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Discussion Starter · #1 ·
Mk2.5 1.6L with an M62 supercharger

We have almost the entire setup installed, it runs and idles (ish) even with a sizable boost leak. an RM racing electronics PNP ECU, bosh wideband+controller.


Not sure on how much the new throttle body should be open while at 0% throttle and how fast its should get to 100%.

Right now when you step on it the engine cuts out almost completely we assume this is because it's not getting enough air (the AFR isn't giving much information as it pretty much just sit's around 14.5 because the AFR targeting setting is on)

We can machine new pulleys etc. pretty easily and figure it out on our own but is there any general rule for what it should sit at on what throttle position? or is this just a boost leek issue and when we solve that tomorrow this will go away?
 

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Single throttle body pre charger, dummy throttle body on the inlet manifold.
why create problems?
 

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For my setup both the throttle were same but you made sure the one closest to the sc was cracked a tiny bit open. My bov was on the other side of Intercooler closer to intake so you didn’t have to worry about over pressurising the system. Make sure the vacuum hose on the wastegate is fed from the intake. Ppl the left it standard on the sc ie just the other side of the first throttle had issues of overboost and melting the sc
 

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A good starting point is to disconnect the cable between the two throttles, hold the manifold TB open and adjust the 0% stop on the SC TB until you're idling at around 2000rpm. Then reconnect the throttles and adjust the cable so they start opening at the same time and get to WOT at the same time. That will ensure the mani TB is controlling the airflow around idle but the SC TB will keep some vacuum through the SC at part load. It might need fine tuning later but that should sort you out to begin with.

BUT don't do that until you've sorted your vacuum leak!

Going lean if you tap the throttle is probably just missing accel enrichment. I'd recommend getting it running properly in steady state conditions first, then deal with the transients with accel enrichment afterwards. Controlling AFR during throttle blips from idle was about the hardest part of tuning my standalone so I wouldn't worry about it yet.
 

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Discussion Starter · #5 · (Edited)
A good starting point is to disconnect the cable between the two throttles, hold the manifold TB open and adjust the 0% stop on the SC TB until you're idling at around 2000rpm. Then reconnect the throttles and adjust the cable so they start opening at the same time and get to WOT at the same time. That will ensure the mani TB is controlling the airflow around idle but the SC TB will keep some vacuum through the SC at part load. It might need fine tuning later but that should sort you out to begin with.

BUT don't do that until you've sorted your vacuum leak!

Going lean if you tap the throttle is probably just missing accel enrichment. I'd recommend getting it running properly in steady state conditions first, then deal with the transients with accel enrichment afterwards. Controlling AFR during throttle blips from idle was about the hardest part of tuning my standalone so I wouldn't worry about it yet.
So this is pretty much what we did and even having the SCTB A significant amount open didn't solve the taping the throttle problem even with boost leaks solved so i assumed it was a software issue (silicone instant gaskets work wonders) considering the gap between the SC and the plate was almost 2mm at one point it was a significant issue. who knew 5mm steel warps when you weld it...

Now i have an issue of the supercharger gets REALLY hot within 60 seconds, it's not boiling water directly ontop of the SC but we've lost our Temp sensing gun somewhere so i don't now exact numbers, I'm pretty sure it's because the bypass isn't opening on idle even if the SCTB is completely closed, i assume this indicates a vacuum leak around there? you can hear the SC getting much quieter if you manually open the valve (it does open if the engine revs a little because the engine/SC are at high RPM yet the TB is still basically closed)

Edit: Just been told to run the bypass valve off the vaccume from inside the intake manifold After both TBs, same place the ECU reads from
 

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Just been told to run the bypass valve off the vaccume from inside the intake manifold After both TBs, same place the ECU reads from
Yep, that'll be it, connect up the bypass as Ra5cal said. The bypass valve should be open at low and part throttle to allow the SC to recirculate all the air it's pushing through.
 

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Discussion Starter · #8 ·
As you are discovering, dual throttle bodies cause more problems than they cure….
all the problems have easy fixes, the problems only having 1 cause seem to not have any fixes...

The problems i am having now are actually aren't a consequence of dual throttle bodies it's a consequence of the software and bypass valve type :p installing the 2nd one was REALLY easy aswell

keeping in mind solving my current problem wouldn't be possible with only 1 TB
 

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Dual TB setup isnt too hard, people just often aren't sure what they are doing which is where they have issues. So many people misunderstand what the TB and bypass actually do on a SC setup. The driveability of a single TB isnt as good.

Think you have it sorted by the sound of it? Ben's suggestion was pretty accurate. Or crack the SC stop screw fully open then adjust it back to quieten things down until the idle starts to be affected, slightly above this is what you are aiming for to make sure the mani TB is controlling the airflow around idle but the SC TB will keep some vacuum through the SC at part load.
 
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Not wanting to harp on, but another advantage of dual throttles is that if any of your DIY pipework fails upstream of the manifold throttle then you can still drive home. Don't ask me how I know!

But, I appreciate it can be tricky to set it up and there is a risk of toasting your supercharger if they're not synced properly.
 

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Just in case relocating the vac source for the bypass actuator doesn't work, they sometimes fail because the seal inside tears so they just let a bit of air in instead of moving. I've never had one fail (touchwood) but some less fortunate people treat them as wear and tear items. You should be able to see the actuator pull in when you start the engine.
 

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Just in case relocating the vac source for the bypass actuator doesn't work, they sometimes fail because the seal inside tears so they just let a bit of air in instead of moving. I've never had one fail (touchwood) but some less fortunate people treat them as wear and tear items. You should be able to see the actuator pull in when you start the engine.
You can test this by putting a vacum gun on the actuator and ensure it holds the set vacum. If it reduces, it’s torn.

I never got the dual TBs to work correctly.
Even when almost perfect. The bloody cables would stretch and throw it out of sync.

I installed a BOV in the pipeline post charger and pre ic. To reduce the pressure when they became imbalanced.

However in the end I just ditched the set up and went for one pre charger. It was much more enjoyable even with the ~0.5 second delay on throttle.
 
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