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#759890 12/20/18 4:59 pm
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kevin Offline OP
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Quote
Another case of temperature effect was shown me by dyno operator Jim Czekala of DynoTech Research. After lunch break, we started up a Yamaha TZ250 two-stroke twin and made a pull, noting that the power dropped off quickly after peak.

“Now watch this,” Czekala said as he made a second pass while the engine’s two fat exhaust pipes remained very hot. This time, power remained high for 200 to 300 revs more beyond peak. Why? Because the hot pipe “acted shorter” than the same pipe when cool. This is because the speed of sound rises with gas temperature. Two-stroke GP bikes made use of this fact to increase over-rev power (power given beyond the peak) by retarding ignition timing, thereby dumping more heat into the pipes. Subtle, these humans.


https://www.cycleworld.com/what-dyn...ps4d-nD82f2uiN_1O4i25FYTOKX_TzBbKd9BnhZQ

^^^this kind of thing is why i don't believe in formulas. cameron's writing always shows up new ideas.


i'm old enough to remember when patriotism meant not trying to overthrow the government.
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knuckle head
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Kevin,.Jim Czekala owns DynoTech , I use his dyno shop...Jim is a personal friend of Cameron...I ran my bike on his dyno and he told me to cut off the pipes shorter and and get rid of the long intakes...Engine made more top end power with a wider torque range...You need to try his dyno.


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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kevin Offline OP
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visiting up there is in the plan. dont have any motor changes planned, just light refresh on the head, fresh rings.

the only hardware changes this time around are different pipes that turn in instead of traditional british turning out, narrow wheels, and repositioning the left tank to let me stand on my head during a run.





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knuckle head
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Jim is much more than a dyno operator..he keeps logs on all testing....He is on face book with some dyno results and tech info, Jim Czekala

DynoTech research


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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kevin Offline OP
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ive been following him on facebook, ever since you gave me his name. that's actually where i got the kevin cameron link.

the only thing i do on facebook.

my machine has been on the dyno one time, and the run was an abort and ended with a seized clutch pushrod- no numbers, no chart. the only thing the operator told me was to use 130 mains in the carbs, and that kept me slow until i bumped it up to 140 and 145, either of which might be fastest depending on air density. haven't tried 150-plus.

i really want to map the spark advance. my twin-plugged morgo is fastest at 30BTDC, way later than stock 38, and i got the best times on the LSR at that figure too. but i'd like to do back-to-back pulls from 20 back to 34, and see what the curves look like.



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knuckle head
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I never messed with the timing...I started out at about 39 degrees the stock head.. Then after it got some port reshaping I set it at 37 degrees for the dyno testing but didn't experiment...So it's been the same,as is the jetting...The only tuning was cutting a few inches off the pipes and moving the exhaust timing to 107. gearing and rider position have changed...So there may be a bit more power waiting to be tapped...or not...........


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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kevin Offline OP
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i think you and i both could pull a few more horsepower out of these things if we screwed our eyes up real hard. but i suspect we're at the point where the limiting factor is the wind, not the motor.

what i mean is that i believe i could go more faster by working the slipstream rather than looking for more torque or rpm. i'll still take what i can get, but the fact that we're all within like 2 mph indicates something, i think.


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One of the reasons for wrapping exhaust systems is to retain the heat in the pipe to give consistent performance


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kevin Offline OP
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in america car people claim that it helps keep the engine bay cooler because more heat is dumped out the end, rather than radiating from the pipes. mostly here with bikes people use it as a styling thing.


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knuckle head
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Wrapping pipes is not allowed in some racing classes...But where it is allowed, do the best engines have it?


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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kevin Offline OP
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Quote
Should I Use Motorcycle Exhaust Wrap?
Our expert weighs in on this trend

By Kevin Cameron Jeff Allen August 8, 2014

Question: Now that bobbers have displaced choppers as our leading form of custom, I see more and more motorcycle exhaust wrap being used. I suppose some people dislike the way chrome or stainless steel exhausts turn blue, although I love the brownish-blue color of my Triumph Speed Triple’s pipes. Considering that the hottest area of a motorcycle engine is the exhaust valve/port area of the cylinder head, it would seem to me that wrapping pipes all the way up to that area will reduce the head’s ability to cool. Am I missing something, or can this lead to issues down the road?

Joe Hutton

Albuquerque, New Mexico

Answer: Pipe wrapping comes from NASCAR, where its purpose was to cheaply reduce temperature in well-filled engine bays. Its current use on custom bikes is a visual theme that builders apparently like, but it has no function. If you walk through racing paddocks at MotoGP or World Superbike events, you will see no woven fiberglass tape wrapped around pipes.

Some years ago John Wittner (builder of Battle of the Twins Moto Guzzis) warned against the use of such wrapping on titanium pipes, which overheat, react with oxygen, and transform into a mass of loose yellow flakes. During the two-stroke era in 500cc Grand Prix, bikes appeared for the Japanese GP with pipes insulated by various means. This was done to meet new noise regulations. Later, it turned out to have undesired tuning effects so its use was discontinued.

Send your “Ask Kevin” questions to [email protected] We cannot guarantee a reply to every inquiry.



"Later, it turned out to have undesired tuning effects so its use was discontinued."


what "undesired tuning effects?"

seems that the tape must have some effect after all, and whether or not it's "undesired" depends on whether it's doing something you like.


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knuckle head
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Some research on line seems to say the thermal coatings, Jet Hot, works well with out over heating the exhaust pipes...It all has to work together, intake ,cam, exhaust,change the exhaust tuning and then you may have to change something else..


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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kevin Offline OP
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works well to do what?

andy suggested that wrapping keeps the pipes at a consistent temperature. that might make it easier to tune consistently at different ambient conditions. czekala points out that the temperature of the pipes makes a difference in their effective length. i don't know how much, because he didn't say, but apparently 200-300 rpm..

all by itself that indicates to me that warming the machine up to a consistent temperature before a run is important, or maintaining a consistent apparent pipe length.


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knuckle head
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It works well to keep pipe temperature hot without making then so hot the pipes actually disenigrate like what happened in NASCAR with pipe wraps... I have said before my bike likes to be fully warmed up before a run...Jim is talking about 2 strokes and the large expansion chambers, yes?


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
Joined: Dec 2013
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kevin Offline OP
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yes, two strokes

but a four stroke should show similar behavior, maybe not so much

2 inches on my 1 5/8 pipes gets me as much as four mph. or rather, being wrong by two inches slows me down by four mph.


i'm old enough to remember when patriotism meant not trying to overthrow the government.

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