Hot Rods Blown Small Displacement Engine CFM

Hello,

I am running a TBS 6v-71 blower on a 311 CI Gen 1 SBC. The engine is built for the blower. Using the standard CFM formula for supercharged engines, the total CFM requirement calculates to 850-950 CFM, dependent upon maximum RPM input.

I would prefer to run dual quads that are purpose built for draw-through superchargers. The smallest CFM carbs available that I can find are 600 CFM x2 = 1,200 CFM.

My question is will I experience any significant issues in street performance if I run more CFM than the calculated maximum CFM for my specific build?

Thanks for your time and consideration.

 

I run 2 750s on my 389 inch Pontiac. Your 311 incher should be about right with two 600s, but the only way to really know for sure is hit your local ch***is dyno and start tuning.

 

Thanks for the reply!

 

I believe it would be just fine, I think there are 500CFM Carter AFB's. This is just my opinion but I would run it.

Pat

 

I’ve got two used 500 cfm Carters on the 6-71 on my 355” SBC. I just matched the jets and metering rods and bolted them on. It runs great without any additional carb tuning. I imagine that it would make more overall power if I took it to be dyno tuned, but it starts great, runs great and seems perfect for that occasional run-through-the-gears. So far the plugs look good too.
I have a pair of 625s also but I’m happy with the way it runs so I haven’t tried them.


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I ran a TBS 671 on my '46, 8lbs of boost, two 650 Holley that were boost referenced. NO issues at all.
Motor was a 355 sbc. I would not worry about your carbs.

 

Thanks, Bob!

 

I have read that the Carter/Edelbrock carbs do not need to be boost referenced. Is this correct?

 

I run Carters on both of my blown cars with no boost reference. I also have an air/fuel gauge to make sure I am not getting ready to buy new pistons.

-Abone.

 

Holley makes 350-400 CFM carbs. Either in 2bbl or 4 bbl.

I am going to be the odd man out here and say that were it me I would be running a pair of 500 CFM Holleys (2 bbl) on it. Center hung float bowls and one turned around backward. If you are worried about too much CFM you can choke it by limiting your throttle travel. The carbs cannot make full CFM without the blades coming open. The flow past the blades is sensitive enough that some guys even slim the throttle shafts to gain some flow.

Like @flamedabone said a pair of 600s should work just fine.