[XL1200R]

Awhile back I could have sworn that Dave63 said that short drag pipes could actually hurt the engine.

I'm not talking about power...I get all that..
My question is, how? If rejetted correctly how would they hurt the engine? Like I said, maybe he never said it but I swear I remember that...
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[83XLX]

I've heard various reasons...they don't draw enough heat from the head, & they allow reversion of cool air that warps the hot exhaust valve are two that come to mind.

 

[XL1200R]

I did a lot of research on it tonight. Basically, from what I have read, it is more or less a wives tail as long as the bike/car is jetted for it. That being said, kinda like an oil question I've found out. Some people will say one thing, some another....



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[ciscokid]

hummmm could be why mine is running hot at 80 mph.
ill switch back exhaust and see

 

[XL1200R]

hummmm could be why mine is running hot at 80 mph.
ill switch back exhaust and see

What did you do exactly?

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[sidedraft36]

By removing the restriction in the exhaust, you increase the flow of air both into and out of the engine. If no changes are made to the jetting to compensate - your mixture can become too lean. A lean mixture burns hotter. That heat will transfer to the exhaust valve, which can cause the valve to eventually burn. The elevated combustion temperatures will also cause pre-ignition/detonation. This can - depending on the severity - ultimately burn a hole in the piston crown, damage the head, and cause all sorts of unhappiness. All of the above, in addition to the fact that the motor will probably run like [email protected]

It is important to think of the intake, cylinder head, combustion chamber, cam(s), and exhaust as a complete system. When you alter one part of that system, it effects all the other pieces, to varying degrees. Can an engine be set up to run efficiently and safely with open/drag pipes? Absolutely. However, that motor would probably be very peaky in its power delivery and excessively loud - making it much more at home on a drag strip than a public road.

 

[XL1200R]

By removing the restriction in the exhaust, you increase the flow of air both into and out of the engine. If no changes are made to the jetting to compensate - your mixture can become too lean. A lean mixture burns hotter. That heat will transfer to the exhaust valve, which can cause the valve to eventually burn. The elevated combustion temperatures will also cause pre-ignition/detonation. This can - depending on the severity - ultimately burn a hole in the piston crown, damage the head, and cause all sorts of unhappiness. All of the above, in addition to the fact that the motor will probably run like [email protected]

It is important to think of the intake, cylinder head, combustion chamber, cam(s), and exhaust as a complete system. When you alter one part of that system, it effects all the other pieces, to varying degrees. Can an engine be set up to run efficiently and safely with open/drag pipes? Absolutely. However, that motor would probably be very peaky in its power delivery and excessively loud - making it much more at home on a drag strip than a public road.

Good way of putting it! Something that I have noticed (my friend has straight shot shot slipons with no baffles) is that having the crossover pipe makes a huge difference. It tones it down a little and once jetted correctly the bike has a lot better power than true drags.

But i digress

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