Tom1980
XS650 Member
I have made a quick attempt at a D shaped exhaust port ring. Please let me know what you think. I can make more blanks if anyone's interested.
-
Enjoy XS650.com? Consider making a donation to help support the site.
XS650.com receives a small share of sales from some links on this page, but direct donations have a much greater impact on keeping this site going.
650performance
XS650 Addict
Please explain the benefits of the D shaped exhaust port ring.
Thanks.
Thanks.
Tom1980
XS650 Member
Well I made these mainly for 1.5" drag pipes and for stock headers when mufflers are hacked off . I Turned the slugs on lath and then went to town with a dremmel to shape them each one took about 15-20 min.
But the attempted benefits are believed to be ( by me and sience.......but not yet tested)
1. D shaped port are thought to help with anti reversion.
2. This will slightly raise exhaust chamber floor. And lesson exhaust port volume.
3. You can tune the exhaust port with a dremmel for more or less flow.
4. They are a easy way to experiment with drag pipes and hopefully lessen the affects of the dreaded drag pipe sag.
5. Its another bandaid attemp to help the guy with a hacksaw and a dremmel?
I will also be making a ring for the inside off my 1.5 drag pipes so I can create a small internal anti reversion chamber.
But the attempted benefits are believed to be ( by me and sience.......but not yet tested)
1. D shaped port are thought to help with anti reversion.
2. This will slightly raise exhaust chamber floor. And lesson exhaust port volume.
3. You can tune the exhaust port with a dremmel for more or less flow.
4. They are a easy way to experiment with drag pipes and hopefully lessen the affects of the dreaded drag pipe sag.
5. Its another bandaid attemp to help the guy with a hacksaw and a dremmel?
I will also be making a ring for the inside off my 1.5 drag pipes so I can create a small internal anti reversion chamber.
Tom1980
XS650 Member
Examples of anti reversion devices.
650performance
XS650 Addict
I applaud your efforts. Because very small changes in port contour can have an effect upon flow - either in a positive or negative manner - I hope that you will consider taking your bike to the local HD dealer and run it on their dyno both with and without the rings installed. Then you have hard numbers and don't have to rely upon feel. Porting has been a huge topic on this and other XS650 forums and readers would be very interested in what you come up with because a simple, inexpensive performance boost is welcome anywhere it can be found throughout the RPM range.
650 Central sells some inexpensive anti-reversion hardware that smooths out the power application on my XS race engine without diminishing ultimate power.
650 Central sells some inexpensive anti-reversion hardware that smooths out the power application on my XS race engine without diminishing ultimate power.
I believe that 1.5 pipes don't need much help, 1.75 are another story.
They have too large a volume. This decreases the exhaust velocity.
The 1.5 is about right as far as diameter. I have no hard proof of this, but most believe the 1.5 pipe is about right for head pipes.
The 1.75 inch pipes need help, this is so because of the inserts that go between the head and pipes as well as between the pipes and mufflers, they sell well.
These may work the same as the inserts by the head.
Leo
They have too large a volume. This decreases the exhaust velocity.
The 1.5 is about right as far as diameter. I have no hard proof of this, but most believe the 1.5 pipe is about right for head pipes.
The 1.75 inch pipes need help, this is so because of the inserts that go between the head and pipes as well as between the pipes and mufflers, they sell well.
These may work the same as the inserts by the head.
Leo
Exhaust port inserts are not corrective devices for oversized pipes; for that you need reducers like MMM's "torque peak optimizer" in the outlet end. I can tell you from experience that MMM's "exhaust port optimizer" works very well indeed in 1.5" pipes, which benefit just as much from increased velocity entering the bends. Reducing exhaust gas reversion is another benefit.
650performance
XS650 Addict
1.75" pipes are never appropriate for a 650 and can also be too large for a 750 that is otherwise stock (or mostly so). 1.75" pipes unquestionably make more high rpm power on a race bred 750, but even with those engines some AMA racers used 1 5/8" pipes on engines tuned for either smaller ovals or TT use.
650performance
XS650 Addict
XSLeo, you probably already have this, but there's some good exhaust info for XS650-based race bikes here:
http://downloads.650performance.com/XS650_750_engine_modiffication_guide_sample.pdf
As you can see, even on high output 750 cc XS engines smaller pipes have their place.
http://downloads.650performance.com/XS650_750_engine_modiffication_guide_sample.pdf
As you can see, even on high output 750 cc XS engines smaller pipes have their place.
Tom1980
XS650 Member
Unfortunately my build is still a few months out so I will not be able to test anytime soon. If any one is up to try it. Send me a message and I'll get some out to you for the sake of curiosity.
This is what it will look like in a 1.5" header.
This is what it will look like in a 1.5" header.
NONclow
Confirmed Laquer Breather
Retention method????
Similar alloy composition as the head for expansion and contraction tolerances???
Similar alloy composition as the head for expansion and contraction tolerances???
I agree that 1.5 inch pipes are better than 1.75 inch pipes. I built the ones on my 75 with 1.5 inch pipe and I cut the ends out of a stock set of head pipes to use the flange to hold them in the head as well as a short section of the inner head pipe.
I cut the stock pipes off out next to the first bend. I then cut the outer pipes off at the vent holes. Careful here just want to cut the outer pipe.
Ground the outer pipe down so the new pipe could slide on to where the weld is. Cut the inner pipe about an inch away from the weld. this way it worked as an insert to keep velocity up and stop reversion.
They work very well.
Leo
I cut the stock pipes off out next to the first bend. I then cut the outer pipes off at the vent holes. Careful here just want to cut the outer pipe.
Ground the outer pipe down so the new pipe could slide on to where the weld is. Cut the inner pipe about an inch away from the weld. this way it worked as an insert to keep velocity up and stop reversion.
They work very well.
Leo
Tom1980
XS650 Member
I don't for see a problem with heat expansion. I made these the same size as the stock flange.
