 ARB as about 1035mm wide but the drop links mount on the inside, the e36 roll bar is about 980mm wide but the droplinks mount on the outside so the droplinks land in virtually the same place and its the right shape to fit around the engine. So once again I took some measurements and made some new ARB mounts and some spacer blocks to set the bar at the right height.

Next up I wanted to get the turbo fitted as there isn't really a lot of room in the engine bay. Now most BMW guys top mount there turbos but in an MX5 there just isn't room to top mount the turbo if you want a bonnet on the car, my only option is to low mount the turbo so I want to do it early to make sure there is room. Originally I wanted to do some sort of tubular manifold but there just isn't enough room to do anything meaningful or worthwhile so I decided my best bet was to create a simple log manifold. So I made the manifold out of some 44mm ID (48mm OD) 304 stainless pipe with 2mm wall thickness, once I had the front section tacked together I decided to test fit it to make sure it would fit and see if I have enough height underneath to do a passive oil drain. The turbo fits but the jurys still out on whether I'll need to run a scavenge pump on the turbo oil drain.

and here it is after the manifold was all welded up

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Well that's pretty much up to date for the moment, I think the next task on my list this week is to make a new core support and get the intercooler, radiator and fans fitted. Once there in that should be everything major to go in the front end. So its onto the Diff, prop and axles after that.
 

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M52TU Turbo Swapped MX5 (No that's not a joke or a typo)
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Discussion Starter · #4 ·
So just a mini update as I had some time after work yesterday to spend some time working on the car. My GFB EX44 wastegate arrived so I started off by working out how I was going to fit that, Initially I was hoping that I keep it down below the chassis leg but there just wasn't enough room. I coped and trimmed a 90 degree bend to fit nicely into the hole I'd previously cut in the manifold and tack welded everything in place. and then test fitted the wastegate.

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The wastegate currently sits a bit higher then I would have liked but I was a tad concerned about its proximity the the plastic valve cover, I may yet trim it down slightly but other than that it all looks good. I've still got plenty of room to snake the wastegate pipe down and back into the downpipe. I will probably end up making the wastegate pipe removable and join into the downpipe via a Vband otherwise it'll be nearly impossible to get the downpipe in and out.

I also started work on the core support, I decided to entirely remove the standard core support to give me more room for the rad and intercooler and replace it with some 20mm steel tube. I need to weld some brackets to it for the headlights and bonnet pins and I need to fabricate some brackets for the radiator when I get chance to grab it out of my storage lock up and start test fitting it. I also wanted to retain the 2 L brackets that link the core support to the crash bar on the front so need to cut some steel plates to tie those back in as well. Originally I had planned on making the core support removable to make it easier to get the engine in and out but as the front crash bar is not removable I didn't see any point as it doesn't really give any additional clearance so I TIG welded it into the car and TIG welded the cut ends of the core support back together. If I have room once the radiator is in I'll add some gussets to tidy it all up.

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Hopefully I'll get some more time this evening to do some more work on the car.
 

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Discussion Starter · #5 ·
I spent some more time in the workshop over the past few days working on the car. I had previously taken the gearbox out the last time the engine was out and hadn't put it back in so first up we threw it back in the car and and then welded the captive nuts to the gearbox cross member. Whilst the car was in the air and I was working on the gearbox I figured id also sort out the gear linkage. At some point I might CNC a custom one from some aluminium but for now I just modified the OEM linkage. so cut, extended and then sleeved the linkage, the steel I used for the sleeve is definitely a bit overkill but it was what I found in the offcut bin and the ID was the perfect fit. Also the chassis mount short shifter I have is crazy short so we'll see that goes once the car is running. I may also need to change some of the shifter bushing things (can't remember what they are called but standard BMW thing on these gearboxes) in the gearbox as there is a little too much slop when its in gear for my liking.

