Grizzly

Hi all,



After spending the last few nights reading up on the size and shape of exhaust port i should need for an engine i'm building using one of Judge ITO's extended port Templates.



I have come to the Conclusion if i open the port to the same size as the outer edge of the 2mm angle then smooth it into the Sleeve (then recut the 2mm angle) this should be enough?



does this sound about right?



Cheers

Chris

Lynn E. Hanover

Well, If that template is a big late closing street port, then you are looking to extend the HP up the rev range so as to have good power up to maybe 9,000 RPM and a fair idle and off idle performance no too far from stock. Even the stock ports would be close enough for that. However why have a die grinder if you don't use it?



Your scheme to remove te stock radius and then reinstall it is as good as any approach. I would make the lower radius more generous than stock and polish that line. Just a stock look to the sides and leave the upper (closing line) a bit sharp, with nearly no radius. I would chamfer that line at very close to the same angle as the chrome. So as to pick up the apex seal very gently. The magority of the flow goes out across the opening line. The rest of that big hole will do things that help intake flow start, and add to overlap

timing so as to get flow going from the intake into the exhaust early. So there is your high end power improvement.



Since, that as you rev the engine, the open time for intake flow is getting shorter and shorter, you need this trick to get all of the intake flow you can. A free flowing exhaust is a boon here. With a poor exhaust system and too much back pressure, none of this works. Note that 2 cycle model airplane engines use exhaust back pressure as a throttle. And it works great. Same on a rotary.





Jump in. It sounds like you have the ideas right.



Lynn E. Hanover

Grizzly

Thanks for that.



I just have two more questions, I noticed the 2mm Chamfer goes all the way around the stock port, an i keep reading thats important to replace the Chamfer on the closing edge? does this mean you don't recut the Side and opening ones?



Also Does the Stainless Sleeve Expand when the engine is running? This is basicly becouse i have read there must be to slightly smaller port to the sleeve (like 1mm smaller all the way round) to stop the flow of gasses catching the edge of the sleeve or going round it?



Thanks.

Chris