Closed Chamber Heads

Dear Racer,

Amateur opinion about your options:
1) Timing adjustment might be the problem and might be the solution
2) Assuming that the easiest fix doesn't work, then you could consider octane boosters
3) You could have your mechanic place a thick head gasket to lower the CR---that *might* work
4) Go back to the original heads
5) Go forward with different heads either iron quench heads with measurements that would insure a manageable CR for pump gas 91 octane--or--aluminum heads, which would be the priciest option.


Warmest regards, Chuck Engles

You need to know what pistons are in the engine.

In my experience with Clevelands and pump gas you need to use a static compression ratio of about 10:1.

How you arrive at that is your choice.

It sounds like the engine has got the TRW domed pistons in it. They bump the compression ratio up to 11.8 to 1. That's way to high for 93 octane pump and even 102 unleaded racing gas.

It's easiest to change the heads rather then the pistons. Simplest change would be to the open chamber iron heads but there are many better heads available.

Quench chamber heads and flat top pistons are normally no more than 10:1 compression, and the Cleveland with 10:1 will run on 91 octane with no issues. So if the dieseling is caused by excessive compression I would agree with Doug, that motor must have pop-up domes in it.

Or does it? What you didn't describe is the motor pinging or detonating as you drove it.

A motor will "diesel" when you turn it off if the ignition & carb aren't adjusted properly. To be more exact, if the ignition advance at idle is too retarded then to get the idle rpm up the idle adjustment must be cranked-in, opening the primary throttles further than they are designed to be opened at idle. This exposes some transfer slots that aren't supposed to be exposed at idle. Thus exposed the slots allow the motor to pull enough fuel and air into the motor after you shut off the ignition to make the motor diesel. Perhaps what the motor needs is simply a proper adjustment of the distributor's initial advance setting to around 16° to 18° BTDC, which in turn will allow you to back-off the idle setting, and close the primary throttles, bringing them back into the range where they belong at idle.

If the motor still has the original crankshaft damper, the timing marks cannot be trusted to be accurate, because the outer ring of an old damper will slowly spin on the hub. So if the motor still has the oem damper it would be better to set the initial advance with a vacuum gage.

-G

A few pieces of low-tech practical advice from a guy who's Pantera used to run on:
1. Lower the idle speed
2. Push the brake pedal, the use of electricity is sometimes enough to stop it
3. If you want to know what pistons you have without taking the heads off, use a lighted inspection scope. Piston has to be in a certain position to be viewable, so pull all plugs and keep trying till you get a clear picture. I just did it on my Longchamp to discover dished pistons, with a Summit scope

You may want to consider installing a water-alcohol injection kit. When used properly it should allow for running 92 octane at your high compression ratio, with the performance benefits, although it will not effect run-on. That can be delt with by the common practice of turning off the key with the car in gear and using the clutch and brake to stop the engine.

16-18 Degrees BTC. I must be losing it. I thought I read here before 8 - 10 Degrees. Could this cause the engine to run hotter?

22 Racer has not said he has a problem with detonation or pre-ignition, so if his problem is just the "dieseling" or run on, he should be able to resolve it.
Something hot inside the combustion chamber is igniting the fuel which allows the engine to run on after the ignition is turned off.
It could be the cooling fans or alternator continuing to supply a voltage to the coil. This can be ruled out by removing any coil wire whilst it is idling when warm.
Check spark plugs, correct ones, maybe go for a colder plug. Post some pictures of the spark plug tips.
Carbon build up, check with a flashlight through spark plug hole, not easy to see.
High idle, wrong timing, over heating, too low an octane fuel, are also causes. You need to find out which one.
There are anti-run valves that some cars used to use. Some attach to the intake manifold and just release any vacuum so stopping any gas being sucked out of idle jets. You can test if this will work for you by pulling off the hose to the brake servo where it connects to the intake manifold when the engine is running on.
You can also use an idle solenoid on the carb. When the car is running 12v applied to the idle solenoid which holds your idle at the normal level, with the ignition off, the solenoid is off and closes the carb throttle blades even more.
Let us know how you get on.

There has been a discussion previously on this Forum of some Pantera’s running on after the ignition is turned off.
But it was not a pre-ignition issue, just voltage continuing to supply the coils & the engine keeps running.
From memory this occurred sometimes when fitting an MSD & a diode installed somewhere in the system solved the problem.
In this situation putting your foot on the brake pedal sucks enough voltage from the coils & the engine dies.
It’s a strange occurrence, but I know of several Forum members here that have had this issue & my car continues to do the same.
Something to be aware of if the problem turns out not to be pre-ignition.

Regards,
Tony.

Yes this is true.

