JUSTINTHECOASTIE

I've lowered vtec to 5.4k and still rev to 8.6-8.8k. At the time, it's mainly street driven and when I do go to the track I lower it to 8.5-8.6k

Slowcrash_101

Have you dyno'ed your car? I can essentially guarantee you're not making much power there. Obviously it's your car and you have every right to drive it as you wish, just saying revving an F22 that high isn't productive.

[media]https://www.youtube.com/watch?v=2JNnzqwTUMI[/media] probably been seen to death but it highlights why f22 has a lower rev limit. The technical jibber jabber starts at 2:35'ish

yamahaSHO

JUSTINTHECOASTIE

If this response was directed to me, yes I have dyno'd my car, check my thread, and many times after that. Reason why I like a higher rev limit is so that I'm higher in my powerband for the next 'up shift'. If you look at those dynos you are referring to, you should note that although power may not increase, power also doesn't dramatically drop of either.

Slowcrash_101

That's what the pistons do right? In conjunction with the valves, the pistons suck air, compress it, expand it(when mixed with a fuel and ignited), and pump it out. So for a given piston speed and travel, said piston will move a certain quantity of air provided the cylinder head ports and valves can provide said quantity. Is my understanding off base? If you exceed the capacity of the head and valves to supply air to the cylinders the car won't make more power, is this not correct?

So given the stroke is longer on the f22 than on an f20, the piston moves faster on the former, than the latter at a given rpm hence power drops off at a lower rpm on the f22 than on the f20 because the head and valves cannot supply enough air past a certain piston speed. Conversely more torque is made at lower rpms on an F22 vs F20 because of higher piston speed at lower rpms displacing more air in the F22 vs F20 because the flow potential of the head has not been exceeded.

If I'm wrong please correct me.

yamahaSHO

That's what the pistons do right? In conjunction with the valves, the pistons suck air, compress it, expand it(when mixed with a fuel and ignited), and pump it out. So for a given piston speed and travel, said piston will move a certain quantity of air provided the cylinder head ports and valves can provide said quantity. Is my understanding off base? If you exceed the capacity of the head and valves to supply air to the cylinders the car won't make more power, is this not correct?

So given the stroke is longer on the f22 than on an f20, the piston moves faster on the former, than the latter at a given rpm hence power drops off at a lower rpm on the f22 than on the f20 because the head and valves cannot supply enough air past a certain piston speed. Conversely more torque is made at lower rpms on an F22 vs F20 because of higher piston speed at lower rpms displacing more air in the F22 vs F20 because the flow potential of the head has not been exceeded.

If I'm wrong please correct me.
[/quote]

The stroke adds to the displacement.

The heads and valves are a completely different discussion.

Slowcrash_101

That's what the pistons do right? In conjunction with the valves, the pistons suck air, compress it, expand it(when mixed with a fuel and ignited), and pump it out. So for a given piston speed and travel, said piston will move a certain quantity of air provided the cylinder head ports and valves can provide said quantity. Is my understanding off base? If you exceed the capacity of the head and valves to supply air to the cylinders the car won't make more power, is this not correct?

So given the stroke is longer on the f22 than on an f20, the piston moves faster on the former, than the latter at a given rpm hence power drops off at a lower rpm on the f22 than on the f20 because the head and valves cannot supply enough air past a certain piston speed. Conversely more torque is made at lower rpms on an F22 vs F20 because of higher piston speed at lower rpms displacing more air in the F22 vs F20 because the flow potential of the head has not been exceeded.

If I'm wrong please correct me.
[/quote]

The stroke adds to the displacement.

The heads and valves are a completely different discussion.
[/quote]

Longer stroke increases the volume of the cylinder this is true. It also increases piston speed for a given crank rpm, or is that wrong? As the length of a lever increases, it's motion ratio also increases. The combination of increased cylinder volume, and increased piston speed is what give you more pumping rates for a given rpm vs a shorter stroke. Or is this incorrect?

Slowcrash_101

I stand corrected, and it makes sense, torque multiplication in a lower gear can essentially give you equal or higher acceleration compared to a taller gear even if the taller gear has a higher power output.

yamahaSHO

That's what the pistons do right? In conjunction with the valves, the pistons suck air, compress it, expand it(when mixed with a fuel and ignited), and pump it out. So for a given piston speed and travel, said piston will move a certain quantity of air provided the cylinder head ports and valves can provide said quantity. Is my understanding off base? If you exceed the capacity of the head and valves to supply air to the cylinders the car won't make more power, is this not correct?

So given the stroke is longer on the f22 than on an f20, the piston moves faster on the former, than the latter at a given rpm hence power drops off at a lower rpm on the f22 than on the f20 because the head and valves cannot supply enough air past a certain piston speed. Conversely more torque is made at lower rpms on an F22 vs F20 because of higher piston speed at lower rpms displacing more air in the F22 vs F20 because the flow potential of the head has not been exceeded.

If I'm wrong please correct me.
[/quote]

The stroke adds to the displacement.

The heads and valves are a completely different discussion.
[/quote]

Longer stroke increases the volume of the cylinder this is true. It also increases piston speed for a given crank rpm, or is that wrong? As the length of a lever increases, it's motion ratio also increases. The combination of increased cylinder volume, and increased piston speed is what give you more pumping rates for a given rpm vs a shorter stroke. Or is this incorrect?
[/quote]

The longer stroke, by itself, is going to pump more air for a given revolution (and the intake tract will see this). Yes, you'll gain more speed for the same rotation as there is more distance to travel in that revolution, but the fact is you will still be filling more space. Whether or not intake path allows or makes use of it all is another subject.

For the most part, you're looking at piston speed from a safety standpoint... Wither it be more wear, overheating, overall vibration from running the motor higher, etc.