Stock Injectors Max Out When?

[4felix20]

This guy is saying he has been running a rich 10 psi on a T3 Super 60 Turbo (.48 AR turbine .60 AR exhaust) for about 2 years. he also has new pistons, crome-moly rings, and a 3mm metal head gasket for lower compression. that's all the info i have of his setup..

i thought the stock injectors maxed out around 7psi?

[SeVa-S13]

Injectors max out from flow (HP), not an arbitrary number like psi. 7psi on a little T3 is considerably different than 7psi on say, a 57trim T4 compressor. That being said, I'm not quite sure the stockers are capable of, but I'd doubt much past 200 at the wheels.

[4felix20]

also said he runs 12 second quarter miles at 13psi. the fact that he is running RICH at 10psi is what makes me wonder.

[SeVa-S13]

Maybe he's using a rising-rate FPR? (FMU) Kinda ghetto, but they work, aslong as you're not pushing too much boost. 13psi on an FMU sounds sketchy to me. =\

[DammitBobby]

Formula for estimating the required injector size. HP X BSFC = lbs/hrThen divide the lbs/hr by how many cylinders you have to figure injector size per cylinder. 2nd part of the formula the industry standard is not to push the injectors past about 80% duty in order to keep them operating safely. lbs/hr /.8 = lbs/hr A very good book to read is EFI is Building & Tuning High-Performance EFI by Ben Strader. Web site is efi101.com

[:: orion ::]

also said he runs 12 second quarter miles at 13psi. the fact that he is running RICH at 10psi is what makes me wonder.

My guess would be that he's an idiot, and running 13psi on an FMU. (That's ~150psi of fuel pressure assuming he's using an 8:1 FMU - But no worries, one day a fuel line will pop and his car will catch fire...)

Also, 13psi from a Super-60 would be in the ~280rwhp range...so 12s are not too far out of reach...could be true if he cut 1.8 60' times and had a light car.

- Brian

[4felix20]

i just learned that he has a 5th fuel injector right before the TB. also, his timing is set to 15 BTDC...

now it sounds believable...i guess.

[AustinSilvia]

just to let you guys know... fmu's can't just increase your fuel pressure to no end. they are completely dependant on the fuel pumps ability to pump fuel. for instance a 12:1 versus an 8:1... if you have a 12:1 it will just max out earlier than an 8:1 but at max they will be pressurized and flow at the same rate, which will be the max rate of the fuel pump. also flow rate and fuel pressure are also related quantities. increasing flow decreases pressure and increasing pressure decreases flow. just wanted to throw that in there.

[BadMojo]

Formula for estimating the required injector size. HP X BSFC = lbs/hrThen divide the lbs/hr by how many cylinders you have to figure injector size per cylinder. 2nd part of the formula the industry standard is not to push the injectors past about 80% duty in order to keep them operating safely. lbs/hr /.8 = lbs/hr

Grassroots Motorsports had a really nice article about injectors back in May of 2004. Conveniently enough, they used a KA24DE boosted and running approx 200hp at the wheels as an example.

Using 80% duty cycle and a BSFC of .6 (.5 for the NA engine) they came up with something like 395cc injectors.

Interestingly enough, they also mentioned that OE Hondas often run near 100% duty cycle at redline. Not really vital info for us, just interesting trivia.

[crzycav86]

Grassroots Motorsports had a really nice article about injectors back in May of 2004. Conveniently enough, they used a KA24DE boosted and running approx 200hp at the wheels as an example.

Using 80% duty cycle and a BSFC of .6 (.5 for the NA engine) they came up with something like 395cc injectors.

Interestingly enough, they also mentioned that OE Hondas often run near 100% duty cycle at redline. Not really vital info for us, just interesting trivia.

What's BSFC? Is it a constant kind of like volumetric efficiency? Help out a noob

[BadMojo]

What's BSFC? Is it a constant kind of like volumetric efficiency? Help out a noob

It's Brake Specific Fuel Consumption.

Here's a nice page that explains a lot of this stuff. One thing that isn't mentioned is that, AFAIK, BSFC will not remain constant throughout the engine's range of operation. The .5 for a good NA street engine and .6 for forced induction are just rough average #s.

http://www.holley.com/HiOctn/T....html

Edit: Every article or book I've ever read has used .6 for BSFC in a forced induction application. I assume that this is a well-established figure to use.

[crzycav86]

Thanks