Hi,
I own a 85' a stock. recently I installed a AFPR (tpis).
I read in another thread that the stock injectors are 24lbs and the pressure is about 35 psi. If I increase the pressure to 40 psi for instance can I gain more power?

Thanks.

The original post:
https://www.corvetteforum.com/forums...tock-85-a.html

 

increasing fuel pressure OR upgrading the fuel pump voltage has a minimal flow gain. Will you feel this power. NO

 

 

Anything you do to increase fuel pressure or increase size of injectors will be over-ridden by the O2 Sensor input to the ECM unless you have it remapped.

 

Computer will pull back the injectors to compensate based on the O2 sensor reading.

By itself this change does not gain you power, you will need to adjust FP after modifications that will allow more air into/out of the engine. That way, the computer is able to easily richen it up when you have given it more air to play with, within its limits.

Spend your money elsewhere, on modifications to help the engine inhale/exhale, unless you're having to replace the injectors anyway, in which case you should add the AFPR while you're in there.

 

Been reading the posts on fuel injectors and seen in here that stock injectors are 24lbs on my 86 I was told the injectors were 60lbs , would that be the reason for hard starting in the morning

 

I agree it would. In fact, with a 383 on a stockish tune with 36 pph, it would barely start and when it did, it would flood the engine quickly. That said, if you did have 60pph injectors, you must have done something to the chip to even get it running, assuming it will. Therefore, I doubt you have 60pph injectors. It is way more likely your injectors are dirty and highly doubtful, except for the placebo effect that adding snake oils to the fuel will help. If they are Multec injectors, toss them for a rebuilt set of 24pph injectors and it could make a difference.

 

Thank you for your reply.
I already opened the stock air box like in the attached image.
I also considering to install OBX headers and Borla exhaust. If I do so, can I gain more power using the above + AFPR?
Thanks.

P.S I also have bbk throttle body.

 

I use a simple rule of thumb. If it is cheap and easy, probably not. So to answer your question, NO!

All that does is dump more fuel. O2 sensor will detect that and shorten the pulse width and lessen the fuel delivery so back to square 1.

If you want more power, you are going to have to work for it. Dyno tune. Before I go there, I would put a better intake then send it for dyno tuning. That is about a $600 process plus transport and whatever misc stuff you need. But to take full advantage of everything, you are going to want to have an intake and header job first.

 

Regarding the ECM. I read about some chips like Hypertech. I read these chips are useless.
I don't live in the US, so I cannot fine any tuner that specializes in C4.

Is there any recommended ECU chip?

 

Hi
TPI's love around 45-55 psi fuel pressure, yes you can feel the difference mid range and top end. But she will water your eyes with very rich idle.
Add long tube headers to compliment the TPI breathing, advance the timing a little add premium fuel and she should run a second quicker in the quarter mile.

 

How so? More pressure, more fuel, more adjustment. Maybe at WOT it might not care about the O2 sensor. I would think that midrange it might. Instead of trying those hacks, maybe he should invest in a chip tune and be done with it and stick at 43 psi.

 

Any chip recommendations?
I don't live in the US.

I read Hypertech is not good enough.

 

Nope. None of them work. Add your location to your profile and maybe someone can recommend a facility closer to you that does dyno tuning. Off the shelf chips aren't that great.

You can try THIS or better yet go to their facility.

 

the other guys are right, higher fuel pressure (above 43 psi measured with the vacuum blocked off) will cause a richer mixture for street use.

if you track your car (drag, autocross, circuit etc) then 50 psi works great when your pedalling hard !

there is a difference between the 2 uses.

 

FYI:
1985 Vette injectors were 30 pounders but the fuel pressure was like static 35 psig or so (28 with vac). In 1986 the injectors were 23 pounders but now the static fuel pressure was 45 (38 with engine running and vacuum applied to FPR). That's why the typical 24's are a good replacement for 1986 and newer or for the 1985 if you upgrade the FPR.
That's also why John @ LPE (RIP) used '85 injectors on his 383's back then. We had so few choices on injectors !

BTW I do not like adjustable FPR's for a number of reasons.

All the L98's under light throttle when running in Closed Loop will self tune and try to get back to the chip's tune - so higher fuel pressure is slowly undone as much as the ECM can: maybe like 10% or so ? However at WOT the ECM goes to Open Loop and uses preset running parameters. Consequently higher fuel pressures or larger injectors WILL affect the A/F ratio at WOT.

Leaner is meaner so typically 13:1 makes more power than 12:1 or 11:1 etc. Basically unless you have done something to alter the engine more fuel will mean less power. Back in the day we ran higher fuel pressures to gain more power at WOT after changing the exhaust etc. Back in the day there was no software to alter your tune - so we struggled with big band aids ! lol

Finally please do not put bigger injectors in your ride unless you edit the chip/e-prom/tune for same. Doing so will ruin your engine as you dump excess fuel into it especially at start up !

 

When Can I get less restrictive chip?
I don't live in the US so I prefer to buy one.

 

How so? ECM will reduce the pulse width so what you gained with higher pressure will be subtracted with lower pulse width.

Why better than what the injector was designed for? Why not simply get a larger injector, have the injector constant changed and not try to ghetto engineer it to work?

 

IOW, please don't do the "Ghetto Engineering". Get the right part and tune the chip?

 

because at WOT the ECM has pre determined settings (according to whoever tuned it)

Im not sure what you are trying to argue about tho ?

I know the changes I referred to make a difference between street and track, because I make those changes in my car all the time.
I know that my car will go faster up a hill at 50 psi, why, because it does, if I set my pressure lower the car will be slower and thats a fact !