Which would be better for a stock 340 rebuild with 8:5 -9:5 compression and stock cam? A performer, airgap or LD340. I'd like to switch manifolds on my rebuild. Also which carb would work best. I've heard allot of good about the Barry Grant carbs.

What year 340 are you building? The LD 340 will not accept the later Thermoquad carbs. The Air-gap will perform and flow better and you can run any carb you want. I am using a Performer RPM on my stock 340 which is basically an Air-Gap without the flow thru design.

Joe

For a stock build I'd go with the LD340. If you plan on more upgrades (cam, headers, head porting, etc.) I'd go with the Air Gap, it has the most potential of all 3 in a performance build.

* The LD 'in stock form' will not accept a spreadbore carb. It was however cast with intentionally thick bosses on the carb mounting surface, so it can be safely hogged out to accept a Thermoquad or other spreadbore carb.

Mine is a 73 340 motor. So it has the low compression 8:5. I though about seeing if I could boost the compression a little, but still keep it stock with a stock cam and use one of these intakes.

If you have the LD340 I would use that. If you need a new intake I would go with a Performer RPM. The RPM and Air gap are the same runner and height only difference being the "airgap" under the runners. I doubt you will see any gain from that and I feel its not worth th extra $100 over the regular RPM


I ran a LD340 on a low compression 340 and it always ran hard. I also used on a 11:1 340 that was ported for a Thermoquad. Great intakes.

Dont under estimate the stock spreadbore 340 intake though. If you all ready have one they perform great as well.

Gotta ask you a couple of questions first. Do you already have one or more of these intakes, or do you have to buy any one of them when you replace it? If building a 73 340, you might want to go with the earlier pistons and cam. 73's were lower compression and cam was a little different too. If your planning on going much over 5000rpm often, then you might look for a set of aftermarket heads. But just for a warmed over decent running 340, the factory ones will do fine. What do you plan on doing with it after the rebuild- daily driving with occasions of spirited driving, weekend warrior, or strictly a strip car with occasional street excursions? The cost of a rebuild for basically the same engine, earlier spec 340 vs. the 73 version should be close. The earlier parts should give you more bang for your buck tho. Just don't go too overboard.

On a basic stock rebuild, I'd use the LD340 if you can buy it reasonable, and modify it to fit the Thermoquad. If you really want performance then go with an air gap and Holley of your choice, with larger cam. The LD340 was a great intake to begin with, and for street driving, it is a great piece.
If you want to go a little faster, then you might want to get a junkyard 360 engine and go with a stroker version/kit for it. No need to go with a forged crank unless you want to go much over 450-500 HP. Cast cranks should last on a street car without too many problems. Just make sure your oiling system is up to par if you go that route.

Let us know what you decide.

If you want to spend money or shave weight I would try to find an LD340. If you're not worried about weight I doubt you will feel any performance increase over the stock iron manifold in your application.

Sheldon

Not im my experience. The Air Gap will probably be better everywhere in the curve vs. a Performer.