injector sizing

Go to www.rceng.com they have formulas that will help. For the Supra use .55 for BSFC and don't exceed 85% duty cycle.

Later, Steve

:hail: to the resurrection of a 3.5 year old thread.

boy i didnt even have my supra 3 years ago :dunno:

I just did some re-caculating....

my best dyno run bpu has been 432 rwhp... /.85 = 508 crank hp

plugging that into the forumla provided, I get that I need 575 cc injectors.... but the stock injectors are only 550 cc?.... what am I missing in the scheme of things?

Supradedupra said:

I just did some re-caculating....

my best dyno run bpu has been 432 rwhp... /.85 = 508 crank hp

plugging that into the forumla provided, I get that I need 575 cc injectors.... but the stock injectors are only 550 cc?.... what am I missing in the scheme of things?

Click to expand...

Increased duty cycle for your stock injectors, probably well over 90%, or higher static fuel pressure. If you haven't increased your static fuel pressure, then it's the increased injector duty cycle. It (higher duty cycle) can be done, but most recommend not exceeding 85% duty cycle for injector longevity and stable AFRs. Better, IMO, to have just a bit too much injector than smaller injectors with higher than recommended duty cycles on an ongoing basis.

Certainly, slightly smaller injectors, with increased static fuel pressure, can be safely run. Decisions like these depend somewhat on driving habits.....a weekend cruiser with occasionals blasts to 16-17 psi or if your car and driving mode are on the "kill" setting everytime you leave your driveway. Hope this helps.

Ken.

Your power goal can easily be met with 720s. I made 789 whp at 1.95 bar with 720s and increased static fuel pressure. Also, with my current stroker set-up, I have dual OEM pumps that feed eight (8) 1000 cc injectors and, so far, I've made 1110 whp at 36.9 psi. I'd recommend getting the second OEM pump as soon as you can in your mod program. Good luck.

Ken.

Why don't you go with 850s? Having run both, from what I've seen there isn't really a downside to 850s vs. 720s. Why buy injectors that are generally accepted to be too small to support the power that the rest of the setup is capable of?

Supradedupra said:

thanks ken...

well, I think I am going with 720 cc denso injectors on an hks fuel rail for my setup.

according to my calculations, (and your .9 duty cycle)... I can produce 673 hp at the crank, which is right around where I think I want to be with my current transmission and clutch setup.

This is around the high 500's to the wheels which is still streetable.

I was told that my stock fuel pump is good for 500 rwhp, and that I should consider upgreading to a dual tt setup which should be good for 1000 hp or so (which is more than enough).

The reason I went with a t-88 is that it has possibilities for upgrades. I can gradually grow into the hp versus being capped at say 500 rwhp with a smaller turbo.

I can always upgrade to larger injectors at a later point

Click to expand...

I had 720`s on a t-78 and they leaned out around 620-650 .Just get some 800`s and be done with it.I now run 880`s and they are fine.Very little price difference if any.

Supradedupra said:

I just did some re-caculating....

my best dyno run bpu has been 432 rwhp... /.85 = 508 crank hp

plugging that into the forumla provided, I get that I need 575 cc injectors.... but the stock injectors are only 550 cc?.... what am I missing in the scheme of things?

Click to expand...

holy mother of....

432RWHP BPU? What boost level was THIS at? 22psi? What was done to the car? Automatic or manual?

Also what octane were you using?

You can easy calculate

same Horsepower as ccm of injector (near maxed out)

550ccm ~ 550HP
720ccm ~ 720HP
850ccm ~ 750HP

and it is always to have some more capacity to be sure