displacement?

[Texan32]

ok, now i have COMPLETELY confused myself. i have been reading past threads and trying to do my own figuring...and now i'm stuck. Is a 416 actually a 416? The reason i ask this...displacement is measured by...bore x bore x stroke x .0007854...with a flat piston. Well, the higher compression pistons have a crown to them, thats how they bump the comp. up. Well, what does that crown measure out to? Wouldn't that make it NOT a 416, but something less?

Also, someone tell me what a 463 stroker consists of....piston/bore...stroke...i don't see why strokers are so expensive...is it because you don't install it yourself?

[wilkin250r]

Displacement has nothing to do with compression. Putting in a high compression piston will not change the displacement.

Displacement is volume. So you you need area times stroke length. The area of a circle is radius squared times pi. Radius is 1/2 diameter, given by the bore of the cylinder. So the equation becomes:

(1/2 bore) x (1/2 bore) x pi x stroke.

Pi is 3.14159265358973238...


Strokers are expensive because it requires several hours of machine work to move the rod on the crank, and then you need to shorten the rod ( or replace it with a heavy-duty rod) and usually involves truing the crank. Many people can split the cases and pull the crank by themselves, but many times stroker "kits" include the labor for the shop to split the cases and re-assemble it together with the new stroker crank.

[YZROOSTINYA]

strokers have LONGER rods , not shorter

[wilkin250r]

Originally posted by YZROOSTINYA
strokers have LONGER rods , not shorter

So how do you keep the compression from shooting through the roof? Spacer plate on the cylinder? Or do they come with different pistons?

[Texan32]

but the crown on the piston IS going to take up some of the cylinder volume

[wilkin250r]

Originally posted by Texan32
but the crown on the piston IS going to take up some of the cylinder volume

True, it will take up some small portion of the total cylinder volume, but displacement isn't equal to total cylinder volume. Displacement is how much air space is displaced by the movement of the piston, and it is constant for a given bore and stroke, the shape of the piston doesn't matter. The shape of the piston will affect compression, but not displacement, because it moves the same distance.

It's a difficult concept to explain in a few words. Imagine two identical cylinders, each with pistons in them. Let's say that the total space left, after the piston, is 457.6cc. The other piston is a little larger because it has a dome on top of 8.32cc. So the total space left in cylinder 2 is 457.6-8.32=449.28cc.

Now move each piston to displace 416cc of airspace. Now what is left in cylinder 1 is 457.6-416=41.6

Piston 2 also moves to displace 416cc of airspace. The result is 449.28-416=33.28cc.

by taking the ratio of the displacement divided by the resulting airspace after displacement, we can see that 416/41.6=10:1 compression

In cylinder 2, 416/33.28=12.5:1 compression. We expect this one to have a higher compression, because it is the one with the dome on top of it.

Just because you start with a smaller volume, it still displaces the same amount because it moves the same distance.