max boost for KA with t25 on stock fuel?

[SilviaSR20DET]

hi, im planning on making a custom t25/t28 turbo kit and was wondering what is the limit for boost on stock fuel system?

[orion::S14]

Probably less than 5psi...

The stock injectors are safe until about ~180rwhp.

Assume 95% duty cycle (too high to be safe) and .55 BSFC... :

270/10.5 = 25.7 lbs/min

[25.7 X 4 X .95] / .55 = 177.56rwhp

- - - - -

370s are only $100...it's better than a new motor!

- Brian

[projectRDM]

Using a rising rate regulator you won't break 6.5psi, and that's a janky ass way of doing it. Buy the 370s and run 11psi cleanly.

[Red]

Guna need bigger then 370cc's to run 11psi.

My 370cc's are ok at 10psi. As long as I dont pass 5000rpms... Then they cant get enough fuel to my engine and I hit lean. My FPR set at 60 will fix this.

I would get 550cc's to run 10psi easy and safe.

[Id-]

umm dude, 370s are plenty to run 11psi on a little T25, on a GTIR T28 that'd be a different story, it'd be on the edge...

but my point is, you cant compare your 20G turbo vs a T25/T28 hybrid; boost is NOT the same for different turbos...

[woodysmom]

What are the largest injectors that fit in ka24de stock fuel rail? You guys were saying that the stock injectors will run lean because it can't supply enough fuel to the engine under high rpm's w/ a large turbo. Then is it true that 370cc injectors will perform exactly the same as the stock injectors up until the point where the stock cannot provide enough fuel? Is this the same with 370 vs 550? Basically i'm wondering if it's always the bigger the better(safer) w/ injectors

[PSI240SX]

if you get the same style injectors you can run 720cc even. But 480-550 will be plenty. What do you plan on running the injectors with? You need some sort of mod weather it be hacked maf, or SAFC, or tuned ecu.

[mellojoe]

I have seen stock injectors with an FMU (which is just basically a rising rate fuel pressure regulator) hit 10psi and 240whp.

This was on a Garrett GT32 turbo, not a T25.

But, you should be able to get 7psi safely on a t25, and push it to 10psi if you dare. Just get on a dyno with a wideband to check your tuning.

But, then again, if you can afford to hit the dyno, you should be able to afford some 370cc injectors (used off an SR20) or some 440cc (used off an RX-7).

PS: I THINK the RX-7 injectors are 440cc. THey might only be 370cc, but for some reason I think they are bigger. The purple top ones are sidefeed like the KA24de fuel rail.

[Id-]

I think you're correct, they are 440cc, cant remember if thats a nonturbo 2nd gen or a 1st gen, but I had no idea they were sidefeed; was under the impression the only sidefeed were the 3rd gen's side feed secondaries at 850cc (which need a special adapter to fit into the stock SR20 rail)

[orion::S14]

I have seen stock injectors with an FMU...

Yeah, but he's asking about stock injectors, no FMU.

And FMU is considered "fuel management"...he's asking about running with nothing to manage the fuel, other than the puny 270s.

(Just so no newbs aren't confused when they see "10psi" and "stock injectors" in the same sentence)

- Brian

[andrave]

rx7 prime's are 550 and second's are 880 I belive, for all recent except the Turbo II, which used 6 550's, I think.....
not sure on that so look it up.
what I do know is the smaller 550's won't fit without the spacer (at least not correctly) but the 850's fit pretty well.

[Id-]

RX7 3rd gen had 2 550 topfeed? primaries and 2 850 sidefeed secondaries
the Turbo II had 2 550 topfeed primaries and 2 550 topfeed secondaries

[s13dan]

i have 370cc on my redtop and i hit fuel cut HARD at 11psi... im running a stock 240sx fuel pump thou so im keeping my boost stock until new fuel pump and injectors..

[Id-]

fuel cut? i wasnt aware there was a fuel cut on the SR motor? i'm pretty sure your pump ran out of fuel or you blew the spark out

[tru_40sx]

u think 440cc injectors off an rb will work with my ka with a basic t25 setup! will i encounter any problems?

[gotta240]

OK- Another turbo newb q-

How is 10psi on a tiny turbo any different than 10 psi on semi's turbo? The way i look at it, 10psi is a "hard" measurement... Meaning the motor shouldn't know if a 6 year old is blowing into the intake or if a solar turbine is giving the air, as long as it is 10psi... RIght? What am i missing?

[bardabe]

OK- Another turbo newb q-

How is 10psi on a tiny turbo any different than 10 psi on semi's turbo? The way i look at it, 10psi is a "hard" measurement... Meaning the motor shouldn't know if a 6 year old is blowing into the intake or if a solar turbine is giving the air, as long as it is 10psi... RIght? What am i missing?
diferent size turbos will blow diferent amount of air. (the reason we have a MAF sensor [ Mass Air Flow sensor] so yes your engine can tell the diference) so eh a t25 boosting 12Psi is like a T28 boosting like 7 or 8 psi. bigger turbo = more air at less PSI

[orion::S14]

It's hard to wrap your mind around (seriously)...BUT...the answer is:

........

1) Boost pressure is NOTHING MORE than a restriction to flow.

2) What matters is MASS AIR FLOW.

..........

10psi from a T25 is probably HALF the VOLUME (half the mass of air) as compared to 10psi from a T3/T04E 50-trim.

Look at it like this: Most KA-T guys make under 300rwhp from 11-12psi out of a T3/T04E.

I'm making 338 at 12spi...because of my cams and tubular manifold, mostly.

I have less flow restriction than others, so the point where some MASS of air flowing through my motor creates 12psi of restriction in the intake...is MORE AIRFLOW as compared to other guys.

i.e. 12psi going through my motor is maybe 38lbs/min of air. 12psi from a basic T3/T4 setup with stock cams and a log manifold might just be 34lbs/min.

Either way, they both create 12psi in the intake manifold...it's just that my setup can flow a GREATER MASS at the same boost.

Restriction to flow. Mass airflow.

Get it?

- Brian