TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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just curious how much power can stock 305 injectors, throttle body, computer, fuel pressure, and fuel pump support? Ive searched but havent found any answers
__________________ Iroc MODS
Air/Fuel- Moddified Holley 650 Dual Feed electric choke vacuum secondary carb, Holley Street dominator high rise intake, mallory 3 port fuel pressure regulator, 14x3 Summit open element air cleaner. 6psi fuel pressure
Ignition- Summit HEI dist, Summit 8.0mm wires. 8 degrees of timing
Exhaust- Hooker 2055 headers and y-pipe, 3" MAC cat delete pipe, 3" Hooker catback
Transmission- S-10 2025 stall torque converter, Superior shift kit w/ vette servo, Energy suspensions mount, B&M super cooler.
Cooling- 180 hi flow mr.gasket thermostat, 195 jet fan switch.
Suspension- UMI tubular non adjustable lower control arms
I dont understand... What is there limiting the LO3 to such low HP numbers? I thought the stock TB could support like 300 HP or something? Is it just the injectors??
__________________ -Adam
1990 Firebird Formula
Bone Stock 305TBI, T5 tranny, 62k Origional
UMI subframe Connectors
I dont understand... What is there limiting the LO3 to such low HP numbers? I thought the stock TB could support like 300 HP or something? Is it just the injectors??
The problem is stock fueling. Stock fuel pressure is ~12 PSI. If you want any more than that you need to change the fuel pump. At that pressure the L03 injectors can't support much more than the stock 170hp. I run a bolt-on L05 with tuning and my fuel injectors are getting up over 95% duty cycle by about 4200 RPM on stock 12 PSI. It's really the fuel pressure that is limiting.
Its when you run fuel pressure up to between 15 and 20 PSI or more and/or run larger injectors that you can support 300 - maybe 400 horsepower with tuning.
The problem is stock fueling. Stock fuel pressure is ~12 PSI. If you want any more than that you need to change the fuel pump. At that pressure the L03 injectors can't support much more than the stock 170hp. I run a bolt-on L05 with tuning and my fuel injectors are getting up over 95% duty cycle by about 4200 RPM on stock 12 PSI. It's really the fuel pressure that is limiting.
Its when you run fuel pressure up to between 15 and 20 PSI or more and/or run larger injectors that you can support 300 - maybe 400 horsepower with tuning.
68# police car injectors at 45 psi will support about 485 FWHP keeping the duty cycle at a reasonable 80%.
The stock throttle body flows reasonably well to 300 hp. With ultimate TBI mods and a pod spacer, it flows decently to about 320 FWHP. Above that a Bored out TBI or a 454 TBI is needed.
That would be engine HP (fwhp). What I did was to take the 55 #/hr that the injectors flow (all stock), multiply by 2 for 2 injectors, then divide by 0.50 for the BSFC (or just multiply 55 * 4).
That gives 220 HP, flywheel.
Then to factor in the DC% at 85, multiply 220 by .85. That gives the 188 HP.
You can change the springs in the stock FPR for more pressure. Can also make it adjustable. Although a particular spring will only have a certain range of adjustability.
68# police car injectors at 45 psi will support about 485 FWHP keeping the duty cycle at a reasonable 80%.
The stock throttle body flows reasonably well to 300 hp. With ultimate TBI mods and a pod spacer, it flows decently to about 320 FWHP. Above that a Bored out TBI or a 454 TBI is needed.
I know it works in theory, and I also know you've done some pretty radical stuff with tbi. Whats the highest fwhp that has ever been proven with tbi?
You can change the springs in the stock FPR for more pressure. Can also make it adjustable. Although a particular spring will only have a certain range of adjustability.
RBob.
were can u get these springs what ones do u recommend i would like to see 15psi outof the stock pump if possible
It would work for that application too. I run a VAFPR but I am not using that feature(yet). I have the stronger spring of two in Aero unit set to 19 lbs. VAFPR offers max pressure at WOT and reduces the FP to improve the idle pulse width(larger pulse width).
Top Down Solutions sells a spring one tick stronger. From there one needs a GM 7.4L TBI high pressure spring >20 lbs.
Stock pump may not be able to hold much more than 12 under load?
Bought a box-O-springs at Home Despot, or someplace. Played mix-N-match 'till I got a measured 25 PSI. Works great !
Needed a booster pump, as the stock pump contains a blow-off at about 14 PSI.
GM "used" to sell one. I hear it is discontinued? I bet they are available somewhere? Try Ebay. I have the part # at home. I would think any manufacturer sells their own aftermarket VAFPR. Mine is Aeromotive unit. Very nice but a bit costly. I chose it since it offers two springs 10-20 and 20-60.
