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Discussion Starter #1
Many have asked me what the limits of the stock fuel pump are. While there is no definitive answer, here are some results of testing on our recently turbo'd GTS:

Stock fuel pump
idle fuel pressure 48psi
on-boost fuel pressure 37psi

MWR 255lph fuel pump
idle fuel pressure 52psi
on-boost fuel pressure 49psi

The car is making 275whp on the stock engine, 6.5-7psi boost. We have our 460cc injectors in there and they were maxing out with the stock pump in there. With the MWR pump we had to scale the tuning way back and the injectors are running at a comfortable pulsewidth now. Tuning is also a lot easier when you don't have to fight the pressure drop-off.

I was watching and any time the boost was up the stock pump was dropping off. You'll notice the MWR pump drops slightly too- that is because of the in-tank regulator. It can't account for pressure drop through the lines, which appears to be ~3psi at high flow rates. This is not a problem. The MWR can flow MUCH more fuel than what's required at this power level.

We do a ton of testing on this stuff and I often forget to share the results with the public. I'm going to try to do that more.
 

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Yeah good info. YGPM MWR....
 

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Discussion Starter #5
And to emphasize the problem, at 7psi I went from 30psi relative fuel pressure (fuel pressure-manifold pressure) to 42psi. That's a big improvement.
 

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great info matt, i cant believe you are making so much power on such a low boost...took me 11psi to make 276HP..of course i know that turbo plays a part in that
 

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Smaay said:
great info matt, i cant believe you are making so much power on such a low boost...took me 11psi to make 276HP..of course i know that turbo plays a part in that
Tune has a lot to do with it too. Remember that they have 93 Octane up there.
 

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Just to clarify further, the stock fuel pump can support power up to ~270whp?

I'm asking because I want to run a small amount of nitrous (50hp) next month and with my ricer math, I should be at approx 180whp anyway, so I'll be ok right?
 

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Good stuff, Matt...

Here's data logs supporting what Matt was saying so you can graphically see the pressure curves.

These are simple dyno pulls taken with identical engine setups and then tweaked tune to take advantage of the extra fueling capacity as indicated by the richer AFRs.

Stock Pump:



255LPH Walbro Pump:



Best,

Phil
 

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Great info - thanks Phil and Matt


Sticky.
 

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So looks like I'll be fine to project up to a max of 270whp on the stock pump......
 

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10-10.5psi final on 9:1 compression. The high/stock comp engines need more gas yet-- but they make more power too, so..........

Also, regarding fuel demand for the SC'ed cars, the TVS has less parasitic drag than the 62, so the fuel demands to achieve the same whp will be greater for the M62 engines than what you see above... In otherwords, if you were/are running 275whp on the stock pump with a 62, you'll see an even bigger pressure drop up top in FP...

Hope that helps,

Phil
 

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So looks like I'll be fine to project up to a max of 270whp on the stock pump......
Depends on your FI system to some degree. Regardless, you're having to run the injectors (if 550s) well into the 90+%DC to get to that kind of power with the stock pump at redline... so you may be able to get away with it, but it's not really "right"-- i.e. very little margin. You should probably pinch the rev limit if you're going to play that game... Just do that math on the DC as you approach redline and see what you've got to play with-- it won't be much with the stock pump. I tried hot wiring the stocker just to see if it helped. I got a whopping 1 psi increase, so no real help there. Just gotta replace it with something better...

PV
 

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MWR 255lph fuel pump
idle fuel pressure 52psi
on-boost fuel pressure 49psi
so on the stock motor
I have mwr 255 walbro
MWR FPR kit w/return line etc...

what should fuel pressure be set to?
those numbers above w/700cc injectors?
 
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