Try a few of each and see?  Xenalook is probably smart enough to know that you don't make money selling the customer what they need, or even selling them what they want -- you make money by selling the customer what they think they want, and what they'll pay for.  If that's TD cylinders with uselessly big* exhaust ports, then that's what you sell.

* And no, I don't know if that makes a difference or not.

  I believe the slit type cylinders were designed for fire protection. Earlier attempts used the welded wire screen on the cylinder. I suppose that the slit restricts the flame from jumping out on start up.  The slit type cylinders have a slightly different porting arrangement than the standard Black Widow cylinder. If you look up inside you will see what appears to be 2 ports just like the Black Widow,  but each port is divided . It looks like you have 4 channels. This is what I believe is what is known as the transfer port which was typical of TD cylinders. The older TD's had the tapered cylinders as well. Some of my older TD pistons have a oil hole also located on the bottom of the rod. I feel the Sure Start cylinders work very well, but they're all not up to par. I noticed that when I purchased some of them for $5.00 when Estes was unloading them. 1 out of 4 though were doing pretty well. They certainly have tremendous ball socket play for new piston rod assemblies. I generally get around 19k + when using the Sure Starts but my Black Widow's do better than that. Ken

hi Kenneth,

I never really realized how much the "play" in the ball socket joint of the rod/piston meant on the Cox engines until I got a resetting tool.  A tightened ball socket joint does give more rpm!

Big Bear

More important: You won't beat a hole through the top of the piston.  That's what it took for me to buy a resetting tool.