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After that I wanted to crack on with the front end so started by making the bosses to weld onto the new core support that hold the upper front bumper mounts and the headlights. Then it was onto getting the intercooler and radiator in. The intercooler was fairly straight forward as the upper mounting bosses sit just below the level of the core support however its size did make fitting it a bit tricky. I went with a 600x330mm intercooler core as that is what most of the BMW guys run on this engine and turbo combo.

The radiator, being a BMW e46 radiator required some modification to mount, firstly I removed all of the funky BMW mounting brackets as I have no idea how the hell they work (they are just a bunch of angled tabs, so I'm guessing its supped to slide into some kind of receiver on the chassis). Next up I welded some aluminium pins onto the bottom so that I can mount the radiator in a more traditional way and then made some brackets with grommets to hold the bottom of the rad.

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I didn't get round to making the top mounting brackets as I'm not entirely happy with the height of it yet. I plan on Modifying or remaking the lower brackets so the rad sits about 15-20 mm lower so that I have room for some decent bracket at the top. I also test fitted the new radiator fans and there is just about enough room for everything. I originally wanted to use standard BMW hoses for the radiator but they aren't going to work so I'm gonna modify the inlet/outlet of the rad and see what I can squeeze in.

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There is about 40mm between the crank nose and the radiator and about 70mm between the front of the turbo and the radiator. So as long as I position the fans strategically and use a low profile filter it will all fit... Just!. After that I decided to jump into something else and start work on the downpipe. It might seem that I'm kind of jumping back and forth all over the place and to some extent I am, but I'm trying to work out some of the tricky nd slightly concerning bits first. The downpipe is fairly straight forward in terms of routing, It comes out the back of the turbo and then twists up and in slightly to clear the engine mount and steering shaft then back and out around the bell housing. That is where it starts to get a bit tricky, there is so little room around the gearbox as the exhaust is on the wrong side. So I wanted to work out the routing now in case I need to change anything.

So I fired up the bandsaw and started pie cutting. The downpipe will be all 304 stainless and will be fully pie cut (no mandrel bends here).

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That's pretty much it for now, hopefully I'll be able to crack on with the downpipe this week after work.
 

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M52TU Turbo Swapped MX5 (No that's not a joke or a typo)
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Discussion Starter · #6 ·
I had time after work yesterday to do a little more on the downpipe but nothing major so didn't take any new pictures. However whilst I had the car on the lift I took some measurements so that I can find and order an air filter that will fit and it suddenly occurred to me that I won't be able to run a draw through MAF If I whack the filter directly on the turbo; But as I have no choice but to mount the filter that way I'll need to find another solution for the MAF.

Now I initially thought there are a couple of options, I could obviously try and run the MAF in a blow through setup and stick it after the turbo but I'm not about to spend hours of my life trying to work out the perfect position for the MAF to get accurate readings, build all the piping to suite and remake the piping again later when I ditch the MAF. So as far as I'm concerned that's a no go option. I know the MS42 ECU's for this engine support running in Alpha/N but that ceases to be the case if you slap a turbo on the engine as the ECU can no longer estimate the air volume; so that's also out.

So it looks like I'm going to have to run an aftermarket ECU straight away instead of using the standard ECU. Oh well needs must. I spent some time today having a look at ECU options and decided that initially I'm going to run a Speeduino based CORE4 ECU as DIY-EFI now offer one for a BMW M52TU/M54 engine and just like the MX5 version it bolts into the case of a standard ECU. If it works out ok I may stick with it, if it doesn't there are a couple of other options I'd looked at that would work (although considerably more expensive).

I'm a little a way away from wiring or getting the engine running so don't really need the ECU yet, but will probably order it at the end of the month.
 

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Discussion Starter · #7 ·
I was able to spend a few hours after work working on the car again so I wanted to focus on the downpipe. Initially everything was going well and until I realised that it was impossible to get the downpipe on and off without first dropping the turbo (which is a pain in the butt). At this point I stopped and had a look and decided that I was making things way to complicated; My initial design had curves in both plains as I was trying to get some more clearance around the steering shaft. In reality it didn't give me any extra clearance and it made the downpipe an absolute pain.

