Torque screw mod for fully debaffled pipes

[diamond_jim]

When the M50/C50 pipes are debaffled and demickey'd, some feel that the loss of exhaust back pressure effects some of the motor's low end torque. I don't believe you lose torque with free flowing mufflers. Instead the torque gets shifted more into the midrange and higher RPMs and no longer spread evenly across the entire RPM range. The torque is still there, but a little bit of that bottom end grunt that the 50s are known for seems to be weaker when too little back pressure is present. Fuel processors can be adjusted to help restore this low end grunt.

Anyhow, I've tried adding a little resistance to the very end of the header, right where the muffler slips on, to create a little back pressure and see how it effects low end torque.

Here's the how to:

Remove the mufflers. At the end of the headers is the section of pipe that slides into the muffler. That section is what I'm working with here.

I drilled a 3/8" hole thru both sides of the pipe.


Tapped out the hole to accept 3/8"-16 threads.


Screwed bolt in and through.


Snug up the bolt.


Then cut off and clean up both sides.


Do the same to the other pipe. Clean up the mess, put your debaffled pipes back on and go ride.

I haven't really had a chance to evaluate it thoroughly yet. I'll let you know when I do. In the end, if I don't like it, I'll just unscrew them out.

Any ideas, suggestions, comments...?

[diamond_jim]

I also ordered the Cobra Fi2000R Friday so it should be here in a few days. I got it for $160 the $7.85 Shipping. For those that would rather I have a PCIII, feel free to pass around a donations can and collect for my cause.

[profane]

You could also look into getting power cones

[diamond_jim]

Originally Posted by profane

You could also look into getting power cones

You mean like these?


The page said that they "help to restore the performance lost when the stock exhaust is replaced with drag pipes... changed the cone angle and reduced the outlet diameter... there was a very noticeable improvement. Improvement was felt in torque and in reduced stumbling when the throttle is opened."

I'm kind of thinking these screws may have a similar effect on torque. If not, oh well. I'll just say screw 'em and get rid of them!

[diamond_jim]

Anybody want to guess how the 3/8" torque screw affected performance?

[old new biker]

Originally Posted by diamond_jim

Anybody want to guess how the 3/8" torque screw affected performance?

Ahhhhhh...................Yeeeeaaaaa.............. ......

[diamond_jim]

As you can guess, I love messin' with my 50. This was an idea I wanted to experiment with.

I couldn't really tell if it added much to the low end. If anything, it added a little back pressure which made the air/fuel mixture a little rich. But it cut the top speed down to about 85 mph. That's because, I'm guessing here, that the engine is having to use power to push the air past the screws instead of directly to the rear wheel.

[Mario]

well I don't know, the first thing that pops up in my head is on a stock setup the air passes through the 3rd plate which you still have, then channeled through the Mickey plate which the bolt seems to have the same amount of free space around it as the three holes do, then you have the baffles. Another thing is the screw has far less aerodynamic resistance then a plate with a few holes. Air should be moving freely around the screw instead of being forced through a hole. Granted that the pressure between the screw and the walls of the exhaust is higher then it is in front of the screw however the flow would be less turbulent, it concerns me that your top speed would drop down to 85. Before you installed the torque screw what was your top speed.

[Mario]

If you have time check on the bolt see how it is holding up I am pretty sure it is ok however if the temperature that it expands is different then the exhaust metal we might have a problem, not a catastrophe but something that may need to be taken into account. It really bugs me that your top speed has fallen. Stock the bike runs around 115 –120 mph at least mine did, if you lost that much then it might be another issue other then your toque screw.

[diamond_jim]

Originally Posted by Mario

If you have time check on the bolt see how it is holding up I am pretty sure it is ok however if the temperature that it expands is different then the exhaust metal we might have a problem, not a catastrophe but something that may need to be taken into account. It really bugs me that your top speed has fallen. Stock the bike runs around 115 –120 mph at least mine did, if you lost that much then it might be another issue other then your toque screw.

