I have purchased a Briggs and Stratton "Elite Series" portable generator, (5500 W).

The engine is a model series 12000.

Unfortunately, last year I had the displeasure of using the generator for two weeks after the power failure from hurricane Wilma. I am working on a method of silencing the extremely noisy system by diverting the exhaust through a standard car muffler.

I have welded a three inch diameter pipe directly onto the face of the existing "muffler", being careful to not cover any of the exhaust outlet holes on this surface.

I have obtained stainless flex pipe to connect to this exhaust extension which I am attaching to a car muffler. I plan to operate the generator in the garage and exhaust through the wall to the outside.

I know just enough about internal combustion engines to know that the back pressure on the exhaust valves is an issue.

I am assuming that I will be adding back pressure to the exhaust port with the addition of this muffler and piping system.

My thinking is, I can drill the holes in the existing engine muffler a little larger to make up for the new added back pressure.

I would appreciate any input that you can provide as to:

Is this a true concern?

Is there a method for determining the additional back pressure I have created and if so would the drilling of the holes compensate?

Am I going to blow by engine by messing with the exhaust?

Your help would be greatly appreciated. The weather forecaster is practically guaranteeing a repeat of last year.

R Saylor

Since the 12000 is a 12 cu in displacement, I see no problem with things the way they are since the smallest car engine that I am aware of is around 92 cid. The only advantages that I know of for back pressure are 1) To keep cold air from being ingested around the hot exhaust valve and 2) put some positive pressure around the valve stems to keep oil seepage from the crankcase to the intake or ehaust. This is only and opinion. I am only a mechanic at best. I would be more concerned that the pipe passes safely through the wall (combustion heat precaution) and more concerned yet, that the garage is properly vented for your own safety. I am glad that you have chosen to put a length of flex pipe in the exhaust line.

I don't think it would hurt at all the way it is now (not putting more holes in it).....

Thanks for your openion. The wall is concrete block and the garage is detached from the house.