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Another hypothetical/give me your best est. question


Guest bastaad525

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Guest bastaad525

okay I picked up my MSD fuel pump today. Just wondering if anyone can make a somewhat educated guess on this. When I dynoed my car ran pretty rich, varying from 10:1 to 12.5:1 A/F ratio and was steady there up until 5000rpm and then jumps to 13:1 and starts to lean out pretty rapidly after that. I'm 99% certain this is just the fuel pump running out of flow at this point, as the math says that the stock fuel pump is good for about 230hp according to SleeperZ and that makes perfect sense and matches up very well with my 199 at the wheels. I think/hope with the MSD the fuel curve wont lean out after 5000rpm, so, just wondering, IF that is the case, I should theoretically have a higher peak HP number right? Right now the HP starts to taper off at right around that same 5000rpm mark when the fuel starts going lean, and I figure the turbo motor should be good for at least another 500rpm... I know this is where hp peaks at stock boost levels and I dont see additional boost moving t he peak down that far. What do you guys think?

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I say strap it down and find out!

Your thinking seems logical. Have you measured teh fuel pressure during the run to see if it si dropping during the higher rpm run? If you see it starting dropping off, there's your answer. There is a flow stagnation on the stock pump at higher pressures, and with increaded pressure comes decreased flow....

The only way to confirm it is to strap-er down and wring it out! :lol:

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Guest Nic-Rebel450CA

I agree, get a fuel pressure gauge hooked up and watch it. Keep in mind though that there are other parts of the fuel system that could be responsible. (Fuel lines, injectors, ECU). Your logic seems accurate in that the problem is likely to be a lack of flow as that is the only real reason that you would lean out at any point. (at least that I can think of)

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Guest bastaad525

I do need to get a fuel pressure gauge. Been thinking exactly what you suggest about dynoing but I dunno if my wife would go for another $75 'wasted' so soon just to see the effectiveness of one mod. I know that most people agree the injectors should be good for a bit more so they shouldn't be the limiting factor or the cause of the lean running. Fuel lines and tank were all cleaned and flushed less than a year ago, and I keep up with filter changes regularly. That pump is not only stock but it is old and making a few strange noises to boot :) I'll get a fuel pressure gauge and get an adjustable FPR (not RRFPR, just a regular $40 MSD boost referenced FPR to replace my aged, stock unit, will most likely run it at stock or near stock pressure though) and dyno again at that point most likely. Hopefully going to have the pump installed today, and hopeful now that I should feel some difference at least on the top end.

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I always check the pumps on the car. Leave the hood cranked and run an el cheapo guage under your wiper. It will only take one time flooring it to redline to know if it's good. I had a stock Supra turbo pump drop from 50 psi at 10 psi boost to 25psi at redline. My A/F's were 13.8 at redline :shock:. and low 10's at lower rpms.

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Guest bastaad525

those numbers are very close to what I ran at the dyno... more and more certain with every reply that it's the fuel pump. Man i can't WAIT to get this thing in there....

 

What do you guys think... good for an extra 10hp on the top end? that being too optimistic?

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