So I decided to cut the downpipe at the point where it kicks up in order to get over the engine mount and continued from there. After some trial and error I ended up with this:

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After that I threw it back into the car and then added a tap to brace it to the bellhousing.

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for some reason when I ordered the steel for this I ended up with brushed stainless instead of polished, it doesn't really make any difference it just bugs me slightly that the first part of the downpipe is polished as I was using some leftover from another job and the rest is all brushed. Once its all wrapped in heat wrap no one will even see it.

I got as far as I could for today as I didn't have any 3 inch flex joints left on the shelf so had to order some more which should hopefully be in later this week. I also ordered all of the stuff to make the waste gate pipe so once thats in I'll get that mocked up as well.
 

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Discussion Starter · #8 ·
Well I'm still waiting on some parts to arrive to continue on with the exhaust so I decided it start mounting the diff but to do that I need to get the axles out. I'd tried whacking the axles out have a BFH when we took the old diff out and got nowhere so after some advice from another nutzer I decided I'd start by making some sort of hub puller style thing to push the axle out. I threw some 10mm steel plate on the CNC plasms and then made this

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Well I bolted it onto the hub and started cranking the bolt down with a breaker bar and a piece of scaffold pole but it eventually just started to bend the bolt. So I conceded that I'd have to chuck it in the press and press it out. I knew this also gonna be a pain as the lower control arm bolt in the hub had seized. So I unbolted the caliper, the coilover and then dropped the hub and lower control arm in one piece, and then it started going south. So I undid the nut that holds the LCA to hub but as it could toward the end of the thread at stripped all the threads off the end of the bolt. I continued on regardless and used the press to get it out, once it had popped it was easy enough to get it out with the impact. This is the state of the bolt

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so now I need to order a new LCA Bolt. I cut the axle in half with a grinder to make it easier to get onto the press and then set it all up with some extra steel plates to level things out.

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well I maxed out the press and applied nearly 20 tonnes of pressure and the damn axle didn't move at all. God knows what's holding that thing in but it definitely isn't coming out. So looks like I'm going to be buying a pair of replacement rear hubs as well.

Hopefully tomorrow will be more productive.
 

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Discussion Starter · #10 ·
So I gave up on getting the axles out of the hubs, I tried putting them in a press, smacking them with a big F**king hammer and tried using a massive hammer drill to get them out but nothing worked... So I gave up and bought some replacements along with replacement lower arm bolts.

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this lot came to about £115 and considering I've probably more time than that trying to get one axle out its money well spent as far as I'm concerned. I removed the dust shields from these hubs as they were slightly worse for wear and I would have had to trim them at some point to fit bigger disks when I get round to upgrading the brakes. So I threw this lot on the car and then started trying to get the propshaft mounted. The BMW propshaft is a 2 piece propshaft so I needed to make something to hold the center bearing. I bolted the prop to the gearbox, took a bunch of measurement and threw together a mount; I ended up having to mount the prop bearing at a slight angle as there just isnt enough room in the tunnel for its full width.

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up until this point I was hoping I'd luck out and the prop would just fit but unfortunately its too long so I'll need to send it off to be modified. After the centre bearing carrier was done I was initially a bit stumped on how I was gonna mount the diff without a prop that's the right length but I couldn't shorten the prop without knowing exactly where the diff sits. After some head scratching I came up with a solution and whipped up a jig.

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So the Jig mounts onto the centre bearing carrier and aligns with the output of the gearbox to set the correct position for the front flange of the diff. I don't have a gearbox jack at present so I settled for throwing the diff on a stack on toolbox's with blocks of wood to get it in position. I used a digital level to get the correct propshaft angle and then bolted the jig to the diff to hold it in position. After that I started making brackets to hold the back of the diff into the subframe which was actually pretty straight forward.

