Twin Turbo 928 fixed and back out there terrorizing the streets!
#391
Race Car
Hmm, many factory turbo systems choose to have the MAF before the turbo. I haven't noticed any problems running 26psi in my '91 SAAB 9000T, and the car is about to cross 200k miles. It is true that you must have a much longer air path sealed from leaks, but I'm not sure the lag you talk about is significant.
Dan
'91 928GT S/C 475hp/460lb.ft
Dan
'91 928GT S/C 475hp/460lb.ft
#392
Burning Brakes
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Maybe not. I seem to remember reading something about throttle plates and MAF sensors, maybe in Corky Bell's book. I can't recall ATM, and I could definitely just be talking out of my *** anyhow. I am of the opinion that MAP/MAT is the way to go regardless. MAF is too finicky and has leak problems. This is one reason why I am going electromotive in my rebuild.
#393
Inventor
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(2) EZK powershift feature with an input from clutch position switch, where the ignition is retarded to x degrees ATDC above y rpm if the clutch is pressed at WOT. Reasonable values for x would be 30 degrees ATDC and for y 4500 rpm.
Number (2) needs a big warning label on it. "Your exhaust manifold may glow like Columbia and your turbo may blow like Challenger. Your shifts will feel and sound like you've strapped yourself onto a booster rocket."
Number (2) needs a big warning label on it. "Your exhaust manifold may glow like Columbia and your turbo may blow like Challenger. Your shifts will feel and sound like you've strapped yourself onto a booster rocket."
If I ever get around to making a mid-turbo, I will try the anti-lag on the EZF. The WOT input (and codespace) could be rewired for the clutch switch.
BTW: to access the terminals on the clutch switch you have to remove it. There are two small phillips head screws which hold it. Note that there are two sets of holes for the microswitch. (It's easy to try and install the switch incorrectly the first time you do it, but only the upper set should be threaded.)
The clutch switch is a normally open type, but as installed, it is normally closed. IE when you push in the clutch, the input to the EZ/LH will be OFF.
#394
Rennlist Member
Niklas is visiting me later this week and we will be discussing these topics and others...
Here's my wish list JDS:
(1) EZK map that has enough range in the top end to tune different WOT boost profiles.
(2) EZK powershift feature with an input from clutch position switch, where the ignition is retarded to x degrees ATDC above y rpm if the clutch is pressed at WOT. Reasonable values for x would be 30 degrees ATDC and for y 4500 rpm.
Number (2) needs a big warning label on it. "Your exhaust manifold may glow like Columbia and your turbo may blow like Challenger. Your shifts will feel and sound like you've strapped yourself onto a booster rocket."
(1) EZK map that has enough range in the top end to tune different WOT boost profiles.
(2) EZK powershift feature with an input from clutch position switch, where the ignition is retarded to x degrees ATDC above y rpm if the clutch is pressed at WOT. Reasonable values for x would be 30 degrees ATDC and for y 4500 rpm.
Number (2) needs a big warning label on it. "Your exhaust manifold may glow like Columbia and your turbo may blow like Challenger. Your shifts will feel and sound like you've strapped yourself onto a booster rocket."
#395
Rennlist Member
On the 944 Turbo the MAF is pre-Turbo. It goes Air Filter - MAF - Turbo - Intercooler - Throttle body. The BOV dumps from between the intercooler and throttle body to between the turbo and the MAF so air stays metered. Boost pressure to operate the wastegate is taken from between the intercooler and throttle body. Boost measurement for control is taken from the intake. Pressure to operate the BOV is taken from the throttle body.
#396
Rennlist Member
I can't remember if John's TT has twin inlet tracts, but it would be possible to have a MAF in each leg and use a combiner box.
We are wortking on a MAF-less system as well...
We are wortking on a MAF-less system as well...
#397
Race Car
#398
Rennlist Member
The system we are working on is for the race car in my avatar, this will run with Jenvey 50mm ITBs and work on Throttle pot for load with airtemp and MAP sensor absolute airmass correction.
A development of that could be a MAF-less system to go with the stock intake, but not sure whether there is a viable market for that product ?
A development of that could be a MAF-less system to go with the stock intake, but not sure whether there is a viable market for that product ?
#399
Nordschleife Master
Thread Starter
Hmm, many factory turbo systems choose to have the MAF before the turbo. I haven't noticed any problems running 26psi in my '91 SAAB 9000T, and the car is about to cross 200k miles. It is true that you must have a much longer air path sealed from leaks, but I'm not sure the lag you talk about is significant.
Maybe not. I seem to remember reading something about throttle plates and MAF sensors, maybe in Corky Bell's book. I can't recall ATM, and I could definitely just be talking out of my *** anyhow. I am of the opinion that MAP/MAT is the way to go regardless. MAF is too finicky and has leak problems. This is one reason why I am going electromotive in my rebuild.
