600 or 750 cfm carb

[Time Travel]

Hello to All! I'm a new member but have been checking out the site for sometime. Fantastic info and great trucks Now to my question. I have a new 350 ho deluxe. It came with a Holley 600 cfm. I'm thinking about changing it out. Would it make sense to change to 750cfm carb. The motor currently puts out 330hp. It know after awhile that 330hp just wont cut it so I will changing out the cam and the manifold sometime down the line. Any thoughts would be appreciated.

[PHOENIX]

WELCOME TO THE BOARD!

What type and brand of carb are you thinking about changing to?

I know many guys here use the Edelbrock performer or thunder carbs that are 600cfm (performer) or 650cfm (thunder). They love them and I believe some are running more powerful engines with those carbs then a 350 ho deluxe.
You could also get a Edelbrock performer 750cfm, but they are recommended for 400cid and larger engines.
Some of us are using the Edelbrock q-jet carbs, I have the 1904 and its 795cfm. I have this on a stock 350 engine and it runs great (or will be again when I get a new distributor ).

Performer Series Carbs
Thunder Series Carbs
Q-Jet Carbs
Edelbrock Carb List

[1FaastC10]

600cfm, no question, unless its a high RPM (6500+) race engine, or a Quadrajet.

[stepside454]

The 350HO makes 330 HP peak horsepower @ 5000 RPMs. 600 CFM is more than adaquete for 350 CI to 5000 RPMs,a bigger carb wont do you any good, infact more likely hurt thorratle response.
If anything Id get a 1" 4 hole spacer to put under the carb, itll help low end most likely.
If anything Id go with a smaller carb on that application, maybe a 570 Holley. Anyway, no need for a 750, the 600 will be fine.

[Time Travel]

Thanks for the info. I'm going to need one sooner then I thought. It turns out the holley is shot. I was also thinking that the 600 would be enough. What have you heard about Demon carb?

[piecesparts]

The Edelbrock performer AFB carb and the Carter AFB carb are actually the same item (with different names) They are both built by Webber from a company called (Magnetti marelli). They have the same parts inside them and their design is the very same. My Carter is full of Edelbrock parts, which by the way are cheaper than buying them from Carter. The carburetors are 625 cfm carbs (square bore). The statement is right about the use of the smaller carb. the 750 cfm will kill off the off-line throttle response seriously. Around town, the truck will slobber and falter badly. If you were driving a camaro with the same motor and a really low geared rear end, you could feasibly get away with the 750. Running the 750 will also put a buildup of deposits on your intake valves and thus limit flow through them, due to a lazy flow of fuel. (Been there, Done that) The 625 will keep the flow velocity up to keep the horsepopwer more even. The 625 will limit your very top end on the motor, where the 750 would give you a little more in RPMs, once again (Been ther, Done That). I would seriously consider a 1" 4 hole spacer as noted above, the 4 holes aligns the flow and does increse horsepower. That has been proven in numerous articles from different engine dyno companies, in more than one magazine (Chevy High Performance, Hot Rod, Super Chevy).

[TIMSPEED]

On that 350 HO, CarCraft did a build up with the RPM Air Gap and a 750, and headers and that motor put out 350bhp.

[1FaastC10]

Originally Posted by TIMSPEED

On that 350 HO, CarCraft did a build up with the RPM Air Gap and a 750, and headers and that motor put out 350bhp.

we're dealing with a truck here, not a race car. horsepower means very little when compared to torque. BTW, did they test the same 350 with a smaller carb? i'd almost bet that it would make more usable power, and still be more drivable to boot with the smaller carb.

[Time Travel]

Thanks Piece or I mean MR.Parts, Sorry boring day at work. I've heard the spacer will only help in the mid to top rpm range and weaken off line response. I don't wont to give up the bottom end pull. Even with a peg leg it's still fun when the rear kicks. I'm starting to go more towards the Edelbrock 625. I've talked to a few people and they have said about the samething about the BG Demon. You have to get THREE of them beofre you find one that works right.

Thanks again!!!!!!!

[stepside454]

hmm.. I disagree, Demons are great, Ive had issues with AFBs being fickle from one day to the next.

[Time Travel]

Tim,
You know the drill. Limited funds!!! I was not planning on changing the carb right now but my holley taking a dump on me I have no choice. I'm still trying to stick to my schedule of suspension, brakes and tranny work. What shocks are you running on your truck? I started a new threard looking for wisdom on that.

[Tom]

I bet that 330hp rating was gotten with a 750cfm carb and 1 5/8" headers

[piecesparts]

The use of a smaller cfm carb will get you a better everyday drive and give you some resemblance of gas mileage. The horsepower is the result of the torgue. My 383 stroker loves nicities like 93 octane and cool evenings, but I can get 15 MPG out of it on the highway. I am running a 91 octane in it for now and it still holds itself up against the small cars. For a truck it is very strong and it has a smaller carb in it. I put the 750 in it for awhile and as I stated the RPM top is easy to get to, but driving around town was like owning a big sucker. I have my truck with the carter/Edelbrock AFB combo and my son's truck has a 350 with an edelbrock 625 in it. The only problems I have experienced is the fact that his needles stuck one time and a good quick tap with a screwdriver butt took care of that. A little tuning was all that I had to do to get them to work good. Demon has a good carb, pricey compared to the Edelbrock line, though. It will beat the hell out of some of the Holley antics.