Rotrex Supercharger thread
09-25-2012, 07:35 PM
#92
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There's no reason that comes to mind for the fuelling to jump around, when you hit the bottom row of the base fuel map, the fuelling is then variable by rpm only.
I would expect the mixture to lean out gradually, not suddenly, as you reach a boost level greater than 100%/516.
I would expect the mixture to lean out gradually, not suddenly, as you reach a boost level greater than 100%/516.
Thanks John
As you can see from my plot, things go a bit wrong after after the MAF hits 100%, the LH doesnt know what to do, and I got knocks. The fuel % just kinda jumps around not knowing how much fuel to inject without the MAF. Really the only way to correctly handle this is with with one of Johns superMAFs, and click the box in your sharktuner for supermaf. You can also trick the MAF with something like the Murf doughnut.
The only temporary way I have found to handle this and continue to add more fuel is with the WOT map. At that point (100%maf) I started cranking in the fuel with the WOT map and it helped in that later runs with fuel ratio and knocks.
As you can see from my plot, things go a bit wrong after after the MAF hits 100%, the LH doesnt know what to do, and I got knocks. The fuel % just kinda jumps around not knowing how much fuel to inject without the MAF. Really the only way to correctly handle this is with with one of Johns superMAFs, and click the box in your sharktuner for supermaf. You can also trick the MAF with something like the Murf doughnut.
The only temporary way I have found to handle this and continue to add more fuel is with the WOT map. At that point (100%maf) I started cranking in the fuel with the WOT map and it helped in that later runs with fuel ratio and knocks.
09-25-2012, 07:49 PM
#93
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The MAF % is the same scale as MAF Signal Absolute. i.e. 100% MAF signal = MAF signal absolute at 516, the bottom row of the fuel map
It is MAF volts on the screen that limits out at Vmaf = 5.2v when in fact there is still some headroom up to 6.1v by some clever tricks we use ..... and this higher volts corresponds to around 450CHP
It is MAF volts on the screen that limits out at Vmaf = 5.2v when in fact there is still some headroom up to 6.1v by some clever tricks we use ..... and this higher volts corresponds to around 450CHP
09-25-2012, 09:09 PM
#94
Race Car
More than likely you are seeing a lot of knocks at the upper RPM range because the intake air temperature is climbing steadily past 150 deg F and peaking out at ~190 deg F or so.
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
09-25-2012, 11:51 PM
#95
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I was just using that pull for referance to show the how how the MAF maxed out at 100%. Looking at that log I would say not only was it hot air, but lean too since the rpms and boost were still going up but the injectors werent
09-26-2012, 01:22 AM
#96
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Get a well-controlled before and after dyno and all of the confusing speculation and estimation will be put to rest. We did before and after dyno sessions when we installed one of Andy Keel's Jag/Eaton blowers at 5 PSI on my stock 89 S4. It was 262 HP before (usually expect between 250 and 270) and 336 HP after. Then we added an X-pipe and it was 368 HP. This was tuned only with a rising rate adjustable fuel pressure regulator (all that was available at the time), but the AFRs were reasonably good.
09-26-2012, 01:30 AM
#97
Drifting
So it would seem that going the way I did with a MAP sensor and just a temp sensor where the MAF use to be is the next step.
Just saying that it makes sense to me, to replace those old ECMs, MAF, and distributors with a more modern system.
Ya its pricey but ...
Just saying that it makes sense to me, to replace those old ECMs, MAF, and distributors with a more modern system.
Ya its pricey but ...
09-26-2012, 05:46 AM
#98
Rennlist Member
Hi Bill,
They won't match except that at 100% MAF signal will be 512 MAF sig abs.
The MAF % is a linear quantity, but the MAF signal abs. is not.
MAF volts is really only useful for some basic MAF tests, like MAF signal at idle.
The MAF signal is processed in two different channels in the LH ECU. "MAF volts" is the signal into the A/D convertor which maxes out at 5.1v. The other processing channel continues up to 6.1v giving valuable extra headroom.
They won't match except that at 100% MAF signal will be 512 MAF sig abs.
The MAF % is a linear quantity, but the MAF signal abs. is not.
