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

 

Your stock injectors SHOULD be fine, but just incase, I'd go ahead and get the 30's to be safe..

 

If it was me I would go with the 30's just so you don't have to worry about not having enough fuel.

 

FWIW:
http://paradox.shacknet.nu/dave88lx/.../injectors.htm

 

What is Brake Specific Fuel Comsumption?


Also everyone has told me i will need #30 injectors for my new setup which i hope to be around 400RWHP, but this chart says i would need larger?

 

BSFS is the amount of fuel it takes to make a given HP..5 is normal for a n/a engine..45 is pretty effecient and beyond a normal hot rod.

 

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.

 

"My" formula does fit the chart. The last entry in the 400 HP section.

 

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.

 

good info

I was going to try and get by with some 30's for a while without the nitrous but it looks like no way