What would porting a 670 holley tbi do to the cfm, I guess the holleys are rated @ 3 inhg. All I did was open up the bores right down to the butterflys, and chamfered the bores underneath. All in all it wasn't much different than the ultimate mods.

Can anyone give a guess what the new cfm might be?

 

higher. but your velocity will drop.

if you want more cfm than a 2" tb unit can provide at wot. go 4bbl.

ive studdied this a lot, asked a ton of questions to a lot of people. no real gains to be seen from going more 670 cfm from a 2bbl. if you need more go 4bbl.

most people DONT need more.

 

4 barrel would be great but, I want to keep with the gm ecm. Still wondering if I should go mpfi, but It seems like a lot of work for small gains (assuming I'm getting enough fuel now I don't think I'd gain over 15 hp).

 

simply porting the tbi wont do much. more gains than a few hp are going to need further tuning and mods.

 

U must not have read my sig! About the only thing I could do is go a little bigger cam (without spending huge money).

 

i was actually thinking about soemthing liek this for my 400motor when i put it together. have you noticed any sort of surge or anythign when you feed into the throttle since you chamfered teh bottom of the bores? i was told tha tthis type of mod woudl create a blast effect from teh air which will cause a sort of turbulance stall in teh air velocities. my info came from a guy who does carbs for a living, it sorta makes sense but hwo dramatic coudl such a small change in diameter in such a small space effect the air velocity?

thanks
tim

 

It ran the exact same after as it did before I ported it. I just thought that rounding the bores and the adapter plate would be better than a hard 90 deg edge.