MAF volts is really only useful for some basic MAF tests, like MAF signal at idle.
The MAF signal is processed in two different channels in the LH ECU. "MAF volts" is the signal into the A/D convertor which maxes out at 5.1v. The other processing channel continues up to 6.1v giving valuable extra headroom.
Funny, that's not what I saw going back through my logs. The % and absolute didn't calculate the same and were somewhat out of sync. I focus on the MAF number rather than % as that is what the Sharktuner maps use. Also, I've never seen a clear relationship between voltage and MAF number. I tried to derive a formula for that so I could use voltage as a surrogate so I could tune the fuel map when I did not have a Sharktuner available by just reading the MAF voltage and RPM and failed to find one that worked.
09-26-2012, 01:05 PM
#99
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Hi Bill,
They won't match except that at 100% MAF signal will be 512 MAF sig abs.
The MAF % is a linear quantity, but the MAF signal abs. is not.
MAF volts is really only useful for some basic MAF tests, like MAF signal at idle.
The MAF signal is processed in two different channels in the LH ECU. "MAF volts" is the signal into the A/D convertor which maxes out at 5.1v. The other processing channel continues up to 6.1v giving valuable extra headroom.
They won't match except that at 100% MAF signal will be 512 MAF sig abs.
The MAF % is a linear quantity, but the MAF signal abs. is not.
MAF volts is really only useful for some basic MAF tests, like MAF signal at idle.
The MAF signal is processed in two different channels in the LH ECU. "MAF volts" is the signal into the A/D convertor which maxes out at 5.1v. The other processing channel continues up to 6.1v giving valuable extra headroom.
09-26-2012, 01:45 PM
#100
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I have a chart of SMAF output volts (measured on pin 7 the LH) versus power....
I don't have a handy graph of what you want.
But I've attached a graph of calculated pweor fopr MAF and SMAF versus MAF volts at pin 7 LH2.2
I don't have a handy graph of what you want.
But I've attached a graph of calculated pweor fopr MAF and SMAF versus MAF volts at pin 7 LH2.2
09-26-2012, 03:00 PM
#101
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Here is a data log taken from the shark tuner while I was doing a tuning run with the stock MAF. As you can see the MAF% hits 100% When I am round 5000/5100 rpms and stays flatlined as the rpms continue to climb. Are you saying that the absolute numbers are still going up even though the % is staying at 100??
Oh and btw, for everyone interested the boot level at 100%maf was 6.7lbs
Oh and btw, for everyone interested the boot level at 100%maf was 6.7lbs
09-26-2012, 03:18 PM
#102
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6.7psi boost was when the MAF hit 100% The 75mm pulley can take you over 8
09-26-2012, 04:30 PM
#103
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Get a well-controlled before and after dyno and all of the confusing speculation and estimation will be put to rest. We did before and after dyno sessions when we installed one of Andy Keel's Jag/Eaton blowers at 5 PSI on my stock 89 S4. It was 262 HP before (usually expect between 250 and 270) and 336 HP after. Then we added an X-pipe and it was 368 HP. This was tuned only with a rising rate adjustable fuel pressure regulator (all that was available at the time), but the AFRs were reasonably good.
09-27-2012, 11:04 AM
#104
I likely will never dyno because I am worried about modern steet drivabilty over peak rpm range HP. I think most good cars can handle another 100 or maybe even 150 Hp OK. It is pretty clear to anyone that if you get beyond that you need to start moddifing to no end or risk damaging your car. The low boost works great for me and I would never own another 928 without it. I don't need to be the fastest car around, but with all the big engines being made again I do want to know that I can keep up with the pickup next to me.
09-27-2012, 02:58 PM
#105
I likely will never dyno because I am worried about modern steet drivabilty over peak rpm range HP. I think most good cars can handle another 100 or maybe even 150 Hp OK. It is pretty clear to anyone that if you get beyond that you need to start moddifing to no end or risk damaging your car. The low boost works great for me and I would never own another 928 without it. I don't need to be the fastest car around, but with all the big engines being made again I do want to know that I can keep up with the pickup next to me.