Performance Q&A Questions - Performance Q&A

Kevin McClelland Jan 1, 2009 0 Comment(s)

Don't Blame The Stall

I have had my '72 Chevelle for about 15 years and had a new engine put in about a year ago. It is a 355 small-block with forged flat-top pistons, 2.02/1.60-inch-valve 461 castings, a new cam with 0.474 inch max lift, and a 650 Holley double-pumper. A little better than the original 307! I was told by the guy who built it that it should push anywhere from 375 to 425 hp. It is not dyno-tested, so I really have no clue. I have a 4,000-stall torque converter. After I light up the tires and come to a stop, the car seems to want to stall. Is the stall too high for this engine, or is there another problem? This car is used only for the street right now. Any help would be much appreciated.
Kenneth Ahern
Fort Erie, Ontario, Canada

Having a 4,000-stall converter makes the engine's life very easy at idle. The higher you push the stall speed of a converter, the less load is placed on the engine at idle. This isn't the problem you're running into.

First, take a good look at your 650 Holley. You must start at the float levels. If the float level is too high, fuel can weep out of the secondary boosters on deceleration. Extremely high float levels can actually slosh fuel out of the secondary bowl vent, which dumps raw gas right down the secondaries. We could go into a long explanation of how to adjust the float level, but if you go to Holley's website and click through the Tech Service tab, then Common Questions, you'll find a great explanation of how to adjust the float levels. Holley also explains accelerator pump adjustments and vacuum-secondary spring tuning. It is a great resource for Holley carb tuning. After you've ensured that the floats are adjusted properly and the idle mixture has been set, this should take care of your stalling problem.

One other thing you may want to look for is that some builders will run full manifold vacuum to the vacuum advance on the distributor. This works well to clean up a choppy idle, but when you are decelerating to a stop, you have high manifold vacuum and high advance. When you come to a stop and the idle comes down and the load goes up, the vacuum drops and so does the advance. Make sure you are running ported vacuum to your vacuum advance can.

These few simple adjustments should help your stalling problem. As for the power of your little small-block, you're probably in the 375hp range. Without all the camshaft specs and the inlet manifold, it's tough to give you a complete answer, but 375 isn't out of the question. Good luck.


Moving Malibu

I was wondering if you could help me with my project I'm building. It's a 0.030-over 454 with 11:1 closed-chamber pistons and a steel 1053 crank. I have two choices of cylinder heads. The first is a pair of cast-iron oval-ports, casting number 336781. These heads have been cut to fit 2.30/1.88-inch valves with 113cc combustion chambers. The other set is a pair of iron rectangular-port heads, casting number 3994026, which have also been cut for 2.30/1.88 inch valves and have 118cc chambers. I'm building the engine with a Comp Cams Xtreme Energy solid lifter cam PN 11-678-5. This camshaft specs out at 282/290 advertised duration, 244/252 degrees duration at 0.050 inch tappet lift, 0.590/0.598 inch max lift, and is ground on 110 centers. I'm looking to get into the high 10s on motor alone. This '80 Malibu will be street driven also, so what would be your choice of heads, and is there a big difference in the power? Thanks.
Fred Reed
Houston, TX

Man, you want to have your cake and eat it too! We sure hope this '80 Malibu is ready to take the power of that big-block you're building. They have been known to twist pretty good when you put power to them. And you better step up to a 9-inch Ford rear or a Strange Dana 60.

With your 10-second goal, you'll need to go with the rectangular-port heads and do some work to them. Hopefully, whoever put the larger valves into the cylinder heads at least ported the bowls to match the larger valves. The benefit of installing larger valves on the inlet side of iron big-block cylinder heads is that you can finally have some type of short side radius. This is the turn from the port floor into the bowl of the port at the valve opening. Also, since you already have closed-chamber pistons that spec out at 11:1 compression, you'll need to mill the heads down to a chamber volume between 110 and 113 cc. This will give you a measured compression ratio in the high 9:1 to low 10:1 range. With the camshaft you selected, you'll need all this compression.

Rounding out your package, you'll need a good single-plane inlet manifold and a Holley 4781 850-cfm carb. The Edelbrock Victor Jr. PN 2902 is a good choice for the rpm range you'll be in. And on the exhaust side, you will need at least a 17/8-inch primary pipe with 31/2-inch collector. Check out Hedman Hedders engine swap headers PN 65216. They fit the bill and will bolt right in.

Your 10-second goal is right up there for a street-driven car, so remember: Keep as much weight out of it as possible. Adding an iron-headed big-block is going to strap down the front end with at least 250 pounds more than a small-block-equipped Malibu. Have fun with your toy and look out for the police!



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