AdrianM

I have a Magnum XLS .91-A 2 Stroke. When I look in the exhaust port it looks like the exhaust opening timing is very conservative. I am getting a degree wheel so I can measure it. How high can i go on a muffler equipped engine to get an improvement? I know that really high ports are for tuned pipe engines and I don't what to go that far. Any suggestions?

How about widening the port slightly? It appears the the sleeve was machined with the ports perpendicular to the center line of the cylinder. On my R/C Car engines all ports are cut at an angle to allow smooth flow into and out of the cylinder.

William Robison

My Feedback: (3)

Adrian:

You can widen the port without hurting anything, but I wouldn't try raising it. Modern 2s engines are pretty well balanced on the intake, bypass, and exhaust timing. Even slight changes can knock the power down.

If you want to experiment have at it, but you should have a replacement piston and liner set handy to correct any mistakes.

Bill.

der_steuermann

My Feedback: (2)

At least the boost port must be cut very steeply. I recommend exhaust timing of 155 degrees...

Sport_Pilot

I agree with Bill. If you increase the exhaust height without changing the intake ports you could hurt low speed torque, since the intake ports are not made for high speed power you may not gain much there. You need to check the timing all of the ports and see what you have. Compare this to other engines and take your pick instead of just grinding out the exhaust port without knowing how it works with the rest of the engine.

der_steuermann

My Feedback: (2)

I thought we're talking top end performance here

OK, let's go more into detail.

Improved intake timing is very important here.

For your Magnum XLS .91 engine the following timing configuration will work fine in combination with any performance oriented muffler system such as 'Ultrathrust' or 'Jett-Stream' providing lots of torque throughout the entire rpm-range:

exhaust: 155 degrees
boost: 117
transfer: 120
intake: 40 ABDC open, 58 ATDC close
Due to the still conservative exhaust timing there's no need to switch to a thinner head shim. And you can always change to a full wave tuned pipe system later resulting in even better top end

der_steuermann

My Feedback: (2)

BTW, I can’t imagine the upper and lower border of your boost window to be right angled – in stock style. That would be quite surprising...

rmh

"muffler equipped" is a very broad field
These "mufflers" can reduce output -relative to open stack performance -a considerable amount--or-- raise performance.
FWIW -- Power is produced by increasing the entire flow pattern thru the engine - just nibbling on one part can wreck the entire setup -
the easiest power addition ?
just try various props -IN THE AIR
trying to find most output in static tests can be misleading -unless you have a lot of background and records of past performance setups as a guide.