if you are running the stock Fiero 15# injectors, yes, I'd crank it up a little - if using the stock 3.4 17# injectors, I'd say leave it alone. but - the right answer is to look at the BLM's. adjust accordingly.
Normal is in-between 40 psi to 44 psi. Use this formula to calculate psi and flow ratings: For example: 17# injector = 16.4lbs/hr @39.2 psi fuel pressure & 17.3 lbs/hr @43.5 psi fuel pressure New flow rating = [square root of (new pressure /old pressure)] x old flow ratio To calculate the hp required to support this new injector size we need this formula: Fuel requirement in lbs./hr = (Max HP x BSFC) / (number of injectors x duty cycle) 17.92 = Max hp x .55 / 6 x 80% Max hp = (4.8 x 17.95) / .55 = 156.4 hp The formula is the key.
Mine both look the same. You can send them out for cleaning and flow testing. They will flow match then scribe each injector with a number. That is what Cruzin Performance did for me at $12 per injector. Very nice work. Rich is a nice guy too.
EDIT: Did you mix the two together?
[This message has been edited by Hudini (edited 01-22-2008).]
It took a bit of searching (with a magnifying glass ) since I had not seen any part numbers on mine but sure enough, in very tiny numbers, there are part numbers etched into the black plastic top. They are located on the top half black plastic where the fat part curves over toward the skinny neck. You can just look at the ones out of the car to make sure the ones in it are the right ones.
On mine the 15# numbers- 3276 5235136 17# numbers- 8074 17109826
I run the stock pressure with my 3.4 that runs the 3.4 injectors with FOCOA headers,darrell morse TB, 272 cam, truleo intake and ported heads but I had a custom chip burned with the use of a wideband sensor. I do have the Holley adjustable regulator just in case I want to tweak it a bit.
New flow rating = [square root of (new pressure /old pressure)] x old flow ratio
This is correct for "simple" injectors, but the Fiero injectors I've tested are apparently a constant-flow-rate design that are relatively insensitive to pressure. I have done my own testing, and there is very little measurable difference in injector flow rates between 38 and 50 psi.
For reference, the stock 2.8 fuel pressure is 43 (+/- 2) psi, measured with the engine not running. Measured fuel pressure will be about 8 psi lower with the engine running, due to the design of the regulator. The regulator actually maintains a constant (~43 psi) difference between fuel pressure and manifold pressure.
I'm running stock fuel pump, rail, and regulator (runs at appx 45 psi) in my 87GT 3.4/Getrag setup.
-seems to work greatn as I have been running 120+ miles a day for the last 6 months without a hitch-
A few more details so you have the whole picture: Hypertec chip, 160 thermostat, Darryl Morse ported throttle body and plenum, Ocelot exhaust, Ported stock headers, New Old Stock Fiero Cam, 17 pound injectors from donor 94 Firebird, 1.6 roller tip rockers, Rebuilt heads, Billet Steel Flywheel and heavy duty clutch from the Fiero Store, Stock bore and pistons on motor with new moly rings, polished and chamfered crank, shotpeened rods with ARP bolts added (extra insurance).
The 3.4 pulls like a train off the line compared to 2.8 and has only thrown an EGR code a couple of times since the engine changeout. It did this with the 2.8 as well. YEP...every dang sensor and the EGR valve are brand new since rebuild...nothing a piece of folded up paper doesn't fix.
Old top speed=About 120 MPH with a tailwind New Top Speed=Don't know yet but sure as hell accelerates to 80 much quicker than with old 2.8 Fuel economy=Averages about 27 MPG according to my cell phone calculator...same as I got with the 2.8
I have been extremely satisfied with my efforts and HIGHLY recommend the 3.4 over the 2.8...and it's a super easy conversion
thanks Hudini. I appreciate it. While were on topic, I was going to get my injectors cleaned, but not sure what kind of shop does this. Any one know? I saw cruz performance online does it, but not sure if I want to ship.