what do you prefer?

I like open exhausts better than slit exhausts because I find them are easier to prime and start. Not a vast difference however.

Phil

Jason_WI wrote:Some say the performance is the same with either but I like the open exhaust. I think there is some exhaust restriction with the slit exhaust with the smaller area available for the gas to escape.

Ditto on the restriction of the slit opening.

I personally like the old open port SPI cylinders where you didn't have to use a piston with a short skirt to open the sub induction gap. None of the slit exhausts allow SPI with a regular piston, except the Tee Dee cylinders Bernie(Cox International) has modified by removing the slit and grinding the exhaust ports lower.

I've read that Cox claimed the slit exhaust cylinder with a boost flute next to each bypass port but no SPI develops as much power as an older non fluted dual port SPI cylinder. If this is true, then a Surestart should have as much power as a Super Bee. And maybe/maybe not a #1 Black Widow(because it's dual bypass ports were ground even deeper than all the others). But all this is just Bla bla bla... they all run pretty good. My slit SPI set with a Killer Bee backplate will kick any of my Black Widows' asses. It's the only engine that ever lifted my PT-19 off the ground without rolling.

i like the open port cylinders because i think they look cool than the slit port cylinders and they are also easier to prime

Open port! (cranky old man voice) "cause that's the way we had 'em when we were kids and we liked it!"

The slit ports do loose some rpm at very high levels, but not really a concern unless your racing or something.

.

open port! hear the hiss and see the orange glow of the plug

When Cox went to slit exhausts (for liability reasons) they increased the porting to compensate for the exhaust restriction; hence there is little difference in performance. Actually, a slit exhaust cylinder will outperform many of the older Black Widow, Golden Bee, etc cylinders.

Where performance really increases is SPI, whether open or split exhaust ports. On reed valve engines only, that is.

Personally, I prefer the open port for 3 reasons:

Easier to prime
Can induce SPI without tampering with the piston
Grew up with the look of the open port

Every one of my slit port engines annoys me for the asthetics of what I think a proper Cox engine should look like


I don't care if I loose 1000 rpm, I would like to have every slit cylinder cut open by Bernie. Some day I may just ask him how much

I myself really like the looks of the slit cylinder.
They look so hi-tech and powerful.
BWAAAAAAAAAAAAAA!
Gimme an open port, thin wall, with unmilled top fin any day.
A thing of beauty.
Bob

dckrsn wrote:I myself really like the looks of the slit cylinder.
They look so hi-tech and powerful.
BWAAAAAAAAAAAAAA!

Bob, we're all going to surround your house and flush you out and hose you down with cold dirty water!

dckrsn wrote:Gimme an open port, thin wall, with unmilled top fin any day.
A thing of beauty.
Bob

Oh, okay, you saved yourself... but watch your step.

K
Bob