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VVT swapped NA & TD04 turbo NB
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Discussion Starter · #1 · (Edited)
It's been a long old project and I've many photos to include whilst I write up but to begin with, the almost finished article, with much more to do (is a car ever really finished). Excuse the lack of artistic flair in the following photos, I've not long had the car back from paint and not had much time to get it out due to issues with my relay.....

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--When I bought her--
She is originally a '91 import that had a 1.6 short nose engine, it was in white from the factory, however the previous owner/s had resprayed it with rattle cans in MG yellow, which had become flaky. This is where the name Ana came from (50 shades of yellow...) and it's stuck ever since.

I had plans for her, being my third MX-5, I knew the first steps were the preventative maintenance tasks, rust and all the other boring bits.

--Work completed so far--
  • Both sills repaired professionally by Unit 14 Autoworks in Saltash
  • Bare metal complete exterior respray including door shuts and inside doors by Hoggy's paint shop in Plymouth
  • Rear GV panel fitted and sprayed by Hoggy's paint shop in Plymouth
  • 1.8 VVT engine swap with working VVT by Unit 14 Autoworks in Saltash
    • MS3 Mini ECU
    • Stock NB2 ancillaries with NA 1.8 alternator
    • Stock NB2 injectors & coils
    • BOFI lightened 1.6 clutch @ 3.3KG with new OEM 1.6 clutch
    • Walbro 255LPH fuel pump, new filters
    • Derusted and resealed fuel tank
    • Toyosports 4-2-1 manifold modified to mate up to NA exhaust
  • Meister R Zeta CRD coil overs fitted
  • Autostar Geo 8.5j wheels
  • Michelin PilotSport 3 tyres
  • Hyperflash bypass on flasher relay
  • Crappy Sony stereo fitted, to be replaced
  • New mohair top fitted by South West Roadsters in North Devon
  • MX-5 parts dual exit backbox fitted
  • MX-5 parts de-cat box (not used on public road)
  • RX-7 80a main relay fitted to replace NA main relay
  • New after market passenger electric window mechanism and motor
  • Install Ground Zero audio amplifier
  • New door speakers
  • MOT
--Work to be completed--
  • Re-wire fuel pump onto separate relay to spread load and heat
  • New Android head unit
  • New steering wheel
  • Fit shorty console (still half sanded off 3D printer)
  • Procure complete red interior.....
  • Tuning
  • ITBs and more tuning
  • Alter suspension ride height
  • Fix leak in boot
  • Repair hard top and repaint
  • Swap indicators in wings to LEDs
  • Make new bonnet stay as current one doesnt fit around VVT engine cross over pipe
  • Measure main relay temp difference on NA relay to FD relay
  • Fit weather strips (might buy new ones but pricey at £90 a pair)
  • Fit proper rollbar
  • Coolant leak

That's all for now folks :)
 

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VVT swapped NA & TD04 turbo NB
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Discussion Starter · #3 ·
A fellow Garage Vary fan! I like!
That's very kind of you to say, thank you :)


I have made a start on the first issue in my list, a bit of back story first:
Since fitting a VVT engine and the uprated fuel pump, the car has been driving fine (at least for an untuned car..). However on my maiden voyage home from the paint shop, the car cut out mid drive. After a few days of soul searching and running round the car with a multi-meter, I discovered that the issue was simply that my main relay had stopped working correctly. I rigged up a 12v power source to it on a bench, and whilst it still actuated, it was clear there was no current passing through it at all.

After I dug a bit deeper, it seemed that a common fault after upgrading things like the fuel pump and ignition system, is for the relay to go due to the amount of extra current being continuously drawn, the relay heats up and plastic starts to melt which could be seen very clearly on the legs of the connector in the fuse box.

This is where things start to get tricky, I opened the relay and the contacts looked OK, I guess the metal must have become non-conductive in some way, maybe the heat has caused it to tarnish a bit. I bent the contacts further up so when it actuates, it does so in a different place and it works again.
So I then replaced the relay with an OEM one from a breaker, took the car for a 30 minute drive and damn, she hot!

After a bit more reading I found that flyin' miata sell the 80a RX-7 main relay (JE16-18-811) listed as an upgrade for people with uprated fuel pumps etc. So on the phone to Mazda and £70 later, an RX-7 relay is being sent to my local dealer. Roll on a week later and it's fitted (no modifications required) but it does still get hot when driven. I've asked around and I can't find any technical data to work on as to how hot it normally gets before it's considered out of spec.

So what do I want to know/achieve:
  1. What is rated amperage of the OEM NA main relay (B6S8-18-811)? I ask this because the main fuse in my fuse box is 60a, though I understand the OEM one is rated to 80a which is the rated limit of the RX-7 relay. Why would a fuse allow more current than the components allow from stock?
  2. How hot does the NA main relay get when used in my set up?
  3. How hot does the RX-7 relay get when used in my set up?
  4. Does moving the fuel pump to it's own relay lower the temperature of the main relay? If so why or why not?
I have bought an infrared thermometer so that I can test the differences between the two relays in my set up.
I would be very keen to know others observations.
 

