Will 850 balanced exhaust be OK on 750 (2013)

[Don Tovey]

Hi All,
just thinking of buying a balanced 850 low level interstate exhaust system & fitting it on my 750 Interstate.
My mates think it will be OK apart from the pipes can sometimes split because of the balance pipe.
They recon I may get a bit more mid range power at the expence of top end power which is fine with me.
Just looking for any other input from those that may have done the same.
My original 750 pipes are rusty & the 850 ones are brand new.
Any info welcome.
Cheers Don

 

[bwolfie]

They will fit, but from all accounts don't do it. The Balance pipe is more hassle than it's worth.

 

[drones76]

Hi All,
just thinking of buying a balanced 850 low level interstate exhaust system & fitting it on my 750 Interstate.
My mates think it will be OK apart from the pipes can sometimes split because of the balance pipe.
They recon I may get a bit more mid range power at the expence of top end power which is fine with me.
Just looking for any other input from those that may have done the same.
My original 750 pipes are rusty & the 850 ones are brand new.
Any info welcome.
Cheers Don

I went the other way on my 850. I installed a 750 system exactly because of the pipe splitting on my original set. I noticed no difference in power before and after. I think the estimate is 1hp difference. For my money it was not worth putting a crossover system back on and risking another broken pipe.

When I did change, I also changed the exhaust nuts to the 750 style.

 

[norton73]

You will also need to add the half moon shaped collets and shorter exhaust nuts to your shopping list if you go this route. I also went from a set of fractured balanced pipes to a set of 750 pipes for my '73 Interstate, barely noticable difference in midrange, but no more worrying about the possibility of fracturing the balance pipe.

Also, the balace pipe will probably rust or otherwise seize when you go to remove the pipes and you will end up taking a hacksaw to remove your system in the future.

 

[ommief]

I got in the balanced 850 pipes from British Cycle for my 73 850 build and they simply wouldn't fit, spigot angle was all wrong. My mechanic had nudged me in the direction of 750 pipes but I didn't listen to him. BC was very good about the exchange and the 750 pipes are nicely snugged up. You do have to get the 750 nuts as well. I did have to purchase a Mk III kickstart lever to clear the gear. Go with the 750 pipes.

 

[nortriubuell]

Hi All,
just thinking of buying a balanced 850 low level interstate exhaust system & fitting it on my 750 Interstate.
My mates think it will be OK apart from the pipes can sometimes split because of the balance pipe.
They recon I may get a bit more mid range power at the expence of top end power which is fine with me.
Just looking for any other input from those that may have done the same.
My original 750 pipes are rusty & the 850 ones are brand new.
Any info welcome.
Cheers Don

Noooo, don't do it Don !!! 850 type head pipes with balance pipes are nothing but trouble and grief :evil: not to mention you get even FEWER exhaust nut threads to hold the pipe in. ... unless you "like" trouble and grief :shock: and "like" to learn things the hard way. This forum is here for a reason. Cheers.

 

[mike996]

Paul Dunstall, in his book, "Norton Tuning," from the early '70's specifically states that there is power to be gained across the entire rev range (and reduced noise) with a balanced system over an unbalanced system. On page 22 his book shows a "Dunstall" balanced pipe system on a 750 motor that is essentially identical to what Norton later incorporated with the 850 motor. Crossover pipes were known to increase power at least as far back as the '60s and maybe long before that. Virtually all modern dual exhaust cars use balanced pipes because it is "free" power, though it was found that an "X" crossover pipe is better than an "H" pipe (like the Norton) so the X is commonly used now.

OTOH, the problems with Norton balanced pipes cracking/ other issues are well documented so it becomes a question of whether you want to put up with the potential hassle.

I plan on doing the same thing with my 850 and have acquired a set of NOS balanced pipes for it. I won't install them until after Xmas because I don't have the collets yet but I'm fully prepared to try it out and then, if they crack fairly quickly, just write it off as something I wanted to "experience."

 

[trident sam]

Hi All,
just thinking of buying a balanced 850 low level interstate exhaust system & fitting it on my 750 Interstate.
My mates think it will be OK apart from the pipes can sometimes split because of the balance pipe.
They recon I may get a bit more mid range power at the expence of top end power which is fine with me.
Just looking for any other input from those that may have done the same.
My original 750 pipes are rusty & the 850 ones are brand new.
Any info welcome.
Cheers Don

Don,
I've got a pair of unused low level pipes (non balanced) here that I will never use, If you want them and will pay the postage you can have them.
if you want email :- trident.sams@gmail.com , or 0151 608 3270.
sam

 

[acotrel]

Paul Dunstall, in his book, "Norton Tuning," from the early '70's specifically states that there is power to be gained across the entire rev range (and reduced noise) with a balanced system over an unbalanced system. On page 22 his book shows a "Dunstall" balanced pipe system on a 750 motor that is essentially identical to what Norton later incorporated with the 850 motor. Crossover pipes were known to increase power at least as far back as the '60s and maybe long before that. Virtually all modern dual exhaust cars use balanced pipes because it is "free" power, though it was found that an "X" crossover pipe is better than an "H" pipe (like the Norton) so the X is commonly used now.

