Pipes and Carburetion

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Nov 21, 2004
:?: 1. What is the most used pipe today and why?
2. Has anybody have any 2 into 1 pipe systems and if so whats the
torque like ?
3. kenny's new bike has a 2 into 1 back into 2 pipe system, anybody
try that before?
4.What performance mods can one do to Amal's, or is it a waste of
time ?
Johnny Rocket said:
2. Has anybody have any 2 into 1 pipe systems and if so whats the
torque like ?

Paul Dunstall's original performance header muffler combo in the 70's was a 2-1-2, researched and developed with a chap called Dr. Blair.
I ran this system on a stock, low compression 850.
If memory serves me right, it was a little weaker off idle came on stronger in the mid and finished harder. It also was able to handle a larger main, I believe a 270. This all happened about 30 yrs ago by a kid who thought he knew what he was doing, but not necessarily so.
The system had maintenace issues. It was a bolt together and with the iso engine, you had to tighten everything up about every 100 mi. The other problem was the center pipe hung low enough to scrape speed bumps there by flattening out. You also lost the center stand, when you store a Norton on a side stand gives all kinds of grief.
With that said I thought I would never want to do it again, however I do have a full set in the rafters and this Combat over in the corner...
:D MichaelB,

Thanks for the reply I'm surprized that more poeple have'nt played with exhaust systems. Since this posting I've tracked down a set of Dunatall 2-1-2 systems. We have a 920 that we're playing with some time here before Christmas we'll be fabricating diffrent pipe diameter system 1-3/8, 1-5/8, 1-3/4 and a taperd 2'',it'll be intresting on the dyno what the diffrent arangment do for torque. Also we'll have to see what they do on the 750 too.

Johnny Rocket

how long have you had your 920 running? I was thinking of doing a mid range torque motor that peeks no higher than 6500 rpm MAX. I am leary of the 920 because of the head gasket and want more info on reliability before I jump on that. like dave asked what cam are you using? I was thinking of something like combat but with more lift. as for exhaust if I rember right kenney dreer found that he needed larger head pipes on his 880cc motors and used 1 5/8. like the other post the dunstall system would fall apart going down the road but I felt like it made more mid range power bit again I was a know it all 20 year old.

PS where are you located???

Johnny, One of the issues with the exhaust is the stock Norton exhaust is such a thing of beauty. It blends so well with beautiful curves of the bike. S style or Roadster. The actual original S exhaust was freer flowing than the Roadster and the repop S muffs. What I've been told is it had a different type baffle and it was louder. I suspect it had more of a perferated baffle verses the elongated reversed punched type of the reverse cone muffs.

Exhaust does make a difference. 30 yrs. ago I was tired of the Dunstall header falling apart so I reinstalled the stock header pipes and muffs. The I installed the dunstall muffs. Instantly smoother idle, quicker revs. Same stock 260 main.
However I always thought the stock exhaust was the nicest looking. (Yes Dave it was a Roadster).

Some people have done some work. Of course Kenny Dreer, Clubman Racing lists a perfromance 1 5/8" with a longer head pipe and a 1 5/8 performance muffler, I think BUB makes a 2-1, Viking makes a 2-1. The list is pretty short.
I am always interested in performance and am curious about your results.
Are you working with different baffle designs also??
:D Bill,

How's it going eh? Cool chopper, I see your a tranny guy, I used to work in the heavy duty industry rebuilding power shifts , I've done some auto tranny but not much. go to the More Power posting there's some 920 stuff there. Where are we located ?

The Great White North, Edmonton Alberta, Canada
The hockey capital of the world !!! This is were the
Great One got his start, Did you hear about the
Heritage Classic game The old Oilers still have
Chemistry we kicked Montreal's ass, Ha Ha Ha


Yes your right about the muffler looks , I'm sure that was a factor in Kenny's new 952, but it dosen't sound good on the computer
My thoughts on the exhaust system is to maintain the original looks but have modern performance and sound, something that sounds deeper yet easy on the ears. I've got a muffler design that incorporates pulses canceling each other out but we'll have to build a prototype first. I dont see much new technology out for the classics, exhaust design has come along way since the 60's there's new material and construction technology.
I'm sure we'll learn something in the next coming months.

Johnn Rocket

great weather down here but we are supposed to have a cold front come through with low 40's :lol: might go for a ride this weekend.the chopper is almost done I sent parts to the chrome and paint shop this week. when I get them back it's put it togather and wire it. the guy that I am building it for was like a kid in a candy store when he took the stuff to be plated and painted. this thing was in his closet for 26 years but all he had was a power unit and frame with rusty wheels. I had to make anything that was a non stock part but like I told him it wont be like the other brand chop in a box bikes!! like they say IF YOU BOUGHT IT IT'S NOT CUSTOM.
I will update the web site when I have newer pic's with it done.

:? I had a chance to thoroughly inspect the Dunstall 2-1-2 exhaust system today, I like the theory. The construction I guess is evident of the time period, the welding looks like a tig weld, I can't say the pipe angles are what they should be, they're to sharp. We'll see what they do on the dyno, they will definatly have an effect on the power curve over stock exhaust systems. We'll defiantly learn something here.

