2 in 1 exhaust system (2010)

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GRM 450 said:
Maybe it's the pumps squirting too much at off to on throttle when you are warming it up ? A squirt every throttle blip and no full throttle to clear it ?
Maybe try turning the pump down or disconnecting them, or different slide/pump ramps ?

graeme
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I've disconnected them. Took the levers out. Definitely a step in the right direction, but still not right.
 
John,

I didn't keep track of the needle and needle jet numbers in my normal race day data sheets, but I'll see if I can find them in my other notes. I bought the carbs new from Ron Wood, the local Dellorto distributor, and never changed the needles or needle jets, so they still have whatever was original.

Ken
 
John, I can give you the specs for 40mm with pumps for 750 Ducati, and 36mm without pump for 450 single if that's any help.
My single does not like Shell for some reason, don't know why, but it just stuffs plugs. (premium pump fuel)

graeme
 
GRM 450 said:
John, I can give you the specs for 40mm with pumps for 750 Ducati, and 36mm without pump for 450 single if that's any help.
My single does not like Shell for some reason, don't know why, but it just stuffs plugs. (premium pump fuel)

graeme
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Any help appreciated. I already have specs for 40mms on my BM, but the 36mm specs would be handy.

Having seen how close I am to Ken's specs, and bearing in mind that the dealers ( in UK) who sold the carbs were told the engine specs and jetted them accordingly, I'm beginning to wonder if I should be looking for a different problem.
 
John,

450 single,
For 98 premium unleaded pump fueel, 36mm 135 main, K6 needle middle knotch, 70/4 slide the rest is the same as you have (pump is worn out and dribbles only) so basicaly no pump.

Old days with BP 100 avgas, 36mm 135 main, K6 needle, 70/2 slide. with pump. (for leaded super 125 main) Long time ago.

graeme
 
John,

I found the rest of my notes about my 34 mm Dellorto carbs. They have the same AB265 needle jet you are using, but K3 needles. As originally set up, the carbs came with 60 slides, K3 needles, AB265 needle jet, 145 main jet, and 70 pilot jet. My first race with them was at Daytona, and I had to drop the needle down to the top groove to get it to stop blubbering badly on acceleration. It would run ok once it got to 6000 or so, but would barely run on open throttle below that. After I changed the pilot to a 65 and raised the needle backup to the middle groove, it ran much better. Trimming the slide down to about a 54 cutaway really helped the low speed response, and I eventually worked down to smaller main jets, and that's pretty much where it's been for the last couple decades.

In my previous post, I said the slide was between a 40 and 50 cutaway, but it's actually between a 50 and 60 cutaway. Sorry for the confusion. I've edited the post to correct it. You mentioned that you had a "40 slide, that I had machined to 55". I'm guessing you meant a 60 slide cut down to a 55, which is really close to what I've been using.

Ken
 
lcrken said:
John,

I found the rest of my notes about my 34 mm Dellorto carbs. They have the same AB265 needle jet you are using, but K3 needles. As originally set up, the carbs came with 60 slides, K3 needles, AB265 needle jet, 145 main jet, and 70 pilot jet. My first race with them was at Daytona, and I had to drop the needle down to the top groove to get it to stop blubbering badly on acceleration. It would run ok once it got to 6000 or so, but would barely run on open throttle below that. After I changed the pilot to a 65 and raised the needle backup to the middle groove, it ran much better. Trimming the slide down to about a 54 cutaway really helped the low speed response, and I eventually worked down to smaller main jets, and that's pretty much where it's been for the last couple decades.

In my previous post, I said the slide was between a 40 and 50 cutaway, but it's actually between a 50 and 60 cutaway. Sorry for the confusion. I've edited the post to correct it. You mentioned that you had a "40 slide, that I had machined to 55". I'm guessing you meant a 60 slide cut down to a 55, which is really close to what I've been using.

Ken
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Hmm. I've looked at the specs of the needles and mine is a little weaker at the bottom end than yours. The slide was a 40 and I had the cutway machined higher to make it a 55.
the whole situation is so close to yours and although mine is a mild tune, ( 10.5 comp, Axtell 5S cam , standard size valves, supertrapp exhaust) I think I must be missing something.

