OREO Speedwagon

I have a stock 76 L-48 and my carb is hosed. So, I'm going to get a new one. I'd like to get something that will serve me well now on my stock engine and also later, if I decide to get it rebuilt.

So, my friend has a 750 Holley. Is that way too much for my stock 350? I thought so, and he mentioned I could have the jets changed so it would preform more like a 650 (which should be about right, shouldn't it?).

That way, if I work the engine over I can rejet it to give me more CFM. I plan on adding an intake, cam, and probably heads later this year.

What do you guys think? Should I get the Holley rejetted? Should I leave it alone and throw it on? Should I say "none of the above" and spring for a new Edelbrock or Demon?

Thanks!

page62

http://forums.corvetteforum.com/zerothread?id=777668

OREO Speedwagon

OK, so from that thread I've learned that 3 people have 3 different opinions:

One guy suggests to buy a new BG Speed Demon
One guy suggests to have Lars rebuild my existing carb
One guy suggests having Lars tune a new Speed Demon

Of which, none really address my original question.

;)

SLine78

Ok here is what I think. Putting on the Holley will require in addition to any tuning (jets, etc) changes, modications to other circuits like vacuum and fuel connections.
Having the original quadrajet rebuilt by a knowledgeble person like Lars will restore your carb to a perfomance level suitable for your existing engine and well as your planned mods while allowing you to retain all of the stock connections.

If you want to go new, I would consider the Edelbrock Quadrajet replacements. Should be close to a bolt on replacement.

Mike

mandm1200

In my opinion a 750cfm on a stock 350ci is too much. Rejetting is not going to make a difference. Putting something that large on will hurt the low rpm punch. Even with an high performace street engine that is going to be too much, even if it is has vacuum secondaries.
An engine is like a pump that takes in air. You can roughly calculate the amount of cfm that the engine needs. Take the maximum rpm multiplied by the cubic inches of the engine divided by 1728 (conversion of cubic inches to cubic feet) multiplied by the effeciency of the engine (figure about 0.9 for stock) divided by 2 (engine only takes in one gulp of air for every 2 revolutions.
Examples:
stock 5500rpm * 350ci / 1728 * 0.9 / 2 = 501 cfm
performance 7000rpm * 350ci / 1728 * 0.94 / 2 = 666 cfm

As you can see a 500 cfm would only be required. More is alway not better and will eventually hurt the performance. If you like many of us and cannot afford to buy a carburator today and then have to fork out money later for another carburator after some mods, you may want to look at a 600 or may be a 650; but not a 750. Be smart and choose a vacuum secondary. The nice double pumper with mechanical secondaires are great but at lower rpm they tend to boog the engine when you put your foot into it.
Changing the carburator will give the car a different attitude. In the late 70's I had a 350 that was well over 400hp. I worked in a garage and had access to diiferent carbs. With the 750, it was sluggish under 4000rpm but ran great and pulled hard to 7500rpm. With a 650, I had much better low rpm response but it faded has I approached 7000 rpm. The 700cfm as you would guess was somewhere in between and that is what I ran almost all the time.
Right now I am in the process of gettng parts together for a 350 for my 76. I choose to go with the Holley 670 Street Avenger. Partly due to the deal I found. The carb is almost new and I got it for $135. The Street Avenger 570 I felt was a little too small if I did anymore mods to it. Some are recommending the BG Demon. I have no doubt they work great, but I don't have that kind of money.

Mike

OREO Speedwagon

Thanks to all, very informative replies! You guys have convinced me to stay low, around a 650 tops, and probably closer to a 600.

I think I'll check out one of those Edelbrock Quadrajets and see what that's going to set me back.

:)