390 strokers: 431 vs 445

[olddog]

Well I spent an hour writing a masterpiece on the subject - from my perspective, and I forgot to save it in a paste buffer before clicking reply. When it forced me to log in a second time, it all PHUCKING DISAPPEARED! Why this site logs you out after a few minutes I don't know, but it is annoying.

If the rotating assembly can spin all day at 7500 rpm and not fail, then who cares what the stroke is? It works. It will not be the limiting factor, up to the 7500 rpm.

If the head and cam combination can be made to allow the displacement to fill the cylinders to get the peak Hp at the desired rpm, then the stroke was not wasted. In any bore size and given head, there is a point at which more stroke does not increase Hp because you just cannot get any more air into the engine no matter how much faster you turn it. That point is typically well past the length of the cylinder block, with good heads.

The rod angle or rod length to stroke length is a factor. The worse the rod angle the higher the side loads and worse it is for wear and longevity of the engine. Often times the rod ratio is better in a stroker kit than other factory engines that have a great longevity track record. Of the stroker combinations I have looked at in detail, I have yet to find a rod ratio that concerned me.

Valve train control is the most likely problem to limit an engine. Bigger valves, long push rods, and heavy rockers are the enemy of a high rpm valve train. Increasing the stroke in a given engine makes no change to any of these components. They will limit the rpm more than likely, and stroke had nothing to do with it.

So this sums up how high the engine can rev. Strokers can rev very high.

As for how quickly can an engine accelerate from 1000 rpm to 6000 rpm it is simple. Linear motion it is:
Acceleration = Force / Mass
For angular acceleration:
Acceleration = Torque / Moment of Inertia

If increasing the stroke increases the Torque, that was a positive change in the right direction.

Moment of inertia takes into account the mass and the distance from the pivot point. Remember the stroke increase does not move the piston at top dead center. It moves in further down at BDC. Often strokers have lighter pistons and rods to keep the rod bolts from stretching at high rpms. The crankshaft may get heavier to balance the rod journals moving out, but it may get lighter. Sometimes we go to smaller diameter rod journals and hollow out the journal. So in some cases the moment of inertia could go down. Also a positive move in the right direction, but maybe not.

Then we have to look at the fly wheel. When you look at a monster cast iron or steel flywheel, it has to be a huge part of the Moment of Inertia. You change to an aluminum fly wheel, and I am quite sure the total Moment of Inertia has to be less than the factory stroke and flywheel. By the way the clutch and pressure plate matter too.

Thus a stroker can easily be made to rev as quick or quicker than the shorter stroke. When we are talking about an 1/8" it just doesn't matter.

[patrickt]

Originally Posted by olddog

...

When we are talking about an 1/8" it just doesn't matter.

Well, in that case I'll just chalk you up as agreeing with me.

[olddog]

Originally Posted by patrickt

Well, in that case I'll just chalk you up as agreeing with me.

Yes Patrick. Giving up 15 Hp because it makes you feel like you could rev the engine higher, even though in reality it cannot, does not matter one iota for a non race car. If it gives you a false warm fuzzy, it was worth every Hp given up, because it is a pleasure car, and it pleased you.

Let's face it, you could easily make up the 15 hp by getting cooler air to the engine or reducing exhaust back pressure. Since you cannot hook the power you have to the ground it probably still doesn't matter. Most of what we do does not matter, but there is no fun in thinking that way.

[Dimis]

Go the 445.
There's no reason not to.

[patrickt]

Originally Posted by olddog

Since you cannot hook the power you have to the ground it probably still doesn't matter. Most of what we do does not matter, but there is no fun in thinking that way.

It's not even that close any more.... I don't think I even opened the secondaries more than maybe twice last year.

[olddog]

Originally Posted by patrickt

It's not even that close any more.... I don't think I even opened the secondaries more than maybe twice last year.

Well, I've been told that owning a Cobra is just a replacement for a less than fulfilling sex life. It may be true because people around here talk like hearing an FE at full song, winding to 7500 rpm, is 10 times more potent than Viagra. That said I must diagnose your problem as a lack of or low libido.

Don't feel bad. Me too.

[cycleguy55]

Originally Posted by olddog

Well I spent an hour writing a masterpiece on the subject - from my perspective, and I forgot to save it in a paste buffer before clicking reply. When it forced me to log in a second time, it all PHUCKING DISAPPEARED! Why this site logs you out after a few minutes I don't know, but it is annoying.

I'm not having the problem you describe - I can stay logged in for hours or days.

Hint: Check the 'Remember Me?' box before you click the 'Log in' button.