short stroke big bore bore vs long stroke small bore?

[ZSNOW]

which is better for motocross, im thinking the short stroke big piston because you would have less side low on the piston and you would be able to spin more RPM. but what do all you motor gurus say?



this is for building a 250x vs a 300ex by the way.

I'm defo no engine guru but a short stroke engine spools up quicker than a long stroke but generally has less torque.


I would think a short stroke would be better for MX.

[400exrider707]

It's stuff like this that I wish chad was still here to explain (chad502ex). There is an ideal set up for a motor... Try searching for these topics under his username and see if you can come up with anything. You can also contact him on the ORG, and 450RHQ. I do believe he posted that info here at one time though... try searching see what you get.

[sc400ex_rider]

big bore short stroke are more peaky mostly upper rpm. a long stroke has more torque because of the leverage on the crank, its just like a long crowbar or leaver or putting a cheater pipe on a rachet you get more leverage.

[NacsMXer]

Depends on the type of track you run mostly. Wide open tracks, short stroke big bore. Tight tracks with a lot of turns, long stroke small bore.

I've run both. I had a stock stroke 440 motor combo and now run a +7mm stroker with a 416 bore. I can tell you the stroker hands down beats the 440 big bore in many ways. The torque just pulls you out of turns and accelerates like a 450 quad. I like it because it still has the throttle response and revs very quickly due to the smaller piston. Like mentioned, it's tough to beat the mechanical leverage offered by a stroker.

Basically, mostly top end running, go for a top end cam and a big bore. If you want stump-pulling low to mid power, go for the stroker.

[ccdhowell]

Most of the new 450 engines have a really large bore to stroke relationship; this is the "new" way to make power and derives from auto racing engines. With a larger bore you can have larger valves to intake and exhaust a higher capacity and that is where the ability to rev quickly comes from in the new 450s, it's the valves.

The older way of making power was to use a smaller bore with a longer stroke; KTM engines today on their 450 and 525 are still this way. They have a smaller bore to stroke ratio. There is allot of leverage in a crank with a longer stroke. The engines will feel different too. A big bore/ short stroke engine that breathes well through big valves will behave similarly to old 2stroke engines, it will rev quickly and have little torque. Just the opposite for a small bore/longer stroke engine, it will feel like you can lug engine all day and it will pull with power from very low rpms.