Turbo: What do you feel is going to be the major output difference between the two engines?
Dan: One is going to run a higher rpm. The shorter rod, in my opinion, is going to increase the piston speed. The long rod is going to slow the piston speed and dwell longer, which is said to allow more air and fuel into the cylinder. Theoretically, the short-rod set up should pick up a lot more power on the top-end, due to the piston speed.
Turbo: So with the short-rod motor, are you expecting the torque to equal the long rod version or fall off?
Bill: That is one of the many things we are trying to find out. Technically, we have results of what happens when this is done to a domestic push-rod engine, but with overhead cam heads being more sophisticated and efficient, it's a whole new can of worms.
Turbo: So as far as cylinder head comparisons go; between the two, would you say porting and cam profiles will be different?
Bill: If we were to get more in-depth into the issue, technically we would have to port the head to provide the best horsepower output to cater to each block. What I have done in this situation is use a full race-spec head, built around a neutral application where it could be run on both engines. Now, if I were to do a head for each, the major difference would be porting the intake ports to cater to a short-rod or long-rod engine.
Dan: (pointing at Brian Crower) Your engine will be the lower-rpm motor, but should produce good torque.
Brian: Well, my engine is running a longer rod, so mine should be able to turn some high rpm. Theoretically, it should be able to do 9,500 rpm forever with no problems.
Dan: Then mine will do 10,500 rpm with no problem! (laughs) Theoretically, the longer stroke will start running out of horsepower at a certain rpm, while torque runs out at 5,250 and then horsepower takes over until it runs out. My engine will be based on the same theory, but when horsepower takes over, mine will continue to produce more power in the high range until it starts to run off.
Brian: Because of the short stroke.
Bill: Then the physics of the horsepower take over in high-rpm compared to the loss of torque.
Dan: With my engine, I look at beating you at the top end of the race. Because your engine will produce more torque, you should beat me out of the hole, but I should be able to catch you in the end.
Bill: (laughs) Brian will be at the track with his Honda-powered tractor and Dan will be there in a Honda-powered dragster.
Dan: (laughs) Brian's just trying to sell cranks to everybody.
Brian: (Sarcastically) Ha, ha, ha!
Dan: OK, this is how my wanting to prove a short-deck, short-stroke engine came about. When I raced Comp, I could have easily went the long-rod-stroke route but I stuck with the high-rpm route. I think this is new to most because this isn't a Chevy Comp Class engine, it's more like an F1 engine minus the turbo.
Turbo: OK, so with the all-motor class set at a 1,600-lb limit, what would you consider is too much or too little amount of torque?
Dan: That's judged by tire spin. So with Brian's motor, if he could hook up the power he is planning to make in the low to mid range then he should be able to holeshot me pretty good-If he could hook up. If you're spinning the tires too much, you're not going forward; if you don't spin the tires, then you are moving forward.
Turbo: To clarify: When you mean spinning the tires, you mean spinning the tire in excess, right?
Dan: Correct.
Bill: This is where tire size and gear ratios come in handy. Due to the different powerbands that engines will produce, gear ratio will also have an effect on how well the car as a whole will perform on the track.
With the short-deck, fast-piston engine, this would be considered a velocity engine so it has to leave at a higher rpm. Judging how much the car weighs, the engine has to make a certain amount of torque in order to not have the rpm fall off. If the weight of the vehicle doesn't shock the engine, the end result will be usable top- end horsepower. With the long-rod motor, feathering the pedal may be your only option because of the torque we think it will produce.
Brian: Think of it this way, we are giving the reader two options and two different routes to take. One should make power at a certain rpm and the other should do it at a different rpm. Each will also make torque at different points in the powerband. This test is a way to give the reader two different choices for their application.