[jim_howard_pdx]

When you think of an engine, remember it is simply an air pump that pulls air fuel mixtures into the cylinder. Compresses them into the combustion chamber. Ignites the mixture. And makes grown men beg for more.

Now say you are displacing 302 cubic inches.

With a stock length rod of 5.09 inches and a crank stroke of 3.00 inches you will be compressing 37.75 cubic inches of swept space into the space that exists between the piston's top surface and the top of the block at top dead center. Also figured in is the volume of space created by the compressed head gasket and finally you add in the volume of the combustion chamber. Dividing the total combustion area by the swept rea plus the combustion area give you the static compression rate. On a street engine you want 9.3 for Iron heads and 10.0 for Aluminum heads.


So the quench area equals the space between the piston top and the head surface (including the wedge). The tighter the quench, the better the fuel burns plus it burns slow and evenly. The looser the quench the easier it is for the air and fuel to be unevenly mixed and you will have pockets of burning fuel plus areas of exploded fuel and unburned fuel that disrupt the flame propogation.

At the wedge around the spark plug I leave it unfilled so there is a walnut of space where the fuel can be properly ignited by the spark. This preignition then becomes a wave front. This is what we mean by flame propogation. There needs to be ignition of the fuel, and then it needs to propogate from the center of the cylinder to the edges as evenly and as controlled as possible.

When an engine pings, the fuel is literally exploding and the force pushes down on the piston which cannot control the force and the piston "knocks in the bore" This beats up you cylinder walls, your piston skirts, hammers your rings, and will destroy your valve guides.

Most Chevy racers worth a darn will not build an engine with over 0.10 quench. The engine will run flat. They will shave the block deck, run high compression pistons and shave down the surface, what ever it takes.

So tight quench allows a slow, long, controlled burn. This builds HORSEPOWER.

Torque is a separate issue I will discuss at another time. s

Now say you want 370 hp from your 302. Your goal is to put 300 hp to your rear wheels. What do you do. Do not look at my idea as where to go. That would be foolish. Why would you want to buy 500 dollars worth of pop up piston blanks, work them for 20 hours, measure and sweat the details and bolt it all up to get a few extra 2 or 3 horsepower at 10 to 1 compression.

Use a good quality flat top 11 to 1 compression piston. Verify the valve reliefs are adequate to your cams lift and duration and valve size. Then use a carbide cutter on a dye grinder to completely smooth the valve reliefs so there are no edges or ridges of any sort. Chamfer the piston edges so they are round not square but NOT OVERLY ROUND. Don't go overboard on me here. Just no edges to store heat, glow orange and predetonate the mixture as your RPM climbs.

I would run a solid roller lifter/roller cam/roller rocker arm set up on stock ported or aluminum heads.

Once you have the piston relieved to 10 to 1 compression, run a cam like this. Comp cam solid roller lifter, roller cam with Intake specs of 225 duration at .050 lift and .550 lift. Exhaust valve should be 235 duration at .050 lift and .570 duration. Port the stock heads to fit felpro 1250 gaskets, or buy some Trick Flow heads like mine. I LOVE THEM. So easy to use and enjoy.

If you have a little extra money go with a 331 or 347 stroker kit. This cam, good heads, and a long rod set up will get you 390 horsepower fairly easily. You will get 14 mpg on a carb or 17 mpg on fuel injection.

Now you just need 3.73 to 4.10 gears and a transmission and clutch that can take the power. You will have a great mild car.

The mods I outlined are for 6,7,8 and 9 second ET bracklets depending on rules of the class. I like to do this mod on NOS engines because they really respond to a smooth combustion chamber surface without ridges and irregularities.

Hope this helps. Look for further speed secrets as they pop up. I think I will discuss torque tomorrow. You will want to read this and try to find where I am looking for people to challenge me.

I am using this as a way to get people thinking about the physics going on in their engines. This is the way to build a good engine that will deliver the results you are looking for.