Fuel Flow and FMU Calculations, Stock and A32 MAF+400cc injectors

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09-05-2005, 12:13 PM

slimer

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Fuel Flow and FMU Calculations, Stock and A32 MAF+400cc injectors

Quote:

Originally Posted by slimer

Since some of us might be using a 3:1 and higher boost pressure soon, I thought that I would update the info on the original post.

Boost--OEM--------FMU------
PSI---- FPR--3:1--4:1---6:1---8:1
0--------43--43---43----43----43
1--------44--44---44----44----44
2--------45--45---45----45----45
3--------46--46---46----46----46
4--------47--47---47----47----49
5--------48--48---48----48----57
6--------49--49---49----53----65
7--------50--50---50----59----73
8--------51--51---51----65----81
9--------52--52---53----71----89
10-------53--53---57----77----97
11-------54--54---61----83----105
12-------55--55---65----89----113
13-------56--56---69----95----121
14-------57--59---73----101---129
15-------58--62---77----107---137

1/2(static fuel pressure at idle) + (Boost PSI x FMU ratio)

Bold still is the onset of fuel pressure in regards to the fmu.
Red is dangerously close to 100% duty cycle.

Remember kids, fuel pressure is fuel pressure, no matter how large or small your injectors are.

Alright. So since I am having to run my A32 MAF for a little while, I have to figure out which fmu disc I am going to run. I thought that I would include some of my calculations in a new thread. The original thread with a lot of good information is here: http://forums.maxima.org/showthread.php?t=288889

If you are using the A32 MAF and 370cc injectors, you need to bump fuel pressure down. Based on my research, it should be 26 psi at idle, 34 psi at WOT. Based on that...

Boost--OEM--------FMU------
PSI---- FPR--3:1--4:1---6:1---8:1
0--------34--34---34----34----34
1--------35--35---35----35----35
2--------36--36---36----36----36
3--------37--37---37----37----37
4--------38--38---38----38----45
5--------39--39---39----43----53
6--------40--40---40----49----61
7--------41--41---41----55----69
8--------42--42---45----61----77
9--------43--43---49----67----85
10-------44--44---53----73----93
11-------45--46---57----79----101
12-------46--49---61----85----109

I personally would not run higher boost levels on this setup.

Therefore, using RC Engineerings formula to convert fuel pressure to figure out the change in fuel flow:
SQ. Root(New Pressure/Old Pressure)*Old Flow Rate=New Flow Rate.

Sq Rt.(26/34)*400cc=350cc

so what does this mean? This means that the flow rate of the injector is still about 45% larger than stock, which will make me really rich.

The main reason why I recalculated this was for my own curiosity of how my car will be running in the meantime, without the z maf.

I have the 4:1 fmu disc in right now, so should I disconnect the fmu itself and run this stock? I am only see 8.5 psi at most and that only bumps fuel pressure a couple of psi at redline. To me it seems like it is not worth it. I will be doing some more research with the wideband and posting my results.

09-05-2005, 08:02 PM

slimer

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i forgot to include that stock fuel pressure makes a 13.1 A/F ratio at idle, while the 26 psi at idle results in a stoich 14.7 A/F

09-06-2005, 12:27 PM

slimer

A couple of Blaxxx's? Lawls.

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Just so everyone knows, having your injectors like this BLOWS!

I tried to accelerate this morning on the highway and it completely stumbles between 3000 and 4500 rpms with an AF of 9.6-9.9. Yuck. At the top end it seems like its fine. Idle is fine, but I just rean real rich the whole way. The round trip is around 30 miles and after I did that initial testing, I took it easy. I wasted almost a 1/4 of a tank.

DO NOT RUN THIS SETUP!

Anyone got an extra z32 MAF?