950 hp small block

[ponchopwr70]

Well in my never ending pursuit to make more power I talked to holley today for a better carb than I have now. They recommended a 950hp. Currently I have a 3310 vs holley 750 with secondary block installed instead of a plate. My car always feels like it dies off at around 5800 at the track. When I first had my engine done I had a 850 dp, kind of old with the choke tower milled off. That had a bad stumble untill 3500 then spun to 6500 like nothing. I ended that because it wasn't very much fun stumbling. My combo is 388 chevy, 10.8:1, 235duration @50 108 ls 507 lift new gm heads with camel humps in front heavily ported and polished by my engine builder friend, 69 z-28 intake dual plane port matched 1-3/4 headers 3700lb car 3000-3200 stall 3.55's with 26" tire. Car has ran 12.65 @107 with the vs 750. What do you guys think? Any experiance with this carb. I tuned both the 850 and 750 to get them as good as I could (jets, squirters, pump cams, acc pumps). So I don't mind tunning (its fun till the cops show up at the house) I just don't want to spend money on something that could stumble again but I think the 950 is a different animal.

[slowcamaro]

Your combo isn't that outrageous. I think a properly tuned 750 or 850 should be plenty. A local guy is running high tens on an 830. 355 250's duration cam spinning ~7k through the traps.

I think its a tuning issue.

[fishtail8]

Might be 5800 is all it wants to turn. Does it feel like it lays over, maybe that's where the setup really stops making power.

[yellow heap]

That cam is probably done by 5800-6000 rpm.
I suspect the heads(also in manifold) are also suspect-I takes alot of work to get any dbl hump head to feed a 383.
My 383 with more cam and much better heads zips to 6000 like a scalded crank monkey with a 650 double pumper
I also think some tuning is needed.
The 3310 holley's are great carbs.

[ponchopwr70]

It falls flat on its face at around 6400 but it doesn't make the power that the 850 did on top. When I had the 850 I ran 74 jets in front with 90 in the back.(i forget what squirters I used or cam but I tried many different combos) The 3310 has 73 fronts and 80 back. I have the lighest spring in the secondary also the 850 had downleg boosters, the 3310 has straight legs. I just have a weird feeling the secondary isn't giving enough gas, throttle response is awesome though heres a link to how the car runs.
http://www.youtube.com/watch?v=SER1gBLn2N0

[gearheads78]

For best ET and good drivabilty I would put a 650 DP on that car. Have you played with timing curve at all? I chased what I that was carb issues on a 383 for 6 months. Went all the way up to a Carb Shop 930 and still was stuck in the 8.30's Went to a 650 DP and dialed in the timming curve and was going 7.60's Mine had a MSD and liked one light and one medium spring the best.

[ponchopwr70]

Timing is good, 38 total all in by 2800, did not go any faster in the quater from 36-40 degree's. Its a hei. There is really nothing wrong with the car just seems like there should be a little more on top based on a seat of the pants assesment although it could have seemed faster on top just because it kicked in like a rochester lol.

[slowcamaro]

Might not hurt to back off the timing a bit. What New GM heads are they? The fastburn/vortec heads I hear like less timing around 32*.

Also try slightly stiffer springs on the mechanical advance, too light and the timing can jump around. I'm all in by 3500. 2800 seems like a rather steep curve to me.

Either way, I think you should have plenty of carb as is

[yellow heap]

If you want more upper rpm power-New cam.
6400 rpm is way hi for your cam-Get out the cam card,I'm sure it will say so also.
Opt shift point is prob 6000-6100.
Keep on wingin that cam and it's goona bite back.

[ponchopwr70]

The heads are new castings of the camel humps, the best camel humps they make but old tech. The cam makes power to 6200 according to cam card. I picked up a tenth just by shifting at 6400 instead of 6200 on the 2-3 shift. Im just gonna try some different carbs when I go to the track in the spring I have some that I can borrow from friends and see what they do. The car is no slouch by any means 1st gear the motor spins to 6200 like nothing, proberly just a case of I need more power.

