Speed Secret # 7

[jim_howard_pdx]

Speed Secret # 7

First lets sumarize our speed secrets.

One was keeping the quench very tight, allowing you to run more static compression ratio without detonation.
Two was to reduce parasitic horsepower loss (reduce the weight of anything spinning or rotating in your drive line, from crank, pistons, and rods, to flywheel, to transmission, to driveshaft, to rear end, axles, to your wheels and tires.
Three was optimizing your static compression ratio to the highest your class allows, and then increasing the dynamic compression ratio by using the proper overlap and valve lift to get extra cylinder pressure.
Four was to reduce the intakes dillution effect by using advanced cam technology.
Five was to use as long a rod as you can on your stock or stroker engine. Look to have the longest swept length of stroke + rod length you can create.
And six was to get your spark advance curve set up for optimum ets. Use the right heat range plug, good cap and rotor, good wires, a magnetic trigger duraspark, and an ignition box and high quality coil.

Now for Speed Secret # 7.

Would you like to get a free 5% increase in torque. Lets say you have a 400 ft lb of torque engine. That would make it a 420 ft lb of torque engine. That would make about 35 extra horsepower for you at the track--FOR FREE.

How can you do this.... Switch to a zero gap piston ring set, and keep a tight piston to wall clearance next time you build.

When I was still in diapers, I build a 500 hp cleveland engine. Everyone told me to run a wide clearance of .005 to .006 so my forged pistons would have less friction and rev faster. At the time, chrome moly ring sets were the rage. So in went a trw 11.5 to 1 compression forged piston, wide clearance and chrome moly rings. The results were ok, 500 hp is always fun. But the blow by was really bad with the chrome rings. They were so hard it took nearly 5,000 miles for them to seat completely. Then the wide wall clearance allowed a lot of cylinder pressure to slide under, behind, and through the ring lands. Blow by was a harsh 7.3 percent! OUCH

Lets look at an example so you can see why this is bad. On a stock 351 cleveland, blow by is 4% for a new engine, and they recommend rebuilding when you exceed 6-8 percent.

What is blow by?

During the compression stroke, your piston squeezes the intake mix, the spark preignites an ignition kernal that starts a flame that propogates from the plug to the pistons edges. This wave front releases high cylinder pressures that exert force against the piston and drives it down the cylinder.

But at the very top, as the pressure builds during the combustion process, hot charged gas flows around the edge of the piston and into the top of the first ringland. It then exerts pressure against the back of the ring pressing the ring hard against the side of the cylinder wall. At the same time, pressure leaks past the bottom ringland and moves right on to the second ring. The same process is continued. Then on to the oil control rings, now the gas escapes into the crank case where it increases pressure and forces air and oil mist out the valve cover baffles.

A 4% blowby means that 4% of the total combustion cylinder pressure is lost past the rings and enters the crank case. This is 4% power that cannot produce torque during the power stroke of your engine. It is lost horsepower.

In the 70's, we used to buy ring sets that were "cut to fit" We then modified them for a "half slide" edge. This is exactly what Childs and Alberts provides for you today with their zero gap ring sets. At the conjoining ends, each is shaped like an "L" and the two "L"s fit together to make an zero gap I. The "L"s slide past one another as they heat and expand, or as they contract.

Use zero gap rings and you will be rewarded by just a 1% blow by. On a 426 Hemi race engine, we pulled a 35 horsepower increase at the rear wheels with just a ring set change. On my 351 cleveland, we pulled an extra 17.5 hp at the rear wheels.

I expect a bunch of engine builder guys to sprout off that ET times will not increase that much from a ring change. But 17.5 rear horsepower was good for a tenth second on my car. More importantly, less blowby means FEWER contaminants reach your oil. It stays cleaner, and provides more lubrication under extreme racing conditions.

Now why run a tighter cylinder wall to piston clearance???? A .0022 to .0035 is where I like to run my forged pistons. .0012 to .002 is where you want to be with hypereutectic pistons. The tight clearance reduces piston rock and that will reduce friction. The tighter wall clearance also seems to concentrate the pressure effect of the combustion gas on squeezing the top ring tightly. This also enhances better cylinder sealing.

If you are doing a rebuild now, or if you are planning one, check your rule book. If it allows you, run a modern light weight racing piston that uses the thinner racing ring sets. You do not have to go microscopic here. Just get them at least a full size thinner than the old thick stock rings. If you have a choice of oil ring control pressure, stay standard. The light pressure oil control ring may do a poor job on your street/highway car. And that is not a good thing.

Here is a historical fact you all may or may not know about. Honda car company was formed because Ford, GM, and Chysler turned down an engineer with a superior piston design. That guy was the founder of Honda motor car company. He had created an improved piston ring that reduced friction, improved sealing, and increased horsepower. He took this new ring technology to Ford, Chevy, and Dodge, and each of the big three decided to use their old thick, heavy, standard rings....

Honda was born as its own car company.

Today, Honda has dominated Cart racing for three years straight. Not by a little, but by a wide margin. So maybe Honda had a better idea.....

The point of the last paragraph is not to allow some Ford "expert" to tell you to run thick, heavy, standard ring set. Run the light, thin, racing rings on a good forged racing slug and you will make MORE Horsepower. Just make sure you chose the racing ring set to have a zero gap ringset TOO.

So let the discussion begin.

I am sure someone will disagree with me.

But remember that all motor, 2.5 liter Honda engines, are running 10's this year, and will run 9 second times next year. I can tell you first hand that the rings and cylinder clearances play an integral part to making that magic happen.

So take advantage of the same great engineering and gain some FREE horsepower.

If you don't, your competitors will!