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M52TU Turbo Swapped MX5
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  1. How hot does the NA main relay get when used in my set up?
  2. How hot does the RX-7 relay get when used in my set up?
  3. Does moving the fuel pump to it's own relay lower the temperature of the main relay? If so why or why not?
Relay current ratings aren't really to do with continues use capacity its more related to switching capacity. You shouldn't really see any temperature increase due to a larger current draw unless you are well outside of its rating. The bigger issue is that if for example you try and pull 100A at 12V through a 60A relay it may draw an arc internally across the contacts as there won't be enough air gap to instantly break the connection. This creates a huge amount of heat and will damage the contacts very quickly causing the relay to fail (either through the contacts melting or the plastic). This is one of the reasons the relays are often rated for much higher AC loads than DC as is AC is far easier to switch.

Relays will get hot/warm in use but this is to do with the coil that holds the contacts open or closed. Moving the fuel pump to a separate relay is a good idea and I would always recommend this if you have seriously upgraded your fuel pump (very large or multiple in tank or external pump) as it means you can run larger feed wires but I doubt it will have much affect on the temperature of your main relay and with a walbro255 pump its probably not necessary.

Its also worth noting that fuel pumps are electric motors and motors are an inductive load meaning they normally draw a huge amount of current at the moment they are switched on and then drop down to there running levels. This is very aggressive on relay contacts over time so if you do switch the fuel pump to its own relay be sure to spec the relay correctly; some suppliers/manufacturers will list a different inductive load rating in the relay data sheet.

thanks,
Nix.
 

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VVT swapped NA & TD04 turbo NB
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Discussion Starter · #5 ·
Relay current ratings aren't really to do with continues use capacity its more related to switching capacity. You shouldn't really see any temperature increase due to a larger current draw unless you are well outside of its rating. The bigger issue is that if for example you try and pull 100A at 12V through a 60A relay it may draw an arc internally across the contacts as there won't be enough air gap to instantly break the connection. This creates a huge amount of heat and will damage the contacts very quickly causing the relay to fail (either through the contacts melting or the plastic). This is one of the reasons the relays are often rated for much higher AC loads than DC as is AC is far easier to switch.

Relays will get hot/warm in use but this is to do with the coil that holds the contacts open or closed. Moving the fuel pump to a separate relay is a good idea and I would always recommend this if you have seriously upgraded your fuel pump (very large or multiple in tank or external pump) as it means you can run larger feed wires but I doubt it will have much affect on the temperature of your main relay and with a walbro255 pump its probably not necessary.

Its also worth noting that fuel pumps are electric motors and motors are an inductive load meaning they normally draw a huge amount of current at the moment they are switched on and then drop down to there running levels. This is very aggressive on relay contacts over time so if you do switch the fuel pump to its own relay be sure to spec the relay correctly; some suppliers/manufacturers will list a different inductive load rating in the relay data sheet.

thanks,
Nix.
This is incredibly helpful and so informative, thank you.

Do you have any insight into what a normal temperature of the relay would be after a spirited drive. I'm getting a bit paranoid now that there is something else causing the relay to get hotter than it should be whilst driving. For what it's worth, my car still has the 60a main fuse in, am I right in thinking that if the car was pulling any higher current than 60a across the main relay, that the main fuse would blow? or is it not that straight forward?

Moving the fuel pump to it's own relay is a minimal job with minimal cost and sounds like it's worth doing anyway for safety but I appreciate that it might not be completely necessary then based on what you've said - at some point the car will be getting ITBs (or I might even go for a turbo again depending on how I'm feeling) so future proofing that too.
 

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M52TU Turbo Swapped MX5
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This is incredibly helpful and so informative, thank you.

Do you have any insight into what a normal temperature of the relay would be after a spirited drive. I'm getting a bit paranoid now that there is something else causing the relay to get hotter than it should be whilst driving. For what it's worth, my car still has the 60a main fuse in, am I right in thinking that if the car was pulling any higher current than 60a across the main relay, that the main fuse would blow? or is it not that straight forward?

Moving the fuel pump to it's own relay is a minimal job with minimal cost and sounds like it's worth doing anyway for safety but I appreciate that it might not be completely necessary then based on what you've said - at some point the car will be getting ITBs (or I might even go for a turbo again depending on how I'm feeling) so future proofing that too.
it depends on the relay and if you can find the part number for the main relay you may be able to find the full datasheet for it (not likely though) but I know that some I've seen relays have maximum coil temperatures of up to 70C (some industrial relays have operating temps of up to 90C) so I wouldn't worry to much. Relays are built to withstand some fairly serious temperatures; automotive relays are often built/specced to operate in engine bays with under bonnet temps of 50C+

Yes once the current through the main fuse surpasses its rating for a period of time it will blow; The main fuse is likely a slow-blow fuse so there will be a slight delay before it blows so that it doesn't blow every time there is momentary spike in current draw.
 

