Fuel for 300whp..?

ZXTOO · Dec 27, 2007

I have a ZX2 and right now the fuel system consists of an SVT pump and 42lb injectors. At 16psi I made 302whp. The fuel pressure was dropping off a bit in the high rpms so we had to dump fuel in to keep the a/f right.
I'd like to keep it at the current power level (or maybe another 20whp) but I want it to be safe. I want to get 60lb injectors but will that be enough? Will I have to get a BAP too? I'm trying to put an end to modding this car so the less I buy the better.

DigitalGT · Dec 27, 2007

Does your ECU see the fuel rail pressure drop and compensate by lengthening injector pulse width or were you manually adjusting the fuel tuning?

42 lb injectors can flow enough to support your power goals. I really don't see a reason to swap them for 60 pounders. All that will do is lower your required pulse width and raise the inaccuracy of low RPM fueling slightly. Your problem isn't pulse width though it's pressure.

The BAP is very easy install and it has a pretty good track record. I would try the BAP first then worry about injectors second. Even with 60 lb injectors, tuning pulse width while having unreliable rail pressure is sorta putting the cart before the horse.

OrangeSVT03 · Dec 27, 2007

You know at 16psi of boost you should see 56psi of fuel pressure....

As a general rule of thumb its 1:1 on the boost/added fuel ratio

ZXTOO · Dec 27, 2007

DigitalGT said:
Does your ECU see the fuel rail pressure drop and compensate by lengthening injector pulse width

Yes. At least I think so, its been a little while since I got tuned and I don't have any of the datalogs. The max hp for 42lb'ers was is supposed to be 305 so I figured I was close to maxing them out.

ZXTOO · Dec 27, 2007

OrangeSVT03 said:
You know at 16psi of boost you should see 56psi of fuel pressure....

As a general rule of thumb its 1:1 on the boost/added fuel ratio

So in other words, I need a BAP. I thought the SVT pump was ok for a good amount of hp. Ugh, more money into the pit, lol

OrangeSVT03 · Dec 27, 2007

On my buddies SVT we datalogged the fuel pressure drop across the injectors, the SVT pump kept up great until 4300 rpm the it all went down hill until redline..... and thats was running around 12psi.

Here are a comparison of with and without the BAP....... Fuel pressure is the Yellow line

BAP OFF

BAP ON

ZXTOO · Dec 27, 2007

Ok so I guess that answers my question. The bigger injectors may fix the problem but they're being over worked due to insufficient fuel pressure.
So I guess my next question is will the BAP and 42lbs support 320ish whp or will I need a BAP AND 60 lbs?

c4uldr0n · Dec 27, 2007

I would check your injector duty cycle to find that out. See what you are running now and make a good judgment. Try to keep your IDC under 90% if you want them to last longer.

-c4

OrangeSVT03 · Dec 27, 2007

I would go with a minimum of 50's... but you're problely better with the 60's

In the above datalogs the factory voltage limit is what caused the fuel pressure to drop off, at 4300rpm the fuel pump was at 100% of the factory duty cycle with the BAP you can go WAY beyond that.

Kenne Bell has been doing that to Mustangs for years without any issues and I dont see any reason that you cant do it to our pumps. I've been running my BAP for about 2 years and with 20psi @ 7000rpms I can still maintain 62psi of fuel pressure.

polarisman14 · Dec 28, 2007

I've heard that 60s may be big enough to compensate for the difference in lack of fuel pressure by dumping more fuel, plus the duty cycle for that would be way lower. If you are going for 325whp like it sounds like you are, you are overworking the 42's--I believe at 85-90% duty cycle (recommended) that you max out at 318whp. I'd go with the 60s.

ZXTOO · Dec 28, 2007

polarisman14 said:
I've heard that 60s may be big enough to compensate for the difference in lack of fuel pressure by dumping more fuel, plus the duty cycle for that would be way lower. If you are going for 325whp like it sounds like you are, you are overworking the 42's--I believe at 85-90% duty cycle (recommended) that you max out at 318whp. I'd go with the 60s.

I'd like to be able to get away with just the injectors if I could. I wanted to stop putting money into my car but injectors, BAP, and a MAF.ia + more dyno time is gonna add up. Has anyone used 60lbs without a BAP?

qqqq · Dec 28, 2007

The only way to stop putting money in a car is get rid of it.

OrangeSVT03 · Dec 29, 2007

Did you even LOOK at the datalogs I posted... that was with 50's.

Just do it right and be done with it before you end up going lean and toasting a piston or two.

orangeZXT · Dec 29, 2007

ZXTOO said:
I'd like to be able to get away with just the injectors if I could. I wanted to stop putting money into my car but injectors, BAP, and a MAF.ia + more dyno time is gonna add up. Has anyone used 60lbs without a BAP?

yeap i had 60's with out a BAP u will need one or a return setup if u plan to go over 300, my FP was still dropping with the 60's

lourenco · Dec 29, 2007

The safe way would be the 60lb injectors and boost-a-pump. Like orangesvt03 said it would be better to do it right than toast and engine. He noted atleat 50lb injectors, but 60lb injectors can be found for a lower price.

ZXTOO · Dec 30, 2007

Yeah sometimes the right answer isn't always the one you want to hear. 60lbs and BAP it is, another $400

OrangeSVT03 · Dec 30, 2007

I know its a real pain to keep dumping money into a car... but look at it this way...

$400 now or a rebuild later.

ZtsFucus · Dec 31, 2007

who makes good 60lbs injectors??

polarisman14 · Dec 31, 2007

siemens/deka makes good ones that are relatively cheap, 200 bucks or less for a set. They are good quality and I haven't heard of anyone having major issues with them. RC makes some 60s or 72s but they are 400-500 for the set IIRC.

William@CFM · Dec 31, 2007

These are the ones.

STFUN · Jan 2, 2008

Er, guys, injector sizing is done based on engine horsepower, NOT wheel horsepower.
For 302hp with an 80% duty cycle and a BSFC of 0.6, he'd be looking at 56.62lb injectors minimum. 60lb injectors at 80% DC and 0.6BSFC max out at 320hp.

orangeZXT · Jan 2, 2008

many have made over 300hp on 42's. and 60's should be good for close to 400 hp

OrangeSVT03 · Jan 2, 2008

365whp on 50's here.

EuroAyres · Jan 2, 2008

orange doesnt that kinda contradict stfun's info. Unless your running 100% DC. By his calcs the 56lbs would be good for give or take 350 wheel hp at 80% so you must be running like 100% with 50lbs right?

OrangeSVT03 · Jan 2, 2008

Maybe.... but I run a seriously modified fuel pressure set up (tune wise)

I've managed to get my fuel pressure to rise as load increases.... its all in the tune settings.

IslandFocus · Jan 2, 2008

Have you figured this out for the Zetecs yet?

Fuel for 300whp..?

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