72 GT750 Project

[Arne]

I haven't seen a set to measure, but the T500 pipes I have dimensions for reportedly at 1.125" od so that's probably 1"bore.

Thanks, I was thinking 3/4" inside diameter, I'll probably see whats available and stay between .75 and 1.0...

[tz375]

Arne, 19mm is pretty small for a 250cc cylinder. Jemco use 2" OD mufflers with a 1" core ID.

[Suzukidave]

I am with TZ .. 1" inside would be about the right size .

[Arne]

Thanks for that, I'll tend to the 1" inside diameter. Its been a few years since the 3/4" stuck in my head...

This fellow likes 7/8" to 1"
http://smokeriders.com/Technical/Suzuki ... t/p35.html" onclick="window.open(this.href);return false;

This guy said the following about stingers:
http://airfoolers.com/?page_id=529" onclick="window.open(this.href);return false;
The tailpipe, or stinger, is as important as any part of the pipe. Its size
and length influences peak power and bottom-end, and can even affect an
engine’s resistance to holing pistons.
In general, smaller stinger diameters create more peak horsepower but
increase the likelihood of melted pistons because they bottle up the exhaust
heat. Big stinger diameters boost bottom-end at the expense of peak power.
Excessively large stinger diameters can hurt performance at all engine
speeds due to insufficient back pressure.
Stingers length is important, too, because it’s part of the total pipe length
and volume. Generally, longer stingers help low and midrange power. Why not
run a long, large diameter stinger? The pipe has to fit on the bike!!!


This fellow likes the stinger to be between .6 and .7 of the effective exhaust diameter (22.8 to 26.6 for this bike, which is about the 7/8" to 1" diameter)
http://freepages.family.rootsweb.ancest ... xpcham.htm" onclick="window.open(this.href);return false;

This fellow had this to say:
Stinger/Silencer
The stinger acts as a bleed off valve for the pipe. It controls the amount of average pressure in the pipe, which a certain amount (2-8psi) is needed to counter the loss of intake charge out of the cylinder and into the pipe. My experiments show that a certain stinger restriction is needed for peak power at peak rpm, and that a little bit more restriction aids low rpm power and detracts from upper rpm power. A pipey motocross bike should have a larger diameter stinger than an enduro bike because it relies on the baffles return pressure wave at the top rpm range in order to prevent intake charge loss out the exhaust port. So the back pressure is not needed and has the negative effect of restricting intake charge transfer into the cylinder from the crankcase. Actually, below 14% of the peak rpm (1,400 rpm for a 10,000 rpm peak) both return waves come back to the cylinder before the transfers open and so have no effect on engine power. Then the only thing countering the loss of intake charge out the exhaust port is the back pressure caused by the stinger. An ideal stinger would be one that is more restrictive below that 14% point. Something like an electronically controlled valve at the end of the baffle would work. Engine designers make the stinger diameter and length ideal for the intended rpm range of maximum use. So a motocross bike would have a less restrictive stinger/silencer than an enduro bike. Longer stingers are slightly more restrictive than short ones but their length is not nearly as important as the diameter. One member on the MacDizzy forum said that dyno runs showed no difference when a 12" stinger was cut down to 4". If the stinger originates at the belly, and not the end of the baffle, then the return wave is stronger at its trailing end which boosts mid rpm power without robbing high rpm power. And the exhaust pulse loses its bark and bite for a much more silent exhaust system (a whopping 84% quieter according to my decibel meter). Although my computer mic doesn't capture the sharpness of the exhaust note exiting a standard stinger, you can watch this video to see and hear how quieter the exhaust is when it exits the belly. Click here to see a belly stinger "channel" before being welded to my pipe. I cut off the previous stinger and had it welded to the belly stinger channel. Then the end of the baffle cone was welded shut. Click here to see the end product.


So, it looks like I'm in agreement that 7/8" diameter to 1" diameter is where I should end up at...

Thanks -

[Arne]

Gordon Jennings would actually be a bit bigger than 1"...
http://www.vintagesleds.com/library/man ... ndbook.pdf" onclick="window.open(this.href);return false;

Having gotten past the business of diffusers and baffle-cones, we can proceed
onward to the lengths and diameters of lead-in and outlet pipes. The latter will, if the rest
of the expansion chamber is proportioned fairly closely in accord with the advice I have
given, have a diameter between .58- and .62-times that of the lead-in pipe, and a length
equal to 12 of its own diameters. It is simply a pressure-bleed resister, which prevents
the free escape of exhaust gases from inside the expansion chamber and thereby creates a
backpressure to enhance the port-plugging efforts of the wave reflected by the bafflecone.

On this pipe, 28mm to 30mm (1-1/16" to 1-3/16") diameter....

[Arne]

I'm not going to do this, but thought it was interesting...

http://www.dragonfly75.com/motorbike/pipes2.html" onclick="window.open(this.href);return false;

[tz375]

Billy Alvarsson of Bimotion recommends 26-28mm ID for a 250cc cylinder.

Slightly smaller works fine at the drag strip where that extra pipe heat helps at the end of the strip but could prove fatal (for a piston) on the street. Nominal 25.4mm should be perfect on a mildly tuned street bike