Thanks in advance,

I am building a 5.7 vortec (383 stroker) factory block, heads and cam. The turbochargers have a .63 hot side, .50 cold side with external wastegates and a 750 cfm intercooler. I am installing scat brand crank, connecting rods, dish pistons (8.5 to 1 compression) etc. I am going to purchase a Barry Grant 750 cfm blow thru carb and a MSD box with adjustable retard. I am planning on running 12 psi of boost and might turn it up to 20.

My questions are, have I matched everything up right? I was told the vortec head's combustion chamber might not handle the pressure. How much horsepower can I expect at 12 psi? I have already purchased the turbos and scat kit. I thought I would ask someone with the expertise before I made any more mistakes.

Thank you for any advice, dave63080

 

12 psi should work good with 8.5:1 compression. For 20 psi you may need to drop it a little more. The hardest part of matching everything, and the easiest ot f-up is the cam choice. A good blower grind should be good for you, but I would actually call comp to get a recomendation for an engine like that.

The vortec heads should be good, but to much pressure any head will need to be o-ringed. I thought about something like that with my engine, but i have no idea where to start tuning a push-through carb.

As for horsepower...... to many variables. I got a streetable, N/A vortec 350 at over 400 crank hp. It depends on the entire combination of parts and tuning. I would say if you don't have at least 450 hp at the tires then something is wrong with the setup.

 

Thank you for the advice doc221978,

I am still scratching my head with the carb. I am planning on a 750 Barry Grant blow thru but on the other side an 800 would probably leave more room for error? Any input?

Dave63080

 

I was just reading into it a little.... The 750 should be big enough, but the 800 shouldn't hurt really. I would recommend getting the engine dyno tuned when your done though. Tuning a blow-through setup is hard to do. I personally wouldn't consider trying. Good luck.

 

a 750cfm carb in blow thru is good for 1600 hp easily, you are FORCING air into the engine, typical cfm ratings for carbs are tossed out the window now.

 

yup. i would keep it a little smaller so that throttle response isn't sluggish (800cfm would suck for throttle response) i bet a 650cfm carb would do EVERYTHING you'd ever need it to.

 

Dave, this is the route that I'm going. The biggest concern with blow-thru applications is fueling. If your planning on 12-psi, possibly 20-psi, then an electric fuel pump is a must....

A 750/800 cfm carburetor is too much for street use, no matter how much you alter it's internals, you'll never seem to get it just right. I would recommend talking to the guys over at The Carb Shop, they are simply the best w/blow-thru applications, hands down....

Here's something to help you sort things out, Click Here....

 

I REALLY appreciate the advise gents,

I have an electric fuel pump ready to go. Finding a dyno any where around here is impossible. I think I am going to wing it and see if I can fine tune the engine myself. Maybe impossible but I'll give it a try. I will take your advise and lower the carb cfm's some.

Thanks again, Dave

 

Tuning is a lot easier today than it was years ago. You can pick up a JAW-WBO2 O2 sensor setup complete for under $120. It has an output that connects to a laptop computer so you can see what your AFR is. It makes tuning easier.

If that was my setup I would go with a 650 cfm carb. 750 cfm isn't bad but is up there. Check out the www.theturboforums.com .........lots of boosted rigs with carbs there.