High mufflers

I see a lot of bikes here with aftermarket high mufflers. When I was road racing our team got an aftermarket muffler system for our four stroke endurance racer. The engineer from the exhaust system company called me to verify the setup of the engine and told me the tuned length and cam timing that we should use. I ended cutting off the head pipes several inches, the collector was under the transmission where the muffler started. The bike ran great on the street. On the track the bike ran well and our small team placed in the top 3 in our class all summer. We won our class at Elkhart and Blackhawk.

With all the apparent rage in having a hot exhaust under the seat, I wonder if anyone has dynoed a VFR with a good lower exhaust and a good high exhaust. I bet the low pipe wins. Starting the muffler another 16" further back can only move the powerband down.

I can appreciate what having a high pipe can do for a motoGP bike where the riders corner on their elbows but on the street, only squids lean over that much.... with traffic, potential for sand or foreign debris on the road surface. Errant distracted and stoned drivers, Ground clearance is not so much an issue.

It wouldn't surprise me if you were right.
It also wouldn't surprise me if there was no discernible difference between the two styles.

One other thing to remember, though:
In a race situation, you have the ability to tune the engine for a relatively narrow RPM range.
In those circumstances, fine-tuning the exhaust makes all the sense in the world.
On the street, not only is that impossible, it's undesirable.
So the criteria for what makes sense on the track doesn't necessarily translate to sense on the street.

Let's face it though, the vast majority of after-market pipes are about looks and sound, not about the best performance regardless of how odd it may look.
I spent $1700 on a Wolf underseat exhaust for my '01 because I liked the look. The added benefit was the sound

Manufacturers will tout HP and torque increases, but I'm guessing the maximum gain you will see from any pipe in real life is 2-4HP.
And that, again, will probably only show up in a relatively narrow RPM range.

And that, gentleman, is the very reason why I got rid of my TB exhaust. Didn't really like the sound, didn't believe the increase in power and I liked the look of the stock better. Interesting discussion guys, please keep on teaching ignorant people such as me please.
C

.......and car drag race guys cut the pipe right where it stops bluing.....

I think so much goes into it, even most aftermarket companies dont really know what they are doing. Did yall notic that the WSK GSXRs have a 4 into 2? I know I will never fully understand the way those things work.

Maybe off topic, but my buddy is amechanic at a HD boutique. He loves bolting on a 2000 dollar aftermarket exhaust and seeing a 18 hp REDUCTION on the dyno chart. and now, like polarbear, I will wait for some clarification from someone who understands.................

Well at one point in time, 4-2-1-2 exhaust sytems were supposed to equalize the backpressure between all the pipes and that was supposed to help midrange performance.
This was similar to the idea behind Yamaha's EXUP exhaust valve.
I've no idea if that's still the prevailing wisdom.

[image: View Post]apex, on 26 April 2011 - 09:03 PM, said:

I can appreciate what having a high pipe can do for a motoGP bike where the riders corner on their elbows but on the street, only squids lean over that much....


....ummm.........what? :blink:


Here's the way I look at it. The VFR already has a good amount of power. If I'm losing 2 hp from my high mount 2 bros (which I highly doubt is happening), then big frickin deal. Getting rid of the stock anchor exhaust probably saves 10 lbs or so, which more than makes up for it. That, and a high mount and undertail shows off the SSSA. And in the case of the 6th gen, lets you show off the SSSA and have room for the nice OEM luggage.

Basically, the main point of an aftermarket exhaust for the street is looks, weight, and sound.

[image: View Post]apex, on 26 April 2011 - 09:03 PM, said:

I see a lot of bikes here with aftermarket high mufflers. When I was road racing our team got an aftermarket muffler system for our four stroke endurance racer. The engineer from the exhaust system company called me to verify the setup of the engine and told me the tuned length and cam timing that we should use. I ended cutting off the head pipes several inches, the collector was under the transmission where the muffler started. The bike ran great on the street. On the track the bike ran well and our small team placed in the top 3 in our class all summer. We won our class at Elkhart and Blackhawk.

With all the apparent rage in having a hot exhaust under the seat, I wonder if anyone has dynoed a VFR with a good lower exhaust and a good high exhaust. I bet the low pipe wins. Starting the muffler another 16" further back can only move the powerband down.

I can appreciate what having a high pipe can do for a motoGP bike where the riders corner on their elbows but on the street, only squids lean over that much.... with traffic, potential for sand or foreign debris on the road surface. Errant distracted and stoned drivers, Ground clearance is not so much an issue.


The engineer gave you a tuned length based on the exhaust pulses + tube size. If you told him you wanted to put your exhaust under the seat, he would have told you to increase your tube size from the collector to the exhaust by a calculation that would have been based on the exhaust gas velocity over the new length.

Because in the end, tuning at that level is all about the gas flow and the nitty gritty facts are that it doesn't matter if the exhaust is low, or high, or wrapped around the bike and pointing in your face - it's about the gas velocity.

Now that that's out of the way...

