88ss Exhaust Design

t ingermanson

t ingermanson

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Does anyone have any experience they'd share with exhaust systems for a starting point for an 88ss?

The bike will be ridden on the street. The cam will be an SS, or perhaps a PW3 (but that seems maybe too aggressive for a 500cc street bike).

The roads it will be ridden on are pretty twisty, so torque is more of a consideration than top speed.

Noise is not a legal concern.

I won't be going to a 2 into 1, just a stock-ish bend on the pipes to keep the engine and primary easy to get to.

I've looked at the Dunstall dimensions and the somewhat-derived Robinson booklet that call for long reverse-cone megas, but I also have heard the tales of the Dunstall high performance design and fabrication brief main factor being the mailing parcel size. I've also owned some garbage Dunstall parts that make me take anything produced under that name with a grain of salt. Anybody ever ridden one his exhaust systems on a Domi?
 
t ingermanson said:
Does anyone have any experience they'd share with exhaust systems for a starting point for an 88ss?

The bike will be ridden on the street. The cam will be an SS, or perhaps a PW3 (but that seems maybe too aggressive for a 500cc street bike).

The roads it will be ridden on are pretty twisty, so torque is more of a consideration than top speed.

Noise is not a legal concern.

I won't be going to a 2 into 1, just a stock-ish bend on the pipes to keep the engine and primary easy to get to.

I've looked at the Dunstall dimensions and the somewhat-derived Robinson booklet that call for long reverse-cone megas, but I also have heard the tales of the Dunstall high performance design and fabrication brief main factor being the mailing parcel size. I've also owned some garbage Dunstall parts that make me take anything produced under that name with a grain of salt. Anybody ever ridden one his exhaust systems on a Domi?
Click to expand...
Not since the early "70's. Lol
 
15 years ago I did a lot of experimenting on a dyno with exhausts on my 500 Dommie race bike.

Mostly with megaphones with reverse cones and with PW3 cam.

I found very good results with minimal megaphonitis could be obtained with hollow Commando peashooters and long header pipes. Also make the inlet tract as long as you can get it because it fills in dips in the torque curve. Don't go to big on header pipe diameter. 1 3/8 " OD like on a Commando is more than enough. You could try 1 1/4.

Experimenting with the cam timing improved top end power at the expense of torque at rpm below 4000. I actually delayed the cam timing by about 8 degree but it really made a hole at lower rpm and the bike then needed a 5 or 6 speed gearbox
 
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johnm said:
15 years ago I did a lot of experimenting on a dyno with exhausts on my 500 Dommie race bike.

Mostly with megaphones with reverse cones and with PW3 cam.

I found very good results with minimal megaphonitis could be obtained with hollow Commando peashooters and long header pipes. Also make the inlet tract as long as you can get it because it fills in dips in the torque curve. Don't go to big on header pipe diameter. 1 3/8 " OD like on a Commando is more than enough. You could try 1 1/4.

Experimenting with the cam timing improved top end power at the expense of torque at rpm below 4000. I actually delayed the cam timing by about 8 degree but it really made a hole at lower rpm and the bike then needed a 5 or 6 speed gearbox
Click to expand...
Great info! Thanks.

Yes, planning on the small diameter pipes and long inlets.

How long did you go with the megas? Long as Dunstall suggests (similar in length to the pea shooters)? Seems like plenty of race bikes have either short or long, but these days with noise restriction cans, it's hard to tell what is what.

Not looking to set any records, just looking to zip around the twisties. Torque is way more valuable around here than top end, and even just a little bit goes a long way. A peppy 35-40 bhp is plenty.
 
t ingermanson said:
Great info! Thanks.

Yes, planning on the small diameter pipes and long inlets.

How long did you go with the megas? Long as Dunstall suggests (similar in length to the pea shooters)? Seems like plenty of race bikes have either short or long, but these days with noise restriction cans, it's hard to tell what is what.

Not looking to set any records, just looking to zip around the twisties. Torque is way more valuable around here than top end, and even just a little bit goes a long way. A peppy 35-40 bhp is plenty.
Click to expand...
I used old commando peashooters with the centres knocked out . So exactly peashooter dimensions.

The header pipes were over 40 inches long from memory. Longer headers gave earlier and improved low end torque.
 
"Won't be going a 2 into 1."
According to past tuners loke Paul Dunstall, Norton, etc on the 500 twin the best power comes from a siamese exhaust system but if you know best . . . . .
 
Bernhard said:
"Won't be going a 2 into 1."
According to past tuners loke Paul Dunstall, Norton, etc on the 500 twin the best power comes from a siamese exhaust system but if you know best . . . . .
Click to expand...
Could you please provide some documentation? I have not seen where Dunstall's notes say that, nor did the Dunstall Domiracers come with 2-into-1 pipes, nor did the Works Domiracers.

I believe the 99 had an option of a 2-into-1 exhaust system, but it didn't use the SS head, so perhaps a different deal altogether.

I asked for anyone's experience in use of a system, as opposed to idle speculation, BS, or insults.

Thanks. You're the best.
 
Sorry, all my notes are locked up in my computer which has crashed, again.
Won't be getting the Doctor out on that.
As the 500 twin has not been made since the 1960s, The Motor Cycle road tests by Vic Willoughby, amongst others , will give you the performance figures. He did say it was faster with the Siamese pipes. I too didn't believe it myself.
I suggest you arm yourself with both types and do what I was going to do, book a session on a rolling road to confirm it.
Do let us know the results.
 
