Kohler To Westerbeke 8 KW

Changed from a Kohler gen to a Westerbeke, the Kohler had 1 5/8" exhaust the Westerbeke has 2" exhaust. Can I hook up the Westerbeke using the 1 5/8 hose, muffler etc. without doing any harm to the genset. This is a gas unit.

Should be fine. Just need some sort of safe adapter to change hose sizes.

Probably. You may create some back pressure, causing the engine to work harder. But even adding water, an engine running 8kw doesn't need a car sized exhaust.

Obviously they have a 2" exhaust for a reason called back pressure, you may get away with it depending on the length of your out let pipe mufflers/water traps (if fitted) etc.

The classic symptoms of too much back pressure include things like a lack of high speed power, poor fuel economy and even overheating. Anything that backs up exhaust pressure into the engine will also back up heat. About a third of the heat produced by combustion goes out the tailpipe as waste heat, so if the heat can't escape it can overload the cooling system and make the engine run hotter than normal, especially at highway speeds.

Obviously if the unit is new it would violate any warranty compliance

Cheers Steve

Good grief. A Honda Civic car with about 100hp uses about 1.5" tube for exhaust, and that exhaust is not cooled by water so has much more volume.

This engine is about 11hp.

I would argue the 2" for 8kW is well oversized.

Also, this is a generator engine, so no such thing as "highway speeds" as per the above post.

Would muffler restrictions be a factor for a 2" dimater exaust for minimal backpreasure on a small hp mptor?

Apologies for the generalization and mention of an auto-motive typical statement in the marine sector (must have been thinking about my drive to work!! )

But, back to sizing. Exhaust flow is determined from the amount of HP the engine makes and the more HP, the more exhaust flow; therefore it will take larger piping and/or less bends, shorter lengths etc., to meet back pressure requirements. Also, a very simple to understand concept (even though most installers seem to forget) is the “bend” equation part of planning an exhaust. Figure a smooth radius 90 degree bend is equal to about 6-10 FT of DRY piping and 15 FT of wet piping. Another good rule of thumb to remember is for every 50 PRODUCED horsepower, the engine makes about 100 CFM of exhaust gases, but this does not include the water and / or steam that becomes part of the mix when water is introduced. That’s why dry piping can be smaller than wet piping, WATER and steam add to the total flow in a substantial manner; therefore once water is introduced, the piping MUST BE LARGE

Also take into consideration the type of muffler,water lock and the overall length of the system, the amount of both dry and wet bends, the amount of water that you inject into the system (some of it, if not all of it), the angle of the discharge AFTER you inject water and how the system exits the vessel. All of these affect the total system back pressure. I am using Volvo engines as that is what most of my experience is with and I am using 3″ Hg or 41″ of water column as the maximum back pressure limit:

Bottom line engine manufacturers usually know "how to" and what size there exhaust systems need to be as in there supplied exhaust outlet size if you want a long running compliant generator (and with in warranty requirements)follow that size is my opinion

Cheers Steve, NZ Chief Eng 1

CaptSteve53 said:

Obviously they have a 2" exhaust for a reason called back pressure, you may get away with it depending on the length of your out let pipe mufflers/water traps (if fitted) etc.

The classic symptoms of too much back pressure include things like a lack of high speed power, poor fuel economy and even overheating. Anything that backs up exhaust pressure into the engine will also back up heat. About a third of the heat produced by combustion goes out the tailpipe as waste heat, so if the heat can't escape it can overload the cooling system and make the engine run hotter than normal, especially at highway speeds.

Obviously if the unit is new it would violate any warranty compliance

Cheers Steve

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Thanks Steve
The reason for this thread is that I am have trouble with all three things that you said. Will change to a 2" system.

Is the Westerneke gas unit the same KW capacity as the Kohler? How long was the Kohler in service with its exhaust setup?

Ski likely knows more about smaller gensets and installs, with requisite dirty hands and education, than any other TF member. I'd not disregard his advice.

The Kohler had 1 5/8 exhaust set up, was 7.5 KW and ran for 20 years. The Westerebeke has 2" exhaust and is 8KW. Do not know whos right or wrong but Capt Steve hit the nail on the head with all three problems I am having.

kartracer said:

The Kohler had 1 5/8 exhaust set up, was 7.5 KW and ran for 20 years. The Westerebeke has 2" exhaust and is 8KW. Do not know whos right or wrong but Capt Steve hit the nail on the head with all three problems I am having.

Click to expand...

So how long has your Kohler been overheating?