carb size

[rjs53]

need help choosing a carb it's on my chevelle not the truck but alot of you guys are running fast so im asking for help. chevelle with me in it 3300lbs motor is a 396 sbc 3.875 stroke 6" rod .30 over flat tops .015 in the hole 11.1AFR210 race head 208-160 valves 66cc, cam is solid roller lift is 676in 653ex duration @ .050 is 268in 274ex 108 LS, victor jr with 1" carb spacer i currently have a 750 dp it's run a best of 11.30 @ 119mph track is 4000'. I have a chance at a 950dp but not sure if its to big any suggestion would be appreciated, thanks

[team39763]

If I remember correctly, a 950 barely flows 800cfm, so it may not be too big for you. I'm sure one of the more experienced guys can tell you for sure. From what I know, the 850 outflows the 950.

[rjs53]

I'm thinking about trying differant main body's or base plates. One problem im having is at idle its fine, wide open is fine part throttle or anything above idle to about 3500rpm it runs like crap if i look down the carb and give it just a little throttle the fuel starts running out of the boosters I checked gaskets, cleaned every opening i could find the only thing i can think of is the air bleeds are to small. would it help to drill them out?

[prostreetC-10]

You start messing with those air bleeds you might as well throw the carb away. Holley does a fairly good job of matching the air bleed size to the carb. You are not going to have a precise enough drill bit to make change without going too big. You might want to think about an HP carb or an HP main body swap. They will come with 72's for idle bleeds and 36's for the high speeds. You can make a big difference just going up or down a few numbers. Just remember that bleeds do the exact opposite of jets. The bigger you go the more you are leaning out the carb by introducing more air into the main and idle wells. Sounds like you may have something else that's more basic going on with your carb.

Correct on the 950 team39763. A 950 is a 750 venturi on an 850 base plate. Not sure why they even call them 950s. They are great carbs though because they do not have near the lean hole to fill up as an 850. Pretty streetable and they do flow pretty good. The 950HP is a good carb and really tuneable. The 850 is a pig with it's 1 9/16th venturi as compared to the 1 3/8th of a 950. Lots of guys running them and having really good luck.

When you say "have a chance at a 950DP"....do you mean an HP? Is it to try or to buy? What brand? Holley? Quick Fuel? Proform?

Okay....going to bed now!

[Marv D]

Thing to do is borrow it, take it to the track and SEE if the motor likes the 950 or not. I'm betting it will LOVE it.

I ran a somewhat similar motor,, (383, 6" rods, JE flat tops, zero decked for 12.3:1, AFR cnc 210's angle milled to 54cc, Lunati roller 262/274 @ 0.050, .625 lift, 1-3/4" supercomps, Supervictor intake and a Prosystems custom 920cfm Dominator that Patrick built for the package. )
You didn't say how heavy your Chevelle is, but that package with a TH400 and 4.56 gears, 32" slick took my 3040 pound Nova to 10.28 @ 126.

If you don't run faster with a 900+cfm carb,,, I'll eat it

[rjs53]

chevelle is 3250 with me in it, 700r4 non lockup with 9.5" convertor 28" tire 4.11 gear. I'm going to put a th350 or 400 in place of the 700 and up the gear to a 4.30

[Marv D]

Woah dude,, you have ANY traction out of the hole with the 700 and those steep gears???? I think the TH and a 4.11 gear with that short 28" tire is a good step. With your 4.11 gear and assuming that 9" convertor is about as efficient as the rest of them,, your around 6400 in the traps. Unless you make more power I wouldn't expect more MPH unless thngs were TERRIBLY off to begin with. So if you change to a 4.30 gear your only going to gain like 300rpm and put it crossing artound 6700. I bet that cam don't wake up till 6000. I know you got a lot of stroke there but I shift my 4" stroke sbc at 7400, cross at 7600. If it's built right,, it will handle it just fine. You know what kind of components you have in there, and if are keeping the valve train in check,, I sure wouldn't be afraid of going to a 4.56 gear and putting some screws to it with a MUCH bigger carb.

but,, that's just my 2¢ . Crossing at 7100 with that cam sure sounds like a better fit to me. But then,,, so would a little more head, more compression, bigger slick, and the slope get's slippery pretty darn quick don't it.

[rjs53]

always spins out of the hole, I tried peddling but it goes right to 2nd an is a dog to half track. tried shifting manually but the 700 wont shift when i do the rev limiter is set at 7000 rpm and a good thing as Ive tried this a couple times, each time i have to let off to get it to shift. the block is a standard 1peice gm block the rotating assembly is eagle, forged crank Hbeam rods and pistons are SRP, plasma molly gapless ring. Im running a MT drag radial, slicks would help. The drag radials might hook better once I get my suspension up to snuff. this car was built for the street but one time to the track and like most I want to go faster. Big block springs up front so no weight transfer. all this may be for the best as I still have the original 8.2 under it I did put some superior axles in it. Ive traded a f#%d short block for a 9" rear just need to get the mounts fabed up. 119mph seems to be the norm for this as spinning or peddling it still runs the same. I haven't put the gears in so a 4.56 might be considered. comp promagnum rockers and stud girdles, no shaft mount but I think it will take 7100