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Old 11-28-2016, 11:35 AM   #1 (permalink)
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Primary tube length for 1L engine

I have a 30hp 922cc 2 cylinder 3,600rpm engine generator that needs a new exhaust system.
Because the OE exhaust system sucks. The muffler is right next to the generator and the tail pipe discharges horizontally at ground level.
I see 5 problem's with this:
1 It exposes people to carbon monoxide.
2 It kicks up dust which will be sucked up by the generator, engine and people.
3 Anything next to the tail pipe will be burnt up.
4 Exhaust heat from the muffler effecting the generator.
5 Noise blasted out the end of the tail pipe.

My solution, fire the exhaust straight up.
The carbon monoxide, tail pipe scorch, muffler to generator heat and dust problems all eliminated.

I have room to make the exhaust pipe primary tubes anywhere from 18 inches long to up to about 5 to 6 feet long max. Then put both primary tubes into a full size car muffler to tame the noise level a little bit more.

I'm going to run this engine hard, if it's not making at least 5 or 6kw then it should be off.
Normal operation could be an inrush of 20,000+VA running with 10,000 to 15,000VA.
So the tube design should be maximized for making full power at 3,600rpm.
Plus more heat that can be rejected by the exhaust the better since these engines tend to run too hot anyways, frying their oil.

What size tube and lengths should I be considering?

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Old 11-28-2016, 11:42 AM   #2 (permalink)
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About the diameter of the manifold X 1,5 with one muffler?

The length is not so mega-important, i'd think the flow rate isn't that great at 3,600rpm
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Old 11-28-2016, 12:02 PM   #3 (permalink)
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Not that I can answer your question, but if you're messing with the OE exhaust, I'd assume you'd have to pick between:
Fuel economy
Maximum power
Emissions.

Pick one; you can't have all three. (The closest you'll get is probably the OE exhaust.)
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Old 11-28-2016, 12:06 PM   #4 (permalink)
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My calculations show to use 3/4" OD tubing (.065" wall), and the primaries should be about 52.5" long. Collector can be 1" OD outlet.
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Old 11-28-2016, 12:15 PM   #5 (permalink)
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I built an exhaust system for an Onan twin 4kw gen set. I had it on a pallet with a 35 gallon tank and a couple batteries. It would fit in the bed of my pickup and power my RV at the drags during the summer. I used a Toyota pickup muffler and it was a little noisy. I restricted the tailpipe from 1.5" to 1" and it quieted down and ran fine.
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Old 11-28-2016, 01:29 PM   #6 (permalink)
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Quote:
Originally Posted by me and my metro View Post
I built an exhaust system for an Onan twin 4kw gen set. I had it on a pallet with a 35 gallon tank and a couple batteries. It would fit in the bed of my pickup and power my RV at the drags during the summer. I used a Toyota pickup muffler and it was a little noisy. I restricted the tailpipe from 1.5" to 1" and it quieted down and ran fine.
I will have to try that, I was just going to stick a flapper on whatever size the muffler happened to be. Which could be 2 or 2.5 inches.
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1984 chevy suburban, custom made 6.5L diesel turbocharged with a Garrett T76 and Holset HE351VE, 22:1 compression 13psi of intercooled boost.
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Old 11-28-2016, 01:33 PM   #7 (permalink)
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Bug - '01 VW Beetle GLSturbo
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Sub2500 - '86 GMC Suburban C2500
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Quote:
Originally Posted by Daox View Post
My calculations show to use 3/4" OD tubing (.065" wall), and the primaries should be about 52.5" long. Collector can be 1" OD outlet.
That is perfect because I was thinking lengths between 3 and 5 feet long would fit best.

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1984 chevy suburban, custom made 6.5L diesel turbocharged with a Garrett T76 and Holset HE351VE, 22:1 compression 13psi of intercooled boost.
1989 firebird mostly stock. Aside from the 6-speed manual trans, corvette gen 5 front brakes, 1LE drive shaft, 4th Gen disc brake fbody rear end.
2011 leaf SL, white, portable 240v CHAdeMO, trailer hitch, new batt as of 2014.
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