Fueling a low boost supercharger
#1
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Fueling a low boost supercharger
I was looking at a Jeg's catalog a while ago (or something similar), and they had some low boost superchargers available for the Mustang that didn't require any changes to the fuel system or computer since the boost levels were low enough for the PCM to deal with.
My question is, since we've got such a friggin' rich car anyway, would it be possible to install a 4 psi or 6 psi supercharger and not need to add a piggyback fuel control? At cruise, the car is closed loop, so the PCM should adapt, right? Does anyone know how to determine how much boost would turn the WOT AFR from 11:1 to 13:1?
Is there domething drastically wrong with what I'm thinking?
~ Matt
My question is, since we've got such a friggin' rich car anyway, would it be possible to install a 4 psi or 6 psi supercharger and not need to add a piggyback fuel control? At cruise, the car is closed loop, so the PCM should adapt, right? Does anyone know how to determine how much boost would turn the WOT AFR from 11:1 to 13:1?
Is there domething drastically wrong with what I'm thinking?
~ Matt
#2
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its quite possible. there was one shown here a short while ago that had no piggy back or alteration of the stock maps in any way.
here https://www.rx8club.com/showthread.p...8&page=1&pp=15
here https://www.rx8club.com/showthread.p...8&page=1&pp=15
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Don't know about SC, but my piggyback was screwed up when I first got it from Greddy, so I was running the stock fuel map with FI. I was running 5.5 lbs. of boost and I was detonating like crazy at high rpms.
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Originally Posted by Fanman
Don't know about SC, but my piggyback was screwed up when I first got it from Greddy, so I was running the stock fuel map with FI. I was running 5.5 lbs. of boost and I was detonating like crazy at high rpms.
So, I'm guessing something like 4 or 4.5 psi is probably safe. I don't have the funds/***** to do a homebrew kit, but it sounds feasible.
~ Matt
#7
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The problem isn't the fuel.....its the crazy high compression ratio and associated ignition advance. You need to be able to back the ignition down from 25-30 degrees at WOT to keep it from detonating. If you could control the ignition advance, its possible that a low boost system could be made to work (me thinks)
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Originally Posted by brillo
The problem isn't the fuel.....its the crazy high compression ratio and associated ignition advance. You need to be able to back the ignition down from 25-30 degrees at WOT to keep it from detonating. If you could control the ignition advance, its possible that a low boost system could be made to work (me thinks)
agreed. my car runs ~9.8AFR over 5kRPM under no boost. This makes me think there is plenty of fuel being delivered by the stock ECU for at least some boost. Of course, that's my 8, not necessarily (or even likely) any one else's.
-MD
#9
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Originally Posted by MadDog
agreed. my car runs ~9.8AFR over 5kRPM under no boost. This makes me think there is plenty of fuel being delivered by the stock ECU for at least some boost. Of course, that's my 8, not necessarily (or even likely) any one else's.
-MD
-MD
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Originally Posted by brillo
The problem isn't the fuel.....its the crazy high compression ratio and associated ignition advance. You need to be able to back the ignition down from 25-30 degrees at WOT to keep it from detonating. If you could control the ignition advance, its possible that a low boost system could be made to work (me thinks)
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No way I'd run boost without fuel control. Closed loop will create conditions far too lean for boost and I believe the MAF bottoms out at around 2psi of boost.
You could probably get away with running less than 2psi, I wouldn't try it, but anything more and I'd start a pool for #of feet till you got an apex seal rattling around.
You could probably get away with running less than 2psi, I wouldn't try it, but anything more and I'd start a pool for #of feet till you got an apex seal rattling around.
Last edited by rkostolni; 12-01-2005 at 07:22 PM.
#12
Originally Posted by rkostolni
No way I'd run boost without fuel control. Closed loop will create conditions far too lean for boost and I believe the MAF bottoms out at around 2psi of boost.
You could probably get away with running less than 2psi, I wouldn't try it, but anything more and I'd start a pool for #of feet till you got an apex seal rattling around.
You could probably get away with running less than 2psi, I wouldn't try it, but anything more and I'd start a pool for #of feet till you got an apex seal rattling around.
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I think that is part of the difficulty with the 8's computer as opposed to other ecu's is that is does remain in closed loop under load. For us, closed loop operation is not only load dependent, but also rpm dependent. That is why Greddy had to use the cold water temp dongle to force it into open loop when under boost.
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Originally Posted by brillo
Are you serious? 9.8? holy crap man, that is so rich you should be smoking.....how are you testing that? what are you tuning with?
BTW: I dynoed +15HP with the canzoomer.
#15
Originally Posted by rkostolni
I think that is part of the difficulty with the 8's computer as opposed to other ecu's is that is does remain in closed loop under load. For us, closed loop operation is not only load dependent, but also rpm dependent..
Originally Posted by rkostolni
That is why Greddy had to use the cold water temp dongle to force it into open loop when under boost.
Fabrice
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