max rwhp with 550cc injectors

[drpimper746]

i am about to put in RC 550cc topfeed injectors and i have no way of telling my duty cycle. i was wondering what rwhp i should run with those in. im thinking about turning it up to 350wrhp. but i don't want over run the injectors.

[the head]

i always wanted one of those hp adjustment knobs

how do you plan on compensating for the larger injector ECU reprogram or SAFC

[kidinthehall]

375rwhp is about as far as you should safely go with 550's

[drpimper746]

i have a safc II. I was going to put it on the dyno and just turn up the boost untill i hit a good rwhp. u think 375 with pump gas or with race fuel.

[orion::S14]

What motor, turbo, etc...all important details.

What do you have for timing control?

Let us know - Brian

[sr240mike]

Formula: (expected hp x 0.55)/#of injectors = lbs of fuel per hour
and
(cc/min) = (lbs/hr x 10.5)

so, 550cc/10.2= 53.92 lbs/hr

53.92 x 4 = 215.68

215.68/.55= 392.14 hp and thats at 100% duty cyle. I wouldn't go over 95% duty cycle.

Here's a helpful chart http://www.megasquirt.info/manual/minj.htm

[dunno]

I'll be damned, math IS useful. I always thought they were lying to me in school.

-Matt

[drpimper746]

i have s14 sr20 with a sc61 for turbo.

[msaskin]

FWIW, most injectors are designed to operate at 80% duty cycles. I really wouldn't recommend going much higher than 90% max for safety reasons. I'm also a little paranoid when it comes to my engine's health :)

You are planning on using a wideband o2 for tuning, right???

~matt

[orion::S14]

Sidefeed injectors can do more than 80% safely...

But pushing them to 100% for extended periods will probably blow something up at some point.

That doesn't hold true for top feeds, but...

I think of 95% as the safe max...leaves a little room for error.

- Brian

[orion::S14]

...so, 550cc/10.2= 53.92 lbs/hr

53.92 x 4 = 215.68

215.68/.55 = 392.14 hp and thats at 100% duty cyle. I wouldn't go over 95% duty cycle.

Oh yeah...to adjust for only 95% duty cycle, it's:

53.92 X 4 X .95 = 204.9

204.9/.55 = 372rwhp is the safe maximum.

[Var]

the megasquirt website says for 350 wheel horsepower for a 4 cylinder car, the injectors should be 534cc. This is for 85% duty cycle. It also says add 10% for turbocharged/supercharged engine. So it would be 587cc if you wanted to run the recommended duty cycle of 85%.

[drpimper746]

yes i have a aem wideband gauge. i will be tuning on a dyno.

[Jeff240sx]

I wouldn't push more than 350 on topfeeds at a proper duty cycle. You can, but when you overheat the injector and blow your motor, you'll be sad.
-Jeff

[Id-]

Formula: (expected hp x 0.55)/#of injectors = lbs of fuel per hour
and
(cc/min) = (lbs/hr x 10.5)

so, 550cc/10.2= 53.92 lbs/hr

53.92 x 4 = 215.68

215.68/.55= 392.14 hp and thats at 100% duty cyle. I wouldn't go over 95% duty cycle.

Here's a helpful chart http://www.megasquirt.info/manual/minj.htm

correct when using the stock fpr... if using any sort of fmu (and tuned right of course) injectors will flow quite a bit more... for instance, my stock sc300 injectors are 330cc/min at 42psi...

course this is tech talk; i'm just not talking about the sr20 specifically

[sr240mike]

Why risk an injector failing and blowing your motor? Why not just buy the right sized injectors the first time and be good to go.

[Powashiftin]

Sorry to bring back this thread, drpimper746 which fuel rail are you using?

[slick240]

shit i just read this and realized im goign to have to get bigger injectors :( im sad

[sykikchimp]

this info was already in the Archive and FAQ forum...

http://www.zilvia.net/f/showthread.php?t=44474

[mellojoe]

A real quick and dirty method:

1.5 * horsepower = injector size in cc (4 cyl)
0.75 * horsepower = injector size in cc (8 cyl)

That will give you a real rough estimate.

And that is for FLYWHEEL horsepower, not WHEEL horsepower. Calculate a 20 to 25% loss for drivetrain to get a rough estimate for wheel horsepower.

So, if you have 550cc injectors, you can see a max of about 367hp which tranlsates into about 275-290hp at the wheels.

If you want 350whp, then you are looking at about 435-467hp at the crank. 660cc injectors would be about 430 crank hp or about 350whp.

Now, these are real rough estimates... but it gives you an idea of how much horsepower you can make with a certain size fuel injector. The other mods are up to you.

[orion::S14]

mellojoe...that's a horrible method.

It is if you use that method and assume that it's WHP...then it's close.

See above...we've done the math and shown that ~360-370 will be the max. That's based on empircal evidence and some math...

- Brian

[Var]

also mellojoe you are on a controversial subject with drivetrain loss. Some ppl say that it's NOT a percentage, because if you have 200 or 500 horsepower, it still takes the same power to turn the drivetrain. Either way the numbers given are for wheel horsepower

[PSI240SX]

I've seen 409rwhp on 550's .... but I wouldn't do it.

[Powashiftin]

drpimper746 which fuel rail are you using?

[drpimper746]

sorry guys i am using some precision 50lbs. topfeed injectors. i am using a custom made rail out of lingenfilter fuel rail. with a SX fuel presure regulator.

[PROJECTRB240SX]

Doesn't the type of fuel matter? Different fuels have different knock support, so this would mean you'd need less of some fuels for the same hp.

IF those calculations are for unleaded 91 then thats one thing but your injector usage will change with different fuels.

[orion::S14]

Doesn't the type of fuel matter? Different fuels have different knock support, so this would mean you'd need less of some fuels for the same hp.

IF those calculations are for unleaded 91 then thats one thing but your injector usage will change with different fuels.

No...your A/F should be the same REGARDLESS of fuel.

93 octane unleaded pump gas or 110 leaded race gas....you tune for the SAME air/fuel ratio...you take advantage of the higher octane gas (more knock resistance) by running more IGNITION TIMING.

- Brian