A fellow a few years ago was running a naked Triumph with an engine build similar to the one I am doing. He forgot to shift into 5th gear and made the run in fourth at high rpm. The head cracked. Knowing this, my plan is to run the hole open until I learn how to do data recording and I get some baseline information about engine temps. Then, after looking at the data, I will close up the hole a bit at a time if I can.

Another thread on this forum discusses crankshaft configuration. I posted some info about work I did to the Triumph crank to prepare it for high rpm use. A reply mentioned road racing Triumphs and 10,000 rpm engine use. It would be unfair to hijack the other fellow's thread. Info on this subject follows.

Currently my target rpm is 7,500 and the rev limiter is set to 8,400. This is higher than the standard Triumph factory red line. It works OK. These engines are very strong. Reciprocating engine parts are subject to stresses when they are accelerated and decelerated. Forces create these stresses and they can be roughly approximated by the equation F = MA where F = force, M = the part's mass, and A = acceleration. Acceleration can be approximated by A = V**2 / 2g where A = acceleration, V**2 = velocity squared, 2 is what it is, and g = the gravitational constant. Basic algebra shows that the internal stresses in an engine increase in proportion to the rpm squared. In other words, doubling the rpm increases the engine stresses fourfold. This is a rough and simplistic statement.

In these calculations from a few years ago, I see that increasing the engine operating speed 1000 rpm increases stresses 25 percent and increasing the rpm ceiling another 1000 rpm will increase stresses over 50 percent.

Horsepower can be calculated by the equation HP = t x 2 x pi x rpm / 33000 where HP = horsepower, t = torque, 2 = two, pi is pi, and 33000 is a constant. Assuming that the torque is the same for all engines, some bonehead algebra shows us that horsepower is directly proportional to rpm. In other words, double the rpm will double the torque. Again, this is a simplistic statement.

This is some of the most useful info I can calculate. In Case 2 the engine operating speed is increased 1000 rpm, engine stresses go up 25 percent, and I get 13 percent more power, 77 horses. In Case 3 the operating rpm is raises another 1,00 rpm, engine stresses go up a whopping 54 percent and I get a measly 86 horsepower.

Big increases in engine stresses = periodic teardowns and inspection + regular replacement of some very rare and expensive parts. The roadrace folks do this. They have no choice. Some LSR people with big money take this route. My budget says a higher 8,000 rpm target rpm with a 9,100 rpm redline is OK. It increases stress about 12 percent and it will give me a few horses.

These simple equations explain why blowers, turbos, fuel, and combinations of all three are so popular. They can provide much more power than spinning the engine faster.