On Pipe – A Discussion about 2 Stroke Exhaust

Hand built exhaust for Kawasaki motorcycle

“On Pipe” is one of those terms that just brings a smile to most of us that rode the old 2 strokes. On Pipe is in fact one of my favorites terms, but more importantly -it is two words that instantly “trigger” your memories of a particular growling of induction noise the engine made as it came into that MAGIC RPM range where power seemingly doubled!

Hand built kit for Kawasaki motorcycle exhaust

We fondly use it to describe the burst/doubling of power that an old 2-stroke produces in a very narrow window of RPM. When the “magic” inside shapes of the exhaust pipes generate a sound wave and send reverse pressure back towards the exhaust port – effectively “Super Charging” the cylinder with as much as 15 PSI.

The combination of 6~8 lbs of forced filling of the intake from the extreme velocity and the 6~8 lbs of reverse pressure coming from the reversion cone deep inside the exhaust could create pressures inside the combustion chamber equal of that of a supercharger. On Pipe performance was never linear. If you built an engine to generate peak numbers – the result is sharp rise/fall before and after the magic rpm.

Kawasaki H1 MACH III 500

For me, no other bike demonstrated this more eloquently or more demonstratively than the famed Kawasaki H1 MACH III/500 of 1969~1974.

Sure, there are your CR500R’s and the most wicked dirt bike I’ve ever ridden – the 1973 KX400, but those were so violent that you had to get in and get out or get hurt. Snick the MACH III into 1st and ease off. Make an easy shift into 2nd at 3~4,000 RPM and pin the throttle….……..4,500…….4,750…..5,000 (an unGodly growl starts)…5,250…..5,500 and the front lofts without pull from the rider and it just keeps pulling all the while making the most unforgettable “Intake Growl” I’ve ever heard. What an awesome memory from the 1970’s – I’ll never forget that Orange 1972!

Hand-built exhaust for 2 stroke motorcycle

Now, back to 2015. Today I’m going to use On Pipe to describe the WORST preservation advice I’ve ever seen/heard given for your Classic Machine. A few years back, I read an article wherein the author stated he kept his antique motorcycle collection “fresh” by starting each one for 10 minutes every month. DO NOT do this! Chances are that you’ve got Mild Steel pipes/exhaust on your Classic. Here’s why –

Kawasaki 750 Motorcycle

I encourage you to start/run/ride your machine yes, but please make absolutely sure that you have at least 30 minutes (more is better) to ride and bring the machine up to temperature so that combustion leaves no condensation (that wet fog/smoke that comes out after start-up) inside your pipes. My articles on Ethanol last week explained the creation Acidic Acid by way of the alcohol and water (condensation and atmospheric), but also remember that Gasoline contains Sulfur. Sulfur and water = Sulfuric Acid. This is NOT what you want hanging around inside your mild steel pipes. I’ve spent more on classic/period exhaust system purchases and restorations that all of the paint, all of the engine builds – hands down. The images I have included are examples of years of searching, begging, and restoring, and easily $20,000 + in cost from the more difficult bikes I’ve restored. The factories don’t make these anymore – The last thing I’m going to do is give them a “10 minute shot of Acid”.

Kawasaki H2 750 Custom Expansion Chambers

I tried to research “when” the automobile companies started using Stainless for the cars and trucks we drive today, but couldn’t put a definitive date. My 1996 Chevy has a full factory Stainless system – something GM did out of mandated warranty for was became an “Emissions System” instead of an Exhaust. They did it for them, not us, but our classics aren’t so lucky. Only my new bikes have Stainless.

Kawasaki H1 MACH III 500 1975

There is one more very good reason to ride longer – the combustion gasses (Sulfur/Acidic Acid, Water) and all get blown by the rings more during start-up since the process is not it’s most efficient without the heat. This nasty/corrosive mixture finds it’s way to your engine oil and can/will etch and eat away at your crankshaft and transmission internals if left highly Acidic. Longer rides will evaporate the Water and Sulfuric Acid thus lessening the elements contributing to the corrosive crankcase mixture.

Research, Restore, Ride, Preserve! Get Yourself and Your Goals On Pipe!


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