Injector Formula

Post by **matt0941** » Wed May 28, 2003 3:19 am

Hi I couldn't find it anywhere (surprisingly) and Maximum Boost's wording confuses me.

But does anyone know the formula for what sized injectors are need for HP/Flow variables. Cause I am switching to a top feed fuel rail and need to know what injectors I should go with. (I don't know much about them

)

Thanks.

Post by **hannibal** » Wed May 28, 2003 3:19 am

Check out this thread Matt...

http://www.nissaninfiniticlub....21932

Post by **:: orion ::** » Wed May 28, 2003 3:19 am

But I wonder if it's needed to go one size higher seeing as how those number look conservative anyway...

250rwhp is easy with 370cc injectors, and their max is closer to 265-275rwhp. Has been proven in many apps, unless I'm mistaken.

And that's not to say that's bad advice - But 240rwhp is a little low to call the max of 35lb/hr or 370cc.

Later - Brian

Post by **hannibal** » Wed May 28, 2003 3:19 am

I think sil80 misunderstood what Maximum Boost said. From what I read, I think Corky Bell means that if you're between sizes, then you should use the next larger sizes (duh!?!) If you're looking for 200 up to 250hp, you should use 370cc injectors. For 250 up to 300hp, you should use 440's, etc...

Post by **sil80drifter** » Wed May 28, 2003 3:19 am

1) :oblivion: matt... I thought we were friends (and u dont read every post I write?! :poke LOL j/k)

Anywho, hope it helped.

2) I did not misunderstand Corky, I did mention "safety and improvement" in that post. If you are at 250whp and you manage to add another 50whp to that (more boost, bigger exhaust/IC, etc), 550s will hold you over WITH a safety margin large enough to probably add another 10-15whp. It never hurts to be able to add a lot more fuel without the need to buy new injectors. And since even the cheapest piggy back (i.e. AFC) can adjust your fuel needs up to 50% in either direction, you will not be running too rich at idle, even if you "only" have 250whp. Btw my goal is 200whp, and some day 340hp at the crank (Koguchi has that and he is the master drifter, so I figure I can't go wrong with that)

sil80

Post by **hannibal** » Wed May 28, 2003 3:19 am

Orion made the point that you dont NEED 440cc injectors to run 300hp (about 250hp at the wheels). If you're planning future mods, then by all means, choose your injectors with those plans in mind. But if you're running a 7psi kit, I dont think 50lb's are worth it.

Post by **matt0941** » Wed May 28, 2003 3:19 am

Thanks for all the replies guys. But I have heard alot of commotion over going with larger injectors and having a crappy idle, is this what the effect caused by larger (too large) injectors and running rich? I will be utilizing a Custom Top Feed Fuel Rail and a Greddy E-manage + E-01.

And thanks for making that post Sil80, sorry I missed it I was uhh... out.... can we still be friends.

Post by **SingleCamSam** » Wed May 28, 2003 3:19 am

If you tune right your idle will be fine with 50lb'ers, probably even 72lb'ers. All depends on your needs though. No point in dropping the extra cash IF (notice the IF) you don't plan on making too much power. But you may want to upgrade later....

Post by **sil80drifter** » Wed May 28, 2003 3:19 am

Forethought is the mother of anti-detonation. Matt, yeh we're cool... E-Manage huh... interesting.

sil80

Post by **WDRacing** » Wed May 28, 2003 3:19 am

Theres a real easy method Matt...Just add 100cc to whatever HP you want to have. Works every time...

WD

Post by **sil80drifter** » Wed May 28, 2003 3:19 am

WHP or crank HP?

sil80

Post by **silviaNE** » Wed May 28, 2003 3:19 am

crank i believe. Having crappy idle is result of improper tuning. Use a piggyback or JWT.

Post by **themadscientist** » Wed May 28, 2003 3:19 am

WDRacing wrote:Theres a real easy method Matt...Just add 100cc to whatever HP you want to have. Works every time...

WD

That formula fails to take into account how many cylinders and thusly how many injectors you have. Is this only a four cylinder formula? I highly doubt 4 444cc injectors would support 400hp, now six might.

Post by **themadscientist** » Wed May 28, 2003 3:19 am

I would trust this

http://www.rceng.com

There is an injector size calculator on their site.

Post by **WDRacing** » Wed May 28, 2003 3:19 am

Why wouldn't 444cc injectors support 400hp?? A simple increase in fuel pressure would enable them to work just fine. And I said 100cc's over your hp goal, not 44cc's.

