Exhaust cleanup early Tecumseh's

markus

Well-Known Member
#1
I have been doing this for a couple of years now, Don't think I ever showed this before though. On mainly 1970 and older Tecumseh rear exit exhaust engines they used a 45 degree "street elbow" plumbing fitting and a screw in muffler most of the time. These elbows are usually pretty restrictive because they are just sloppy cast and very thick at the inlet/male threaded side.

A simple thing I have been doing before installation is taking a multi stepped drill bit and drilling it out till I start to hit the first cut of threads. This takes that big flat restriction out of the flow and the bit marks on their own will step it into 45 on its own pretty good too.

This current engine I am working on is a 3.5hp that I have done a few extra things to internally. so to go along with some of the other things I have done to try and squeeze whatever I can out of it, I also took a little extra time to totally smooth out the cuts the drill made in the fitting and shaped the edge so its a pretty fluid transition from block to the fitting when installed in the port for the best flow. I carved a little more inside as well and did get it opened up a tiny bit too cant get much out of there though.

On the stock 7 hole muff they have a tendency to be flared inward as well from when they get threaded. So I also gave it the same drill treatment and curved it outward so the step into the muff is smooth as well.
Does this really do anything.....cant say for sure, I've only ever done it on new builds so I cant compare in an apples to apples, but its a quick and easy thing to do and should help with the flow.

Left upper and lower are stock uncut, center bottom is opend with the drill bit only, right upper and lower are drilled and then smoothed and shaped:
 
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