[jim_howard_pdx]

I just replied to a different thread and said, d a m n, I should share that with all the rest of you Ford Oval Blue Bleeding racers out there.

This is only what I purport it to be, a single and simple speed secret I learned from watching the best and most successful racing legends pull rabbits from their hats.

This is not intended to be the "best secret" ever, or even an "important secret." It is just a little thing that may help a few of you pick up a trophy or two. And that is what it is all about. WINNING.

So here it is, my very first thread titled "speed secret for today".....

Back in the 70's we used to always buy high dome 12.5 or even 13.5 to1 domed pistons. Then we would machine the valve reliefs for the cam lift and valves sizes we were campaigning, and then we used a dye grinder to totally smooth off the piston top.

In some cases companies would sell us the forged domed pistons NON machined on the top, so we could cut only the material we needed for valve clearance and NO MORE. Then we went to work on the piston top with a dye grinder and completely smoothed the entire surface of any ridge or angle that could store heat, glow like a torch and cause pre-detonation at high rpm.

We would clean up the combustion chambers too, but you have to know your rule book and what you are allowed to do and not to do for the class you race at. Sometimes we would pocket port heads and polish the combustion chambers and then bead blast or shot peen the ported surface to make it look like stock cast iron. It would pass tech inspection and flow like a DEMON.

Getting back to the piston top, we actually wanted to keep the compression to about 11.5 to 12.25 at the upper edge, because we were using extremely high lift, which mimicks the power produced by static compression changes. We cut the dome smooth and removed enough metal to produce a minimum 0.08 quench with the compressed gasket across the entire piston surface other than the wedge of the combustion chamber.

Now to keep quench tight on as much of the piston as possible, we wanted to reduce the wedge area just to what was needed to start the flame propogation. In most cases that was about 80% of the stock wedge. In order to reduce the wedge but keep some strength in the head we would angle mill the head, sometimes as much as a quarter inch on one side and by only a few hundredths on the exhaust side.

Many people watching the process thought we were trying to increase the static compression ratio, but we were really after having just the 0.08 quench area. If successful, we would have great flame propogation from spark kernal radiating out evenly to the edge of the piston. You will see swirl effects this is good and normal. YOU WANT SWIRL, because it helps pack very dense air fuel charges into the cylinders. That is why the closed chamber Cleveland heads make so much more horsepower than the open chamber 2V heads. You just cannot achieve a tight quench with the open ports and maintain enough air fuel in a tight wedge to create excellent ignition.

Do not remove too much of the wedge, because there needs to be a very dense fuel charge around the spark plug to establish the flame propogation. Otherwise you never burn the total fuel that has been compressed. You end up with really stupid, incomplete burns.

Expect to have to have a competent machine shop square the head bolt faces on that angle milled head. Plus you will need to
counter mill the intake manifold and sometimes dowl fit it to the head to provide proper intake port to head port indexing. Don't be surprised if you don't have to drill your intake manifold bolt holes enlarged, so you can move it forward or back as much as an 1/8 inch to get perfect port match.

When piston coatings first came out, we would coat both the entire surface of the piston and the entire top of the dome. We tried coating the back of the intake and exhaust valves found it did nothing to affect HP or torque.

Running the coatings allowed us to bump up static compression by 1/2 to 1 point. When you take a 383 from 11.25 to 12.25 compression ration you get an additional 30 horsepower or so at the rear wheels. This is not insignificant. Often it was the coating that provided the extra compression ratio, so if the rule book said you had to use a stock piston, and 11.5 was all you had, the coating would put you at 12 or 12.25 compression!!!!

This is a good secret to share with you guys. Run a dished piston with less quench when you are building for torque, like an off road truck or boat engine. Run a very tight quench when you are after higher horsepower.

I do not know all the physics on flame travel under velocity and compressed combustion, but to keep things simple the flame travel is broader, slower, and the fuel burns more complete when you keep the quench area really tight. I learned that from watching a Smokey Yunick engine being torn down after winning its bracket at the Winternationals. I wish I could have taken pictures of that combustion chamber and piston top for you to see.

The burn pattern was perfect from the spark kernal to the extreme edge of the piston tops and there was no area of any piston that showed combustion generated turbulence. In fact, the flame pattern indicated the effect of the intake charge swirl that Smokey was famous for.

All of our modern heads have strong engineering provisions to generate enhanced intake swirl, but it is up to you to build a piston top that reduces quench to the optimum amount.

Just as a historical asside, Smokey Yunick worked for FORD for almost two years during the time Bunkie brought over Shinoda from GM to design the 69, 70, and 71 models. Smokey helped sort out the 302 Boss engines for track racing. That is why you see a 780 CFM holley strapped on to those engines. It was the same carb he used to get the 396 to 425 HP.

He helped get the 302 BOSS set up for the new trans am races. Bet you CHEVY guys never knew that, and I bet you FORD guys never knew a CHEVY guy was responsible for our DOMINATION in trans am racing. Smokey was a true genius when it came to making horsepower.

I hope this helps all of you realize just how complicated and exciting quench can be!

Go quench safely out there and take home some trophies for all your hard earned money and effort!