theboss84

I have just finished rebuilding my TB's and replaced the stock fuel pump to the 85 model. I want to increase the fuel pressure as per recommendations on the forum. I have removed the plug from the rear TB and am trying to figure out what the process for making the adjustment is. It looks to me as if without the tool from the outfit in Arizona that I am going to have to remove the regulator and make and adjustment then reinstall it and see what it did. I cannot figure out how to make the adjustment with the regulator on the TB tower. Please explain. Thanks in advance.

billschroeder5842

Why do you want to increase the pressure over stock spec? The reason the L83 has fuel pressure issues is because the stock pump in the tank looses capacity over time. When people switch to the 85-89, the factory pressure is higher to the regulator (virtually) guaranteeing that you have 100% stock spec fuel pressure--- which is plenty for a factory or even moderately modified engine.

theboss84

Thanks for the input. My reason for upping the furl pressure is that as I have been reading post from several corvette forums that bumping up the fuel pressure to 14-15 will make the L83 more responsive.

billschroeder5842

Yes, the bump will make the L83 "more responsive" if the pressure is less than factory spec to begin with. The most you will get is 100% of spec as the regulator will be operating at 100% efficiency. You will not be pushing more fuel through the system, just the optimal/designed amount.

This is a great fix. Also, bump your timing up to 10-12 or whatever your engine likes.

playsdixie

If you really want to, you'll need to install an adjustable pressure regulator...84/85 regulators were not adjustable....can't see how it would help or be needed unless you change injectors....

Tom400CFI

84 regulators most certainly ARE adjustable, and '84 owners have been adjusting them for 34 years now.

Adjusting helps b'c the '84 came with a pressure setting lower than what's optimal for the engine. MOST '84's ('82's and '82 & 83 CFI F-bods) will pick up decent power and driveablity with a bump in FP to the high end of the spec or possibly a bit higher -depending on the car.

corvettenorway

any mods on the manifoil ? .. if not try 13 psi .. 12 deg timing .. and yes i do have a crossfire ....

Tom400CFI

listen to corvettenorway.

Hot Rod Roy

Help me out, here. How does increasing the fuel pressure improve the performance of the car? Will increasing the fuel pressure change the air/fuel ratio? Will it increase the compression pressures in the engine? Will there be more air flow because if the increased fuel flow? Or what?

Tom400CFI

You already know this! I think...right?

Typically (on other/newer cars), it doesn't help. But this is LOW hanging fruit, on a CFI car. I think (thought?) all us CFI owners know that the car came with a marginal fuel pressure....barely enough. Every CFI that I've fooled around with loved more pressure than the setting they were assembled with. Some, needed a fuel pump to get there (in conjunction w/a FPR adjustment). Anyway, the answer is that the initail specs and set up were so sloppy that in most if not all cases cars came with too low a fuel pressure and could stand to benefit from more fuel; they were running too lean. Maybe that was to make the CFI meet their criteria...but whatever the case, almost universally, the cars run better with more fuel...which means that they were too lean from the factory.
How can that be? Like I said, to meet criteria. or just sloppy specs. Look the stock FP spec allows a whopping 50% variation in fuel pressure! That's GM's SPEC! That is garbage. That being the case, it's not at all unreasonable to expect an improvement with some analysis and fine tuning of the sloppy system. Does it make sense that a car is going to run the same from 9 PSI through 12 or 13 PSI? 'Cause that is the spec range. No, that doesn't make sense. Would a TPI run the same, at 36 to 39 psi (with the fuel pressure regulator vacuum hose connected) through 55 PSI (with the fuel pressure regulator vacuum hose connected)? Probably not.

Here is more; my CFI car ('83 Trans Am) was rated at 170 hp. What do stock '83 CFI Camaro's and TA's run in the 1/4 mile? OVER 17 SECONDS, IIRC. I increased my FP, advanced my timing*, installed shorty headers and Y pipe, opened my CAI/Cowl valve removed the mechanical fan and closed off the under hood snorkel and went 14.5 @ 95. That's a 3 full second chop, and a 15 mph gain from crappy headers, exhaust and "free tuning/mods". Takes about 230hp to go 95 mph in a 3300 lb car. -That was w/o even touching the manifold. Evidence that GM left a LOT on the table with their "tune" and specs.

So:
It improves performance by give the engine what it wants; a richer A/F ratio
Yes, it will change the A/F ratio. For sure.
No, it won't change compression
No, it won't change air flow

*I didn't arbitrarily "add FP and timing" either. I didn't have access to dyno's back then, so I used the drag track. I made passes until I knew what the car would run, then started changing a thing, and making more passes. Over time, I got it dialed in and got the car running the lowest number that it would run; the 14.5/95 number, on that 305/CFI engine. So the fuel and timing were not arbitrary. "just throw fuel at it!" No. "Feed it what it wants". Yes.

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PatternDayTrader

You get slightly better atomization at the injector tip with higher fuel pressure ….