looking for carb. advisr

[Mark#32244]

Hello ,

My holley is old and I found a small gas leak the other day. Last night I was reading through the archieves, and Joe Lucia had a old post regarding carbs. One thing he said stood out, "NOTHING MAKES A CAR RUN BETTER THAN A NEW CARB." I was planning to rebuild it, but this makes good sense. Now I need help picking a new carb for my vette.

I have a 1970 LS5 4 spd, The engine has been rebuilt, The Heads and Intake have been changed, they came off a 71-72 "LS6" Chevelle And it has a large cam " dont know the spec, but it has big lope, and very little vacuum at idle. It currently has a Holley DP, w/ mech. secondarys.

I use the car only for play Street use.

What is the best carb, cfm, jets, ect. for this setup?

Thanks

mark #3244

[Jack H.]

Re: looking for carb. advisr

I'll let another with greater experience than I in performance carbs answer. From what I know of this forum, you'll get a wealth of good alternatives to explore.

But, start thinking about what you'll do with the original carb. There are three basic alternatives and some of them aren't wise.

(1) You use it as a core to offset/defray the cost of your replacement

carb. Not a good move because you'll get minimal value and deprive

a future owner of the car the thrill of restoring a factory original

part....

(2) You can set it aside and 'warehouse' it for a future owner (maybe

yourself). Nice move, altruistic to the sport/hobby, but doesn't

get you any financial benefit today.

(3) You can offer it for sale to a rebuilder or another NCRS member

using the free ad benefit of Driveline. Either way, your car

loses a factory orignal part, but you gain $ and some fellow

enthusiast gains.

Tain't no 'right' answer. Just a choice of alternatives. Personally, I'd keep the carb and have it rebuilt by a pro, but Joe and I really DO differ here and there's no one to say who's right because we 'could' both be right....

[Jack H.]

Re: looking for carb. advisr

I'll let another with greater experience than I in performance carbs answer. From what I know of this forum, you'll get a wealth of good alternatives to explore.

But, start thinking about what you'll do with the original carb. There are three basic alternatives and some of them aren't wise.

(1) You use it as a core to offset/defray the cost of your replacement

carb. Not a good move because you'll get minimal value and deprive

a future owner of the car the thrill of restoring a factory original

part....

(2) You can set it aside and 'warehouse' it for a future owner (maybe

yourself). Nice move, altruistic to the sport/hobby, but doesn't

get you any financial benefit today.

(3) You can offer it for sale to a rebuilder or another NCRS member

using the free ad benefit of Driveline. Either way, your car

loses a factory orignal part, but you gain $ and some fellow

enthusiast gains.

Tain't no 'right' answer. Just a choice of alternatives. Personally, I'd keep the carb and have it rebuilt by a pro, but Joe and I really DO differ here and there's no one to say who's right because we 'could' both be right....

[Joe L.]

Re: looking for carb. advisr

Mark----

It appears to me that your primary concern is functionality and driveability. Originality should not be a concern since your engine is largely non-original. As a matter of fact, no 1970 Corvette big block originally used a Holley carburetor.

If I were going to retain your current engine configuration with its square bore, GM #3963569 manifold, I think that I'd use the 71 LS-6 carburetor. This carburetor is a 780 cfm unit with vacuum secondaries. It also uses a divorced choke which is compatible with your manifold. In my opinion, and apparently also the opinion of GM's 1960's engineers, vacuum secondaries are the way to go for street operation.

The 1971 LS-6 manual trans carburetor, Holley List #4803, was reproduced by Holley until recently. They've been discontinued now, but there are still some around in vendor stocks. They are expensive, though. Expect to pay around $500 for one.

Another option, since originality is not a major concern, would be to go with an "aftermarket type" Holley. If you go this route, I'd recommend a Holley O-3310. This is a vacuum secondary carburetor of 750 cfm size. It has a manual choke, but you can add an electric choke(Holley #45-223)easily. If it were me, I'd also add a secondary metering block to this carburetor to replace the secondary metering plate supplied with this carb, but that's not absolutely necessary. The nice part is, you can buy this carburetor, BRAND NEW, and including the electric choke kit, for about $235.

If I were in your shoes, the choice between having your carb rebuilt and buying a new one for this price would be a "no brainer".

[Joe L.]

Re: looking for carb. advisr

Mark----

It appears to me that your primary concern is functionality and driveability. Originality should not be a concern since your engine is largely non-original. As a matter of fact, no 1970 Corvette big block originally used a Holley carburetor.

If I were going to retain your current engine configuration with its square bore, GM #3963569 manifold, I think that I'd use the 71 LS-6 carburetor. This carburetor is a 780 cfm unit with vacuum secondaries. It also uses a divorced choke which is compatible with your manifold. In my opinion, and apparently also the opinion of GM's 1960's engineers, vacuum secondaries are the way to go for street operation.

The 1971 LS-6 manual trans carburetor, Holley List #4803, was reproduced by Holley until recently. They've been discontinued now, but there are still some around in vendor stocks. They are expensive, though. Expect to pay around $500 for one.

Another option, since originality is not a major concern, would be to go with an "aftermarket type" Holley. If you go this route, I'd recommend a Holley O-3310. This is a vacuum secondary carburetor of 750 cfm size. It has a manual choke, but you can add an electric choke(Holley #45-223)easily. If it were me, I'd also add a secondary metering block to this carburetor to replace the secondary metering plate supplied with this carb, but that's not absolutely necessary. The nice part is, you can buy this carburetor, BRAND NEW, and including the electric choke kit, for about $235.

If I were in your shoes, the choice between having your carb rebuilt and buying a new one for this price would be a "no brainer".

[G B.]

Tough to tell.

Over the years Holley has made a bunch of different double pump carb models. They weren't all race carbs; some were installed on the GM assembly line and some were even sold as "street" replacements for Quadrajets.

However, I'm going to assume that you have a racing carburetor (maybe a List #4779 or 4781?) on your big block. You can certainly run one of those on the street, but you will get a crisper part-throttle response and better fuel economy from a 4-barrel with vacuum secondaries.

Holley still makes direct replacements for most factory Corvette carburetors. I suggest that you try one of those from a pre-smog model year. The '66 427/425hp carb is a good unit, and so are the '66-7 390hp models. The only drawback to buying a Holley carb with a "factory" list number is the price. They all cost more than $500. But the up side is that you get a design properly engineered for a 427 on the street. And, you can easily hook up the automatic choke.

[G B.]

Tough to tell.

Over the years Holley has made a bunch of different double pump carb models. They weren't all race carbs; some were installed on the GM assembly line and some were even sold as "street" replacements for Quadrajets.

However, I'm going to assume that you have a racing carburetor (maybe a List #4779 or 4781?) on your big block. You can certainly run one of those on the street, but you will get a crisper part-throttle response and better fuel economy from a 4-barrel with vacuum secondaries.

Holley still makes direct replacements for most factory Corvette carburetors. I suggest that you try one of those from a pre-smog model year. The '66 427/425hp carb is a good unit, and so are the '66-7 390hp models. The only drawback to buying a Holley carb with a "factory" list number is the price. They all cost more than $500. But the up side is that you get a design properly engineered for a 427 on the street. And, you can easily hook up the automatic choke.