I had a chat with a drag racing friend who made a telling comment. "If you've got a carburation problem that doesn't make sense, look at the ignition"

Even though it works OK with the Amals there is a chance that an ignition weakness may show up with different carbs.

I have the chance of a track day next month, and I think I'll take a box of jets and needles and do some serious testing.

Thanks for the advice. I think we've hijacked someone else's thread here so I'll get some testing done and start a new thread when I have something to report.

Meantime, here's my favourite toy

2 in 1 exhaust system (2010)
 
Nice looking bike. Please do let us know how the track day works out (in a new post, of course :D ).

Ken
 
I notice that with the Maney two into one exhaust system the header pipe diameters look larger than on my own bike. Does that adversely affect the throttle response ? On my own bike, the ID of the header pipes exactly matches the ID of the stubs which matches the ID of the exit of the port - i.e. NO STEP.
Somebody posted above that they lost midrange when fitting a 2 into 1 pipe - I found that happened when the outlet of the collector was too small. My tail pipe diameter is a diameter which give the total cross-sectional are of the two header pipes - NO RESTRICTION.
 
Exhaust pipes are 1 5/8" OD, and cause no problems with throttle response in the rpm range we used on the race bikes (5000 to 7000 rpm, or 7500 with the short stroke). The exhaust port diameter is smaller than the exhaust pipe ID, and works quite well that way.

Ken
 
I have a bit of a theory that when the first commandos were built, the cam design preceded the design of the exhaust system. And the cams were ably derived from Norton's experience with the SOHC Manx, Then the exhaust system was created to shut up the noise. Also best performance doesn't necessarily coincide with what you get when you set the cam up to the marks. And that particularly applies to the 2 into one exhaust systems.
 
acotrel said:
I have a bit of a theory that when the first commandos were built, the cam design preceded the design of the exhaust system. And the cams were ably derived from Norton's experience with the SOHC Manx, Then the exhaust system was created to shut up the noise. Also best performance doesn't necessarily coincide with what you get when you set the cam up to the marks. And that particularly applies to the 2 into one exhaust systems.
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So, let me get your hypothesis clear: Norton, despite nearly two decades of experience building twin cylinder pushrod twins, including a few years of experience building a near identical 750cc pushrod road going twin to the Commando engine... threw away all of this and based the Commando cam design on their 350 and 500cc overhead cam Grand Prix racing engines...!?I

I struggle to understand why they would do this, and have to ask, what evidence are you basing your hypothesis upon?

And, can you please help me understand the link between 500 and 350cc overhead cam SINGLE cylinder cam design and 2:1 exhaust systems...?
 
The question in my mind is about where the cam for the Tom Phillis Domiracer came from. I suggest that there were probably two types of cam in twin cylinder Nortons as there are in old Triumph twins - the road cams and the race cams. So the question is where did Peter Williams get the cam design for the commando. The next thing is that I am certain that for a 2 into one pipe the exhaust valve timing must be different from that used with twin pipes. If you try to get more torque by advancing the cam so the inlet opens earlier, the error in the exhaust valve timing compensates in part for the more restrictive pipe. The object of the exercise is to set up the standing wave in the pipe easily. With my own pipe there is not even a trace of megaphonitis or a 'cam spot'. Why only complaint is that it is too loud, which to my mind means the exhaust opening point is probably not at the optimum - lost energy. With a Triumph twin the problem is easily fixed as the cams are separate. The trouble I have with the commando engine is that it seems most guys simply fit the cam to the marks and use separate pipes. As far as I can see only one person besides myself has mentioned the effect on torque of advancing the cam. So who has done the experimentation, Eddie - yourself ? How many times have you changed cam timing and exhaust pipe configuration ? And I am not talking about dyno tuning - what you see is not necessarily what you get when you ride the bike.
 
