injector question??? - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

g2ic02 · 03-01-2005, 06:02 PM

to start off i have a redtop sr20det with full exhaust and fmic and i searched...after i had searched for a while i found a post with a formula that takes horsepower at the fly and converts it to how large of injectors you need at a certain duty cycle.....with that in mind i found at 80% duty cycle the stock 370cc injectors are good to about 320hp @ fly....to me this doesn't sound right(i will try to find the thread)....so on to my actual question....i am looking for injectors to go along with a Z maf and my t28. I plan on making roughly 250-270hp. Which injectors should i get; the s15 4??cc, or go with 550cc. I plan on rom tuning. Thanks in advanced..

g2ic02 · 03-01-2005, 06:06 PM

To figure out what size injectors you need, use the following calc..

Injector Size = Expected BHP (brake horsepower (at flywheel)) x BSFC (brake specific fuel consumption)/Number of injectors x duty cycle

A good BSFC for a performance NA street engine is .45-.50 to be on the safe side, lets use .50.

Lets use 90% duty cycle..

So if you expect 220 bhp.. 220 x .50 /4x.9 = 30.5 lb/hr injectors.. round up. so 31 lb/hr

to find cc/min multiply 31 x 10.5 = 325.5 cc.. in general, if you have two injectors sizes to choose from one being 310, and one being 360cc.. always round up to the next closest size.

this is what it said in the thread posted by sykikchimp

Flybert · 03-01-2005, 06:35 PM

If you are going for 250, you can stick with stock injectors but if you are going to be going with 270 or higher, I'd suggest upgrading to S15 480cc or a 550cc. Personally, I'd just go for the 550cc because you will want to upgrade in the future.

bchumley · 03-02-2005, 02:36 PM

this is interesting to hear, cause I've been having a real hard time determining which injectors to run. I expect about 500 bhp, and was thinking either 740cc or 850cc injectors. this equation points me towards slightly smaller ones. hmm. any thoughts?

SPEC_R_SILVIA · 03-03-2005, 08:56 PM

i have the nismo 740cc's in car and there good for 450rwhp on pump gas but thats pushin it 95% Duty i guess it cames down to how much power you want

trixxxr4_kids · 03-12-2005, 02:42 AM

be lazy and average out 75-85 HP per 100CC of your injectors
so lets say you have stock 370s average that the max is at 300-340
its like guesstimating (WARNING!not to be taken entirely serious)

03-01-2005, 06:02 PM	#1
g2ic02 Zilvia Junkie Join Date: Jul 2003 Location: minnesota Posts: 480 Trader Rating: (3) Feedback Score: 3 reviews	injector question??? to start off i have a redtop sr20det with full exhaust and fmic and i searched...after i had searched for a while i found a post with a formula that takes horsepower at the fly and converts it to how large of injectors you need at a certain duty cycle.....with that in mind i found at 80% duty cycle the stock 370cc injectors are good to about 320hp @ fly....to me this doesn't sound right(i will try to find the thread)....so on to my actual question....i am looking for injectors to go along with a Z maf and my t28. I plan on making roughly 250-270hp. Which injectors should i get; the s15 4??cc, or go with 550cc. I plan on rom tuning. Thanks in advanced..

03-02-2005, 02:36 PM	#4
bchumley Zilvia Junkie Join Date: Jun 2003 Location: Hartville, OH Posts: 329 Trader Rating: (0) Feedback Score: 0 reviews	this is interesting to hear, cause I've been having a real hard time determining which injectors to run. I expect about 500 bhp, and was thinking either 740cc or 850cc injectors. this equation points me towards slightly smaller ones. hmm. any thoughts? __________________ Bret http://www.cardomain.com/memberpage/687020/1

03-03-2005, 08:56 PM	#5
SPEC_R_SILVIA Join Date: Mar 2005 Location: us Posts: 12 Trader Rating: (0) Feedback Score: 0 reviews	i have the nismo 740cc's in car and there good for 450rwhp on pump gas but thats pushin it 95% Duty i guess it cames down to how much power you want __________________ [IMG]

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03-01-2005, 06:06 PM	#2
g2ic02 Zilvia Junkie Join Date: Jul 2003 Location: minnesota Posts: 480 Trader Rating: (3) Feedback Score: 3 reviews	To figure out what size injectors you need, use the following calc.. Injector Size = Expected BHP (brake horsepower (at flywheel)) x BSFC (brake specific fuel consumption)/Number of injectors x duty cycle A good BSFC for a performance NA street engine is .45-.50 to be on the safe side, lets use .50. Lets use 90% duty cycle.. So if you expect 220 bhp.. 220 x .50 /4x.9 = 30.5 lb/hr injectors.. round up. so 31 lb/hr to find cc/min multiply 31 x 10.5 = 325.5 cc.. in general, if you have two injectors sizes to choose from one being 310, and one being 360cc.. always round up to the next closest size. this is what it said in the thread posted by sykikchimp

03-01-2005, 06:35 PM	#3
Flybert Post Whore! Join Date: Mar 2003 Location: none Posts: 3,862 Trader Rating: (7) Feedback Score: 7 reviews	If you are going for 250, you can stick with stock injectors but if you are going to be going with 270 or higher, I'd suggest upgrading to S15 480cc or a 550cc. Personally, I'd just go for the 550cc because you will want to upgrade in the future.

03-12-2005, 02:42 AM	#6
trixxxr4_kids BANNED Join Date: May 2003 Location: san diego Posts: 56 Trader Rating: (0) Feedback Score: 0 reviews	be lazy and average out 75-85 HP per 100CC of your injectors so lets say you have stock 370s average that the max is at 300-340 its like guesstimating (WARNING!not to be taken entirely serious)