Smoothing/porting Tecumseh - Snowblower Forum : Snow Blower Forums
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post #1 of 12 Old 03-08-2017, 02:12 PM Thread Starter
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Smoothing/porting Tecumseh

Anyone mess around with smoothing out the bowl area by the valves. I'm cleaning up and doing a valve job an a LH358SA. I can't see the harm in doing it while I have the valves out.

The casting has lots of rough edges that cause turbulence on both the intake and exhaust.

It has a fix jet carb, so if it made any improvements I might notice a lean hunt under load...next winter...

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post #2 of 12 Old 03-08-2017, 02:31 PM
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This I Remember.

A while back my jet mechanic next door neighbor was overhaulin a Harley engine for 1 of his scooter riding buddies. and that guy wanted him to do the same on that engine. and my jet mechanic neighbor said he would lose torque on the engine by doing that. there is a reason why that stuff is there it is there to mix the fuel and air up all nice and pretty. just like a fine martini that is shaken not stirred. so you get all of that oomp out of zee engine when you need it the most.

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MAHALO!!!!!!!!!
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post #3 of 12 Old 03-08-2017, 03:15 PM
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PS93

Great analogy !
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post #4 of 12 Old 03-08-2017, 06:15 PM Thread Starter
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I left the rough casting as is, if nothing else, it's one less thing I need to do in my already to short of a day.

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post #5 of 12 Old 03-08-2017, 06:23 PM
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Back in a previous life I built drag race engines...I used to port 289 Mustang engines , put huge 421 Pontiac valves in them.....screw in studs, high lift cams .....One thing I learned. Leave the porting rough....never polish. The gas/air stream needs to be really mixed well, and polishing hinders that. BTw....I still have the Quikway valve grinding machine..anyone want a five angle valve job! How the **** did I get from that to Tecumsehs??????
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post #6 of 12 Old 03-08-2017, 10:10 PM
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I remember in a far distant life, that a Norton motorcycle mechanic told me roughtly the same thing.

I asked him about smoothing out the rough parts and he said, in a thick scottish accent, "Ach, they are suppose to be rough as a badger's ***hole to mix the brew"

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post #7 of 12 Old 03-09-2017, 10:35 AM
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Originally Posted by RIT333 View Post
PS93

Great analogy !
YEAHHHHHHHHHHHHH Some days I am on fire!!!!!!!!!!!!!!!!

Long LIVE THE POWERSHIFT!! MAY IT NEVER RUST IN PEACE!!
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post #8 of 12 Old 03-09-2017, 11:42 AM Thread Starter
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Quote:
Originally Posted by skutflut View Post
I remember in a far distant life, that a Norton motorcycle mechanic told me roughtly the same thing.

I asked him about smoothing out the rough parts and he said, in a thick scottish accent, "Ach, they are suppose to be rough as a badger's ***hole to mix the brew"
Hah, That's funny.

I've done quite a bit of porting, mostly on GM big blocks, Buick 455s in particular. Cleaning up the rough edges do yield flow bench results, but this is a top end improvement. There is no top end concerns on a Tecumseh.

The polishing is a big no no. The roughness actually decreases flow resistance by creating a thin air buffer which the mass of flowing air flows against with the lowest resistance. A polished surface will cause the mass of air to drag itself against the metal surface causing friction.

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post #9 of 12 Old 03-09-2017, 12:20 PM
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YEAHHHHHHHHHHHHH Some days I am on fire!!!!!!!!!!!!!!!!
Yep - And other days, we wish you were ! LOL
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post #10 of 12 Old 03-09-2017, 01:13 PM
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Quote:
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...I've done quite a bit of porting, mostly on GM big blocks, Buick 455s in particular.
Growing up in Detroit, I have fond memories of seeing, hearing and riding in one of the first 1970 Chevelle SS 454 LS6's in the neighborhood. Weren't too many of those around.

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