What type of exhaust for power. (2019)

Would twin exhaust pipes help the engine to make more power than a two into one?

Has anyone got any dimensions for a successful twin pipe design?

Current set up is:

Maney stage 3 head
JS stage 2 cam and followers
JS rods and pistons
Maney (Minnovation) 2 into 1
36mm carbs
rev limit set to 7200rpm
920cc

Is it harder to get the noise level down to 105db with twin pipes?

I guess that if more power is available then it will be further up the rev range and the power band smaller, but would this be a big problem with a 920?

Thanks Ralph.

Ralph, There is a poster on here, Snotzo, who models engines with ancilliaries using the Blair software set.

He has modelled my exhaust and compared it with the Steve Maney design. It isn't really a question of making more or less power but rather a trade off in where you make it. It is pretty even and you are unlikely to improve much, certainly on a cost benefit scale you will be better off using what you have.

As for dimesions, they are no mystery and carry over from '70s works Norton experience with minor variation. Nigel at NRP has a good insight into what is needed having made both Maney style an separate systems. If you want to try it he will build a sytem on your bike and is highly recommended.

You may have seen that in the past Watson used Maney style on the 920/960/1007 bike and separate pipes on the 750, but this was because the Maney system doesn't work with a 90/270 degree crank which the smaller bike used. Nigel made all of Watson's exhausts and he makes stuff for Minnovation!

And seriously, are you short of power?

You might get a little benefit at noise testing, simply because the total volume of silencer you use can be greater.

Though it has to be said that at UK noise tests I have been close at times too. French and Belgian ones have been less of a worry!

My limited dyno testing of exhausts definitely found the Maney system best when using a long duration cam.

Standard 1 3/8 pipes and peashooters were good but gave away quite a bit of mid range.

1 1/2 pipes didn’t work well at all.

Various long tapered open Megas I had from previous jobs (some worked awesome on Triumphs and Nourish motors) didn’t work well either.

With less duration on the cam (tighter radius on the lifters) the stock 1 3/8 pipes and peashooters were best.

As you have a big and long duration cam, IMHO you’d be better off going back to Nigel at NRP and asking him to look at better silencing on your current Maney style set up.

The capacity of the motor is often a factor. A larger capacity motor usually delivers more torque, but even with that - separate pipes with megaphones, can make the bike difficult to ride well. If you fit a 2 into 1 exhaust system you usually lose 2000 RPM off the top of the rev range. However with a Commando engine , that 2000 RPM is usually above the top of what the motor will cop mechanically. So you fatten-up the midrange. Noise is always a problem, even with a 2 into 1 system - if your motor is performing well. It is difficult to keep the noise levels down without stifling the motor. In the end you probably have to tolerate a small loss of power. I think the Exup system on modern bikes was invented to cope with this problem.

I have a similar set up as storm 42 , JS 2 cam longer rods and lightweight pistons. The Vvs in a RH10 head are standard diameter with 32mm Premier carbs on standard manifolds
Swapping from two separate pipes into open peashooters, a copy of a Maney 2 into 1 gave me more mid range power and torque with very little drop at the top of the range. Ask Fast Eddie for noise levels as he has one my systems.
Regards Mike

On my bike, Mike's exhaust isnt any louder than my Duc with a Termi exhaust.

The Emgo peashooters I had on previously were definitely quieter with the same motor:

Hi Ralph, My engine spec is extremely close to yours ,I run separate pipes Built by Nigel at NRP Loads of grunt and never any problems with noise test.

Gaining top end power was never a problem with large 4 cylinder motors, especially when they have 4 valves per cylinder. However if you use radical cam timings, noise becomes a problem. Exup is a butterfly valve in the exhaust which is controlled by revs and throttle opening. An answer for a Commando might be to make a couple of copies of the Wal Phillips fuel injectors from the 1950s. They were pretty crude, and when you turned the fuel on, it was easy to flood the motor. If you fitted two of those to a Commando and got the set-up accepted by the guys who make the rules - the next step might be a well-hidden full engine management system with proper injection system and Exup under the bike.

With my bike, I use a 2 into1 exhaust which has a tail pipe the same cross-sectional area as the total of those of the two header pipes. My 850 is advanced 12 degrees to compensate for the greater back-pressure. With any petrol engine as it runs charge gets stuffed down the exhaust pipe then bounces back into the combustion chamber. With a 2 into 1 exhaust, it probably works like an expansion chamber on a two stroke. And is especially effective when you use methanol fuel, because the heat build-up is not so great. However the noise my bike makes is horrendous.