On the 944 Turbo the MAF is pre-Turbo. It goes Air Filter - MAF - Turbo - Intercooler - Throttle body. The BOV dumps from between the intercooler and throttle body to between the turbo and the MAF so air stays metered. Boost pressure to operate the wastegate is taken from between the intercooler and throttle body. Boost measurement for control is taken from the intake. Pressure to operate the BOV is taken from the throttle body.
There's precisely one reason to place the MAF upstream of the turbo. That's to accommodate crank-case breather system that is fed to the intake. Unless the air-oil separator is perfect, in a system where the MAF is downstream of the turbo, the blow-by oil may interfere with the MAF wires. More blowby oil, worse the problem.
If you either have perfect air-oil separation (like for example a well designed dry sump system) or if you don't hook up the crankcase ventilation system to the intake (either vent it to atmosphere or to the exhaust), then MAF as close to the throttle plate as possible is generally the best thing to do.
I can't remember if John's TT has twin inlet tracts, but it would be possible to have a MAF in each leg and use a combiner box. We are wortking on a MAF-less system as well...
The system we are working on is for the race car in my avatar, this will run with Jenvey 50mm ITBs and work on Throttle pot for load with airtemp and MAP sensor absolute airmass correction.
A development of that could be a MAF-less system to go with the stock intake, but not sure whether there is a viable market for that product ?
The system we are working on is for the race car in my avatar, this will run with Jenvey 50mm ITBs and work on Throttle pot for load with airtemp and MAP sensor absolute airmass correction.
A development of that could be a MAF-less system to go with the stock intake, but not sure whether there is a viable market for that product ?
The only reason to do the pre-turbo MAF version would be to create a California-legal version of the kit with all the testing procedures and plastic bags of exhaust gas. I doubt that this is commercially feasible and/or that John Kuhn has any interested in dealing with that hole insane asylum... ;-)
The same applies to MAP conversion with the stock intake manifold. MAF system is superior in every other way except that the hot wire is sensitive to oil from the crankcase breather, which is a problem for boosted cars that need to feed in the evacuated gas upstream of the turbo.
#400
Supercharged
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John's system has dual intake tracts. If the MAF were to be moved to upstream of the turbo, that would mean using two MAF's anyway, because one would need double the housing area for the low-pressure side. The voltage averaging circuit is trivially easy to make and digital dual-to-single MAF emulator only marginally harder. (I've done both, which tells you that it's REALLY easy.)
With the STer when you set your tune you're only measuring a % of the are coming in and then plugging in a fuel value for it. As long as that doesn't change over time, it's fine. So if a single MAF setup measures 20% of the air, I'm only measuring 10%. Still works. It also avoids having to use a special-built SMAF - not saying that's bad, but it's easier to source a standard MAF.
#401
Drifting
Mine is set up as a secondary rev limiter. The primary rev limiter is set at 8200 rpm with a fuel cutoff. The secondary is set at 6000 rpm with spark retard. It's only active when it sees another input. I'm using the clutch switch. When that switch is triggered, it defaults to the 2nd rev limiter. The limiter has a lot of spark retard authority. Mine is setup to pull about 65 degrees of timing. Fueling is not changed. So spark goes from ~30 BTDC to 35 ATDC. It throws a TON of energy into the exhaust. I also richen the mixture from about 12:1 while under boost to about 10:1 during anti-lag to try and lower the exhaust temp a little.
This works for both flat shifting the car at wot, and also launching the car at full boost. You just have to be careful not to use it too often or too much or you'll tear up the turbos and exhaust manifolds.
#402
Nordschleife Master
Thread Starter
Yes, that's how it works. Mine is set up as a secondary rev limiter. The primary rev limiter is set at 8200 rpm with a fuel cutoff. The secondary is set at 6000 rpm with spark retard. It's only active when it sees another input. I'm using the clutch switch. When that switch is triggered, it defaults to the 2nd rev limiter. The limiter has a lot of spark retard authority. Mine is setup to pull about 65 degrees of timing. Fueling is not changed. So spark goes from ~30 BTDC to 35 ATDC. It throws a TON of energy into the exhaust. I also richen the mixture from about 12:1 while under boost to about 10:1 during anti-lag to try and lower the exhaust temp a little. This works for both flat shifting the car at wot, and also launching the car at full boost. You just have to be careful not to use it too often or too much or you'll tear up the turbos and exhaust manifolds.
Not exactly... I have dual intakes - one MAF. With the STer when you set your tune you're only measuring a % of the are coming in and then plugging in a fuel value for it. As long as that doesn't change over time, it's fine. So if a single MAF setup measures 20% of the air, I'm only measuring 10%. Still works. It also avoids having to use a special-built SMAF - not saying that's bad, but it's easier to source a standard MAF.
If you ever get the urge to add another MAF to make your system symmetric, the MAF signal averaging circuit components are less than $20 I recall.
#403
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If the MAF output is a voltage signal, then the averaging circuit is indeed trivial, but should cost you something like 20 cents...It's two resistors and a common ground...
#404
Nordschleife Master
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