Johnny Rocket
In the original paperwork with Dunstall pipes, they talked about the system being tuneable. With the slip connections one was supposed to be able to 'tune' the engine by varying the header lengths and the center pipe connection. With my limited abilities it appeared to run a little stronger with the center slipped down, lengthening the headers. this however made it more prone to hitting speed bumps etc.
Good luck, I am very interested in your results.
I have been lurking about for a couple of months and finally joined recently.
I havn't been without a Norton of some sort since 1966 and have been through most of the issues on this list, although there are some I admit, that I am suprised by and are news to me.
I ran a 2-1-2 Dunstall for 8 years on a Combat and later on a 850 with great success, that is, once installed properly, there was never an issue of having to adjust the fittings every 100 miles or every 1000 miles. As to the loss of the center stand, you could purchase the Dunstall stand which mounted to the crankcase bolts via a crude two piece alloy bracket, which I still have. As far as a performance increase, that is hard to quantify in hard numbers, as I never bothered with a dyno, as if there was one available. All I know was that I was always in front before Dunstallisation and after.
In the mid 80's I used a Norvil based system, tightly bent pipes, with open megas, except for about 5 inches of fiberglass near the reverse cone. The pipes where 1.75 od. Along with this I installed 36mm Del'orto Pumpers on a Combat head modified by Duwayne Williams of Lakeland Fl. He was a founder of the FGPRRA. This combo would pull 7500 rpm in a heart beat with a 21 tooth sprocket in 4th gear. Again, I never saw a dyno so no real data. So, yea, I am really interested in seeing some hard numbers and testing. And yea, I still ride them hard at 57.

I went through exhaust hell with my Commando about 2 years ago.

I started with a stock system and it was great. I wanted to try something different as the chrome was getting bad.

So I ordered a 2 into 1 from Viking exhausts. It sounded terrible and hit the ground on right handers. I jetted accordingly (down jetted a bit), what ever I did the performance sucked. The exhaust had a bad weld and ended up splitting, so I returned it.

On the return deal, because I was still on a mission, I shipped it back and did a deal so they would send me a complete 1 5/8 system. Headers and tail pipes. (I run 34 MM amal MK11's). I jetted accordingly. Again it sounded terrible, lost the Commando growl, and performance was OK but lost a bit of topend. Problem was it was too heavy, and within 300 miles the weld had split on both tail pipes, and chrome was peeling off. The extra weight on tail pipes flexed the headers and possibly damaged threads. ( I have my shims real tight, so hate to think how this would have been with sloppy shims!)

After much complaining Viking sent me standard exhaust system complete, and warranted the chrome. It has been on ever since and perfect (2 years) except I have a dodgy R/H thread in Ex port, that requires attention. I suspect due to me being frustrated while R/R ex. or heavy 1 5/8 system flexing.

I have photos of all this, if anyone is interested I'll post here. Let me know,

Jerry, glad you posted the info on Viking, we had thought about ordering up a 2-1 set. Viking must use very thick wall tubing to make that much difference in total system weight. I order plain thin wall 180's and 90's for system construction in that size and havn't observed that issue.
Is Viking located in U.S., or is it offshore?

An Old Zealand mob.

Were u the "Jerry" tah offered a pattern for the "Dunstall" centre stand plates ? I lost your email !

If you can help, please sned a cardboard pattern to:
Reg Ellis
C/o Wavell Heights P.O.
150 Hamilton Rd.
Wavell Heights. 4012.
Queensland, Australia.

It would be much appreciated.

With Thanks,

They are in NZ.

I think they do a good job overall and dont want to run down their services or products.

They took care of me at the end of the day!

I am not sure if they use thicker steel or if there is more of it due to the extra size. The steel was thin where it split, and the weld was not complete.

I noticed the split when I sliced my finger open on it while cleaning my bike! :!:
I havent heard duwayne's name to often lately, but he sure built some fast nortons back in the 70's & 80's. the only trouble was not if but when it would expload. I here that he is still around doing some head work. he did a set of 8valve ducati heads for a friend a few years back.

I take it you are from fla and retreated from what it has become here. a lot of old timers are heading up your way and I am one that is looking to go SOON!!

katescottageiom said:
I ran a 2-1-2 Dunstall for 8 years on a Combat and later on a 850 with great success, that is, once installed properly, there was never an issue of having to adjust the fittings every 100 miles or every 1000 miles.

Welcome Jerry,
My first Norton was such a bittersweet experience, I always wondered if it was my inexperienced, youthful exuberance that caused my problems. I have already proven to myself that most of them were. The one thing I haven't exorcised is the Dunstall 2-1-2 pipe system.
I have only met two other people who have run this system and their experience was not unlike mine. 100mi may be on the short side, but there was always constant fiddling.
Your post has given me hope as I have a set stashed in the rafters. But I am not going to do it till I have a way to store the bike in an upright position.

Keep on, keeping on!!
Bill, I lived in Orlando in the Pine Hills area and then in Sanford.

I moved to Atlanta in the mid 70's; purchased a "retreat" on 7.5 acres in the 80's and moved in permanantly in 1990.

Believe it or not, one of the major draws for me was the close proximity of some of the best "racing " public roads to be found on this side of the Pond, and ofcourse, the great people.

On my way to work I can hit at least the ton on a regular basis, and find out very quickly what modifications actually work.

If you need some help or information about this area, contact me or you can go to my website. I am a Real Estate broker.
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