4bbl + Turbo

[Vitamin Pepsi]

Has anyone ever done a 4bbl + turbo mod? 

 

plus something like this chevy v8

 

[datzenmike]

At 7K a 2.8 liter motor only needs about 350 cubic feet of air per minute. So a 500 cfm 2bbl Holley would be more than enough and simpler than a 4bbl.

[ggzilla]

That 2-bbl flows more air than a holley 350 4-bbl

[izzo]

Yes, its been done before.

[DanielC]

My understanding is that with a turbo, you do not need a big carburetor.  The turbo will expose the carburetor to a fairly high vacuum, while the manifold pressure is above atmospheric pressure.

 

I think carb CFM ratings are for either 1.5 or 3 inches of vacuum.   If the turbo is providing more vacuum than that at the base of the carb, the carb will flow more air.

[EricJB]

The chevy is a blow thru set up. Quite a bit has to be done to make it work. When you pressurize the carb like that, it tends to spew fuel out the throttle shafts and empty the bowls. The carb has to be set up for the pressure, and a higher pressure fuel system, with a regulator that increases with the boost. Or you can put the carb in a box and pressurize it.

 

A draw thru set up allows more pressure with less work.  

[Z-train]

A blow thru is ALWAYS Plan B.

[datzenmike]

Daniel, yes. That's why a 4bbl isn't really needed and just adds complexity.  

 

A blow through allows more power for the same boost by increasing the efficiency from using an inter cooler.

[Driftease]

Draw thru has many disadvantages too low boost capability, water or methanol injection is the only option for cooling the charge, hard starting, sluggish response and very limited mounting locations for the draw thru as the turbo should be mounted slightly higher than the intake plenum and as close as possible volume wise to the intake ports to keep the airspeed up. It is usally easier to make jet changes on a draw thru setup and no other mods need to be done to the carb other than tuning. Personally I favor the blow thru if it has to be carbureted but there is no replacement for fuel injection.