acotrel said:
The question in my mind is about where the cam for the Tom Phillis Domiracer came from. I suggest that there were probably two types of cam in twin cylinder Nortons as there are in old Triumph twins - the road cams and the race cams. So the question is where did Peter Williams get the cam design for the commando. The next thing is that I am certain that for a 2 into one pipe the exhaust valve timing must be different from that used with twin pipes. If you try to get more torque by advancing the cam so the inlet opens earlier, the error in the exhaust valve timing compensates in part for the more restrictive pipe. The object of the exercise is to set up the standing wave in the pipe easily. With my own pipe there is not even a trace of megaphonitis or a 'cam spot'. Why only complaint is that it is too loud, which to my mind means the exhaust opening point is probably not at the optimum - lost energy. With a Triumph twin the problem is easily fixed as the cams are separate. The trouble I have with the commando engine is that it seems most guys simply fit the cam to the marks and use separate pipes. As far as I can see only one person besides myself has mentioned the effect on torque of advancing the cam. So who has done the experimentation, Eddie - yourself ? How many times have you changed cam timing and exhaust pipe configuration ? And I am not talking about dyno tuning - what you see is not necessarily what you get when you ride the bike.
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Well, I haven't done any experiments with cam timing on my Norton. Lots with exhausts and other stuff but not cam timing. Its set up as per JS instructions and seems to work very well. So to be very honest, given the faffing around it takes to do this on a Norton, and the inherent compromise situation, I do not intend to.

As I have said before, I personally cannot see the point in trying to design a 2:1 system when Steve Maney has already done such an outstanding job of this. His system boosted mid range and top end on mine, noticeably so. I don't think I've ever heard anyone say anything different either. I'm not saying that no one else should re invent this particular wheel if they so choose. But to do it properly is a real can of worms, and I'm too lazy, I'll just follow Steves lead!

By the way, I am totally with you re Triumphs. I used to run different cam timing for different tracks when I was really keen!

I wasn't aware that Peter Williams designed the Commando cam for '68 either, in fact I didn't think he was even at Norton then... I thought his input was with racing cams, not the stock cam.
 
acotrel said:
So the question is where did Peter Williams get the cam design for the commando.
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I believe the "SS" Atlas/Dominator performance cam, that won several Thruxton Races in the early 1960's, became the standard 1S cam in Commandos. If others know differently please correct.
 
To answer your question about where PW got the Commando cam design, he didn't get it anywhere, because he didn't design it.

Peter Williams didn't go to work for Norton until November or December 1967, working in the drawing office, so he couldn't have been involved in cam design for the Commando, which, as WZ507 pointed out, used the same profile as the old SS high performance cam from the pre-Commando twins. He appears to have been involved in the design of the 4S racing cam for the short stroke 750 in '73, and eventually did his own design, the PW3, which he designed for Mick Hemmings and Norman White in the mid or late '80s. He was laid off at Norton in 1975, and went to work in the racing drawing shop at Cosworth the following year. He worked on the design of a variety of engines there, and learned what he called "the Cosworth formula" of cam design, which he said he used in designing the PW3. I bought one of the first PW3 cams from Norman White during a visit to his shop in 1988, and he told me the story of how he and Mick Hemmings commissioned Peter to do the design. An interesting side note is that when I plotted the cam profile I noticed that it looked very much like the Axtell #3 grind, except for not having the flat top that Axtell used on the lobes.

Ken
 
acotrel said:
I have a bit of a theory that when the first commandos were built, the cam design preceded the design of the exhaust system. And the cams were ably derived from Norton's experience with the SOHC Manx,
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That is a wild claim Alan, that you haven't researched much ?
sohc cams used lever followers, and the profiles and timing are RATHER different to the bumpsticks on the twins.
Since they didn't rev much, cammy singles used high gearing to TORQUE their way around the track....

2 in 1 exhaust system (2010)


The manxs did know much about getting the inlet valve open good and early, and optimised pulse tuning etc...

And as others have already pointed out, the Commandos' cam came straight from the earlier SS dommies and Atlas.
 
I believe that Peter Williams based some of his camshaft development on the work his father had done on the G50 Matchless and AJS7R. He certainly wasn't involved in the production Commando camshaft. Buy his book.
 
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