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Want to read an in-control rant?  Read on…

Pipe Temperature and Clutch Performance

On the dyno, an engine operating at a hot coolant temperature with a cool pipe exhibits a different performance curve than an engine with a hot pipe. This discrepancy becomes evident when riding in real world conditions, such as negotiating turns or sidehills with intermittent full throttle inputs.

The aftermarket exhaust pipe’s temperature fluctuations during real-world riding conditions can explain why some pipes, initially impressive on the dyno, disappoint in practical mountain riding or backcountry scenarios. Unlike the controlled environment of a dyno pull, where the engine coolant temperature and pipe temperature are meticulously~obsessively managed, well, out in the snow, in the field or hills, trees, these temperatures can vary significantly than from what the dyno operator is running.  Remember, the dyno operator is in reality racing his competitor, another dyno operator.  Who makes the most power wins, no matter the cost to the customer.

When the engine operates at part throttle and transitions to full throttle intermittently, different sections of the pipe experience varying temperatures. If the aftermarket pipe is designed for 8000 RPM but consistently pulls at 7800 RPM, it indicates that the pipe is too cold to operate optimally at 8000 RPM. Only when the pipe is adequately heated does it bring all sections to the right temperature for optimal performance.

Dyno operators often fail to replicate the actual engine coolant temperatures experienced by riders in snowy conditions. The inability to simulate real-world scenarios can lead to misleading results on the dyno, “You think what you see on the dyno is going to happen out in the snow”, but, the aftermarket pipes may not perform as expected during initial full-throttle pulls in the snow.  And guess what you blame?  The clutching.  Nope, the pipe you’re using now has a different power shape than the stock pipe.

An analogy; Its like a person playing darts.  The clutch weight mass [grams and clicker position] you use is the dart.  You shoot the dart at the dartboard, looking to hit the bullseye [8000 rpms] but just as you’re throwing the dart, someone with a stick is moving the target.  Dart does not hit the target in the middle, rather to the side of the bullseye.  And you blame the dart.  Nope, the target moved Mister.

In conclusion, the key to optimum clutching lies in understanding and managing pipe temperature. The clutch, akin to a dyno itself, responds to the engine’s power output, which is closely tied to the temperature of the exhaust pipe.  The flyweight grams you use is like a mirror of engine torque. Clutch settings must align with the moving power peak, influenced by the dynamic changes in pipe temperature during real-world riding. It’s essential not to blame the clutching system outright, as its settings are fixed; instead, attention should be directed towards addressing the challenges posed by aftermarket pipes in achieving the desired power peak RPMs.

My recommendation.

1] Do not install aftermarket exhaust yet.

2] Keep engine stock exhaust

3] install clutch kit

4] install the suggested pdrive pivot bolt and clicker position.

5] Go test the clutch kit and make engine run at 8000 rpms full throttle.

6] Make sure you think the clutch kit runs very good for you and is matched to the engine power.

7] after you think the clutch kit run goods at 8000, THEN change to aftermarket exhaust pipe.

8] clicker up one number to get the engine to rpm faster.  Most aftermarket pipes in the real world environment make their power by virtue of rpm increase.  Try to run 8200,  like say with a jawz or SLP pipe.

9] Try to run the aftermarket pipe at 8200 rpms because when on snowmobile It will be better at 8200 than at 7800 to help backshift strength.  You should have strong backshift when change throttle, off and on full throttle.

Ok, now, what if you go to high elevation like 8000 feet + and see low rpms compared to what your setting sheet says?

  • You clicker up, have low engine speed.
  • You clicker up more, still, have low engine speed.
  • You pull out flyweight, still have low engine speed.
  • You pull flyweight grams out, change to a higher clicker(s) and still have low rpms 75, 7600.

What is happening?  I know, blame the clutching, say the clutch kit doesn’t work.  Everything you’ve done to the primary clutch that in-theory should raise engine speed and it doesn’t.  Keep blaming the clutch kit?

