throttle body vs carbureted CFM?

[fe66comet]

OK if I have a carbureted CFM requirement of 1000 CFM, how does that translate to an injection throttle body size? My thinking is with a more dense charge with the lack of fuel and more efficient intake design that would affect total CFM requirements.also I would think velocity would play less of a factor than total volume alowing with bigger ports and throttle body more cfm in a given displacement? Any thoughts?

[sumfoo1]

Usually it works out the same the difference is... smaller TBs have higher flow rates because they don't have the venturi choking them down.
IE a standard 4150 style 4 barrel throttle body can hit 1000cfm no problem where usually on a carb you're looking at a 4500 series.

A 4500 series throttle body can hit 2000cfm no problem


Basically CFM=CFM they are both rating total airflow.

But like you said on a carb motor you're affecting fuel flow too where on EFI a huge flow throttle body may lose a hand full of hp and some tq down low but  will give it back on the top end but you're not affecting fuel delivery so its not nearly as drastic.

[My427stang]

Within limits, you cannot over size a TB.  It merely becomes too sensitive to small throttle movements off idle.

I'd also argue that you can't really oversize a carb as much as people say, but there are limits to what you can manage for a signal at the booster, but with EFI, go big

[jayb]

+1 on that.  With some creative leverage you can minimize the issue of a touchy throttle also.

[fe66comet]

I am thinking I will tune my throttle body spacer to adjust CFM to keep velocity up. The Wilson I ordered is a single 90mm that flows 1170 cfm. The scummit (pun intended LOL) calculator calls for 980 CFM. I am not sure if 200 CFM carbureted is really going to be that much of a throttle issue on a stick car? I suppose also the air induction tube and filter could also be tuned to adjust but I haven't got that close yet. Thanks guys Jon

[67 Fastback]

The progressive Tripower set up on my car works a treat 3 x 600 cfm throttle bodies . Has great throttle response and hang on when all 3 are open .

[My427stang]

I am thinking I will tune my throttle body spacer to adjust CFM to keep velocity up. The Wilson I ordered is a single 90mm that flows 1170 cfm. The scummit (pun intended LOL) calculator calls for 980 CFM. I am not sure if 200 CFM carbureted is really going to be that much of a throttle issue on a stick car? I suppose also the air induction tube and filter could also be tuned to adjust but I haven't got that close yet. Thanks guys Jon

Don't restrict anything, just make the smoothest, straightest, flow you can.  You aren't affecting velocity in the port with a restrictor plate, only in the restrictor plate.  Plus, FEs don't have a port velocity issue, not really even with TPs.   

[fe66comet]

I guess I will go 3.5 inches and call that it, it is only .043 less than my TB so I can run a cylinder hone inside and clean it up.