My 1971 with a 700r4 and 2,100 rpm stall converter stalls in gear on hot days. The engine is a rebuit 350 with unknown internals, iron heads, aluminum Edelbrock low-rise Performer, and a 600 cfm vacuum secondaries Holley rich at idle. I'm guessing flat tops with a very small cam with since it pings on 87 octane and runs out of steam after 5,000 rpm. When the outside temperature is around 70 degrees f, the engine maintains 160f and starts and stops fine. At 80f and above, the engine stabilizes at 200f in traffic and stalls at a stop when in gear. I had a problem with the fuel boiling out of the carb after shutdown that was solved by removing the exhaust heat riser and installing a 3/8" insulated spacer under the carb. I'm running 10% ethanol and don't have an interest in running 0% since it's not practical to find when driving several hours from home.

I have thought about running aluminum heads with no exhaust crossover. Also, I thought that it would be fun to try a modern combustion chamber on a small flat tappet cam. The problem is that I don't know if the aluminum is going to be cooler or dissipate heat to the carb. Has anybody with a similar problem tried a similar solution?

 

What sort of idle rpm are you seeing when the car is idling, hot engine & trans, in gear, foot on the brake?
A/C? If so, does it make any difference to stalling if the A/C is on or not?
Lastly, what sort of timing curve are you running? This can have a huge effect on temps.

 

The car idles at 1,000 in park and 800 in gear with my foot on the brake when warmed up. I don't have the choke hooked up and have it pinned open. The car starts and idles easily and has no problems while warming up. The timing is 12 degrees at idle and 34 all in by 3,500. It has a new HEI distributor that I did not take the time to curve. I am not running AC. Since my car is a 71 originally with AC and no radiator expansion or overflow tank, I run the radiator about 3" low to keep it from burping coolant when shut down.

The power steering pump was making roaring noises and killing the engine at idle when approaching full lock on the steering wheel. After replacing the pump, that cause went away.

The car had been sitting for several years when I bought it. Leaks and failures started happening as I drove it that I've been correcting as they happen.

 

All that sounds pretty standard -- except for the high idle. My '72 TH400 idles around 600 in D, 800ish in P. I don't know if/how an automatic may cause stalling if it's got such a high idle, so it's likely something else. (You might want to back off the timing a degree at a time until the pinging disappears.)

When it stalls, does it start right back up with just a turn of the key? If so, I'd lean toward an electronic glitch. If not, I think a fuel issue would be more likely.

 

Do you have a vac advance can?

Try plugging your vac advance can into a manifold vacuum port on your carb (test with your finger if you don't have a vacuum gauge).

If that helps, really dial in your timing following @lars' instructions (though you are pretty close already).

 

The engine restarts on the first turn when hot but the starter struggles a little like the car has too much advance. The starter does not struggle when starting the engine cold.

 

Running your radiator 3" too low of coolant can have major effects on the engine. You want the engine to be able to push the excess coolant from the engine to the radiator's overflow container. The 16 lb radiator cap will provide you with ~261* (F) of over heating protection as long as the system is able to pressurize and stay that way. Normal operation with a functional overflow system will keep the radiator full ready for maximum cooling.

You need to have an overflow container on or near the Radiator that allows the excess coolant to have a place to go. As the engine heats up, your coolant will expand and require more room so it gets pushed into the overflow jar down by the side of the radiator. As the engine cools down the coolant shrinks and is drawn back into the radiator. If you have a broken vacuum hose or a faulty radiator cap then it might not get pulled back into the radiator and a bubble of air forms inside the radiator.

A Functional Coolant overflow system is crucial to a well running, cooler engine. Air inside the radiator is a "bad" thing as it prevents cooling from happening. Keeping the coolant level full inside the radiator should help the engine run cooler.

The timing is the other place that might need attention, it sounds like your timing might be a bit on the retarded side but it needs to be re-set to the factory numbers. Check the vacuum hose as well to ensure that they are not leaking any vacuum.

Aluminum heads are a nice thing when you have to lift the cylinder head off the engine block. They do not give off so much heat that the engine will run cooler, they help. Iron heads work just fine in many applications.

 

Since it restarts right away, I'm leaning away from a fuel delivery or heat-caused boiling over problem.

Because the starter has no problem cranking when cold, timing doesn't seem to be the issue. The starter may be getting heat soaked which raises resistance, resulting in a lethargic starter. GM did have a heat shield for the starter which are pretty easy to install. Some folks use a welding blanket-type insulator to block the starter from exhaust heat. Could also be combined with poor cable connections at either end.

Even though the HEI is new, I'm wondering about the module acting up. The stalling did not happen, as far as you know, prior to the new HEI distributor? I'd start with checking all connections at the module. I'm not versed in HEI, so can't offer much else on it.

(I don't think changing out to aluminum heads will do anything to solve the stalling problem. Get your stalling fixed and then think about playing with heads for performance.)

 

My car has several things wrong that need to be corrected. Once corrected, I'll post the final results and settings.

Here is where I stand.
I read Lars paper and discovered that I'm using his overall method for setting timing. My timing at 34 degrees total is not as aggressive, but the car pings at 34 degrees on 87 octane under hard acceleration. The car does not ping on 93 octane at 34 degrees. Per Lars, I moved the vacuum advance from ported to manifold. Changing to manifold vacuum bumped the idle from 1,000 to 1,200 when warm in Park at the same carb settings. I was able to lower the idle to a steady 900 in Park/750 in Drive. The engine temperature stabilized at 180 degrees in stop and go traffic at 84 degrees F if the gage is correct; down from 200 F. The engine responded really well to the change in advance from vacuum. It cruised on the interstate at 170 F in overdrive at 1,800 rpm at 70 mph. The car did stall in traffic, but it was not a struggle to keep it running by pressing a little on the accelerator; before it was a struggle to get moving. The smell of gas in the garage is not as bad as when I was shutting the car down at 200F.

At the lower idle speed, there is a 100 rpm bump in idle speed when applying the brakes. I have a new brake booster on order. Because of the vacuum leak, I did not bother to check the idle timing between ported and manifold vacuum or set idle mixture.

1971 AC cars did not come with a radiator overflow. I have purchased a reproduction overflow tank for a 1974 that is not yet installed.

 

Glad to hear you already had some success, and have Lars' papers.

After you get the vacuum leak squared away, check that the vacuum can is operating in the correct range, and has 10-12 degrees of advance baked in (too much can be bad, too).

But a big improvement already!

 

Vapor lock is a logical cause...especially if you are using ethanol-laced 87 octane fuel. It boils at lower temp than 100% gas. Blocking off heat riser passage under the carb can be beneficial, as can adding a heat shield under the carb (and an extra gasket).

If you haven't done so, you NEED to run your distributor advance can directly from manifold vacuum (rather than GM spec'd ported/timed vacuum source). That will allow the engine to run cooler at idle, improve idle quality and make your engine happier.