Fuel psi under boost

[joeyd0730]

hey all, i have a s-trim on my 91 gt. just got it back on the road after sitting 4 years w blown motor.heres the deal. i am now using aftermarket fuel rails and a in-line aeromotive regulator and a vortech fmu. it is set at 42 psi at idle w vacum line off. last time i drove the car 4 years ago from what i remember i was hitting around 70 psi of fuel press at 10 lbs of boost. now at 10lbs of boost i am anywhere between 95 and who knows what because my gauge stops at 100 psi. i know it has something to do with the in-line regulator. i do have a vacum line attached to the regulator and the fmu. what do you guys suggest, scrap the fmu? or is 90 psi of fuel press correct for that amount of boost. i spoke with vortech they said average is 12 psi of fuel pressure for every 1lb of boost. to me that sounds nuts. that is well over 100lbs of pressure. thanks for any help, joe

 

[Daggar]

Joe--

Do yourself a favor and either get it dyno tuned or get a wideband 02 meter for your car. You're stabbing in the dark with playing the "Guess my fuel pressure game". The ideal fuel pressure is going to be different for every combination. Air/Fuel ratio is the only thing that matters when you're talking about the correct delivery of fuel.

 

[1988WHTGT]

Not trying to hijack, but anyone know a good place to get an s trim or know anyone with one for sale?

 

[stang8urimport]

wtf? What does that have to do with this thread? crapola

 

[1988WHTGT]

He said he had an s trim on his car

 

[droptop93]

first off do yourself a huge favor and get rid of the FMU...they're just overpriced bandaids and cause more harm than good. buy properly sized injectors and MAF, and then you will have a much better starting point.

My car has around 47psi of fuel pressure at idle (with the vac line on) and increases 1:1 with boost. I don't remember exactly what the FP is with the vac line off...but I will double check and let you know.

My car stays at 11.2:1 A/F all the way across the board. Slightly rich, yes...but better rich than lean.

 

[joeyd0730]

cool deal drop, let me know. so your running 1lb of fuel per 1 lb of boost? what is your totals under boost, i am running 36 lb injectors.77 massair and 70 throttle body, w a 190 intank and a external t-rex.

 

[2badazzstangs]

FYI, don't know if this helps but my car has fuel pressure around 38 psi at idle and about 80 psi under boost. I have a procharger p600b with an 11 lb setup, 255lph inline fuel pump, and 30 lb injectors.

 

[QDRHRSE]

first off do yourself a huge favor and get rid of the FMU...they're just overpriced bandaids and cause more harm than good. buy properly sized injectors and MAF, and then you will have a much better starting point.

My car has around 47psi of fuel pressure at idle (with the vac line on) and increases 1:1 with boost. I don't remember exactly what the FP is with the vac line off...but I will double check and let you know.

My car stays at 11.2:1 A/F all the way across the board. Slightly rich, yes...but better rich than lean.

I run a 1:1 boost referenced regulator as well...I think that's whats going on. It works good. Throw the FMU in the trash! The boost referenced regulator adds 1lb of fuel for every lb of boost. I run my car at a base of 42lbs with 36lb injectors and it hits about 55lbs at full boost.

 

[joeyd0730]

thanks guys, those numbers are much more reasonable than my 95-100 psi at 10 lbs. from what i remember a few years back when i had stock fuel rails and stock regulator a wat at 60-65 at 10 lbs of boost. the aeromotive in line is 1:1. i will eliminate the fmu and keep you all posted, thanks again, joe