tuned pipe design, center bleed vs end bleed

[v_tach]

Can anyone shed some light on what the differences are concerning
performance between a tuned pipe that utilizes a side bleed as compared to a
more traditional end bleed? My understanding was that it was more a
consideration to fit the application rather than the performance or
characteristics of the pipe itself.

Thanks for any input, v_tach

[Fanman_UK]

On Thu, 12 Aug 2004 01:01:00 -0400, "v_tach"

Post by v_tach
Can anyone shed some light on what the differences are concerning
performance between a tuned pipe that utilizes a side bleed as compared to a
more traditional end bleed? My understanding was that it was more a
consideration to fit the application rather than the performance or
characteristics of the pipe itself.
Thanks for any input, v_tach

You understand correctly. The tuned length of the pipe is from the
piston to the centre of reflection of the last element of the
expansion box (assuming you mean 2-stroke types). The stinger position
does not alter the tuned length, although it must still be of the
correct diameter and length regardless of where it is located.

On many tuned exhausts the stinger is in fact welded into the
expansion box such that about half of it is inside. This reduces the
un-supported weight of the stinger and helps prevents vibration from
snapping it off.
Fanman_UK

To reply by email remove the "fanman"

[Ken Roberts]

Post by Fanman_UK
On Thu, 12 Aug 2004 01:01:00 -0400, "v_tach"

Post by v_tach
Can anyone shed some light on what the differences are concerning
performance between a tuned pipe that utilizes a side bleed as compared to a
more traditional end bleed? My understanding was that it was more a
consideration to fit the application rather than the performance or
characteristics of the pipe itself.
Thanks for any input, v_tach

You understand correctly. The tuned length of the pipe is from the
piston to the centre of reflection of the last element of the
expansion box (assuming you mean 2-stroke types). The stinger position
does not alter the tuned length, although it must still be of the
correct diameter and length regardless of where it is located.
On many tuned exhausts the stinger is in fact welded into the
expansion box such that about half of it is inside. This reduces the
un-supported weight of the stinger and helps prevents vibration from
snapping it off.
Fanman_UK
To reply by email remove the "fanman"

so you're saying the way i have it is probably wrong?

http://www.hoverclub.net/2003/2003-07-26-12r-ready-to-go/index.html

wow, i need to get more recent pictures up!

anyway, the expansion box, as you call it, has a port out of the middle
somewhere. the silencer is the stock silencer, but it was a short length of
pipe that i couldn't use between the pipe and the silencer, so i had one made
to put the silencer where i wanted it.

i'm not sure if i could make a short stub like the original part work, and it's
not the same diameter anyway. it's maybe 1/8" bigger than stock.

[Fanman_UK]

Post by Ken Roberts

Post by Fanman_UK
On Thu, 12 Aug 2004 01:01:00 -0400, "v_tach"

Post by v_tach
Can anyone shed some light on what the differences are concerning
performance between a tuned pipe that utilizes a side bleed as compared to a
more traditional end bleed? My understanding was that it was more a
consideration to fit the application rather than the performance or
characteristics of the pipe itself.
Thanks for any input, v_tach

You understand correctly. The tuned length of the pipe is from the
piston to the centre of reflection of the last element of the
expansion box (assuming you mean 2-stroke types). The stinger position
does not alter the tuned length, although it must still be of the
correct diameter and length regardless of where it is located.
On many tuned exhausts the stinger is in fact welded into the
expansion box such that about half of it is inside. This reduces the
un-supported weight of the stinger and helps prevents vibration from
snapping it off.
Fanman_UK
To reply by email remove the "fanman"

so you're saying the way i have it is probably wrong?
http://www.hoverclub.net/2003/2003-07-26-12r-ready-to-go/index.html
wow, i need to get more recent pictures up!
anyway, the expansion box, as you call it, has a port out of the middle
somewhere. the silencer is the stock silencer, but it was a short length of
pipe that i couldn't use between the pipe and the silencer, so i had one made
to put the silencer where i wanted it.
i'm not sure if i could make a short stub like the original part work, and it's
not the same diameter anyway. it's maybe 1/8" bigger than stock.

It really depends on the original state of tune as to the effects of
changing the stinger. Its difficult to judge dimensions from your
image, but it looks like a fairly narrow exhaust system designed for a
wide spread of power.

