55chevlover

I recently assembled a '91 350 from a Camaro that falls flat above 3800RPM at WOT. The engine has been bored 30 over, 9.5/1 pistons, headers, 52mm throttle body, Siamised ported intake, new 24# injectors, 1.6 ratio roller rockers, Chevy Hot Cam, tuned chip to match assembly. Base timing was set stock and fuel pressure at idle is correct. I am wondering if I have a fuel delivery issue that I am not getting enough fuel thru the stock fuel pressure regulator, maybe a timing issue due to the knock sensor (the valve train is a little noisy) or maybe a weak spark. I have replaced and upgraded all the internals in the distributor. The engine starts and idles fine. It also has great pull under load up until about 3800 rpm where it just seems to "fall flat". I can rev it to well over 5000 RPM in park (don't like doin that but I'm trying to narrow down possibilities). Anyone have any notion as to how I can narrow down my possibilities here? What is the max horsepower the stock fuel regulator will feed?

Tuned Performance

iTrader: (92)

Have you checked your fuel pressure under a load ? Was this Dyno tuned or did you supply your tuner several logs ?

55chevlover

Thanks for your assistance. No I have not checked my fuel pressure under load. Any suggestion as to how I may do that safely? Also, I gave the tuner my stats and they tuned a piggyback chip that I then installed. The nearest dyno is 75 miles away so I hope to figure this out without having to trailer my car there. I failed to mention in my first post that this is a TPI engine. I apologize if that was not understood by those offering help.

Tuned Performance

iTrader: (92)

Doesn't sound like a very good tune if they didnt have several datalogs to go bye. You might be able to power brake a few times with a feel pressure gauge resting on the hood or cowl so you can see it. Is this a brand new issue ?

55chevlover

This issue has been since the engine was first run. It only has maybe 500 miles on it if that.

Tuned Performance

iTrader: (92)

You should start with a fuel pressure check then post a data log using tunerpro.

55chevlover

I recently purchased a laptop with the intent of installing a tunerpro program for that purpose. Obviously thats a little more involved but it is planned near future. In the mean time I will try the powerbrake idea this weekend.

Tuned Performance

iTrader: (92)

Once you have a log I will be more than happy to try to assist you.

ASE doc

To answer your question on how much HP the stock regulator will support, it depends on injector size, and fuel map programming. The factory regulator will maintain full throttle fuel pressure at about 40psi. Injectors are rated at 40psi which means that your 24lb/hr injectors will output 24lb/hr of fuel fully open at 40psi. Since injectors are only operated at 80% max duty cycle to prevent overheating of the coils, this means that your injectors will supply 19.2 lb/hr at their operational limit at 40 psi. To know how much power these injectors will support, or better yet, how much fuel your engine needs(lb/hr), there is a formula that I might remember if I hadn't suffered so much brain damage during my extended reckless youth.

The good news about injector ratings is that they are merely a rated output based on nozzle size and pressure. Injector output will increase in a linear manner with pressure. This means that your 24 lb/hr injectors will output 36lb/hr at 60 psi.

Just an educated guess, I would say that 24lb/hr injectors at 40psi is a little on the small side. I would recommend that as a base, you set fuel pressure at 60psi and tune around that. 19.2lb/hr will have you setting your full throttle injector on times too close to the max and you risk running the engine lean. Another critical issue in this discussion is your fuel supply. I would be much more concerned trying to support your modified engine on the stock fuel pump than on the stock regulator.

I do not believe that the injector size has anything to do with the performance issue you're having. tunedperformance is on the right track there. You need to connect a scan tool and datalog to see what the engine control system is doing.

55chevlover

Thanks for your knowledgeable input. I am in process of purchasing a ALDL cable to connect to my laptop and already have downloaded the tunerpro program. I will present more data as it becomes available. Thanks again.