Anyone ever try raising the cylinder 1mm off of the crankcase and deck the top of the cylinder 1mm. I was told do this is I want more power. This would be raising the transfer ports up. Anyone ever try this. 400 2 stroke of course.

 

smokin,

That sounds like a great way to DECREASE performance. Without the longer piston stroke, all you're doing is lowering the compression ratio.

 

Dontknowcrap,

Again, your name says it all. If you can't make a constructive comment, please stay out of these forums!

 

Raising the cylinder on a 2-stoke moves the ports upward. This lets the piston drop below the ports, and also keeps the piston from going all the way past the port on the upward stroke. Neither one of these things are good. They will decrease power because the port is unshrouded too late in comparision to the piston position. The location of the piston and the size and shape of the port is what controls "port timing". The only thing raising a cylinder can help is with a stroker crank because the stroke is longer and the piston moves farther up, and with long rod since the pin height is higher. The best way to alter port timing is with a good port job. This kind of stuff is hard for me to explain, so I hope I didn't confuse anyone.

 

Thanks for your responses. I'm going to find the guy that told me to do that and kick him in the teeth.

 

I've done the thicker base gasket/shaved head trick on several sled engines and it does increase top-end power at the expense of some low end. Never tried it on a single cylinder engine but it should do the same thing.

 

I would recommend a porting job. If you raise the cylinder, you lower compression. So then you have to shave the head, just to get back where you started. Also, you are raising both the intake and exhaust ports equally, and a good port job isn't done quite that way. They increase both the size and timing of the ports. I think that is a far better way to go.

 

That's a big AMEN Farmr!!! Doin' it right saves burps down the road.

 

[img]i/expressions/face-icon-small-smile.gif[/img]Hey guys, there could be huge power gains to be made on the 400 cylinder by raising it. I typically raise the exhaust port about 1mm for trail porting and more (not saying how much)when race porting these things. The transfer ports are far from being completely uncovered when the piston reaches BDC. These cylinder are extremely mild from the factory and need quite a bit of work on them. I am now running a .140 over cylinder on my sport. If I can get my hands on another good cylinder without having to buy a new one, I am going to make a screamer out of it. There should be no reason why I cant make 80-90hp out of one of these. There is plenty of meat still left on the intake after porting and enough on the top of the cylinder that you could do exactly what he's talking about.That's the nice thing about auto clutches.You can make power at 8000rpm's and set the clutch up for it. Better get the degree wheel out and make some good port mapping, though.This is going to take some time and work, but I suspect the power gained will be tremendous.Cheers everyone!

 

Not to discourage experimentation Bubba, but if you could see the "rooms of destruction" at Hot Seat and HPD. There's been lots of R&D, and LOTS of sacrificed parts. HPD's latest creation nets around 87 hp with a variable exhaust power valve. That's at 416cc by the way. Like I said, not meaning to discourage you, just maybe trying to save you some time and money.

Ken