How wide can an exhaust port be widened?

[Fastjeff57]

I'm working on a Merc 850 (four) block that has ridiculously mild porting. (Only 4 small, round holes vs. the three large ones used on all the other 99 cube series Mercs--twins, triples and sixes.) Whacking out the area between the pair of holes in the center (of four) would produce an opening 1.365 " wide. Is that a bit too wide for sensible ring life (non-racing application)? I notice other motors on this site (like the fabulous 99 looper project) that seem to have far wider openings than this.

Thanks!

Jeff

[Gene East]

Jeff,

It appears no one wants to take the risk of telling you to go ahead and cut out that web for fear of creating a problem with ring breakage. I don't know how wide is too wide either.
Since this is a "non-racing" application you might want to consider simply "squaring out" each hole and going a little wider with the 2 outer holes without changing the height of the port. This will allow the engine to breath better without risking destruction by hanging a ring.

[Fastjeff57]

Thanks, Gene. That's what I'll do.

Jeff

[zul8tr]

Don't make sharp corners in the square up, small radius is easier on the rings .

[Dave S.]

Best off get a newer 75 hp 4 cly...... ports done .... no rot issues.

[Fastjeff57]

Is the porting different in the later motors? I'm not so sure.

The one I'm working on (1974) has 4 small exhaust ports (vs. the 3 large ones used on the other 16.7 cube/ cylinder direct charge Mercs). And super mild--the exhaust has to come up .181 inches just to be similar to my ordinary triple! What were they thinking...

Jeff