Thanks for the analysis, Mario. I was wondering if the torque bolt would be the equivalent in back pressure as the stock baffle/mickey. Apparently it's not. When doing 50 in 5th gear, it has a slightly weaker than normal roll-on acceleration until it hit about 80. Then it kind of crept up to about 85mph. The steady high volume of air was too much for that size of an obstruction.

The bolt only introduced pressure. It did not assist flow as well. Whereas the cones do both by design. I bet if you only ran around town and did little highway riding, a smaller diameter bolt, say a 1/4" bolt, might do the trick for restoring a little back pressure, fuel efficiency, low end torque, etc.

[Mario]

maybe spread it out, put lets say three small bolts in line with each other spaced apart down the exhaust if you can, it won't be a sudden rob of air space but still apply pressure. The torque screw is a good idea just needs a little more trial and error. I was thinking (yea I know bad idea) you still have the 3rd plate and then the torque screw then the wave guide correct, oh and what was your top end speed before the bolt.

[diamond_jim]

I don't know what top speed was, but it was easy to reach 100. It was maybe 115-118. Not sure.

Their order (with exhaust flow) was torque bolt-3rd plate-waveguide. The waveguide I think supplies a little obstruction to flow. Not a direct obstruction, but the fact it forces the exhaust to take a 90 degree turn. But the problem is that the size and distance of the waveguide is constant while the engine rpm and therefore exhaust gas pressure is changing. The amount of resistance the exhaust encounters with the waveguide increases or decreases relative to the engine rpm. The more flow, the more resistance.

Hmmm. I'm gonna make some changes to the waveguides and try it again.

I also got my Cobra Fi2000R in today!

[Mario]

You have gone too far to go back now <mischievous smile>, good luck let me know how it goes I plan on something similar but requires more destruction.

[Artimus36]

Diamond Jim,

At least now you have a nice threaded hole to mount an a/f monitor, or a couple of spark plugs for the flame-thrower effect......

(apology to your wife for putting the flamethrower idea in your head)

[wildwolf]

I think you should put your Cobra Fi2000R on and try again that roll on for top speed.

[DrBob]

Originally Posted by wildwolf

I think you should put your Cobra Fi2000R on and try again that roll on for top speed.

I agree. Exhaust mods really screw up the mixture, so a properly dialed in Fi2000r should bring back the top end.

[nicocorea]

Originally Posted by DrBob

I agree. Exhaust mods really screw up the mixture, so a properly dialed in Fi2000r should bring back the top end.

Would someone kindly explain how exhaust mods can affect the mixture entering the cylinders???

[ertyqway]

Diamond Jim,

I just had an interesting brain-wave for you on the wave guide. What if it was spring loaded or somehow set up to have a variable opening depending on exhaust pressure? I'm thinking of something like a spring-loaded trap door with stops on it so it never fully closes or opens all the way.

Like you need another exhaust-mod project, but this strikes me as an interesting direction to take the wave-guide.

[diamond_jim]

Originally Posted by ertyqway

Diamond Jim,

I just had an interesting brain-wave for you on the wave guide. What if it was spring loaded or somehow set up to have a variable opening depending on exhaust pressure? I'm thinking of something like a spring-loaded trap door with stops on it so it never fully closes or opens all the way.

Like you need another exhaust-mod project, but this strikes me as an interesting direction to take the wave-guide.

Funny you should mention that. Apparently we think alike. I thought about that as well. I weighed the two options of having a hinged plate that compressed a spring and one that had a spring anchored in front of it and pulled on the spring. I felt the second was probably more viable but I think any of the designs have too many variables. With the waveguides you can accurately place them so they are both equidistant from the exhaust port inside the pipe. With spring action, if one spring is more giving than the other then the back pressure balance would be off. Plus there's the issue of exhaust heat changing the spring properties. I'm sure there's a way to do it and if done right it would work good. But that level of preciseness is currently beyond my level of patience.

Great thinking though!

[ertyqway]

I was thinking of a light-weight torsion spring mounted on the back of the plate where you currently have a rigid angle bracket. It would look exactly like what you currently have, except that the connection would be flexible rather than rigid.