[Shaker455]

Frank,
An HP 950 is a bad combo of parts from Holley and it will cause more problems than your encountering now.

Also, the 750 that you already have is almost the same size as the 950 execpt it has an 1-3/4" base vs your current 1-11/16"

A well prepped 850 annular will work wonders for your combo as I have built a few custom units for even 350's and the end results were a 4 tenths gain.

Your 850 downleg can be reworked/modified and even converted to annular boosters

If you like shoot me a PM or Email.
Jeff

[ponchopwr70]

I ended up ordering a pro systems carb which is the same idea as the 950 holley. Why are they trouble? I was going back and forth on annular vs dog leg. Also I herd good things about pro systems so I gave him a shot. I herd that the 950 was a good carb also.

[Shaker455]

I've reworked many of his units espically the 4150's

I hope you have better luck.

[68Formula]

Maybe the Pontiac is finally rejecting the Chevy donor. Try dropping in a 455.

[ponchopwr70]

I hope this carb works it wasn't cheap. amcmike you must be a pontiac fan! I would love to put a 455 in it, someday, if anyone wants to donate one Ill take it.

[Shawn MacAnanny]

I've heard good things about pro systems. I am only running a 750 although my engine is only a 346 it still puts out around 525-550 hp on stock heads and should run about 10.8-10.9 in the 1/4. I wouldnt think you would need a 950. A 750 or 850 max i would think. I'm running a similar cam with a good bit more lift than you as well.

Perhaps your dual plane intake is holing you back at higher rpms in combination with your cam? Are you running any sort of wideband setup?

[ponchopwr70]

No wideband but I can get access to one. The cam and intake are fine I think. Once I get this carb on in the spring Ill report the new times.

[Shawn MacAnanny]

The 108 LSA is what going to drop your powerband WAY down in RPM. Is it advanced any? I have a 110 advanced 4 degrees (if you had your cam card it will say +2 or +4 or if it says ICL ' intkae centerline' like 106 that means its a +2 108-106=+2) And my power band pulls to about 7000rpm.

I think a 950 is honestly just way over kill. Thats something for around 700hp IMO. I'm interested to see times though. I'm young i dont know much about the carburetion but what i do know from my experience is a 750 is more than ample for my 525hp+.

[CarlC]

I agree with heap. That cam is done at the RPM's you are currently turning.

The max RPM on the cam card is an average based on engine size. Average is 327-350CI. Your 383 will cause the the range to drop. A larger carburetor is not going to cure this limitation unless the current carburetor is acting as a restrition at high-RPM. Some testing with a vacuum gauge will help diagnose this, but for the cost of a big top-of-the-line carburetor vs. the performance gained it is likely that the money would be better spent on something else.

[ponchopwr70]

The carb that I'm getting is a 750 body with an 850 baseplate which is what a 950hp is. But I don't think it is a 950 cfm carb more like a 830 cfm or what ever. But my understanding is that its good to have a carb that can flow more than you can use on top as long as you can keep up velocity at lower engine speeds, which is what this carb should do. By keeping the venturi the same size as a 750 I won't have the lean condition when I open the butterflies like I did with the 850, but when I'm in the higher rpms with the butterflies open I'll be able to flow just as much as the 850 due to the smoother airflow of the bowl work and the bigger baseplate. Also I understand seat of the pants dyno can be off but there is no question when I had the 850 on this engine the rpm came quicker. Also with my current combo I run quicker in the quater by shifting at 6400 6500 so I know the cam card is close. I'm not looking to get more rpms out of the engine, just the acceleration like I felt before. Heres a rear wheel dyno graph when I had smaller headers, 2.5 exhaust and junk converter. It ran 13.0 when I did this. Now I have 1-3/4 headers 3" oval exhaust with x-pipe and smaller conveter and run 12.65 but I don't think the graph will change a real lot from before to now. I will post times with the new carb for sure just have to wait till april when The snow goes away. Its kind of an expensive experiment but I hoping to see improvements, but you never know might not work either.