2 into 1 Exhaust (2015)

Fast Eddie said:

Mike, I think Jagbruno’s engine is sloping, ala Cdo.

Jagbruno, please study the pic of one of Mikes pipes on my roadster, it should give you some idea.

My guess is that one would fit OK, with the following caveats:

1. I don’t think your fairing would fit, you’ll either have to remove the bottom half, or cut it to allow the front pipe bend to protrude (racing Manx style)!

2. The fitting kit that Mike provides makes fitting to a Cdo so easy that even I could do it! But you would have to make / adapt fittings to suit your application.

3. The pipe will effect jetting, so you will need to dial it in to get best results. On mine, it made the mixture richer. Don’t ask me why, I don’t understand such things!

4. My advice would be to buy the pipe in bare steel, so you could add or remove brackets if necessary (although Mikes finished ceramic coating is superb inside and out).

So, with a little improvisation, I can’t think why it wouldn’t fit. Then your bike will sound (almost) as good as Yves !!

I’ll leave you to discuss prices etc with Mike, but quality doesn’t come cheap! Suffice to say however, the workmanship and overal quality of Mikes pipes is truly superb.

If you want the ‘hot rod’ look and sound, then this is the pipe for you!


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Thank you Nigel! Yes, my engine is sloping.

It looks fantastic! It definitely wouldn't clear my Dunstall fairing. But what I am really afraid of, is that possibly it wouldn't clear the front frame cradle tubes or worse, that the front wheel might touch it when the forks are in full compression.
Actually, when I bought my bike as project, it had a 2-1 exhaust on it. As I tried the bike for the very first time after rebuilding the engine, less than half a mile from'Yves' workshop on a 'legendary' Belgian heavy lorry road, I hit a 6 inch deep pothole with the front wheel while traveling at about 70Mph. The rear of the alloy mudgard made contact with the exhaust tube which pressed it onto the tyre. I will never know how I managed to keep the bike upright on the black stuff.
Upon my return to the workshop a few minutes later, my face white as a plain yoghurt, and still shaking like Jamaican maracas on Carnival night, Yves wouldn't believe me, as we had checked the clearance statically before.
But the tyre mark was there on the inside of the alloy mudguard. Off went the 2-1. I never had any problem since.

The timing side pipe, the one that crosses over, sits quite close to the cylinder block and inside the frame rails, so it’s quite impossible for the wheel to touch it (unless you’ve had a serious head on collision) see the photo below and you’ll see what I mean.

As to whether it would clear the frame tubes I can’t say for sure, but I think it would. Mikes system is very close to the original Maney system and lots of those have been fitted the featherbed Commandos.

How about borrowing Yves pipe for a trial fit, send photos of it to Mike, and he could estimate whether or not his would fit OK.

Brooking 850 said:

Here is the latest dyno result on my bike for the finished exhaust system.
I have raced it at two different tracks 6 hours by road apart over two weeks and there is a distinct power and torque gain with this system.
It has been suggested I go a little leaner with this, although I tend to err on the rich side and our hot summers are well on their way.
No other changes were made to the bike other than the exhaust system from 2 x upswept pipes into hollow peashooters to the 2 into 1 system.
Regards Mike

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Hot summers won't make your motor run leaner, but very cold weather will. If you are simply worried about over-heating when you have got the jetting right, that is a different story.

Ridding high cools fuel and less density leans so does a good exhaust make this worse?

Ms Peels expedient 2-1 experiment adapting old headers let one header cross behind guard which seemed plenty of space till leaping into into rough creek beds and striking ground hog pasture holes to clank with steering jerk - finding steel fender lost the punch out, fist size dent vs tint ding - so next time set may be more like comnos, both pipes go straight down beyond fender collision range before merging or angled off any way ya like. Hitting a parking lot cement car stop then a water meter hole on landing w/o cover on at 50 was required for Peel extra progressive 6" travel to finally clash to realize my over sight. Forks took it up w/o any bother like teeth on bars but rear impact following kicked butt out of saddle almost over bars.

Maney system seems to me to be a dual pipe separated system only merging in the collector muffler, similar to obnoxious looking dragster Norton choppers w low system rather than thigh level. Nil common tube length for the pressure waves to draw out the following. Implies should work as good as any separate pipes but not as good as actrels or hobots 2-1's. Take the effort to Look up what it takes to make a current state of the a tri-y or stepped header to see may still be room for improvement. Plug in all the data for calculators and for public presentations but only expensive extensive trial error or quick luck out matters in the end. A great 2-1 doe not add to top end, so no dragster do it but it should not hurt top end so all road racers should.

