how do you select throttle body size?

[DarkoStoj]

On the injection throttle body i'm buying for the camaro I have the choice between 1100cfm, 2200cfm, and 3300cfm. 355ci revved to ~6500, ~20lbs boost

 

[Fryguy302]

If I remember correctly, you run a roots blower on the camaro? If that's the case, run the biggest one you can find.

If the TB is BEFORE the boost maker, run the biggest one you can. If it's AFTER the boost maker, it barely matters how big it is.

 

[soap]

Calculate the cfm the engine will "ingest" and go from there. Raj's comment is spot on though, you do not want any restrictions in flow prior to the supercharger (throttle body, MAF, filter, inlet tubing etc).

EDIT.......Based on my calcs (and depending on the intercooler efficiency and volumetric efficiency of that blower, I assumed 0.9) you will be at 1420cfm. So my "guess", the 2200cfm unit will work for you under the criteria you mention (355ci, 6500rpm, 20# boost)

--Joe

 

[cjmatt]

You find the maximum CFM the motor will possibly injest, then find a TB a lil bit bigger

 

[soap]

You find the maximum CFM the motor will possibly injest, then find a TB a lil bit bigger

You make a good point.

--Joe

 

[Sean]

go with the 2200cfm darko.

 

[Fryguy302]

Way back in the day, I used to run KB blowers on a 302 EFI Mustang and we did a TON of dyno testing. The car was weak by today's standards, around 500rwhp on 110 race gas, but any amount of restriction that we removed from before the blower instantly made more boost and more power. Even when we went bigger than what was "needed" by the calcs.

 

[Sean]

Way back in the day, I used to run KB blowers on a 302 EFI Mustang and we did a TON of dyno testing. The car was weak by today's standards, around 500rwhp on 110 race gas, but any amount of restriction that we removed from before the blower instantly made more boost and more power. Even when we went bigger than what was "needed" buy the calcs.

I have found the same to be true. In fact one of the most cost effective lighting mods is to port the blower inlet or replace it and change the TB. even without a pulley it can add almost 2 lbs of boost on a really bad inlet casting.

I have never seen a situation where you can over feed a blower. The trick is in having a nice long prgressive linkage that lets you control the throttle really well. Big TB's and roots blowers can be very touchy.