One of the reasons I bought my 05 VFR is because I liked the look of the exhaust. I replaced the stock exhaust with a Staintune system for the looks, the sound and the weight reduction. I prefer the underseat exhaust on my VFR vs the lower exhaust on other VFRs because it shows off the wheel, but more importantly, because I don't have to loosen or remove it to remove my rear wheel. This, of course, doesn't apply to your bike since it doesn't have a single sided swingarm.

ps - I hope Trace chimes in on this soon.

Another point to consider is crash survivability. A high, underseat exhaust might survive a crash better, as it is protected. A high exhaust is still somewhat protected by the angle of the swingarm. If you were to lay your bike over gently on its side, you might see that the exhaust won't hit right away. A lower exhaust might be more prone to hitting the ground sooner. Another reason for the new small lower mount exhaust is supposedly mass concentration to lower/centralize the CG of the bike. I have a high mount on my VFR, partly for ease of maintenance. It allows me to access certain parts on my bike easier then the stock exhaust, but my VFR is hardly stock, so take what I said with that in mind...

As said above, it's not about performance, but about the looks and the sound.
Even weight reduction is not that important to most VFR owners who shell out tidy amounts for aftermarket exhausts.

P.S.
If anyone is disgusted with the loss of 2HP and wants to get rid of their TI high-mount exhaust for cheap, I'll take if off your hands :491:

P.P.S.
Wish I had the skill to get offended at this remark :laughing6-hehe:

[image: View Post]apex, on 26 April 2011 - 09:03 PM, said:

I can appreciate what having a high pipe can do for a motoGP bike where the riders corner on their elbows but on the street, only squids lean over that much....

[image: View Post]Rice, on 27 April 2011 - 08:54 AM, said:

P.P.S.
Wish I had the skill to get offended at this remark :laughing6-hehe:

[image: View Post]apex, on 26 April 2011 - 09:03 PM, said:

I can appreciate what having a high pipe can do for a motoGP bike where the riders corner on their elbows but on the street, only squids lean over that much....


I cornered on the street on my elbow... once... :laughing6-hehe:

Prefer to keep it to the knee though :laughing6-hehe:

Spot the difference....................... :fing02:



[image: Posted Image]





[image: Posted Image]

In the first picture the bike is on the centerstand and in the 2nd there are wheel stripes & lug cover.

What did I win?

:laughing6-hehe:

[image: View Post]timmythecop, on 27 April 2011 - 03:04 AM, said:

.......and car drag race guys cut the pipe right where it stops bluing.....

I think so much goes into it, even most aftermarket companies dont really know what they are doing. Did yall notic that the WSK GSXRs have a 4 into 2? I know I will never fully understand the way those things work.

Maybe off topic, but my buddy is amechanic at a HD boutique. He loves bolting on a 2000 dollar aftermarket exhaust and seeing a 18 hp REDUCTION on the dyno chart. and now, like polarbear, I will wait for some clarification from someone who understands.................


:laughing6-hehe: Now, THIS is funny. But it still makes sense to bolt it on since people are getting them for looks and sound. Still funny though... (but I'm definitely in the wrong business ..... :biggrin: )

C

SebSpeed is right on point with his reply, its all about velocity, regardless of the mounting position or style. The other thing that comes into effect is the tip placement and direction its pointing. You'll never know it makes a difference because on a dyno there's not enough airflow going around the bike to make a difference. But when you're riding, the air that moves around your bike will create a vacuum effect on the end of your exhaust and that will increase exhaust velocity. For years and years people have talked about "Back pressure" when talking exhaust. Truth is, that term means nothing, has no real value and I believe somebody kinda just made up or got misconstrued from another topic. The reason the velocity plays such a big roll is because the more you have the more "scavenging" you get. So when you have the exhaust setup right, there's a flow in your exhaust, think of it as a siphon action, get it started and it keeps going. So that way, when the exhaust valve in one cylinder is closing and the intake valves opens for the brief overlap, that siphon action pulls the last of the exhaust gasses out and actually pulls a little fuel/air mixture into the cylinder before its even going down on the intake stroke. This is another reason why its important to have a crossover pipe or primary collector, pulses from other cylinders increase scavenging from the ones in the last stroke, this plays a big role in making the most horsepower from your engine.

That being explained a little, that's what you have to think about when thinking modified exhaust, think of it in terms of airflow. Diameter and length are your biggest determining factors. And as I mentioned, the exhaust tip and where its placed and in what direction will play a good part in what kinda gain you'll get at road speeds.

[image: View Post]timmythecop, on 27 April 2011 - 03:04 AM, said:

.......and car drag race guys cut the pipe right where it stops bluing.....

I think so much goes into it, even most aftermarket companies dont really know what they are doing. Did yall notic that the WSK GSXRs have a 4 into 2? I know I will never fully understand the way those things work.
WSK rules are based on Production Bikes and the stock GSXR 1k sports 4 into 2 so the race version is required to run the same config if I'm not mistaken.

Maybe off topic, but my buddy is amechanic at a HD boutique. He loves bolting on a 2000 dollar aftermarket exhaust and seeing a 18 hp REDUCTION on the dyno chart. and now, like polarbear, I will wait for some clarification from someone who understands.................
Many aftermarket Mods can hurt/reduce power & torque numbers if the Fuel and or Ignition is not modified to support the needed change.
Good exhaust systems and designs are a pure science! :fing02: