OP I'm assuming you already have an F.I. kit or are you going to run the built block without F.I. and then add the kit shortly thereafter.

Yeah, currently running GTM stage 2 turbo kit.

Ok, I must admit that i was wrong on saying that bigger injectors will use more fuel, since the tune does determine everything. I think i meant to say that it has the potential to be more fuel consuming.

To OP, i think you should call forged performance to ask what fuel pump they are running. I think a 255 should be fine with 6 725cc, but it is probably pushing the 255 to max, 300 should be enough for 850cc. As for the drive shaft, i don't think it is a must, again talk to either forged performance or GTM about this. Most likely, the car is fine without it.

i think they did use the 300 on that but dont hold me to it

I am out of town, but I will ask when I get back to Houston.
The other concern is they have built this on a 7AT and are waiting to do transmission upgrades before more boost.

I personally wouldn't want to run anything more than 85% duty cycles on the injectors.

Back to the OP's original question, you will likely have less tq down low with the lower compression pistons. If you can spool the turbos fast enough, that may not matter. The nice part about the FI kits on top of the stock motor is that you mostly maintain the down low power (even though this car is pretty weak torque-wise). Can't wait to see the results though. I'm sure you will make some monster power.

I agree, trying to figure out which injectors will be around that number at 630-640whp.

There is a formula that you can use to get in the ballpark. If I can find it, I'll post or link it for you.

Thanks for the info. Just got word that the block will be shipping out in 2 weeks. Also, I opted for all the coating services available from GTM.

I'm excited to see the numbers as well! Also, I had a couple other questions. As far as the block goes, I know that I'd be safer keeping it at around 600whp. My question is, does it matter how much psi it takes to get there? What I mean is, if the car is only making 560whp at 17 psi (just an example) would it matter if i crank it up to 21psi to go hit 600whp?

Here is a link to an Injector calculator. Based on your goals of ~580, I put in what the crank hp is (since that is what you would be using for the formula) once you factor in the generally assumed 15% drivetrain loss (puts you just shy of 670hp), I came out with an estimate of an injector size of 733cc with an 80% duty cycle. I would be willing to say that either 750cc or 800cc injectors would give you a comfortable overhead without being way to big.
--edit--
I should also say that if you go to 85% duty cycles, you could possibly run a 700cc injector.

Awesome, thanks Skeeterbop!! Is there any way to tell what my walbro 255 can handle? Probably gonna go for 750cc or 800cc injectors, you think i'll have to upgrade my fuel pump?

I don't have an answer to that. I just know how to find formulas :tup: But if I had to guess, I would say that you might be able to take the injector flow rate at w/e pressure you will be running and add them up. Then find a pump that will supply the total flow at your desired pressure. That is just me making assumptions though so take this with about 10 pounds of salt.

A few articles about sizing the fuel pump:
Stealth 316 - Fuel Pump Upgrade Guide
Calculating Your Engine's Fuel Requirements from Fuel-Pumps.net
Fuel Pumps and Horsepower|Aeromotive

That third one is IMO (after reading them) the clearest.

Thanks, skeeterbop, that was very helpful.