The longer and narrower the stinger, the greater the chance of
overheating problems, so you were correct to enlarge the diameter.
You say there was only a short piece of pipe on the original, but did
the pipe extend into the expansion box? If the engine is not in a high
state of tune there will be considerable leeway on the exhast design.
Start to tune the engine and then you need to get it right or risk
holing pistons on a regular basis. This is more critical when using a
separate pipe for each cylinder.

Fanman_UK

To reply by email remove the "fanman"

[Ken Roberts]

Post by Fanman_UK

Post by Ken Roberts
so you're saying the way i have it is probably wrong?
http://www.hoverclub.net/2003/2003-07-26-12r-ready-to-go/index.html
wow, i need to get more recent pictures up!
anyway, the expansion box, as you call it, has a port out of the middle
somewhere. the silencer is the stock silencer, but it was a short length of
pipe that i couldn't use between the pipe and the silencer, so i had one made
to put the silencer where i wanted it.
i'm not sure if i could make a short stub like the original part work, and it's
not the same diameter anyway. it's maybe 1/8" bigger than stock.

It really depends on the original state of tune as to the effects of
changing the stinger. Its difficult to judge dimensions from your
image, but it looks like a fairly narrow exhaust system designed for a
wide spread of power.

it's the stock equipment that came in a ski-doo snowmobile. it seems to have a
fairly wide power band, or at least good midrange, though i haven't really spent
much time in the upper range. all i can say about the upper end is it's there.

Post by Fanman_UK
The longer and narrower the stinger, the greater the chance of
overheating problems, so you were correct to enlarge the diameter.
You say there was only a short piece of pipe on the original, but did
the pipe extend into the expansion box? If the engine is not in a high
state of tune there will be considerable leeway on the exhast design.
Start to tune the engine and then you need to get it right or risk
holing pistons on a regular basis. This is more critical when using a
separate pipe for each cylinder.

the fittings don't extend in. it was just the ball coupling that normal exhaust
has, where the male end is expanded to resemble a ball and the female end is a
cup, then springs go on it to hold it on.

i thought the single pipe was worse for about everything. it's good to know it
helps in some way.

Post by Fanman_UK
Fanman_UK
To reply by email remove the "fanman"

[Frank Damp]

More years ago than I like to admit, I worked as a development/test
engineer for Norton-Villiers. We had quite an extensive road-racing
and moto-cross efforst, all built around the Villiers "Starmaker"
2-stroke single, in either 250 or 360cc versions.

In those days, long before finite element analysis and computer-based
fluid dynamics, we used a scientific paper published by a professor
Phillip (I think) Blair of Queen's Univeristy Belfast to design the
2-stroke expansion chambers and silencer (US - muffler) systems. If I
remember correctly we got about a 15-percent power improvement, even
with the rather crude mathematical analysis that was possible back in
the mid-60's. I'm sure there's a modern CAD version of Dr. Blair's
work around someplace.

The AJS motocross machinery was very competitive back then, but you'd
be hard pressed to find anyone who remembers.


Frank Damp
Anacortes, WA, USA

[v_tach]

Thanks everyone for the replies.

Frank, with your knowledge and experience, can you comment on the
differences (if any) in performance between and end bleed and center bleed
tuned system?

v_tach

Post by Frank Damp
More years ago than I like to admit, I worked as a development/test
engineer for Norton-Villiers. We had quite an extensive road-racing
and moto-cross efforst, all built around the Villiers "Starmaker"
2-stroke single, in either 250 or 360cc versions.
In those days, long before finite element analysis and computer-based
fluid dynamics, we used a scientific paper published by a professor
Phillip (I think) Blair of Queen's Univeristy Belfast to design the
2-stroke expansion chambers and silencer (US - muffler) systems. If I
remember correctly we got about a 15-percent power improvement, even
with the rather crude mathematical analysis that was possible back in
the mid-60's. I'm sure there's a modern CAD version of Dr. Blair's
work around someplace.
The AJS motocross machinery was very competitive back then, but you'd
be hard pressed to find anyone who remembers.
Frank Damp
Anacortes, WA, USA

[Frank Damp]

To be honest, designing for a single-cylinder motorcycle application,
we ever considered anything other than a conventional "in at the
exhaust port and out the tailpipe" design.

We did make four special trials versions of our motocrosser, used by
an RAF team in the International Six Days Trial. They had an
additional spark arrestor and a "cherry-bomb" type glass pack added on
at the end. We didn't look at any "center bleed" arrangements. I'm not
sure Dr. Blair's thesis even described one. Maybe he addressed
multi-cylinder, single pipe systems, but it's so long ago (1967) that
I really can't remember.

Frank Damp