Ollies930

After looking at CPI cylinders and T-Rex cylinders, it occurred to me that the rear boost ports on stock Banshee cylinders, as well as in Athena, Vito's, RDZ, etc., have relatively narrow boost ports. But in a lot of the ported stuff that I have seen pictures of, nobody seemed to widen these even though there is a lot of room available. On CPI and T-Rex cylinders there are two side by side, which appear a lot wider than the stockish ones when added together. Is there a good reason why not to do this? It seems like an obvious improvement to me to gain intake flow and window open area and there does not seem to be any water jackets or other physical hindrances in the way. Any thoughts on this based on experience?

With pistons sticking out 2.5mm the intake is 131 and the exhaust port is 198. The intakes are where they were from the factory, just a bit of radiusing of the edges and I raised the exhaust main port 1mm to open it before the boost ports. If I could let the piston come out another .015" or .38mm, then the exhaust would end up at 196.6 and the intake would be at 129.2. It is quite peaky right now and has very little power down low, this should help a bit.

Does anybody know what the maximum safe distance is, that a Wiseco 573M06800 (68mm bore for 5mm longer rod) can stick out of the bore, before the rings start to snag on the top edge of the cylinder? If I remember correctly, the ring lands are 3.5mm down from the crown. Not one hundred percent sure though. Any help is appreciated, thanks.

Awesome, thank you!

Has anyone ever tried something different than the standard plugs for gasoline? For instance a NGK BPR8EIx Iridium plug with extended tip? From what I have read on other two stroke race motors, the extended tip gave a few extra horsepower, presumably due to a quicker burn from a more centralized location and the Iridium part should help our old ignition systems produce a better spark. Or so goes the theory. Question is, has anybody actually tried this and been able to quantify any gains/losses on a dyno?

Does anybody have a conversion chart for the Mikuni 042 hex jets, comparing jet number with inside diameter? From what I understand, these jets are not numbered according to inside diameter, but flow rate instead. My jets currently are drilled to .067" ID, would love to know what the corresponding jet number would be.

The kit I bought is actually for a stock stroke, as far as I know there is no other Athena kit available. For the port timing to be reasonable, the pistons have to stick out 2.5mm above bore. That way I ended up with 130.5-131 on the intake transfers.

Thanks trickedcarbine, that is exactly what I was trying to explain. As for welding, with the amount of filler needed to make a decent shaped port, I am afraid it would completely distort the bore. Am I incorrect?

Has anyone tried different combustion chamber shapes without altering compression to see how the power curve was affected? Most of the interchangeable domes I see advertised are very similar to the original factory shape. From what I have read about the most recent two stroke 125 and 250cc GP engines (early 2000's), they favored a shallow, flat roof (or torroidal roof if you ran a Honda), with the sides ending about parallel with the stroke and squish bands about 50% of bore with tightest possible squish following the piston dome and running sharp edges at the squish/combustion chamber interface. Has anyone ever seen anything or tried something like that for a Banshee? Might be worth a bit of power?

Before this turns into an Athena bashing thread, I do understand that CPI cylinders are miles ahead of the Athena cylinders. However, I am trying to build a competitive vintage race bike (RZ350) and monoblock cylinders are not allowed. Therefore I am stuck with stock sleeved or Athena cylinders. I chose to go with the Athena 68mm kit due to the triple exhaust ports and the Nikasil plating. The rules allow up to 450cc so I am using a 7mm stroker crank to get me to 443cc. When I ported the cylinders, I found that where the ports already were, I pretty much just opened the ports up downward to where the piston sits at BTC and with the piston popping out 2.5mm at TDC the intake ended up almost 131 degrees and with opening the center exhaust upward 1mm just so it did not expose the secondary exhaust ports at the same time I ended up with 198 degrees. With these numbers in mind and not wanting to pop the pistons out of the bores any more than that, there was no shaping of the radii on the top of the intake ports. From the factory they appear to be nearly 90 degree turn into the cylinders, but there is a very sharp turn in on the large radius. Would there be any benefit to put epoxy on the long side radius to help the air turn into the cylinder, or is there no measurable benefit to be had?

Unfortunately I do not have any pictures of the domes, but it sounds like I will have to send my domes to Noss so he can copy the outside dimensions in order for me to get the combustion chamber shape the way I would like it.

Does anybody know if the Athena domes can be interchanged with the Noss or Coolhead ones? Want to keep the Athena head for stock appearance and cost reasons. I already talked to the gent at Noss, but he did not know if his inserts would drop into an Athena head.