if stock 305 heads flow 140cfm then thos should bebie to support up to 300 right?

when whould you want to get a 670sfm TB? on a 305 what mods would make this worth getting?

 

The 140 cfm is on the exhaust side ...I think 187s can support 300 hp on a 305 TBI ...if the rest of the setup is bang-on. But I also think you'd be pretty close to the limit of what the heads could support given that you can't have too much cam and maintain street "driveability" and "tunability" with the TBI computer. Of course, if you just stick a huge cam in you could make more than 300 hp with these heads ...but you'd lose street manners and the TBI would either be a bitch to tune or you'd need EBL (which I've never used, but have been told that it can handle the big cams). That wouldn't be an ideal, or even a sensible, way of doing things, but you could get 300 horses that way.

With a "street-friendly" cam, which will also "cooperate" with the computer (although serious tuning would still be required), I think 300 hp is attainable with the stock (unported) TBI heads (187s) ...but that's probably the outer limit.

If you want to go above 300 hp with a TBI 305 then I think some head porting is in order ...or higher-flowing, non-swirl ramp heads (well-ported, non-swirly heads could make up to 350 hp with a TBI-friendly cam).

Only the hottest 305 would need a 670 cfm TB. That kind of flow would only be necessary on a 305 that was making over 400 hp at 6000 rpm or more ...and even then it would probably only make a few horsepower more than 570 cfm. This is pushing the limits of a hydraulic roller TBI 305, in my opinion.