OTOH, the problems with Norton balanced pipes cracking/ other issues are well documented so it becomes a question of whether you want to put up with the potential hassle.

I plan on doing the same thing with my 850 and have acquired a set of NOS balanced pipes for it. I won't install them until after Xmas because I don't have the collets yet but I'm fully prepared to try it out and then, if they crack fairly quickly, just write it off as something I wanted to "experience."

The crossover pipe on the Laverda 750 SFC seemed to work well, it was an 'X' under the motor. I don't believe the crossover on the 60s Triumphs did much except lower the noise. My feeling is that the crossover might give as bit more power because it gives twice the outlet for the gases, and might overcome some of the back pressure from over-restrictive mufflers which can stifle the effect of a decent cam. However the best power comes when the exhaust acts the same way as an organ pipe , it tends to make bike more top end, so I always use two into one exhaust with skinny header pipes, and larger dia. tail pipe - too loud for road use..

 

[Don Tovey]

Hi everyone. Thanks for all the replies. It looks like a big no no for the 850 balanced system as its not suitable.
Special thanks to Sam for his offer which I have accepted.
I have to say this site is brilliant with the wealth of knowledge available. Cheers Don

 

[Rohan]

Paul Dunstall, in his book, "Norton Tuning," from the early '70's specifically states that there is power to be gained across the entire rev range (and reduced noise) with a balanced system over an unbalanced system. On page 22 his book shows a "Dunstall" balanced pipe system on a 750 motor that is essentially identical to what Norton later incorporated with the 850 motor. Crossover pipes were known to increase power at least as far back as the '60s and maybe long before that. Virtually all modern dual exhaust cars use balanced pipes because it is "free" power, though it was found that an "X" crossover pipe is better than an "H" pipe (like the Norton) so the X is commonly used now.

It is very noticeable that no-one has been able to produce a dyno chart showing this 'free power' though ?
Reducing noise is perhaps more what it was about. ??

It was also noticeable that Nortons had a 2-1 pipe in the early 1960s for dommies, mostly as an option, and it DID produce more power.
And they had dyno charts to show it - but the extra power all happened over 4500 rpm.
Not exactly helpful for most riding....

Its all over and done here now, great result of forum power at work - but I'd agree too about those troublesome and pesky balance pipes.
Guaranteed to crack, as the label on the pipes should have said...

 

[mike996]

"
It is very noticeable that no-one has been able to produce a dyno chart showing this 'free power' though ?"

I agree that I have never seen a dyno test on this for a Norton. Dunstall states in his book that the balanced pipes were worth 5.8 HP at 5500 RPM over a megaphone-equipped commando motor. But he does not specifically state what, if any, power increase existed between the stock 750 exhaust/stock mufflers and the balanced pipe with stock mufflers. IOW, he seemed to be comparing a racing exhaust to the balanced pipe exhaust. He goes on to state that the megaphone-equipped engine had 2-3 more HP than the balanced system at 7000 RPM. But the 5.8 HP at 5500 is far more valuable for street riding than 2-3 HP at 7k.

But I'm going to try a balanced system just because I CAN!

 

[Matt Spencer]

Should stop the pipes flopping around , anyway .

Think its just the SFCs that had the X flow set up .

Noise Regs probly had a large part to do with it .
The Tri / Nor set up was quoted as ' increaseing low end tourque ' , closer to the head the lower rpm's it enhanced .
Obviously its a varyation on a 2 - 1 - 2 , So mufflers less strained . also breaking up the peak amplitude -
shock wave , by overlapping them . and to a degree provideing variable length tuned pipes :?
as the pulse can go the easyist path - the outlet pressure being lower & more constant . perhaps .

youd think the cross over pipe would ty the headers together and STOP them coming loose .
Doses of coppercoat regular CRC applications on bolts stop them just rotting .
Might pay to back of the cross pipe wen theyve settled in , for retourqueing flange nuts first ,
pipes aligned . Then belt crossover with a 4 x 2 before tightening the pinch bolts . :lol:

Likely half the trouble with the splitting is alignment process . Though thermal expansion obviously occurs .

maybe a piece of this , polished or chromed would solve it . And you could make up endless storys as to its purpose for telling at the pub . :wink:

 

[acotrel]

I am surprised that the two into one pipe used on the Matchless 650 CSR of about '63, actually allowed the motor to perform at higher revs. The tail pipe after the join seemed too small. It might depend on where the join is located ? I think on that model AMC had solved their problems with the twin ? (Too late ).

