So the bigger the engine, the lower the RPM limit on parts?

[Kyrah Abattoir]

I can't do things halfway, so i've been attempting to build the most massive engines possible, and i always get part failure due to high RPM, after this i did the opposite and built the smallest possible engine i could and it easily reached maximum RPM.

I don't think i've seen this mentioned anywhere?

[UltimateBMWfan]

Yes, the more bore & stroke an engine has, the farther the pistons have to travel/ the heavier the parts are. The more robust the parts are, the more likely they will fail at low RPM. Hard to explain, I'm sure someone else will explain it much better. It works kind of like spinning a ball on a string that's short vs long, it's harder to get the long one to spin at the same speed as the shorter one.

[Crom]

If you increase stroke-length, you increase the distance a piston needs to travel to during one engine rotation. To maintain same RPM, piston has to travel much faster which generates significantly more heat on the piston rings and increase the stress on crankshaft. That results in increased chance of failure.

Either reduce stroke length, RPM limit or use pistons which are lighter or have less friction.

[dogwalker1]

Try more bore and less stroke?

[Daffyflyer]

Yep, shorter stroke means slower piston speeds for a given RPM. That's why the non-turbo F1 engines had lots of cylinders for their capacity (2.4 V8) and a really short stroke, so they could hold together at high RPM :)

[Mike]

Alot of that will come down to taste, I'm a sucker for the high rpm engines so I've always got to keep the stroke low enough that it won't implode. On the other hand, I can increase the bore to get more capacity, but then it tends to be quite a bit heavier as the engine block is bigger! Ahhh, compromises!

[Brassoid]

This seems to me, like realistic modelling of inertia & momentum by the simulation.

Each piston is a mass which rapidly reverses direction at the end of each stroke. A bigger, heavier piston requires more force to decelerate/accelerate it at the end of the stroke than a small, light one. Likewise, the faster the piston is travelling, the more force required to make it change direction at the end of each stroke. So a combination of big chunky pistons and high rpm puts a lot of strain on the conrods and bearings, and increases the risk of failure.

It's not necessarily a bad thing to have a large capacity, low-revving long-stroke engine. It will make its best power & torque at low/medium rpm, giving long-legged in-gear responsiveness, and refined engine noise, which will suit certain design briefs such as GT cars or cruisers. Hot-cam screamers are fun, but not very relaxing for freeway cruising.

[freax]

try losing a piston or two. more pistons isn't necesserially better.

[Daffyflyer]

Originally posted by freax:

try losing a piston or two. more pistons isn't necesserially better.

In terms of RPM, for a given capacity, the more pistons the better.