550cc injectors good for how many lbs of boost?

[S13FASTBACKSR]

How do I determine how much boost I can lay down with my 550cc injectors until they start leaning out?

[DrifterProdigy85]

Boost has nothing to do with it. Only real way is to have something that calculates the Duty Cycle Used of the Injectors. Typically, 550cc injectors are good for 350whp. You can get 350whp from 15psi from a GT30R or 10-12psi using a GT35R. I always make sure i run larger injectors than i need. I use 740cc with my 2871R because i know they wont get maxed out.

[S13FASTBACKSR]

ya i want to run 850's on the 30r but for now i can only afford to run my current 550's...so its not the boost you can run on them that determines the a/f ratio being too lean..its the duty cycle? i read somewhere that you dont want to exceed 80% duty cycle..do you know anything about that? thanks for the input

[Chezedik]

+1, you need to know the amount of air. Really HP or TQ would be a better bet than boost. but a set of 555's is good to about 350whp at 100% DC.

[S13FASTBACKSR]

100% duty cycle is no good..it is not safe..do you know what duty cycle is? that is the percentage that your injectors are open. So at 100% your injectors will be open the whole time the engine is running..this will cause richness, misfiring and a bad a/f ratio..you dont want to exceed 80% duty cycle maybe 85..

[Chezedik]

Yes, I know exactly what duty cycle is. I also know that I said it was good to about 350 rwhp when maxed out. But thank you any how.

BTW, the problem with 100% duty cycle isn't because they will just cause richness, it is the problems associated with them binding and locking open. When this happens, you run rich to the point that they will probably cause engine damage.

[S13FASTBACKSR]

so ya they are good for 350whp you are saying but at 100% duty cycle..lol you couldve added that they are good for 350whp in an unsafe manner and probably 325whp would be a lot safer..good thing i know 100% DC is a no go ..im just kidding bud thanks for your help though i appreciate it

[exode]

on my gt2871 i can only push 20 PSI max and get about 370rwhp

i run 18 psi to be safe with 55lb. msds and i get around 360rwhp

[exode]

i'm having trouble editing my post, sorry for the double.

Leaning out those injectors also greatly depends on the gas you are using, the climate you are in, atmospheric pressure, etc. I run a tuned ecu with an SAFC and a wideband now, I can make nice little adjustments to my AFR to keep those injectors running at prime. I'm fairly favored with the race gas I get my hands on and the altitude I'm at, it depends alot but for me those are my numbers

[S13FASTBACKSR]

alright cool thanks a lot man..just to be sure...55lb injectors equal out to slightly bigger than 550cc injectors?

[Chezedik]

http://www.rbracing-rsr.com/fuelinjectors.htm

S13, you're probably right. I guess it could have just gone without saying and said 325whp. In reality though, the whp ceiling does depend a lot on supporting mods. I have seen people in the 375whp area, although they surely must be maxed at that point. In any case, that is some serious power in an S chassis.

EDIT: 550ccm=52.37lb/hr so 55lb/hr=577.59ccm

[S13FASTBACKSR]

ya 375whp has got to be maxing out those injectors and in a very unsafe manner too..thanks for for your help and by the way thanks for doing the math for me

[Chezedik]

Now, my fuel pressure is at 55psi which is still safe and should be helping atomization (something with the Walbro, IDK), but my DW 555's should behave as if they were 627s at that psi, so that should be good at .85DC and .45BSCF for about 375rwhp.

[S13FASTBACKSR]

wow 375whp on 555's with only 85% DC? thats great ..but what does .45BSCF mean? and also my FP is at 52psi and im running a walbro 255lph fuel pump too so on 550's i should be good until what? 360 safely? or am i wrong?

[Chezedik]

According to the link above in the calculator it is about 403chp at 80%DC (*.8=322whp), so my calculations may be a little off, but you get the point. 350whp is not unattainable with 550s, even at 85% DC.

BTW, BSFC is Brake Specific Friction Coefficient, or essentially a measure of how efficient your engine is. The lower the number, the higher the efficiency. While you must dyno to get an exact number, it is generally assumed .45 for 4 valve engines (DOHC).

[S13FASTBACKSR]

oh ok i see..interesting..ya now i got a pretty close estimate of what 550's can produce so im glad of that..thanks for that link by the way..i didnt see it until you just said that

[Chezedik]

Sorry, I used the wrong information in that acronym. It is Brake Specific Fuel Consumption, but the rest of the info is pretty much correct.

I just looked at the DW flow sheet and it says that set should be capable at 80%DC and .5 BSFC is 338hp. So about 355hp.

[S13FASTBACKSR]

cool thanks man..i'll have to look at the DW site..by the way that 355hp is at 100% DC correct?

[Chezedik]

Nope, 355 is assuming an 85% instead of 80 and a BSFC of .45 instead of .5. It is just throwing darts, but it helps get the point across.