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I only tack welded the the mounts in for now as I'll need to drop the whole subframe out to properly weld them. So after that I started working on the front mount for the diff which is slightly trickier as I wanted the front mount to bolt into the subframe so that I didn't have to take the whole subframe out out to press the bushing in. After more head scratching, some grinding, plasma cutting and a lot of welding I came up with this

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So the bottom of the diff sits slightly lower than I would of liked but its a pretty big diff and its position was partly dictated but the correct propshaft angle. The bottom of the diff sits at the same height as the lower subframe brace so its still an acceptable height but between the size of the diff, the location and the mounting ears on the diff, sneaking a 3 inch exhaust around it is gonna be a massive pain.

So that pretty much it for progress for the moment, I did do a bunch of test fitting of various things and I came to the conclusion that I've got no option but to run a scavenge pump on the turbo. Either the line would have to run virtually flat the entire way to get to the rear part of the sump or it'd have to be really short to the point of being nearly impossible to get on and off. It wasn't an unexpected discovery but it is an expense I was hoping to avoid.

Hopefully this week I can crack on getting everything in the front end together.
 

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Discussion Starter · #11 ·
OK so here's an update for last couple of evenings work.

I previously mentioned that the turbo sits too low to easily have a gravity drained oil return and that I'd conceded to using a scavenge pump. Well I spent some time doing some research and decided that was a terrible idea; it seems that most peoples experience with scavenge pumps is lots of leaks and pump failures and the consensus is that if you're gonna run one run a turbo werx pump. Awesome problem solved I'll run one of those... or so I thought. turns out they are not currently available in the UK and importing one from the states is getting on for £600-£700. Not a chance.

So I decided I'd have another crack at sorting a gravity drain return to the sump. I threw together an -AN10 return line and mocked it up to work out where I'd need to feed it back into the sump and this is pretty much it:

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So after researching a fair amount most turbo manufacturers allow a turbo to be clocked as far as 15 degrees from vertical (which incidentally according to garret, if you feed cold water on the low side and take hot from the high side it actually reduces temps slightly) and the return line should be no less than 30 degrees from horizontal for "extended lengths". I've got the turbo clocked somewhere between 5-10 degrees and the drain angle is slightly less than 30 degrees but as its so short it hopefully wont cause to much of an issue. when I next pull the engine out I'll modify the oil pan for the oil return fitting.

with that out of the way I wanted to tie up loose ends. To get the intercooler in I had to trip the very front corners of the chassis legs and I hadn't welded a cover plate over then yet; so I took some rough measurements and made these plates

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I cleaned of any surrounding paint and then welded them in place.

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The trimming of these corner sections does mean that I wont be able to use the OEM tow hooks on the front but seeing as how they went in the bin a long time ago I don't have a problem with that. I've always just run either a custom tow hook or an FIA compliant/approved tow strap.

with that out of the way I started work on the second iteration of the lower rad mount and ended up with this. I only made one brace as I wanted to do a proper test fit and clearance check first.

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Well I'm happy with the new rad height but that's about it. I evidently got some measurements wrong and wasted about 10mm between the intercooler and the rad, it doesn't sound like a lot but its the difference between the fans comfortably clearing the crank pulley and them being about 3mm away. Also the front brace that joins the lower bracket to the crash bar is a complete fail, not only is that also slightly too long and pushes the rad in another 5-10mm but it also interferes with the front bumper. So this evening I'll be working on version 3 of the radiator mounts and I've decided to do it completely differently to ensure that everything is exactly where it should be.

Stay tuned
 

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M52TU Turbo Swapped MX5 (No that's not a joke or a typo)
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Discussion Starter · #12 ·
OK I've been wrestling with radiator mounting and the lower rad support pretty much every evening this week and I'm still not done with it but I thought I'd throw up a mini update. I have managed to get the radiator mounted where I'm happy with it. I mentioned previously that version 2 of the rad mount left too much space between the intercooler and radiator, well after fitting the filter on the turbo, the lower rad outlet was hitting the turbo/filter. So for version 3 of the mount I did things slightly differently and ended up mounting the rad off centre to get all of the clearances required.