When I went through my exhaust testing exercise one of the issues is that the available range of cams are mostly for 750 or bigger engines. These have different rod stroke ratios than the 500 hence my comment about actually retarding the PW3 cam that was fitted to my 500. For a given crankshaft location the piston on a 500 is a different proportion of the way up or down the bore compared to a 750.

The 500 is more difficult to tune out megaphonitis and that's the reason why I went with the longer headers. Phil Read reportedly had issues with megaphonitis on the Domiracer when he tested it at the TT in 1963. Eventually deciding to use a Manx single in the race.

Where is is going is that I think using a 2 into one similar to that marketed by Maney and now made by Brooking850 on this site coukd be a good option for the street in that it reportedly controls megaphonitis. There is at least one quick 500 racing here in NZ that uses this exhaust. I have no personal experience however

As far as I am aware this exhaust has nothing to do with Dunstals design.
 
t ingermanson said:
Great info! Thanks.

Yes, planning on the small diameter pipes and long inlets.

How long did you go with the megas? Long as Dunstall suggests (similar in length to the pea shooters)? Seems like plenty of race bikes have either short or long, but these days with noise restriction cans, it's hard to tell what is what.

Not looking to set any records, just looking to zip around the twisties. Torque is way more valuable around here than top end, and even just a little bit goes a long way. A peppy 35-40 bhp is plenty.
Click to expand...
Re the cam choice-
Warning- 850 results ahead-

A few years back Comnoz mentioned that he had fitted a PW3 to a customer's 850.
Jim did before and after dyno runs. After fitting the PW3 there was a 6 HP loss of power in the midrange and a 2 or 3 HP gain at the top, IIRC.
The customer loved it, I guess the middle lag made the stronger top feel even better, a bit like a 2 stroke power band!
Seems likely that a PW3 in a 500 would also affect that midrange quite a lot.

Glen
 
As far as I am aware, nobody but Nortons have made a camshaft for getting the best out of the 500 twin.
The Domiracer 500 tuned by Doug Hene for Reads IOM TT allegedly allowed it to rev to
10, 000 rpm!!. And after Read finnished with it in pratice, it was ridden into 3rd place behind
Hailwood and Read that year by an Aussie called Tom Phillips after losing 1,000 rev at the top end.
 
worntorn said:
Re the cam choice-
Warning- 850 results ahead-

A few years back Comnoz mentioned that he had fitted a PW3 to a customer's 850.
Jim did before and after dyno runs. After fitting the PW3 there was a 6 HP loss of power in the midrange and a 2 or 3 HP gain at the top, IIRC.
The customer loved it, I guess the middle lag made the stronger top feel even better, a bit like a 2 stroke power band!
Seems likely that a PW3 in a 500 would also affect that midrange quite a lot.

Glen
Click to expand...
I believe you're right. There are a few racers/builders who have utilized the PW3 that I've spoken to, and they've all reported an increase in power in the top end with some fiddling with timing as John has mentioned in a previous post, with a lot of fiddling with exhaust and intake to fill that hole in the middle you mention, and/or a 5 or 6 speed.

That cam in the 500 only sounds good, because that motor does rev much more freely, particularly with the lighter piston/long rods. It could be pretty fun to build and run the small motor instead of thinking I can build a big cc hotrod and not get into too much trouble. The roads here are tiny and twisty, or way over capacity, so a big hotrod can't really be used to it's full potential.

I've already got a good SS cam that I'll probably use in the motor to play it safe with the relatively fragile 88ss crank. When I started this project, there were fewer time and money constraints than there are now, so less fiddling and more riding sounds better and better.
 
Bernhard said:
As far as I am aware, nobody but Nortons have made a camshaft for getting the best out of the 500 twin.
The Domiracer 500 tuned by Doug Hene for Reads IOM TT allegedly allowed it to rev to
10, 000 rpm!!. And after Read finnished with it in pratice, it was ridden into 3rd place behind
Hailwood and Read that year by an Aussie called Tom Phillips after losing 1,000 rev at the top end.
Click to expand...
That IOM motor is well known to be a completely different motor, with very few (if any) compatible parts with the road going 88. I'm certainly not chasing the ghost of the '62 Domiracer on this bike. I'm only smart enough to know that I'm far dumber than any of those engineers.

If I was intending to go nuts with a bike for the sake of racing, I'd start with my CB450 with 10 more bhp from stock.
 
Bernhard said:
As far as I am aware, nobody but Nortons have made a camshaft for getting the best out of the 500 twin.
The Domiracer 500 tuned by Doug Hene for Reads IOM TT allegedly allowed it to rev to
10, 000 rpm!!. And after Read finnished with it in pratice, it was ridden into 3rd place behind
Hailwood and Read that year by an Aussie called Tom Phillips after losing 1,000 rev at the top end.
Click to expand...
Tom Phillis.

He was the first person to do a 100 mph lap of the IOM on a pushrod bike. The Domiracer.

Also the first person to win a World Championship race on a Japanese bike. Which I didn't know until I looked him up on Wiki 5 mins ago.
 
For road use and good mid range a small bore siamese pipe into a straight thro absorption silencer works very well and makes a good racket as well. Does not look racey but if it more important to pose then its not for you. Its what the factory used on their winning production racer .
 
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