XJet

I've got a range of Cox .049 engines here -- some have the open exhaust ports and some have the two slits. My question is: is there anything to be gained (in terms of power) by converting the cylinders with the slits into open-port units?

Will the increase in exhaust port area promote better breathing or have the transfer ports in these cylinders been optimized to work best with the scavenging patterns created by the twin-slit design?

IT strikes me (especially given how exhaust throttling works) that these slit-port engines with their very limited exhaust port area must be less efficient than the open-port equivalents (the number of transfer ports, etc notwithstanding).

Tim Wiltse-RCU

X,

You would not see any real gain by removing the slit on those cylinders to make it worth the work. The real gain in power would be to add a cylinder with Subport Induction. They seen to breathe ok.

Later,
Tim

BMatthews

While I suspect that you're right about a bit of extra power the trick would be machining the bridges away without distorting the cylinder. Cox cylinders are quite soft so extra care would be required.

Jim Thomerson

There are Cox 049 engines with twin slit exhausts where the bottom slit is actually for subpiston induction. It is never uncovered at the bottom of the power stroke, but is uncovered at the top. I've seen a couple of these, also others where both slits acted as exhaust slits without subpiston induction. One dimension that varies on Cox engines is the height of the crankcase. Perhaps this is why some engines need extra gaskets, or even gaskets under the cylinder, and others don't. Given the precision of their operation, I do not understand why this dimension is so variable. I was somewhat surprised to discover it. I have talked with at least one Cox expert who agreed with my observations.

Jim

Tim Wiltse-RCU

Jim,


The cylinder you talk about is the cylinder from the GOOD Killer Bee. The bottom slit should also of been alittle wider that the top as well. The newer KB's have plain product engine twin slit cylinders, they have the same bupass ports but no SPI. That is the only twin slit cylinder that has SPI.


Later,
Tim

optech

My Feedback: (9)

Just out of curiosity, could one machine away some of the piston skirt to get a little SPI?

Thanks,
Mike

Tim Wiltse-RCU

Yup, you sure can!!!

Later,
Tim

Tim Wiltse-RCU

So just of fun over the weekend I cut down a piston on my lathe to offer SPI on a twin slit new style bypass cylinder( sort of poor mans Killer Bee cylinder). Mounted it on the engine on my LS150 and I will have to say it was an improvement!!! My tach is on the wack so I don't have any rpm numbers but I could hear it really unload in the air. It sounded so cool....like a Jap's Zero coming in on a bombing run!!!

Later,
Tim

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