After It was in position (partly held there by cable ties) I wanted to work out a plan for the radiator hoses as BMW use an O-ringed push lock connector for most water connections including the rad hoses. a quick measure immediately pointed out that I'd need to trim the top rad hose by about 15-20mm so I carefully cut the metal crimp off the hose with a grinder and pulled the plastic hose end out. I roughly held the hose in place to identify where I needed to cut the hose, now normally I use a jubilee clip and a Stanley knife to cut hoses but my workshop is a bit of a mess and I couldn't find either so instead I cut it on our upright bandsaw. Now I can not stress enough how clean of a cut this gave! I am never going back to using a Stanley knife. :lol:

Anyway I threw the hose end back on and connected it back into the car. Next up was the lower hose which by some bonkers lucky coincidence just fit without any modification. When I say it fit, it really fit.

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The photos don't really show it but it is tight as heck and that lower hose perfectly clears the filter, turbo compressor housing and the chassis leg. In some parts there is probably only 4-5mm clearance but it should be enough. Hopefully I can get the radiator mounting all finished up over the weekend and get the fans installed to check clearances. After that I'll probably start on some plumping and get the fuel lines, turbo oil feed and turbo water lines sorted
 

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Discussion Starter · #13 ·
So I recently hit the first real hurdle in this project and as of yet I haven't settled upon a solution. When I first planned this project I knew that I'd need to sort something for rear axles and I had planned on having new shafts made up. But this is pretty expensive and I've had quotes from about £450 a pair up to £700 a pair. Its not outrageous but I also wanted to look into other options so I'd spent a lot of time looking through a CV joint suppliers catalogue and found an outer CV that should fit onto the BMW shaft and then slide nicely into the MX5 hub.

The hub in question was from a Mazda 626 mk3 and has the correct outer 26 spline, the correct 25 internal spline for the BMW shaft and the correct seal diameter. It did indeed fit perfectly into both the hub and onto the shaft but when I disassembled the BMW axle I realised something. BMW use an outer plunging cv joint and a fixed inner cv joint, Mazda use a fixed outer and a plunging inner joint. So what this gave me was a driveshaft with virtually no plunge whatsoever (or near enough, the inner BMW CV joint, does has some movement, I think its about 16mm) which is pretty useless. I also realised here that If I had have spent a bunch of money on custom axles I'd still be in the same position.

I spent a bunch more time trying to find a 100mm CV joint that has enough plunge and it appears that they just don't exist, GKN list one with +-20mm plunge but nobody actually sells the damn things.

As the BMW axle is virtually the exact length I need I had considered trying to use a BMW wheel hub on the rear, the only issue is that the MX5 hub shaft diameter is 40mm where as the BMW hub shaft is 42mm. Even though the hubs are induction hardened, in reality the material can still be turned using carbide lathe tools so I could turn it down to the correct diameter. The main issue with this solution is that I'd be stuck with a 5x120 stud pattern on the rear and that really, really limits my wheel selection (no one and I mean no one make a 15 inch 5x120 wheel) as It limits me to wheels with custom drilled PCD's. And then brakes could also be an issue on the rear as I'd need to find new disks that would work.

I have also considered using a different diff but trying to find a diff with a ratio of between 2.9 and 3.1 is proving to be tricky.

Well I'm gonna put the diff and axle issues on the back burner for the time being as I could always just throw an MX5 diff and axles back in to get it driving. The 4000RPM at 70MPH is gonna suck though.

To get over this rather annoying blow I opted for some retail therapy and bought fuel injectors ready to start work on the fuel system. I had originally spec'd out 630cc Siemans Deka injectors as they flow more than enough fuel and come highly recommended in the BMW community. However they were out of stock everywhere so I opted for an alternative and upgraded to the 875cc versions instead. These are direct plug and play for the M52tu engine and at about £300 for a set of 6 they are an absolute steal!.

