Darkshot

iTrader: (4)

I just picked up a set of L98 heads yesterday for 50 bucks. I'll look into porting but I'm trying to keep this cheap and easy. They'll be worked over by a machine shop before installation. My questions are about TBI fueling.

1.) I've already got a TPI pump, so I can basically fudge around with the spring to get whatever pressure I want, correct?

2.) If I go with the Cop 501 camshaft (212/218, .488/.495, 112) will I be able to use a constant fuel pressure? There is no CA legal Vacuum-Referenced fuel pressure regulator that I know of so I'm trying to choose a power level (camshaft) based on whether or not it can use a constant fuel pressure. I have 68# injectors as well as 90# injectors in my garage to choose from for this.

ownor

iTrader: (5)

are they the F-body L98 cast iron heads (64cc) or the Y-body L98 aluminium (58cc) ones? just thought i'd mention this. seems like a nice catch anyways!

as for #1, correct. i think http://www.top-downsolutions.com/ is offering one of these higher psi springs.

#2, very good question actually as for the non-vacuum AFPR, that's gonna be interesting. as for the injectors, i dont know how much psi you can run without running into problems with your idle tune, but using RBob's excel spreadsheet (iirc based on 80% duty cycle and .45 BSFC) your 68lb cop injectors will support 320fwhp and 90lb early-454 injectors about 420fwhp @20psi.
how much were you aiming for?

hth, ownor

Darkshot

iTrader: (4)

I'd like to run as much horsepower as I can while leaving the induction system appearing stock. That means I have to use the FPR that's inside the TBI unit. This is the primary concern and I'll sacrifice whatever power I have to to make this so. This car is a daily driver.

ownor

iTrader: (5)

fueling in stock appearance shouldn't be a problem imho, other than the afpr not being a vacuum-referenced one - i simply don't know about that one.
you need to pass visual inspection i guess. can you maybe put some kind of CAI or an open element on there, and what about exhaust? if the L98 heads are aluminium, they will be pretty obvious for a trained pair of eyes if i may say so.

Darkshot

iTrader: (4)

Not worried about the air cleaner because that's easy enough to swap out every 2 years for a visual inspection (I use one from an L69) I have emissions legal 1-3/4" headers and exhaust, and the L98 heads are cast iron. And I am running EBL.

thomas1976

What happens is at higher fp 19+ psi (may be different for bigger injectors) fueling is not wery pricise at idle and lower trottle, resulting in low trottle and emission irregularities.

Turbo city has a VAFPR (to adjust with the right combination of springs and shims) that fits at the stock location, or you could modifie your stock one. Although Iv read that both will allow some minor imprecise fueling due to the stock regulator conception. Now if fueling will be precise anough to pass inspection has to be tested.

Darkshot

iTrader: (4)

Wow, this is news to me...I always assumed they were external (not sure why). I guess that throws out that restriction, maybe I'll go with a bit bigger cam even

ownor

iTrader: (5)

same here, i wasn't aware that there were vafprs for the stock location! that definately sounds like something to look into. interesting information thomas, thx.

thomas1976

There used to be a stock one too. Here's someone that used it. There some more members that have experience with the stock VAFPR. Lets hope they chime in.

https://www.thirdgen.org/forums/engi...ector-pod.html

Darkshot

iTrader: (4)

Yes let's hope!

Ronny

iTrader: (1)

GM used a VAFPR in some 7.4L TBI applications. I bought mine from gmpartsdirect.com. It comes with a spring that is way too strong(>25 lbs?). you need to use the stock spring or the topdownsoutions somewhat stronger one. A FP gauge is a must. Some use an Aeromotive remote VAFPR that comes with two differing springs. then you fab a block off plate and add a custom gasket. VAFPR needs to be used with an ECU that offers support for it. EBL is what most of us use. I dont believe GM puters wont work.