do i need 30lb injectors?
#1
do i need 30lb injectors?
I have home ported heads, cc305 cam, electric water pump, JH long tubes, 255 fuel pump, adj fuel regulator, all the other bolt ons excpet at bigger throttle body. I am wanting to know if i will need the 30lb injectors or not. Thanks people
#4
#7
Tuner Formula Its just math!
Here is a formula that i know several tuners use including my own. I see it used quite a bit so i ASSUME it is accurate.
Expected horsepower x .625 / number of cyl.
example in your case:
(400 x .625) / 8 = 31.25 so I would go with a 32. You can always choke the down a bit with PCM tuning. Hard to choke them up! BTW i was in the exact same boat and went with 32#'s. Hope it helps.
Expected horsepower x .625 / number of cyl.
example in your case:
(400 x .625) / 8 = 31.25 so I would go with a 32. You can always choke the down a bit with PCM tuning. Hard to choke them up! BTW i was in the exact same boat and went with 32#'s. Hope it helps.
#9
Using 0.625 in the formula assumes a BSFC of 0.50 #/HR/HP, and a duty cycle of 80%. That is a good, conservative approach. Actual "tuning" numbers need to be substituted for the BSFC if you have them. A well tuned performance motor, running without a power adder, can operate at 0.45. My engine dyno tune showed up at 0.45-0.46 range. If you are running a blower, or dry nitrous, you need to look at BSFC's above 0.50. Myh 275-shot dry nitrous tune ran 0.53 #/HR/HP.
The correct number for duty cycle is also a bit subjective... 80% is good for all types of injectors.... some can be pushed to 85-90%. But if you are selecting new injectors, I'd use the 0.50 BSFC and 80% DC.
There is no down-side to a larger injector. The reduced duty cycle extends injector life, and allows the injector to put more of its pulse width into the intake stroke. Obviously you need to program the correct flow constants and offsets for the specific injector you selected. One potential problem with a really huge injector is the inability to turn it down to the below 1.0 mSec pulse width required for idle, but as long as you are talking 42#/HR or less on the stock PCM, you shouldn't have a problem.
The correct number for duty cycle is also a bit subjective... 80% is good for all types of injectors.... some can be pushed to 85-90%. But if you are selecting new injectors, I'd use the 0.50 BSFC and 80% DC.
There is no down-side to a larger injector. The reduced duty cycle extends injector life, and allows the injector to put more of its pulse width into the intake stroke. Obviously you need to program the correct flow constants and offsets for the specific injector you selected. One potential problem with a really huge injector is the inability to turn it down to the below 1.0 mSec pulse width required for idle, but as long as you are talking 42#/HR or less on the stock PCM, you shouldn't have a problem.
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autoxr166
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09-25-2015 04:21 PM