038 port widening

[dieguy]

How much can I widen the exhaust port on an 038 mag 52 MM piston?

 

[wi50]

put the jug and piston on, trace the exhaust port on the piston when it is at TDC. Now you will be able to see how much margin is between the port and the sides of the piston skirt. You'll want to leave some material to seal the gasses, depending on the mods being done. Do not cut to much and end up with a free port (air gap). Everyone's got different opinion on how much material to leave 1mm, 2mm etc. For a work saw though I'd leave a fairley decent margin.

 

[dieguy]

038 port

Thanks I will leave 2MM minimum

 

[trappermike]

Be careful widening the exhaust port on an 038 Magnum,it has the widest stock exhaust port I've seen on a production saw,approaching the maximum on a daily work saw.A little widening may be ok,but not much. Be sure to chamfer the upper and lower edges of the port well,as this is important with a wide exhaust port.

 

[Rusty-880]

There's a lot more to porting than widening them, I read the posts on here about porting and widened the ports in my 880. I wasn't impressed. I since found online a book written years ago on two stroke tuning. Two Stroke Tuners Handbook by Gordon Jennings. Find it, download it and study it.
Ports must be to a specific Time/Area ratio and takes a little working out. My saw bogged a lot easier after I widened the ports. Swapped a stock cyl on and checked the time/area ratios. After widening the ports Intake was timed for 5000rpm, Exhaust at 4700rpm and transfers were left as stock because thats what the info on here said to do (Stihl claims peak power at 8500rpm so the ports are a long way off). Only pulled the cylinder and measured the ports a couple of nights ago and havn't had time to work out new port sizes and shapes yet.

 

[husq2100]

Jennings is an excellent reference, but remember it is for bike engines which are different to saw engines due to their bore/stroke ratio

 

[Texas HotSaw]

In Jennings book you will also find a limitation to how wide a port can be before the ring starts catching the edge of the port.
It's been a few years, but I think it's around 65% of the bore.
Any wider, and bad things happen.

The book is on-line here: http://www.bridgestonemotorcycle.com/documents/2stroketunershandbook.pdf
(it takes a while to load)