Hey guys what would be a good size carb for a hot 340 setup for the steet?

Plans are
340 .030 over with ported and polished J heads with 2.05 intake and 1.60 stainless longer than stock valves, 62 cc polished chambers,W2 style rocker setup with 273 adjustable 1.5 rockers, TRW flat tops around 10.3:1 compression, Comp XE274 solid lifter cam, prted Edelbrock T5 intake or Air gap copy,1 5/8 ceramic coated Hooker headers to 2 1/2 exhaust through chambered mufflers and dumped before axle.

All in a 72 Duster with a 4 speed, 3:91 rear and 28" tall drag radials. I have a Holley 650 vac secondary carb on my 318 now, will that do or should I set up to a 650 or 750 double pumper mechanical secondary carb?


Hoping for a little over 400HP, the desktop dyno and comps dyno both have it at 450hp 435Tq. What do you think for a carb?

Butch

750 dp 450hp seems high maybe 420

Yeah I was thinking 450 sounded awful high, thats why I said I was hoping for a little more than 400hp. Might go bigger cam if my compression ends up being closer to 10.5:1 to bleed off some pressure. Just starting to peice it all together. The motor I got had TRW dome pistons and looks like it was at 12:1, going for pump gas now so gotta tame it down a bit.

So you think the 650 Holley will be too small, a 750DP would be better? Thanks

Butch

I forget, I'll have to look tonight after work. Motor probably wont be ready to go in the car till spring so I have time, but I figure if I come across a good deal on the right sized carb I can jump on it if I know what a good size is.

Butch

On the below 340, my last carb was a Promax 650 vac sec and it ran good. I would say that it is a good all around cruising carb that definately out performed my Edy 600 and 750cfm units by a long shot.
My current carb is a QF Super Street 750cfm Annular (735cfm actual) DP and the response from this carb is much crisper than the 650 vacuum secondary unit.

I would definately suggest a 750-ish DP on your build!!

I ran a 750HP on my old 340 swinger, much milder motor than yours and it ran perfect. I thik I had 28 squirters, 72-80 jets. .030 over 340, Mild ported J heads, stock 340 cam, 1.6 roller rockers, RPM air gap, TTi headers, auto 3.55's. Car ran 13.80 w/ the holley and 14.02 w/ a carter 625.
I like 750Dp's very tunable for whatever your application.

I still run a 650 Holley on my mild 340. It didn't like the 750 we tried, lost several MPH and 3 tenths. I'd say try what you already own, and go from there.

Thanks everyone. I quess I'll pick up a 750 DP if I find a good deal on it, otherwize I'll try out the 650 and see what it does. Raining here so I cant check the #'s. but is there anything you can do to a 650 to improve flow? Also can they be converted to a double pumper?


Butch

The 650 would probably keep up with the 750 up until 5000 rpm or better. So for the street you may not need 750.

Planning on a couple trips a year to the strip to have some fun once it finished, so I quess a 750 DP could help.

Butch