WD

Post by **themadscientist** » Wed May 28, 2003 3:19 am

four 444s won't do it. Crunch the numbers. you would need 75lb squirters to keep from having to crank the pressure up to hideous levels and running them wide open.Using my worksheets which are based off the RC ones you would only be able to support 230hp using a BSFC of .60, a fuel presuure of 43.5 psi and a maximum duty of 80%. You can increase fuel pressure to say 60 psi and run the duty to wide open and maybe MAYBE cover 300hp but I wouldn't bet my pistons on it.

ok 100ccs over the hp goal, so 550s. They will cover 300hp with 4 at a marginal rate. You can crank the pressure to 5 kilo if you want and run the duty to 100% and you won't make it man, sorry. My formulas are begging for 75lb injectors for 400hp on a four.

Post by **hannibal** » Wed May 28, 2003 3:19 am

the formula from Maximum Boost is really similar to the one on RC Eng's site. Corky Bell uses a BSFC of .55 while RC uses .60 (for turbos). Also Bell assumes that you would run at 100% cycle with no problem while RC uses 80% as max duty cycle. I guess thats part of the reason you're supposed to step up an extra size with the formula from MAx Boost

Jay

Post by **SingleCamSam** » Wed May 28, 2003 3:19 am

If 550's will only cover 300hp at a marginal rate, then how is d240t supporting 350hp at stock fuel pressure with 50lb (525cc) fuel injectors?

Post by **sil80drifter** » Wed May 28, 2003 3:19 am

the formulas have safety margins. he may be running on the edge of detonation. but that's where max power is anyway.

sil80

Post by **themadscientist** » Wed May 28, 2003 3:19 am

that's at 80% duty, they may be pushing the injectors wide open. at a high fuel pressure. No two motors are the same, some have higher or lower Brake Specific Fuel Consumption than others. Real world testing is the only sure answer. When thowing around theoretical numbers around I always err on the side of caution.

Post by **SingleCamSam** » Wed May 28, 2003 3:19 am

Sounds like good policy.

Post by **WDRacing** » Wed May 28, 2003 3:19 am

Nah....boost it till she blows. Caution is for the weak.

WD

Post by **themadscientist** » Wed May 28, 2003 3:19 am

I only do that with my own car, I obsess when I working with someone else's car. Drive it like ya stole it!

Post by **McAdam** » Wed May 28, 2003 3:19 am

easy forumla to find out what you need for injectors, pretty simple.

injector size X number of cylinders -------------------- = hp injectors are capable of 6

so basically on a 6 cylinder 550's will net you 550hp. but always err on the side of caution. I am shooting for around 300 and I am getting '85 RX-7 GSL SE injectors (680cc's and in the junkyard!! wahoo!!! cheap!) which should be good for: 680(cc's) x 4(number of cylinders) = 2720 <--- divide that by 6 = 453 1/3 hp! m plenty o' safety!

Post by **sil80drifter** » Wed May 28, 2003 3:19 am

hey I'm so happy that someone finally realized that RX-7 injectors can be used! yeeh! I am getting 550s from a T II, 89-91, so that they are already high impedance (12 ohms, need smaller resistors than low impedance older gen injectors, although I'm not sure it matters if you use resistors anyway), or if i can't get those then just stock 440s (or 460s, can't remember) from a same year range NA. Btw, I thought that the GSL SE's were 720s, or at least that's what my buddy told me. Maybe I'm just confused. Way to go McAdam, did u happen to read my pushes for FC injectors in eariler posts? I was almost about to give up telling everyone, and just do it myself and show ppl that it can be done. Now I have a comrade in arms. Maybe we should just go rotary, port the hell out of it and do 11s NA, at like 11k rpm..... *drool*.... maybe I'll do that after tha KA-ET thing.

sil80

Post by **McAdam** » Wed May 28, 2003 3:19 am

Actually, I am from the CA board and we were discussing RX-7 cause they are plentiful in the junkyard and they are low impediance, which the CA computers like heres the thread rx-7 injectors .

NO rotary for me!!! I've laready had my fill. I picked up a 88 rx7 convertible as a project, (blown motor, what a shocker) bought a motor for it, which eneded up being blown as well (stupid Ebay). $500 paper weight. appearently they go bad sitting on the shelf, thats so lame. a thin layer of teflon is applied to the rotor housing, and if the motor sits unused for more than a year, it starts to flake off and kills the apex seals. at least thats what a guy at the junkyard told me when I was looking for another motor.

McAdam

Injector Formula

Injector Formula

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