Opening Angles of Ports?

[David Armstrong]

I'm not an engine builder, so please excuse the dumb questions.

I was looking at the technical information on the engines listed in the TAG USA web site. There is a spec there called "Opening Angles". On the PRD Fireball the spec sheet says the Exhaust is 174 degrees. The Leopard and Easykart 125 show 171 degrees. The Vortex Rok shows 184 degrees. And the Sonik VX shows 179 degrees.

My question is how do they get this measurement? And what does it mean? The higher the degrees, the farther up the cylinder the exhaust ports are? Does this produce more power? I did notice the higher the degrees an engine has, the more weight it has to have in the class.

Thanks for the info.
Dave Armstrong
Jacksonville, FL

[Pete Muller]

David,

A better term would be "exhaust duration" -- quite simply; how many degrees of crank rotation the exhaust port is open.

VERY generally speaking; the higher the exhaust port, the more peak power the engine might produce. There are many other items that determine power, but exhaust port height is a key ingredient.

Pete

[David Armstrong]

Pete,

Thanks for the explanation. One more question if you don't mind.

On the Leopard Spec sheet, it shows the exhaust port at 171 degrees max. A footnote says "Angular Reading by Inserting a 0.2 mm Gauge".

Does this mean they stick a 0.2mm feeler gauge in the top of the exhaust port, rotate the crank until the top of the piston touches the gauge, set the degree wheel to 0, rotate the crank around until the piston comes back up and touches the 0.2mm gauge and read the degree wheel? The reading should be in the neighborhood of 170 degrees.

Is that how they would measure to come up with this spec?

Again, Thanks for your help.

Dave Armstrong
Jacksonville, FL

[Chuck McCue]

Hey Dave,
Are you going to tech port heights at Jax?
_________________
Chuck McCue

[Pete Muller]

David,

I don't have that spec sheet in front of me, but that sounds 100% correct to me.

Pete

[al nunley]