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I'll probably get them in the rail and start work fitting the manifold to start working out the intercooler routing this weekend whilst I'm waiting for the rest of the plumping parts to arrive.
 

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Wow - you've got some skills. I presume youre a fabricator by trade? I like how you are happy to throw whatever time, money and imagination is necessary to overcome any problem that crops up on what, it must be said, is a pretty ambitious project. I must confess I initially thought this looked like a project that would ultimately fail, but I clearly underestimated you. Can't wait to see where this goes.

Well written and photographed too.

Anyway, back to it.
 

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Discussion Starter · #15 ·
Okay so first up, I yoinked the scabby old injectors out. Not actually sure what the flow rate of these is, but I figured I'd get them swapped early.

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Next up I threw the new injectors into the rail, attached all the lips and then pressed it into the manifold. Immediately I noticed that there is a good 10mm gap between where the rail bolts down and the rail itself. I pulled one of injectors back out and confirmed that the new injectors are longer by about 10mm. After some googling and checking a BMW specific supplier that sells them for these engines I confirmed that on the older M50/M52 engine they are a straight swap, on the newer M52TU/M54 engine you need a 10mm spacer. No biggy, I had some 16mm aluminium round sat around so chopped up 4 10mm spacers, bored a 6mm hole through them and found some new longer bolts to bolt it all together. Job done

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So time to throw it on the car. The manifold hasn't been back on the engine since I tore the engine down about 8 weeks ago to change the head studs and gasket so I wasn't 100% sure it wouldn't foul on something in the engine bay but thankfully it didn't and there is plenty of room around it.

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That right there is Insta Finished! job done.

Joking aside, I don't have the right coupler to go on the throttle body and the couplers for the turbo and intercooler are still delayed so I'm probably gonna start on the wastegate and see about getting the downpipe finished up.

OK so yesterday after swapping the injectors I changed my mind and decided the driveshaft issue was a problem that I needed to fix sooner rather than later. As such I spent most of yesterday coming up with a solution, I've some more parts which should be in next week and hopefully if all goes well I can make a mock up axle and send of for new shafts to be made.

With that issue out of the way I decided to do something a little different to start off with and wanted to progress the bulk of the work on the core support. I decided to be a bit extra here a plasma cut the company logo into the core support.

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the holes either end are there so that you can easily get a socket onto the top intercooler bolts. After a lot of careful welding it came out like this:

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after a quick hit with the wire brush and a quick coat of red primer it ended up like this. The welding isn't the prettiest but trying to TIG weld 1.2mm sheet to 1.5mm wall thickness tube without anything warping is not a fun job.

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After that little detour I figured it was about time to actually crack on with the downpipe. I'd been putting this next bit off slightly as getting the exhaust around the gearbox crossmember was going to be a pain and I'd kind of accepted a while ago that the best solution was oval pipe. So I started by trimming the crossmember slightly to add some extra clearance and then using some dies in the press formed some oval pipe and some oval to round converter thingy's and then started welding. Unfortunately due to the lack of room down that side of the gearbox I couldn't fit the vband so the exhaust is effectively a single piece from the turbo to the back of the gearbox (just before it goes into the CAT). I haven't welded this piece onto the rest of the downpipe yet as I wanted to put in an exhaust hanger somewhere on the gearbox crossmember but here's the next bit:

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I am still waiting on some quotes for modifying the propshaft but hopefully in the next week or 2 I can get that sorted as well. Over the next few days though It'll probably be more exhaust work
 

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Discussion Starter · #16 ·
Wow - you've got some skills. I presume youre a fabricator by trade? I like how you are happy to throw whatever time, money and imagination is necessary to overcome any problem that crops up on what, it must be said, is a pretty ambitious project. I must confess I initially thought this looked like a project that would ultimately fail, but I clearly underestimated you. Can't wait to see where this goes.

Well written and photographed too.

