670 CFM TBI Killing Gas Mileage

I have a quick question. I need a new TBI for my truck, and i was thinking about getting the upgraded 670 CMF TBI. People are telling me that i should not get it due to the fact that it kills your gas mileage. If it does, is it a big difference?, does it even pay to get it, or should i stick to stock?

Thanks
Ryan

No real advantage to this with a stock cam, exhaust and efi programming.

No real advantage to this with a stock cam, exhaust and efi programming.

I have a good exhaust, headers and all. K&N intake. No Cam or EFI Programming. So it would be a waste of money and gas? I may put in a cam in after i rebuild it.

At best you may gain some power in the top rpm range but possibly loose some midrange torque, I wouldn't do it until I did work to the engine that would would increase it's breathing potential, like the cam or some head work.

Yeah i just read a bunch of reviews on this unit, and they all said it was too much for a stcok 350. looks like im going with a stock replacment. Im thinking this would be good for a 383 in the future though.

Thanks for your help

I put the 670 CFM Holley unit on a '88 K1500 350 four years ago. I though it was probably too much for it but I was planning to stroke it in the future anyway. As far as putting this on a moderately stock (stock long block but with headers, high flow cats, Flowmasters, K&N filter, performer intake, MSD, etc) 350:

Pros: a much needed increase in mid and upper range power. The stock cam is pathetically flat in the upper ranges and having the passing power was great, but ....

Cons: The TPS supplied with the kit wouldn't adjust enough (needed different angle fit so the stock unit wouldn't work.) I had to drill it out some and then play with the voltage (different from the recommendations, I can't remember which way) to prevent hesistation. The truck also lost around 1.5 mpg. I can live with it. But, it was accompanied with the TBI dumping too much fuel and 'thumping' the exhaust when it was cold and idling like it had a 3/4 cam in it. It wasn't as violent as a backfire but was definitely fuel igniting in the exhaust. After speaking many times to techs at Holley they just said it shouldn't be that way and the computer would 'learn' after a while. Well, after about a month, it did quit and has run quite smoothly for four years. (I've had too many other projects running so the 383 hasn't materialized for this truck.)

In the end, not really worth it unless you're going to make the 350 breathe some more as already mentioned.

thanks guys, thats all the info i need. I think im going to stay stock for now, then get the 670 cfm for the future stroker.