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VVT swapped NA & TD04 turbo NB
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Discussion Starter · #7 ·
it depends on the relay and if you can find the part number for the main relay you may be able to find the full datasheet for it (not likely though) but I know that some I've seen relays have maximum coil temperatures of up to 70C (some industrial relays have operating temps of up to 90C) so I wouldn't worry to much. Relays are built to withstand some fairly serious temperatures; automotive relays are often built/specced to operate in engine bays with under bonnet temps of 50C+

Yes once the current through the main fuse surpasses its rating for a period of time it will blow; The main fuse is likely a slow-blow fuse so there will be a slight delay before it blows so that it doesn't blow every time there is momentary spike in current draw.
That's amazing thank you. I've got an infrared thermometer on the way so will have a play and see what temps are like.

Just one last question if you dont mind, is there anyway an issue post relay could have an adverse affect on the relay, say a short circuit or high resistance somewhere?
 

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M52TU Turbo Swapped MX5
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That's amazing thank you. I've got an infrared thermometer on the way so will have a play and see what temps are like.

Just one last question if you dont mind, is there anyway an issue post relay could have an adverse affect on the relay, say a short circuit or high resistance somewhere?
not particularly, if there is a short heat will always build up in the point of highest resistance which is normally the fuse. The same with high resistance, it will cause a voltage drop across the point of resistance, that voltage has to go somewhere so its converted to heat across the resistance. It shouldn't have any affect on anything else in the circuit
 

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Discussion Starter · #9 ·
not particularly, if there is a short heat will always build up in the point of highest resistance which is normally the fuse. The same with high resistance, it will cause a voltage drop across the point of resistance, that voltage has to go somewhere so its converted to heat across the resistance. It shouldn't have any affect on anything else in the circuit
Perfect - my mind is at ease now, I'll stop obsessing over the weird suspected short I found on the switched live (white/red).

Thanks again :) nice MX-5 by the way, will subscribe to your thread.
 

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Discussion Starter · #13 ·
MOT passed with no advisories :D

Its been an audio day the last two days, in between showers and extreme heat cycles.

Started by making some DIY water covers for my new cheap door speakers.

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Used the lid of a blank CD spindle, for one and a haribo tub for the other. Cut both to size with a dremel and then sealed them on with some silicon.

I managed to run a remote cable under the centre console carpet, and quickly realised that I would never get any more cables down there, so routed a set of RCA cables down the drivers side into the boot.
Next, I spent the best part of an hour shouting at the drivers door as I tried to feed a new 16 gauge set of wires for a door speaker, eventually I came out on top and decided to call the wiring a day.

Next up I made up a mount for my Ground Zero Class D amp, but of marine ply I had in the garage, cut to size and a cable channel put in, finally sanded and painted:

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- Left to do -
  • run wire for passenger door speaker
  • wire amp in to power etc
  • continuity test head rest speaker wires
  • choose new headrest speakers
  • split rca signal from stereo into 4 channels from 2
 

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Discussion Starter · #14 ·
A quick update, been too busy recently to properly document this - plus, it's nothing ground breaking really. My turbo mk2 decided to lose all brakes at 70mph on the drive back from having it's brakes sorted, simply because I made the gamble on chinesium calipers. Lesson learnt.

So back to the mk1......

  • wired passenger door
  • amp fully wired up
Everything seemed fine, tested the set up and suddenly I lost the left channel. Had a play with the volume and suddenly the right channel lost, and the left came back on loud. Immediately I thought that there must have been either some current issues or the amp was faulty. However after I had a little sit down and some advice, turns out the issue was likely the gain knob or the x-over switch. To test this theory I moved the input and output over to the other two channels and sure enough all was working fine.
Cleaned up the gain knob and x-over switch with some brake cleaner (yes I know it's conductive but, it does evaporate) and after 3 goes, it was finally good.

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- Parts Used -
  • Ground Zero GZHA Class D amp with a whopping 80w RMS x 4 channels!!
  • VIBE amplifier wiring kit, consisting of a remote signal wire, chunky power and ground and RCA lead
  • Pioneer TS-R1750S speakers - just budget speakers but I needed to gauge what 40w RMS was like before moving onto the headrest speakers, may revisit and upgrade to 80w RMS
  • Cheapy Sony A410BT head unit, plans to upgrade this to an Android unit in future as I want to be able to utilise Android Auto, Tuner Studio and RealDash
  • Amazon Basics 16 gauge speaker wire
 
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