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Old 04-04-2020, 01:52 PM
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Default Briggs twin opposed exhaust

Working on getting the big Briggs ready for the Gator project. I made a custom exhaust for it; my usual scrap pile salvaged bends work. This one is the handles from an old pressure washer cart. 1⅛" ID 2 into 1, into a 2" glasspack. It sounds AWESOME. Throaty and loud but not overpowering. The muffler will be supported once it's mounted in the gator.

This old engine is a real champ. I picked it up 10 years ago, cleaned it up, got it running, drained the gas, covered it with a towel, and put it on a shelf. It got its first whif of fuel and fired right up in about 2 seconds today.

I will not be modding it for high speed. Aftermarket flywheel and rods are stupid expensive for these engines, and the stock iron flywheels are notoriously dangerous above 4000 rpm. I might advance the timing a little and put a 46ci cam in it, but that's all.

I am going to sand blast the exhaust and paint it.
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Old 04-04-2020, 02:04 PM
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With these type of engines... I see alot of the exhaust manifolds biased to one side or the other...
Do these types care about runner length to a Y, for running?
I was under the assumption that motors need to have an equal length cylinder runners to a collector of some sort..
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Old 04-04-2020, 02:48 PM
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Quote:
Originally Posted by mckutzy View Post
With these type of engines... I see alot of the exhaust manifolds biased to one side or the other...
Do these types care about runner length to a Y, for running?
I was under the assumption that motors need to have an equal length cylinder runners to a collector of some sort..
It doesn't really make that big a difference. Granted, an equal length header will always be better for high performance engines, but this isn't one.

I think the main reason you usually see these engines with straight runners into a can is for packaging, sound, and simplicity. Takes up less space and cheaper to build. A 2 into 1 manifold will scavenge exhaust gases better than dumping into a can muffler though, even without being symmetrical.

Asymmetrical headers sound better too.
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Old 04-04-2020, 03:46 PM
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Interesting....
I bet the small opposed style makes a different noise unto itself, of that like a single or V-twin Briggs.

I know my neighbors JDM subi wagon sounds like a kinda like V8...
These are pretty cool engines...
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Old 04-04-2020, 03:51 PM
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Quote:
Originally Posted by mckutzy View Post
Interesting....
I bet the small opposed style makes a different noise unto itself, of that like a single or V-twin Briggs.

I know my neighbors JDM subi wagon sounds like a kinda like V8...
These are pretty cool engines...
I used to have a WRX. Those asymmetrical headers sound amazing.

For comparison, the N/A models have symmetrical headers and sound like a straight 4.

The Briggs opposed twin is technically a 180 v twin. The pistons move left and right in unison with each other.

An Onan opposed twin is a true boxer, where the pistons both hit TDC at the same time.
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Old 04-04-2020, 04:18 PM
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Oh I see.. so they( the briggs above) have a wasted spark coil like most other "v-twin" types...
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Old 04-04-2020, 04:46 PM
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Oh I see.. so they( the briggs above) have a wasted spark coil like most other "v-twin" types...
Exactly.
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Old 04-04-2020, 09:11 PM
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It fits!
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