550cc Injectors 350whp about the safe limit?

[turbozxi]

Hi I am a NooB but did search theres a few topics but just am looking for clarification. Can Side feed 550cc injectors produce 350rwhp safely? be using a Walboro 255lph and straight fit nismo or Toda injectors 550cc with a Power FC on my black top 1994 S14 sr20det.

Looking to keep the engine stock and just add on bolt ons for a nice daily driver. Any relavent help would be appreciated.

:)

[Inland180]

YESSS!!!! 550cc injectors are more than enough for 350whp.!! :)

[turbozxi]

Thank you sir the engine is capable of living with that power level to I hear correct? :bow:

[kandyflip445]

With proper tuning, yes.

[NZO]

I believe 550s will be running pretty high duty cycle at that power level which is why I went with 740s. I dont get why anyone would get 5xx injectors when 7xx are only ~$40 more and offer a lot more room for safe operation.

[turbozxi]

Well for idle quality and deceleration reasons mainly, i know people will say if its tuned well blah blah, in reality I have found the right sized injectors for the application will work best. In saying that I think around 370 rwhp is achievable with 550cc's but then thy are begiinning to run a dangerous duty cycle. 350rwhp is the safe limit I am fairly sure?

Cheers guys

[wootwoot]

I was going to get 740's for My 275whp set up that I'm building, but some 550's fell in my hands so I'll take it. I would personally not push 550's over 330whp at stock fuel pressure, but I'm a frady cat. 740's wont mess with your idle or deceleration at all if the proper rom tuning is done. You could try some of the rc engineering 650 cc's that Scott from Enthalpy has just started tuning on someone elses car(see FreshAlloy for detail). They are at 363whp on those things safely.

[orion::S14]

550cc = 52.4lbs/hr

You have 4 of them...

Assume 90% duty cycle as a safe max...

Use .55 BSFC...

...

[ (52.4 * 4 * .90) / .55 ] = ~343rwhp as a *safe* maximum.

The number's don't lie...

- Brian

[SPEC_R_SILVIA]

so what are 740's safe for

[pgt892]

550cc = 52.4lbs/hr

You have 4 of them...

Assume 90% duty cycle as a safe max...

Use .55 BSFC...

...

[ (52.4 * 4 * .90) / .55 ] = ~343rwhp as a *safe* maximum.

The number's don't lie...

- Brian
Shouldn't you use .57 BSFC for a turbo application? And 550cc/min are 56.64 LB/hr. [(56.64*4*.90)/.57] = ~357rwhp. BTW I am using conversion of CC/Min = LBS/HR x 9.71. Let me know if I did something wrong.

[pgt892]

so what are 740's safe for
Using the same BSFC of .57 that I used above and the conversion of CC/Min = LBS/HR x 9.71. 740CC/Min = 76.21 LBS/HR. Using a duty cycle of 90% on a four cylinder.
[ (76.21*4*.90)/.57] = ~481RWHP.

[orion::S14]

1) Your lb/min conversion is off...you divide "cc" by 10.5 to get "lbs/min".

2) BSFC is up for debate...It varies car-to-car, and depends on A/F. But...I have seen with my car that if you back out the BSFC using a known RWHP and duty cycle (I have done this, from my dynos), that .55 is pretty close.

For example...

Running 370cc injectors at 8psi, I made ~248rwhp. That was 98% duty cycle, as recorded by a Techtom CMX-100.

So....(35.2*4*.98)/.55 = 251rwhp theoretically...pretty damn close.

- Brian

[pgt892]

Ok, thanks for the help. I have been using the wrong information I suppose. And I agree that BSFC is up for debate, but I see where you get your figure from.

[turbozxi]

I was going to get 740's for My 275whp set up that I'm building, but some 550's fell in my hands so I'll take it. I would personally not push 550's over 330whp at stock fuel pressure, but I'm a frady cat. 740's wont mess with your idle or deceleration at all if the proper rom tuning is done. You could try some of the rc engineering 650 cc's that Scott from Enthalpy has just started tuning on someone elses car(see FreshAlloy for detail). They are at 363whp on those things safely.
I like the sound of the 650cc injectors does Enthalpy sell them? Or are they to be used with a modified fuel rail etcetra?

[SPEC_R_SILVIA]

if 740s are good for 450rwhp am one happy camper

[wootwoot]

THey are RC injectors I believe. Search around on Freshalloy to get more information. They are stock fuel rail though

[turbozxi]

Thanks I thought the RC's were top feed I'll check it out. BTW anyone know where to buy a z32 MAF at a good price? :hitit:

[z0iid]

i will scan the article I have at home (can't remember which magazine) but they left stock injectors on a 300zx - and were able to get 800+hp (dynoed).

So....why spend money on aftermarket injectors....money can be better spent elsewhere.

/my 1/50th of a dollar.

[Id-]

550cc = 52.4lbs/hr

You have 4 of them...

Assume 90% duty cycle as a safe max...

Use .55 BSFC...

...

[ (52.4 * 4 * .90) / .55 ] = ~343rwhp as a *safe* maximum.

The number's don't lie...

- Brian

sure they do, those numbers are NOTORIOUSLY WRONG for all sorts of motors...
according to that calculation SupraTTs cant make 500rwhp on 550cc injectors that they have stock... but guess what? they do it ALL THE TIME
according to that calculation a stock SC300 can't make 375rwhp on stock injectors... but i've seen plenty make MORE THAN THAT... .55 might be good for a SR20, but by no means should this formula be taken as be-all-end-all for motors...

the BSFC rating is very different for all sorts of motors and there are a lot more variables to toss in,such as head design, intake manifold design, motor type (rotary anyone?), octane (RON and MON) of gasoline used, etc

personally I wouldnt go over 370whp unless I had race gas, then i'd run it up past 400whp...
i'm sure you know all this, i'm stating it for correctness and so some newbie doesnt come in here and take this half-truth as the word of god