Torque Production - 10 Torque Tactics

Although we talk about volumetric efficiency as a measure of an engine's breathing capability, it is mass flow that gets the job done. At standard temperature and pressure, air weighs 0.076 pounds per cubic foot. Adding heat to it makes it weigh a whole lot less. Air can pick up heat all the way through the induction system. Let's work our way backward through the induction system by starting at the intake valve. The only reason the intake runs cooler than the exhaust is that it is air cooled. Unfortunately, that makes the air valve heated!

The intake valve in a race engine runs a lot hotter than you may suppose. In a dark dyno cell, I could see the intakes just slightly glowing on a four-valve, fuel-injected formula engine I was testing. This meant they were in the neighborhood of 950 degrees. How much heat do you think the air picked up as it went by those valves? The first move here is to get a thermal barrier coating on the intake valves. If the budget allows, next are the intake ports and manifold intake runners. Then, insulate the intake from all sources of engine heat. That includes insulating the underside in the lifter valley and moving the thermostat somewhere remote rather than leaving it on the intake manifold. The last move is to pick up cold air to feed the carb. By making these moves you may find that the fuel atomization is now inadequate, so some booster re-evaluation may be needed.

Big ports don't make horsepower-the right-sized ones do. The best-sized ports are those which produce the desired flow along with good port velocity to enhance cylinder ramming from the intake and evacuation around TDC for the exhaust. The trend for Cup engines for the last five years has been progressively toward smaller but more flow-efficient ports. The result has been greater output over a wider rpm range. Because the intake port length of a small-block Chevy is fairly constant at about 5 inches, regardless of which 23-degree head is being used, the cylinder head industry has found it convenient to quote port area in terms of port volume in cc's rather than a mean area in square inches. This is OK as long as we are all on the same page. In selecting a cylinder head, don't be tempted to assume bigger is better. It is more productive to err on the side of slightly too small than too big when making a selection here.

We covered this subject in last month's issue, so I won't go into too much detail. It's sufficient to say that a cam with the LCA 2 degrees too wide (angle gets bigger) can cost as much as 25 lb-ft, whereas one with the LCA too tight (angle gets smaller) barely loses any. A similar situation exists with advance and retard. A cam with an advance 2 degrees too far loses almost nothing, but a cam 2 degrees retarded can lose as much as 10 lb-ft. The key to making torque is to have the optimal valve events for the job. Read last month's LCA story for the facts. Fast intake accelerations on and off the valve seat also make for better torque. The same, however, does not apply to the exhaust. These, when opened more slowly but over a longer period, produce better results on a race engine.

About the most obvious statement I can make is that the purpose of the rings is to seal a cylinder and separate oil from the space above the pistons from the space below. The better that is done (consistently while minimizing friction), the more torque the engine will make. Over the years, I have spent a lot of dyno time testing ever smaller top-ring end gaps. As expected, the torque and power rises as the gap sizes decrease-that is until the temperature-induced ring expansion involved causes the ends of the ring gap to butt. At this point, friction goes up, the temperature of the ring goes up even more, and presto-the top of the piston parts company from the bottom.

Such tests and experiences indicated that I needed a ring capable of running big gaps without leaking. Total Seal's gapless top ring (I am not a big fan of installing a gapless ring in the second groove) does just that. It seals near 100 percent (my numbers, not Total Seal's) with a 0.030-0.040 end gap. This provides a full seal without any chance of a seizure. I have tested these rings in the top groove every which way, and the results always look good. These days, I use Total Seal rings in everything I build or rebuild-be it a Cup engine or a nearly stock street unit.

Exhaust systems for a racing engine are all about dimensions. Correct dimensions create the possibility for big increases in torque and power. Incorrect dimensions bring about less than desirable consequences on the track. About now, most of you are expecting a solution toward getting the pipe dimensions right. Unfortunately, exhaust system design, especially for a two-plane cranked V-8, is by far harder to deal with mathematically than planning a minimum fuel trajectory to Mars. But there are a lot of basic pitfalls that can be avoided to get those extra pound-feet simply and effectively.