Tinkering with exhaust

Status
Not open for further replies.

jbruney

VIP MEMBER
Joined
Jan 5, 2019
Messages
2,264
Country flag
I shed my stock exhaust on the 850 many moons ago and installed the 750 type with no balance pipe, also at this time dumped the ratty holed pea shooters for some shorty muffs. These have been gutted for years and are truly loud when the right hand is fully twisted.... Well I thought it to be running great, although always staying a might rich and noise fatigue being awful after 30 or so miles.... The crux of the biscuit now... Last week welded 7" extensions onto mufflers thereby taking them 3" past rear axle... Still very loud, but perceived noise is not noticeable when riding. Added to this the slightly rich situation has practically vanished, and most impressive is that the acceleration seems to have increased quite a bit.... Tell me it's my imagination and that I just like the drop in noise level.... I'm getting older now and therefore could be imagining all of this perhaps as senility and wishful thinking consume my grey matter.
 
Perhaps, but I sure like the wild roar being kinda behind me. I had forgotten the sound of my motor at 5k going down the road..... It still sounds like a Norton and all that entails.
 
When you get the valve timing and exhaust system which deliver best power, the bike is usually too loud. I doubt that Exup on modern bikes is about providing more midrange power, but more about noise. If you change to a hotter cam you often get more torque right across the usable rev range. Exup probably cuts the top off the power curve, but midrange is still better than it might have been without the hotter cam. In Australia, many guys simply remove the Exup and live with the noise.
 
You must study in 'Joe's Garage' for the answer you seek.
 
Funny, I'm actually watching 'The Torture Never Stops' on Quello , New York Halloween concert from 1981 filmed Live at The Palladium, a 2hr tour of the great man's music :)

Hmm, possibly a subconscious choice given the title ;)
 
When in my early teens an older friend and scooter mentor who was a Bandido taught me an appreciation of FZ's music and the relationship it has to motorcycling at WOT. Been warped ever since.
 
Funny, I'm actually watching 'The Torture Never Stops' on Quello , New York Halloween concert from 1981 filmed Live at The Palladium, a 2hr tour of the great man's music :)

Hmm, possibly a subconscious choice given the title ;)
The great man. Justin Bieber?
 
this is a question only the central scrutinizer can answer.....the man is from my home town !
 
Jacking with the exhaust was just part of my 1000mi. round of maintenance & improvement assault on my Commando. Clutch/primary, drive chain/sprocket, trans oil, fork oil, etc. Still have motor oil/filter this week & tank flush...… Someday the ominous layshaft bearing.
As a reward I am lead to understand I shall receive a ride today. I hope your machines are as pleased with you.... Via con Dios amigos.
 
"Tell me it's my imagination and that I just like the drop in noise level...."

Well, assuming it's not your imagination, REMEMBER - you modified the exhaust originally by installing the 750-type pipes on an 850 which came with a different (balanced) exhaust. SO...if you are saying that the mods you made improved the performance of the wrong (750) exhaust on an 850, that's reasonable. But I'd bet you would find that the 850 balanced exhaust that the bike came with does at least that well... ;)

OTOH, for those not wanting to deal with the balanced exhaust, your mod sounds like it might be a good thing. I would have attributed the "improvement" to imagination and/or the almost always wrong butt dyno however, the change in the mixture you mentioned shows that there is definitely a difference!
 
If you have a motor which revs to 10,500 RPM with separate pipes and you fit a 2 into 1 system, you can lose 1000 RPM off the top of the usable rev range, but noticeably fatten the midrange. When you fit a more restrictive exhaust system, you usually just lose a bit off the top. In both cases, the jetting will change.
 
Those pipes went on back then because they were all the Norton dealer could lay hands on. The mufflers were a lost cause therefore the aftermarkets. Also didn't notice much difference in performance but still knew little about the machine back then. What I do know for certain is that something has definitely improved; diminished richness & more of a fast snap between 4k-6k. Bike is in more of a hurry & have to be watchful of the old motor. I ride this daily and poke it good at least once each time, and what I'm saying is it's noticeable. I believe it's only a matter of luck in getting it to breathing more closely to the way it was meant to when all I intended was moving the thunder aft.
 
Those pipes went on back then because they were all the Norton dealer could lay hands on. The mufflers were a lost cause therefore the aftermarkets. Also didn't notice much difference in performance but still knew little about the machine back then. What I do know for certain is that something has definitely improved; diminished richness & more of a fast snap between 4k-6k. Bike is in more of a hurry & have to be watchful of the old motor. I ride this daily and poke it good at least once each time, and what I'm saying is it's noticeable. I believe it's only a matter of luck in getting it to breathing more closely to the way it was meant to when all I intended was moving the thunder aft.


You say the change in performance is noticeable - but if you improve torque, you often will not notice an improvement until you raise the overall gearing. What you lose off the top can reappear lower down in the rev range, and you might not feel it. The 750 and 850 Commandos are different concepts as far as power delivery is concerned. The 750 is probably more of a top end motor where the 850 is designed to pull harder. Ashley has the 2s Combat cam in his 850, it would be interesting to know what pipes and jetting he uses.
 
It's not like I have to hang on for dear life.. It's just that there's something that wasn't there prior to the change, and it seems for the most part to be right at that point. At almost 25k this motor only touches 6 for a moment and back off, however it feels as eager as it did 40 years ago. I just thought it to be a pleasant surprise to have a minor improvement which was unexpected.
 
Tuning a race bike is easier than tuning a road bike. With a race bike, because the corners and straights repeat all the time you are practising, it is easier to pick up if you have made an improvement. You can tell when you are doing things faster or easier. On public roads you get the same effects from tuning, but it is more difficult to tell. What your experience says to me, is you have good feel for what your bike is doing. Many guys who race, do not have that level of sensitivity. When you are developing a bike for racing, it is extremely important. You spend a lot of time going round and round in circles, taking note of what is happening.
 
"I believe it's only a matter of luck in getting it to breathing more closely to the way it was meant to when all I intended was moving the thunder aft."

The way it was "meant to" is with the balanced pipe, as delivered from the factory and as noted in the Norton tuning manual as the optimum exhaust for the engine. So until you do the the same "test" with the OEM balanced pipe, you can't say that the changes made are 'better' than stock since 'stock' was with the balanced pipe.

I'm pretty confident you would find the balanced pipe to be at least the equal of the 'extended' pipe.
 
Mike I'm sure it would be better, but that's not really what I was after because the old girl does very well by me. Besides I like the shortcut when having to remove the system too, also easier for me with my setting by ear methods which will probably be with me until I die.
However when I replace these the whole system shall go back to stock for when the grandson gets it, but right now it works and I'm having fun aplenty with the angry bitch.
 
Status
Not open for further replies.
Back
Top