Which Exhaust is Best for Low-End Torque?

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The cam, exhaust and gearing work together. The usual aim is to get more power. Some high-powered motorcycles use Exup which is controlled butterfly valve in the exhaust. It is supposed to increase torque, however race cams make the exhaust system work harder. I suspect Exup is used to defeat the noise, so that hotter cams can be used - giving an overall increase in torque. My 2 into 1 exhaust system with the cam advanced 12 degrees, pulls hard from low revs to high revs, however the noise is appalling. With any form of restriction, it is normal to lose power at the top of the rev range. With race cams, pulling from low revs is usually weaker until they really start to work. In the scheme of things, a normal Commando cam is a race cam. There might be cams which were used in Dominators which were more docile and quieter.
The history of Triumph 650s was a progression from mild to hot cams, and Nortons are probably similar. Not many Triumph Bonnevilles of the 1960s had the E3134 race cams on both inlet and exhaust. Most guys probably did not know there was an E3134 profile cam with the extension for the points which has a different number. I think it was used in the 650cc Thruxton Bonneville. Most Bonnevilles had the Tiger110 cam grind on the exhaust - E3275. You would not think a race cam on the exhaust would make much difference to performance - however it does - at the expense of bottom end power and noise.
 
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Welcome. As mentioned, put tractor cogs in. 19T

Are you referring to a 750? 850?
Year? Model?
 
Trying to make a Norton Commando more docile and usable in traffic was probably an objective, however Peter Williams was a road-racer. A Commando is a detuned Atlas. And probably better for that. With most old motorcycles, if you ride them away from a stand-still without using much throttle and feel what is happening as the revs rise, you will feel a surge of power as the cams begin to work with the exhaust system. With a bike with race cams on both inlet and exhaust, the power band often begins at 4000 RPM. A milder cam on the exhaust makes it less pronounced and improves bottom end. It is timings and not lift which is important. A higher lift cam does not change the shape of the power curve.
 
The first time I ride any motorcycle on a race track, I feel which way it turns if I gas it when on a lean. I also feel where the powerband is in the rev range. If the power band is high and the bike does not over-steer when you gas it, you can get into trouble in corners. You do not have to be riding the bike fast to find out what it does - it is much better to find out when you are riding the bike slowly. I only ever ride slow motorcycles, I just ride them a bit faster.
 
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acotrel said:
Trying to make a Norton Commando more docile and usable in traffic was probably an objective, however Peter Williams was a road-racer. A Commando is a detuned Atlas. And probably better for that. With most old motorcycles, if you ride them away from a stand-still without using much throttle and feel what is happening as the revs rise, you will feel a surge of power as the cams begin to work with the exhaust system. With a bike with race cams on both inlet and exhaust, the power band often begins at 4000 RPM. A milder cam on the exhaust makes it less pronounced and improves bottom end. It is timings and not lift which is important. A higher lift cam does not change the shape of the power curve.
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FFS
How many more times are you going to trot out the same WRONG information
How can a commando engine be a detuned atlas engine????
When an atlas has low compression concave pistons???????
Absolutely bloody ridiculous
I suppose a combat engine is in an even lower state of tune!!!?
I wouldn't mind if we didn't have to go through this over and over again
 
For your info...The first thing to do for an Atlas is to run the biggest hole saw down the muffler and remove the colossal restriction. Now it can be tuned better and make a bit more power.
 
Noahsmith said:

Need better acceleration at low RPMs, especially for city riding. Any suggestions for motorcycle exhausts that enhance low-end power​

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I realise it's not what you asked (and this'll have potential to open up the single versus twin carbs debate yet again)
But a single carb gives great bottom end power
And for city riding just how quick do you need to accelerate?
A standard commando is no slouch off the line
 
I run Cocktail shaker mufflers on my 850 Norton with 1/2 baffles they work very well at low RPMs and gives very quick response when I open the throttle from low to high RPMs, but then my motor is not stock and built to breath and get the exhaust out fast, they perform great and sound great, I been running these type of mufflers since the early 80s, I gave up on stock mufflers a long time ago and also ran Dunstall muffler for a few years in the late 70s, but the shorter open mufflers work best for my Norton, but the best mufflers I ever ran was a set of Cambell short reverse cone mufflers, they work best for low down and performance but I ended up putting them on my old Triumph and sold the bike with them on, what a big mistake I did selling that bike with the reverse cone mufflers on as I originally brought them for the Norton.
 
For low RPM acceleration, the stock exhaust is hard to improve on.
High test gas with higher compression or more ignition advance . . . .
 
Info on cam timing parts.

JSM stepped key for the cam sprocket gives 2 degrees advance or retard, but the change is subtle.

RGM sells an adjustable degree cam sprocket keyway slotted for various combinations of advanced or retarded cam timing.

Stock exhaust is probably best, but I really have no idea. I have not ridden a Commando with stock exhaust since 1985. :)
 
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