No, you have that “X” brand aftermarket pipe on there that’s not choked correctly for high elevations.  Or, the muffler you’re running is not choked correctly for high elevations.  The exhaust system, whether it be the pipe, or the muffler, or a combination of the two, are not making the same [sufficient] internal pipe pressure at full throttle like your stock exhaust makes at high elevation.

Pipe pressure article *click*

Your exhaust that runs 8200 at low elevation, now wants to run 75~7600 at the high elevation you’re at.  Its not the clutching.  You think another vendor’s clutching is going to work correctly up at high elevations too?  You pull my clutch kit out and install an SHR kit, or a HRSS kit or Bikeman, or whoever, you name them.  No, you’re going to do the same thing.  That other company is going to suggest you run a weight known for that pipe at high elevations.  But you end up doing the same procedure.  You try to make the clutch settings get the engine to go 8200 full throttle and it wont.   You clicker up, you pull flyweight out, it run worse.  Same thing, different clutch kit!  It’s not the clutch kit!  Its your exhaust pipe not having the same internal pipe pressure that the stock exhaust has at elevations.

Oh and make it even worse is running 94, 95, 98, 102+ fuel octane.  You’re at 8000 plus feet and running fuel octane that needs 150 pounds compression or more to run properly, but at 8000 feet, you have 105 pounds compression and expect the engine to run even close to 8200?  The exhaust pipe will never get hot enough to run at its rated rpms.   Yeah it will run 8200 with no drive belt on the clutches.

In the end you are going to be playing with the flyweight grams to try to make sure you hit the target rpm that aftermarket pipe is supposed to make.

And if you can’t make the pipe’s rated engine speed by spending 2~3 hours changing flyweight and clicker positions, then stop the madness.  Go back to your hauler and install the stock exhaust, reset the suggested clutch weight and go and drive around with 8000 rpms for the rest of the time you’re at high elevation.

WHOA, I just spent $1000.00 on this pipe, this can’t be happening, no, its the clutch kit! ! !  What the fk is wrong with this clutch kit?

See, the reason the clutching gets bashed, is because the person bashing, usually has a basic understanding of clutch tuning and HAS NO knowledge of exhaust systems, AT ALL.

Basic clutching, IF need more rpms, THEN reduce weight. Clicker does this or that. Spring forces does this or that. That’s the basics of clutch tuning and what they are doing is applying that basic clutch tuning knowledge to what they “believe” the pipe is going to do for them.

The pipe guy selling is banging the gong “15 hp, 15 hp, 15 hp…” So that’s what’s drilled into your head. Hardly anyone asks what engine speed is this pipe going to run at now?

Regarding the exhaust pipe; all they see is the advertised dyno sheet showing 15hp increase at a power peak 400 rpms below what the pipe will actually run at in the real world. Dyno sheet says 7800 but reality it runs at 8200. The pipe comes in with no paperwork, its just put the pipe on with no careful planning.

Another belief; “The pipe has 15hp and I should have to add weight, huh.”

Ermm, what if the pipe makes power by virtue of rpm increase? Now what?

Some pipes make the power, some pipes don’t. But always, when the owner can’t get the pipe to work [because of the environment and/or situation the owner put the pipe to work in]….the clutch kit gets BASHED ! ! !

Owner bashing on internet] This clutch kit is Junk.
Clutch tuner “me”] No, your exhaust pipe isn’t working at 8000+ feet and its NEVER EVER going to work up there with the way you have it set up. AND no matter who’s clutch kit or what brand of kit or your own clutching, you’re NOT going to get it to run 81~8200 rpms.  You can have clicker 10 [TEN] and its still not going to rev 8200.  The only way its going to rev 8200 is if you take the drive belt off and hold er’ wide open. There, now you’ll get 8200.

You can’t clutch to that F@#%NG exhaust pipe because up there at 8000 plus feet, it only creates the internal pipe pressure to run at 7500 rpms, NOT 8200.

Its not the kit, its your JUNK pipe.

THEE End !