Hello

I am in the process of building my first boosted engine. I have a good inline 250 chevy. I modded a Holley 2300 350cfm 2 bbl with .078 drilled pvcr's , jetted to 70 and running a 6.5PV, .110 needle / seat and completed all of the necessary Hanger18 mods. Also a modded Holley FPR for 1:1 referenced boost.

I will be running a GN T3 turbo from the original manifold and boosting through a carb hat.

***My question?? When boosting a modded carb, is it a two step process of tuning it right with out the turbo boost and then again when I have boost to the carb? It seems that when forced air is applied ( boost ) the adjustments will change when compared to a normally aspirated carb setup.

Also, do all of my vacuum ports need to be closed? two on carb and one on intake manifold?

Thanks, the board has been a huge help already

Shad in Nashville

 

boosting a carb is very difficult and dangerous. the fuel pressure has to exceed the boost pressure otherwise the boost pressure will stop the flow of fuel into the venturi. the complete carb must be enclosed in a plenum. there were a few oem vehicles in the 80's running turbo carb'd vehicles and they were very unreliable. if someone offers a fuel injection conversion then thats your best bet.good luck on your build.