What is the limiting factor in RPM/redline and powerband?

[Viperoni]

Crankshaft weight, stroke, connecting rod length/stroke ratio, piston weight and piston pin strength from a rotating assembly point of view.

For the valve train, valve, spring and retainer weights as well as spring strength (for pushrod engines, also have to worry about lifter and pushrod weights, as well as the lifters in general).

 

[Howard]

Originally posted by: spidey07

Originally posted by: Sureshot324
F1 engines have a really short stroke, meaning the piston doesn't move up and down very far. This means that the piston doesn't have far to go to complete a full engine rotation.

shorter stroke = less inertia?
Same piston acceleration, but shorter stroke?

Redline is proportional to such things as bore/stroke ratio, the inverse of moving mass, head flow at high speeds, airflow at high speeds (in all areas from the manifold to the intake runners to the intake ports through the combustion chamber out the exhaust ports into the exhaust header(s) out the collector), and perhaps the cylinder/displacement ratio (proportional to cyl/disp, not disp/cyl).

 

[Howard]

Originally posted by: spidey07

Originally posted by: Sureshot324
F1 engines have a really short stroke, meaning the piston doesn't move up and down very far. This means that the piston doesn't have far to go to complete a full engine rotation.

shorter stroke = less inertia?
Same piston acceleration, but shorter stroke?

If you reduce the stroke, the mean piston acceleration decreases.

 

[Howard]

Originally posted by: Viperoni
Crankshaft weight, stroke, connecting rod length/stroke ratio, piston weight and piston pin strength from a rotating assembly point of view.

For the valve train, valve, spring and retainer weights as well as spring strength (for pushrod engines, also have to worry about lifter and pushrod weights, as well as the lifters in general).

Don't have to worry about the springs. He didn't say a word about reliability.

 

[Sureshot324]

Originally posted by: spidey07

Originally posted by: Sureshot324
F1 engines have a really short stroke, meaning the piston doesn't move up and down very far. This means that the piston doesn't have far to go to complete a full engine rotation.

shorter stroke = less inertia?
Same piston acceleration, but shorter stroke?

Think about it like this. Say you have a short stroke engine where the piston moves 4 inches down then 4 inches up. Then you have a longer stroke engine where the piston has to move 8 inches down and 8 inches up.

In the longer stroke engine, then piston has to move twice as far to complete one rev, so if revs were equal, the piston would need to move twice as fast.

 

[Goosemaster]

You have to have a good-quality needle to get the good speeds

 

[Monkey muppet]

I'm not very good at remembering stats like those posts above me - but I'm suprised that no-one has mentioned why a 2-stroke engine can rev much higher

I think it's to do with the valve return rate. I belive Ford designed one to fit into the Ka, but abanded it due to reliability

 

[gsellis]

Originally posted by: Monkey muppet
I'm not very good at remembering stats like those posts above me - but I'm suprised that no-one has mentioned why a 2-stroke engine can rev much higher

I think it's to do with the valve return rate. I belive Ford designed one to fit into the Ka, but abanded it due to reliability

Correct, no valves on most designs. No valve train inertia, no valves with inertia, no springs to worry about not being able to put the valve back in place quick enough.

 

[Zenmervolt]

It also has to do with mean piston velocity. Longer stroke means lower revs because the picton travels farther for each revolution.

Let's say that one engine has a 4 inch stroke and another has a 2 inch stroke. At 1,000 RPM, the first engine's pistons are travelling 8,000 inches per minute, while the second engine's pistons are travelling 4,000 inches per minute. The higher the average piston velocity, the more stress it takes to control the reciprocating motion. F1 engines have large bores and very short strokes, believe it or not, the average piston velocity is lower (very slightly) for an F1 car at redline than it is for a NASCAR engine at redline because of the NASCAR engine's much longer stroke.

ZV

 

[Zenmervolt]

Originally posted by: gsellis

Originally posted by: Monkey muppet
I'm not very good at remembering stats like those posts above me - but I'm suprised that no-one has mentioned why a 2-stroke engine can rev much higher

I think it's to do with the valve return rate. I belive Ford designed one to fit into the Ka, but abanded it due to reliability

Correct, no valves on most designs. No valve train inertia, no valves with inertia, no springs to worry about not being able to put the valve back in place quick enough.

Meh, can get the same net effect on a desmodromic 4-cycle engine. No valve springs. The problem with 2-cycles is that they have terrible emissions and there is no engine braking (because if the throttle is closed, there is not enough oil going through the engine to lubricate it at higher than idle RPM, so two cycle cars, like old SAABs, have a one-way clutch that will not allow the transmission to spin the engine).

ZV