 

[chasbmw]

BMW airheads went from a single balance pipe to a twin pipe set up from 1981. BMW claimed increase in midrange, but it was probably done to reduce noise as BMW and the other air cooled bike manufacturers were paranoid about noise regs.

 

[mike996]

"if that pipe gave " free power " , then riding at a constant speed , you would feel the bike accelerate when opening / closing the valve no ? ."

Unless there is some load on the engine there would be no noticeable effect. Cruising along on a level road takes just a few HP. Also the effect of any mod to the intake or exhaust system affects power in a specific RPM range. So if you open/close the valve at an RPM that is not within that range, even under load, there would be no effect (either good or bad).

The way to perform the test you describe is to have the bike accelerating at WOT and kicking the valve open/closed as the bike accelerates. Since Dunstall claimed that there was a (considerable) power gain at 5500 RPM, that's the range I'd initially try. I'd have the bike in 3rd gear, go to WOT and, as the bike went through the RPM range open/close the valve, repeating the tests at say around 3500, 4500, 5500 RPM and see if I could tell any difference.

The reality is that IMO, even if there is some benefit, and I think there probably is a bit, it probably is not noticeable and, for that matter, the butt dyno is notoriously unreliable. We used to see mods done to cars where the owners raved about the increased power they could feel, only to find that on the dyno/track, the car was making less power and was slower than before the mod.

I guess the way I look at it is that Dunstall published his book with the info; unless he just flat lied about it, it seems as valid as any other publication re performance mods for specific engines/vehicles. I wish I had a dyno available; I'd love to do such a test just out of curiosity. I'd be happy to find either that there is some power to be gained OR that Paul was, as Granny used to say, "greenin' us."

 

[Bernhard]

Tried both a standard 2 into 2 exhaust and a balance pipe at the cyl head and did not notice any difference, only running bike on a dynometer will show up a couple of BHP difference.

If you really what something to show a difference that is virtually free of charge, insert a small plastic funnel on the front of the bike and run a thick rubber heating hose back from it into the airbox, you will feel an extra surge of power at 60 mph.- don’t ask me how I know!

 

[mike996]

You gotta watch those "surges."

From my experience, a surge of power is often caused because there is a flat spot in the acceleration curve to that point and the surge feels like added power where, in reality the engine is just recovering from the loss in the rev range below that point. That was a typical issue with people putting larger carbs on cars and no other mods. They would get this big surge as the engine finally caught up with the carb and remark on all the power they were now getting. Dyno tests inevitably showed that the engine now had a big hole in the power curve compared to stock below that RPM. The car "felt" faster because of the surge but was actually slower.

Not saying the "funnel bike" is either faster or slower than stock but sometimes things are not as they seem!

 

[Matt Spencer]

Tried both a standard 2 into 2 exhaust and a balance pipe at the cyl head and did not notice any difference, only running bike on a dynometer will show up a couple of BHP difference.
===============================================================
If you really what something to show a difference that is virtually free of charge, insert a small plastic funnel on the front of the bike and run a thick rubber heating hose back from it into the airbox, you will feel an extra surge of power at 60 mph.- don’t ask me how I know!

==========

Can be tricky . most dynos wont do 60 mph . 8) point to point & a stop watch can be usefull , if its a quiet area . put in a datum for repeatability & use a few shiney paint tins . do 40 to 60 or whatever .

 

[mike996]

"To keep the bike at a constant speed at 5000 RPM , the engine has to produce x hp ."

Sure it has to produce some HP to hold the speed but the carb slides are at some minimal opening so there is no more air available to add power so it can't make any difference. To make more power you have to flow more air. If you don't provide the additional air on the input end, you can't move any more using the output end.

So basically the only way you can measure something like that is with the bike at WOT so that maximum air/fuel is accessible to the engine. THEN, if the pipe helps somewhere in the rev range, it can actually demonstrate whatever it can or cannot do. The engine has to be loaded to check power output. On an inertia dyno you can only do WOT runs, you can't load/hold the engine at some specific RPM which is a much better way to evaluate such stuff.

Of course, the BEST way to evaluate power changes is on the track but that takes a lot more time. I have seen a car/engine show power increases on the dyno and the same car/engine show a power DECREASE on the track due to airflow differences in the intake system based on the difference between sitting on a dyno and moving at 70+ mph.