Matching outside exhaust port window edge to case?

Tim van Schyndel · Jun 22, 2016

I have noticed that the outside edges of the exhaust port windows are close, but don't match the case. Other than the port top edge, is there any benefit in matching the side and bottom outside edges to the case for the returning pipe pulse or would this impact on the earlier exiting exhaust gases?

Cheers

Tim

Terry Keeley · Jun 22, 2016

YUP!

Tim van Schyndel · Jun 22, 2016

Terry Keeley said:
YUP!

Thanks Terry, but YUP to which????

Will it negatively impact on the exiting exhaust gases or will it positively impact on the returning pulse later in the exhaust cycle??

Cheers

Terry Keeley · Jun 22, 2016

Sorry, didn't quite get what you meant. I wouldn't touch the sleeve but if the case is blocking some part of the port as it's cut in the sleeve i would match it.

Tim van Schyndel · Jun 23, 2016

Thanks Terry!

Jim Allen · Jun 25, 2016

Tim,

The photos show the additional piece added to the exhaust nozzle of the Nelson engine between the cylinder's window & the beginning of the tuned pipe's header. The difference with & without can be easily seen with a simple bench test. High end RPM's are increased approximately 500 on this .45 cu in engine.

Jim Allen

Tim van Schyndel · Jun 27, 2016

Jim Allen said:
Tim,

The photos show the additional piece added to the exhaust nozzle of the Nelson engine between the cylinder's window & the beginning of the tuned pipe's header. The difference with & without can be easily seen with a simple bench test. High end RPM's are increased approximately 500 on this .45 cu in engine.

Jim Allen

Thanks Jim

In your opinion, would matching the outside edges of the exhaust port (of the cylinder liner window) to the case work like the Nelson engine you have shown, OR, would the "port/case matching" be to close to the cylinder to have a positive effect considering the variances of the CMB engines appear to be smaller than the Nelson engine shown on your photos?

God I hope that made sense but I think I know the answer based on your email and photos!!

It appears that the CMB and NOVA style exhaust port to manifold styles are far from optimum as the lack of bolt on manifold hinders the matching opportunity to achieve the example shown with the Nelson.

I have also sent you a PM regarding the De Laval Nozzles which I would appreciate your experience.

Regards

Tim

Jim Allen · Jun 28, 2016

Tim,

I'm not familiar with what the CMB exhaust nozzle looks like. In general terms the nozzle should be aimed in a downward direction, approximately 15* to 20* & decrease in area when compared to the cylinder's exhaust port window area. There should be enough length for a gradual change from the approximate rectangle shape of the cylinder's exhaust window to the round shape of the end of the exhaust nozzle. The beginning of the tuned pipes header should also be tapered before the first diffuser sections.

I sent you a PM about the De Laval Nozzle.

JA

Matching outside exhaust port window edge to case?

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