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Author Topic: Question about the upswept exhaust.  (Read 1244 times)


  • Bulleteer
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Question about the upswept exhaust.
« on: January 26, 2010, 11:11:51 am »
Put mine on today.
Went for a short ride.
Nice pipe. Really really loud. Well worth the money.

But I noticed the bend pipe turning hot and blueing when it cools down.
Im not bothered about the color just curious if this is normal.
Or this is a sign of a leaking ex. valve.
Performance is super.


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Re: Question about the upswept exhaust.
« Reply #1 on: January 26, 2010, 11:16:25 am »

From what Iv'e heard and read in Pete Snidal manuals, Blueing of the bend pipe happens due to retarded timing. Sometimes even due to excessively lean mixtures. That said, the experts here might be better placed to answer this query.




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Re: Question about the upswept exhaust.
« Reply #2 on: January 26, 2010, 11:31:11 am »
I think it's likely that the lower restriction in the exhaust caused a leaner mixture, which then heats up the exhaust pipe more.

Since there's no O2 sensor on your bike,the ECU has no idea that anything has changed.

However, you might be ble to "fool it" into richening up the mixture, by re-positioning your Throttle Position Sensor, to make the ECU think you have the throttle open more than you do, and thus have it squirt more gas in at the smaller throttle openings.

That would have to be a "trial and error" experiment, to see how much you need to move the TPS to "recalibrate it" for your needs.

But, I think it would work.


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Re: Question about the upswept exhaust.
« Reply #3 on: January 27, 2010, 02:43:29 am »
Thanks ace already tried that it didn't make any difference.
It all depends on how the code is written i.e. on my ECUs we take the base vale as the start position. So no matter where you set the TPS its base reading just becomes the new base. Off course if it exceeds a certain voltage say 1.5 volts as the base then the MIL Lap will trigger.

I was also thinking of trying to tune it with playing with the map sensor. i.e. try a stronger signal point or a weaker one. Even the oil temp sensor could help.
But the problem is it also bumps up your timing. Which is not a good thing on an engine that is already getting too hot.

What we really need is base line readings for all sensors and TPS i.e. when idle this is the value you should expect to see.
When HOT this is the value you should expect.

Guess its time for another WB o2 data logging session.

Ideally I was hoping to hear from other upswept ex. header guys i.e. is your pipe turning blue.

I think it should because it doesn't look like its a double walled pipe. where as the stock pipe seems double walled.

My gut tells me if I go for a long hard ride at night Im pretty sure my pipe will start to glow a cherry red.

May look cool.


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Re: Question about the upswept exhaust.
« Reply #4 on: January 27, 2010, 07:17:42 pm »
I have the upswept exhaust on my bike, but it's just been too cold to ride.
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Re: Question about the upswept exhaust.
« Reply #5 on: January 27, 2010, 11:47:45 pm »
Ok I had a dream last night.
but its to do with exhausts. In one dream Im a two stroke engine and in the next Im a Bullet engine.

I understand 2 stroke engines pretty well.
So the engine is a heat exchange unit. It converts gas+air into heat which in turn powers the engine.
Tuning an engine is making the most of that heat.

The more power you make the more heat your going to make.
Now you can control where this heat gets made and how its used.

On a two stroke we play with this heat. We move it around. We can keep it in the cylinder or we can move it to the exhaust.  If we move it to the Exhaust. It changes the tuned length of the Ex. Making it shorter. (Hot air is faster). The trick is to keep moving this heat arround. We can control where exactlly this heat happens anywhere in the engine from the cylinder to the end of the tail pipe.

What I noticed about the engine after installing the performance ex. is that the amount of heat being produced or stored into the complete exhaust system is absurdly high.
That is wasted energy which could have been used to drive the engine forward. Or over heat the cylinder.

My theory is that there is something either from the sensors or the ecu map it self which is backing off the timing pretty aggressively.
That is the only reason I can think off. To confirm this I will have to take ignition timing readings at various RPM points and sensor settings.

Either that or I have an air leak lol.
Or like ace pointed out. Without the o2 sensor the engine has no way of knowing something has changed. And its just lean.
but if this was the case you would feel the engine is lean.
i.e. reves build but you dont feel the power. This isnt the case here.
The power is very much there. So much so that soon I think the bike will start doing power wheelies. THis is not a symptom of a lean engine.

But If it was an air leak then it should show up in the way the bike runs right i.e. some misfiring or rumblings getting on and off the throttle. This doesn't happen its sharp and crisp throttle response.


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Re: Question about the upswept exhaust.
« Reply #6 on: January 28, 2010, 04:13:35 pm »

Should receive my upswept exhaust soon and will let you know what happens.  I find that my down pipe from the cylinder head has already turned that colour blue you are describing!  I use my bike extensively and it doesn't seem to have gotten worse, just a pretty coloured bluish tint to the pipe now. 

Looking forward to getting rid of the Bazooka Silencer.  Seems excessive somehow.
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Re: Question about the upswept exhaust.
« Reply #7 on: January 29, 2010, 12:24:08 am »
Your going to love the new exhaust.
It sounds nice and really works well.

I think you guys in the US / UK will see more gains than we chaps see. Because your going from two cat cons to nill.
vs us guys who are going from 1 cat con to nill.