Injectors for 3.1 Stroker

[E30arsen]

Hey guys, I'm in the home stretch of my stroker build need some help on injector sizes for my engine. I've spent hours googling trying to find out what some other people ran, some people said 24 lb injectors but I'm not sure if that's with the stock motronic ecu or with a megasquirt?



Spec:
3.1 stroker
Ported heads with 288 cam
long tubes
extrude hone intake manifold
Big bore throttle body
Megasquirt gen 2
10:1 compression

[digger]

A while back in early days if my build I ran 24lb on motronic with custom chip. Was running about 80% duty cycle. Should be fine for you. As you have MS you could easily run bigger to, it's unlikely you will need them based on your current specs IMO

[e30davie]

This is a pretty handy calculator.

http://www.not2fast.com/turbo/glossary/turbo_calc.shtml

Using 3.1L and all the turbo things at zero. at 8000rpm and 85% volumetric efficiency at 12.5:1 AFR. it reckons you need 264cc injectors x 6. This is with a specified max duty cycle of 85%.

The suggested 24lb injectors are 252cc.

24lb sounds like its in the ball park. As the calculator is a bit conservative with the 8000 rev limit.

[E30arsen]

Thanks a lot guys. I just wanted to double check the info I found. It's really hard to come by reliable info on 3.1 strokers

[ForcedFirebird]

I don't believe in those calculators so much.

I just made 255whp on a set of 19lb ford injectors (rated at 2.5bar, running at 3.5, so more like 21lb) - and ran out of injector on an m20 with 19lb (at 3bar) injectors at 208whp in another car. We also made 350whp on a set of 36lb injectors in a turbo m20 at 80% duty...

The injector style, and brand have a lot to do with it. The 19's on the m20 were customer provided and realized on the injector machine that at 80% duty and above, they sprayed very poorly.

For a 3.1 stroker, 24lb should be plenty, but if in doubt, go with 33 or 36's which are abundant as they came in the Pontiac supercharged v6's in the late 90's.