Anyway, back to it.
Thanks

I am indeed, I work for myself so can be somewhat flexible with what time I spend on the car especially If It's a quiet day. To be honest there have been times where I've looked at it and thought "oh crap there is no way this is gonna fit, this was a bad idea" thankfully it's all been pretty smooth so far.
 

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Discussion Starter · #17 ·
As promised more exhaust work, It took several test fits and a few sections had to be modified before I was happy but the Downpipe/ front exhaust section is now in one piece and the cat is in position.

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Ignore the absolutely terrible harness bolt plates, they are another thing on my list of things to fix at some point and they cable ties on the exhaust are just to help support the sections whilst I build it.

So the exhaust is pretty straight forward from here on, although I need to wait until I have the axles in before I can commit to the routing around the diff. I'll probably tac everything up until just before the diff and then switch back to doing the wastegate.

I've also ordered all of the fuel system parts and all of the hose and fittings to finish plumbing the turbo so I can get the all tied up this week as well.

Its slowly getting there!
 

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Discussion Starter · #18 ·
No progress and there likely won't be any today as I agreed to help my brother fix his mini cooper. However the postman did arrive early this morning and deliver all of my fuel and oil line fittings:

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6m AN-6 Teflon line for fuel feed and return

1m AN-4 Teflon line for turbo oil feed

2x 5/16 (8mm) hard line to AN-6 adapters

2x AN-6 straight fittings

2x AN-6 90 degree fittings

2x AN-6 to 5/17 (8mm) quick disconnect (BMW use quick disconnects on the fuel rail)

2x 14.5mm Banjo to 8mm Barb for turbo water feed/return

1x 14.5mm Banjo to AN-4 for turbo oil feed

2x AN-4 90 degree fittings

1x 7/16-20 UNF to AN-4 for turbo oil feed (for some reason my turbo seems to have a 7/16 UNF thread for oil feed but standard metric for water)

Should be a few more deliveries later today as well
 

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Discussion Starter · #19 ·
So more parts arrived,

Got the oil sump gasket (this is so I can pull the sump off to weld in the oil return fitting) and got my new fuel pump. As this car's primary purpose is as a daily and not a track weapon or drift slag I decided against going for external pumps with swirl pots. Instead I opted for a 340LPH in-tank pump in the form of this AEM unit.

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Its not actually listed a straight swap part for an MX5 but it has virtually the same dimensions so I'll make it fit and I think I'll run fresh (and larger) wires to it at some point
 

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Discussion Starter · #20 ·
So I didn't really got much time to do anything on the car this evening as I was pulling a Mini apart to find out why the clutch doesn't release... FUN...

I did get a few more parcels though and I did get time to design some prototype parts. Both of my new driveshafts arrived ready to make a mock up. After a fair bit of googling I found an axle that would work... and once again I've had to resort to VAG parts. So for the inner part of the driveshaft I settled on using the rear driveshaft/cv from an Audi S4. The S4 driveshaft is a similar setup to the MX5 driveshaft with the fixed outer and plunging inner joint and replacement inner joints are easily available and affordable. The only downside is the inner joint is a tripod joint but considering the S4 model the joint is from produces nearly 400hp I'm not too concerned.

Obviously Audi driveshafts aren't going to bolt up to a BMW diff so I need an adapter, after taking some measurements I threw something together in fusion and fired up the plasma cutter to create a prototype.

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Hot of the CNC Plasma. After a little cleanup they looked like this:

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So the inner set of holes bolt to the BMW diff flange and the other set bolts to the driveshaft, the plan was to tap the outer set of holes to an M10 thread. Unfortunately plasma cutting 10mm steel is always a big inaccurate as the plasma stream start to deflect so the edges start to taper. It'll work for prototyping but I'll have to get the final parts either laser of CNC cut. These will however allow me to make my mock up axles to send off to be fabricated.

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It's probably gonna be a slow week as I've still got a dissembled Mini in the workshop where my car has been living. Hopefully before the weekend I can roll my car back in and start cracking on.
 
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