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post #1 of 8 (permalink) Old 03-21-2015, 08:06 AM Thread Starter
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Default exhaust temp different

I just noticed that the exhaust temperature is different from each side. I'm not sure if that's normal. Do the heads operate at different temperatures or could there be something wrong? 2002 TC.
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post #2 of 8 (permalink) Old 03-21-2015, 08:09 AM
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Originally Posted by imgeno2 View Post
I just noticed that the exhaust temperature is different from each side. I'm not sure if that's normal. Do the heads operate at different temperatures or could there be something wrong? 2002 TC.
rear cylinder runs hotter as its behind the front one and copping its heat plus its own

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post #3 of 8 (permalink) Old 03-21-2015, 09:48 AM
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Yup , what MBX said ......

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post #4 of 8 (permalink) Old 03-21-2015, 10:58 AM
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how did you come to that conclusion. with your hand or a temp gun

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post #5 of 8 (permalink) Old 03-21-2015, 02:09 PM Thread Starter
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First I saw more vapor coming out of the right side, then I placed my hands in front of the exhaust. That's when I noticed the temperature different
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post #6 of 8 (permalink) Old 03-21-2015, 09:39 PM
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thats no way to tell. give it up your on the wrong road

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post #7 of 8 (permalink) Old 03-21-2015, 11:13 PM
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The rear cylinder in a Vtwin makes more hp than the front which has as much to do with why it runs hotter normally as getting bathed in the front cylinder's heat.

The front cylinder runs in the wake of the front wheel and fender which pushes much of the air you would expect it to be getting away.
That air deflected by the front wheel returns closer to the rear cylinder than the front depending on the size of the front fender and wheel. It's not a bad thing as the back cylinder will be making more HP and needs whatever cooling it can get.

The rear cylinder benefits from sharing part of the intake tract and exhaust with the front cylinder. This is where the extra power comes from. On the intake side the front cylinder does the work of accelerating the air in the air box from almost stopped to getting it moving towards the engine. About the time the air finally gets to speed the front cylinder intake valve closes and there is no where for the air to go. The air has a lot of mass and is compressible. Because it is now traveling quickly it has inertia. It piles up in the air box and bonces back and forth in pulses. Because the intake of the rear cylinder opens shortly after the front cylinder air intake valve closes, at some rpm's the rear cylinder benefits from these air pulses that are traveling towards the now open rear cylinder intake valve. It is similar to having a pressurized manifold in a motor with boost. The air is traveling the proper direction and has inertia, life is good. Intake designers try to capitalize on this by designing the intake size and length so that the rear cylinder will get the most air at speeds where the motor is driven or raced depending on what the bike is being tuned for.
That is why intake tuning, air box design, is so critical and can add so much power.

Something similar happens on the exhaust stroke. At some speeds depending on the design of the exhaust, the exiting exhaust pulse of the front cylinder pull the exhaust out of the rear cylinder in their wake. Greatly increasing scavenging. Something that must be taken into account when the cam is ground for the rear cylinder if the exhaust is designed well.

Unfortunately there is too much physical time between when the rear fires till the front fires again for the front cylinder to benefit much from the intake tuning and exhaust scavenging effects of the rear cylinder. Until you are running very much faster. Faster than these motors get run.

No biggie though. Having one cylinder running different than the other means that one can be tuned for power where the other lacks it and gives a wider power band if that is done. Which in this day and age is almost always done.


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Last edited by Joe_; 03-21-2015 at 11:25 PM.
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post #8 of 8 (permalink) Old 03-22-2015, 08:18 AM Thread Starter
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WOW, that's the most complete answer anyone can ask for. Thank you
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