Back in the early 1960s, most of the top A graders rode Manx Nortons - the quicker smother guys usually seemed to have bikes that were quieter. It might have been because their cam timings were not so radical and their bikes were more tractable.

Ralph
Have you got Steve's silencer kit?
I was too stressed with the standard set up when noise testing. Steve used to warm his bike up then be very steady on the throttle, always passed! I ran plus or minus everywhere I was tested. Basically replaced the end cone with a holder for supertrapp discs. I run them all. Felt safer at noise testing. Strangely when I had to change the engine back to the 750 it was far louder, raspier.
I have a NRP 2 into 1 for the 750 as until Brooking made his set up I couldn't find another Maney exhaust.
Chris

Chris, when you say you ‘run them all’ do you mean all the plates? And, do you run the open or closed final alloy plate? And do you know what dB readings you got?

I’ll be making up an alloy end for my Brooking pipe and using supertrap plates cos there’s no way mine would pass track day noise tests as it is! So I’m keen to try and understand what’s what here...

Mine passes a WOF (MOT). But the guy I take it to I'd an ex flat tracker.

gortnipper said:

Mine passes a WOF (MOT). But the guy I take it to I'd an ex flat tracker.

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Sadly the guys at track days in the U.K. have sound meters, and orders to follow...

Do you know how loud yours measures?

Excessively loud exhaust can be caused by an over advanced ignition.
The standard balanced pipes can help reduce the noise but how they will effect power I haven't a clue.

No I don’t, I’ve not taken it to a track day with noise meters yet.

Here in the U.K. there are some circuits where every single bike passes at or 1db under the threshold, and unless it’s outrageously loud you’ll be OK. They don’t really seem interested in the actual dB figure, just not passing the threshold by ‘too much’.

But there are some circuits that take it a bit more seriously, brand new Ducati Panigles with bog standard factory exhaust fail at these circuits.

I even muted down my Commando when it had stock peashooters on, at one of the relaxed circuits. I gave me a sticker saying it was 1 dB under. Same as my mates louder bike. I asked the tester to tell me exactly what it was and he just replied ‘it’s passed’ I asked him several times but just got the same answer. The fact that I was trying to actually understand the figure and correlate that to my baffle ‘design’ and understand cause and effect was all rather lost on him and his colleagues.

So it’s all a bit hit n miss here, and to be safe, you need to know you have options to really quieten it down if needs be.

SteveA said:

And seriously, are you short of power?

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No, but.

I know Nigel and he made me the pipe that is on my road Commando, he also made the Maney style one on my Seeley which I got through Minnovation.

The but above, At the last race, which was a bit damp, I was struggling getting back on the power from a closed throttle, it was causing problems (slides). I fitted a couple of new plugs which helped a lot, I felt it was dropping onto one on a closed throttle and banging back in when I touched the throttle. I got to thinking that if a twin pipe setup would move the power up the rev range a bit, it might make the off throttle transition a bit less fierce. And of course if there was a bit more power to be had then I wouldn't say no to that.

I might pop over to Nigel's and have a word.

Thanks.

Fast Eddie said:

My limited dyno testing of exhausts definitely found the Maney system best when using a long duration cam.

Standard 1 3/8 pipes and peashooters were good but gave away quite a bit of mid range.

1 1/2 pipes didn’t work well at all.

Various long tapered open Megas I had from previous jobs (some worked awesome on Triumphs and Nourish motors) didn’t work well either.

With less duration on the cam (tighter radius on the lifters) the stock 1 3/8 pipes and peashooters were best.

As you have a big and long duration cam, IMHO you’d be better off going back to Nigel at NRP and asking him to look at better silencing on your current Maney style set up.

Click to expand...

It does pass, the last race it tested at "104 with the rattle" said the man. I hadn't realised but the rivets in the mudguard had worked loose, the tester said that the rattles can make 4 db difference. But for once they tested us away from the armco and in the open, it has been close at times elsewhere. I will have to go and talk to Nigel.

acotrel said:

I think the Exup system on modern bikes was invented to cope with this problem.

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Hmm, I don't think I would get away with that.