Installing the Pantera Electronics engine and fan controllers fixed this into a non issue for me.

Thanks for all the input. I'm assuming the dieseling when turning off ignition must be a compression ratio-octane issue. When running race fuel, the car did not diesel at all, only after running premium pump gas (with no race fuel) did the car start dieseling. Before I used pump gas, I was told it may diesel without race fuel due to the closed chamber heads. We were concerned the compression was too high for pump gas and it appears to have turned out this way. The car runs so strong with these closed chamber heads, I really prefer to keep them if I can come up with a solution other than resorting to race fuel. Thanks again

Octane booster is an obvious choice.
Most comparison studies I’ve seen on the octane boosters available show it has very little real effect to octane levels & only pushes up octane by points.
Which is .5 or .6 etc instead of a whole 2 or 3 octanes.
On our race buggies that used to run high compression bike engines I would mix up my own fuel.
I would start with the highest octane pump gas available & add 20% toluene & 10% acetone.
Both of these are reasonably cheap as they are commercial solvents.
Toluene & Acetone is what the Formula one team’s used back in the 1980’s to brew up the special fuels during the turbo era, (These solvents are also present in pump gas to boost octane).
From what I have read 30% Toluene is about the safe limit & 15% Acetone for a street engine.
Although the F1 teams used to get into 65 to 70% Toluene.
The reason not to run too much Toluene is it simply makes the engine hard to start when the engines cold.
I would also add a cap full of R40 castor oil to aid valve lubrication.
Fairly cheap to do, raises the octane safely & the performance advantages are very noticeable.
Just don’t get it on your paintwork.

Regards,
Tony.

quote:

Originally posted by 22 Racer:
Thanks for all the input. I'm assuming the dieseling when turning off ignition must be a compression ratio-octane issue. When running race fuel, the car did not diesel at all, only after running premium pump gas (with no race fuel) did the car start dieseling. Before I used pump gas, I was told it may diesel without race fuel due to the closed chamber heads. We were concerned the compression was too high for pump gas and it appears to have turned out this way. The car runs so strong with these closed chamber heads, I really prefer to keep them if I can come up with a solution other than resorting to race fuel. Thanks again

It all isn't this simple. First you need to determine if you have an excessive compression ratio engine. Anything over about 10.5:1 actual static will be a problem for pump street gas and a closed chamber Cleveland head.

Next, it may not be a compression ratio problem. The Pantera does have this issue of the original design of the radiator fans causing engine run on after the ignition is turned off.

Lastly, these engines need 16 degrees initial timing at idle. They like 36 degrees total in "Boss 351" configuration.

They will not accept a fast distributor advance on pump gas. Best they will take is all in by 5,000 engine rpm.

The days of having full advance in by 2,500 rpm on pump gas are long gone. That is 106 race gas territory and even at that, they are very sensative.

IF you are going to attempt to add home made octane boosters be sure that the rest of the fuel system will accept it without eating the tank and fuel lines.

You also need to worry about the brass floats in the carb, or carbs (weber ida's use brass floats too).

Brass floats in the carbs should be changed out to the nitrofil types if you are using any kind of fuel with ethanol blended in. Here in the US that's everyone.

The stuff just eats up certain metals. Brass is not particularly immune to it although it seems to be on a slower digestive track.

If this is a compression ratio issue there is nothing that will fix it except a minimum real
103 octane rating.

I tried Sunoco 102 Unleaded racing gas and it did not solve the problem.

Also aluminum heads don't necessarily fix it either.

The cause is the inability of the fuel octane to resist detonation, which is igniting of the fuel just from compressing it. That's how a diesel engine works and that's why this is called dieseling.

PanteraDoug,

It is my understanding that water/alcohol injection will address the detonation issue, which would be my primary concern with running such a high compression ratio on street gas. Dieseling is an annoyance but detonation will cause a walk-home failure. If you want to maintain the performance that higher compression ratio gives, I see this strategy as an alternative to octane boosters or mixing your own gas. I would not aggressively retard timing to avoid detonation as that will reduce performance and can quickly raise exhaust gas temperatures, again leading to premature critical component failures.

Water injection? You won't prove it by me. I tried the Spearco unit about 1978. right after Sunoco dumpted 96 Ultra.

Saw it again the other day in the back of the garage. It kind of appears every so often like a ghost ship at low tide.

There are several issues with the water injection. Timing, imjector sizing, ignition timing.

Jetting Webers from scratch is easier.

In order to kill the detonation the quantity of water will bog the engine.

You also need to remember that you are substituting water vapor for atomized fuel and the result is a big drop in horsepower.

Been there, done that. Doesn't work. Not like you want it to anyway. Go to plan B.