new header pipes

Looking for a new set of header pipes.
have seen stirling motor works @ commando specialties offerings...one twice the price of the other.
Any one had any experience with these ?

I bought the Commando Specialties 1.5" headpipe set and I am very satisfied. Some same the 1 3/8 pipes are better but went big.

Since the OD of those 1.5" headpipes is the same as the OD of my peashooters, the normal female/male fit is not possible, and a butt joint with a slip over coupling becomes the next option. For $7 I bought a single 1.5" automotive chromed tail pipe tip, cut it in half and cut a split down the centerline of each piece - that made two slip couplings with a two clamps per coupling. A 1" strip of beer can on the inside of the coupling but on the outside of the butted joint, seals it completely.

And I bet you had to empty the Beer Can before that too . :wink: Putting the pipe Joiner inside'd tame it for the city . But It IS usual to go for Maximum Output , as you have done . :lol: 8)

I've read that bigger (1 1/2") pipes are not necessarily better?

Dave
69S

I think they did just what you'd predict, hurt a bit at low end and moved that hurt to the high end. If riding in anger, I've gotta to watch the tach, she'll easily hit valve float in all 4 gears, 20 tooth on the countershaft.

Commando specialties pipes sound like good quality from thier specs, any one had the stirling motor works ones?
I have a 920 with CNW Keihin carb kit and o/s valves & flowed head , any views on pipe size ?
I like my bottom end torque .

Matt Spencer said:

But It IS usual to go for Maximum Output , as you have done . :lol: 8)

Click to expand...

By who ? Lotta bikes have gone down in exhaust size, gives better low down, as mentioned above.

Yes I know you can get bigger bore Commando pipes. And mufflers ?
But who rides at redline all the time ?

I do, in racing, but still on the standard pipe diameter. Bigger pipes are for those with an inferiority complex I am told- though I don't quite understand the connection..........- nothing to do with more performance if you are running a Commando-based Racer.

larger dia is lable to be freer flowing , with a lower overall pressure . Therefore heat would be evacuated conducting less to the pipe .The camshaft and porting would be more pronounced than the exhaust untill gas speed in the exhaust system became sufficent for the force of the inertia of the chage toward the end of the pipes to create peak vacum about the time
the exhaust valve opens . As they say .
Creating less tractability at lower rpms but response coordination to the throttle at higher ( upper half of ) rpm's .
Therefore requireing the correct gear to be engaged for any worthwhile change in increase in acceration .

However , combined with a generous degree of pulling back the timing at lower rpm's combined with refined atomiseation of the carburation , reasonable performace is maintained in traffic if it is kept below the revolutions at which the shock wave
from combustion is mergeing continuous in the aft exhaust system .

Generally it would require large volume expansion chamber type ' mufflers ' , the theory being , on a multi cylider
high rates , C.F.M. are achieved wist the energy / shock wave is still within the large volume exhaust system .

The triple pass peripheral discharge mufflers use this principal to a degree combined with reversal of sound waves
in a attempt to reduce the amplitude at the exit .

However , if a cascade effect is achieved at the primary section of the exit from the pipe ( header ) the pulse effect
inlet / exhaust possible with runners into and exiting the area of combustion .Feeding this area unutilised charge increases the pressure differential and enhances the effect .
Even if it does emmulate a doodlebug haveing a shaft run .

Smaller diameters and lengths may enhace this at lower rpms than the maximum .Whilst this will create a moe accomadateing power band , as the hp is effectively BMEP x RPMs , the maximum PEAK Hp figure would be obtained at the highest RPMs the BMEP is able to be obtained , cuncurrent with dimensional integredy of the workings .

To the point , where , say , the system was configured to achieve peak output about 8000 RPMs , if it initially
created excavation at say 6000 , and created no impediment below those RPMs , The Rate of INCREASE of RPMs
will still be accelerateing when the next gear is engaged at the maximum SAFE operateing speed in the pressent gear .

Or , in laymans terms , she'll go like a cut cat . And be audable for some distance, as the combustion process is
continueing aft of and outside of when the combustion chamber is closed .Also requireing some degree of attention to operate satisfactoraly .

Augmented Discharge I would think correct as to description .
The olde glass pack chambers absorb a limited form of this effect .
Noteably the ' Thruxton ' Cigar silencors ( :lol: ) for T 120s volume
being in respect of this .

As would Interstae Silencors over Roadster . A slight but discernable shift in powerband upward .Regards ' enhancement '.

So I get the impression that the standard pipes are the go unless I fork out for a special tuned exhaust system.
Any one else recently got a new set of headers , and have an opinion of them , good or bad ?

Aren't there several british bike shops in Perth - seen 2 mentioned here just recently.
What do they offer ?
Being able to potentially try them for fit and finish is worth a lot - you see some horror stories about replacement pipes...

There are 1 3/8" headpipes on racebikes to be sure but it bears noting that the headpipes in this thread are not 1 3/8"

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It is interesting to note that if you do the math on a Combat spec Norton using the formulas in "Tuning for Speed" the maximum horsepower at 6000 rpm comes with a headpipe diameter of 1 1/4 inch. Jim

I had best Combat results after some disappointing bogging set ups on 1.5" 2-1 Dustall megaphone but only after I put a plate over the end with almost 2" hole in the center. Was too boggy to hardly get to pavement and way too loud on wide open megaphone but it did come on cam nice near redline. Otherwise its hard to beat the stock set up in factory-ish Commando. There is a theory that going up a size gives less resistance d/t less boundry layer into the jet flow. The real issue on mormal-ish Cod's is the fit and finish of 1 3/8 headers.

Thanks to every one for your comments

Just be aware they come in a variety of fit and finish like a box of wrapped chocolates.