Post some dyno and or video comparisons so I can see the differences Steve and Alan.
Seat of the pants riding on two different continents and two different types of riding/racing doesnt mean that other systems are useless!!!
I use feed back from my customers in many parts of the world that use dynos as a work tool to see if before and after fitment of the exhaust system makes any changes to performance .
Most post on here.
Thanks Nigel for pointing Jagbruno the way forward.
Regards Mike

My own dyno experience showed the 2:1 gave a 5bhp peak increase and an even greater mid range increase. So my own experience is certainly different to your suggestions Steve.

However, with a milder duration, the benefits were greatly reduced.

I’m very optimistic that with the 2S style 86c/12c in the 920 motor, the 2:1 will earn its place on the bike once more!

I'm all for merged exhaust systems as always paid back the efforts on two to eight cylinders for me. Just pointing out the terminology and pulse extraction function confusion on what looks like a 2-1 but is more like long separate headers that merge in a muflfer like exit instead of into somewhat long common tube one pulse helps the following pulse out before muffler/silencer. Look into Tri-Y headers for the science and trial/error involved connecting opposite firing jugs together. Real 2 to 1's are most known for low-mid range assistance while separate pipes for the upper rpms. Race power engines often benefit from weaker low rpm power for better hook up/launches till road speed allows more hook up as it hits power band exhaust really designed for. Maney has proven design for top end power made more along lines of separate headers is all I'm pointing out.

Fast Eddie said:

My own dyno experience showed the 2:1 gave a 5bhp peak increase and an even greater mid range increase. So my own experience is certainly different to your suggestions Steve.

However, with a milder duration, the benefits were greatly reduced.

I’m very optimistic that with the 2S style 86c/12c in the 920 motor, the 2:1 will earn its place on the bike once more!

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Eddie, you mentioned 'an even greater mid-range increase' - that is not a measurement. I don't use a dyno, but as I understand it, most of them these days rely on spinning up a heavy flywheel and measuring it's acceleration rate. When you measure the torque output of your motor on the dyno, you are also spinning up the flywheel inside your motor - so two flywheels are involved.. How reliable is the torque measurement you get off the dyno and how is the torque measurement calibrated ? What I do know about is the difference between separate pipes with megaphones and a silenced 2 into 1 pipe, when racing. The 2 into 1 pipe makes the bike much more manageable and flexible. My 850 motor has had almost nothing done to it and it pulls like a train. However I have raised the overall gearing several times and the bike has accelerated faster each time when coming up through the close box. To my mind, that is a nonsense. The peak horsepower increase is irrelevant unless you are trying to outrun somebody at the end of a long straight. Doing well in racing with a Commando engine is more about getting around corners faster and getting on the gas earlier - that takes torque and good handling rather than top end power.
In road racing, you often have the choice about where you can lose a race - at the start of the straights or at the ends of the straights, depending on the gearing. If you get near the next corner first, the other guy either has to ride around you at very high speed or get blown off in the next corner. Many will back off first, before attempting the high speed passing move. It is the reason a good front brake is critically important on a race bike.

Not quite sure what your point is Al. You criticise the validity of using a dyno as a measure... what else would you propose?

Frankly mate, whatever else you propose, you’re kinda on your own, as the rest of the world has generally accepted them.

Of course, you are correct, my statement of “even more” is not a measure. My meaning was that it was ‘even more’ than the 5bhp increase seen at peak. Sloppy of me I know, but it’s enough to make a valid point, and I frankly can’t be arsed digging up the old dyno print outs to find the precise figure. Cos it ain’t relevant.

Your ‘peak horsepower only being relevant on a long straight’ is an amazingly absurd statement, especially from an experienced racer. Peak horsepower is seen at the corresponding revs in every gear, so is beneficial in every gear used during acceleration, from first to top. This is EVEN MORE so when using a C.R. gearbox... as YOU keep telling us you do...!

acotrel said:

Eddie, you mentioned 'an even greater mid-range increase' - that is not a measurement. I don't use a dyno, but as I understand it, most of them these days rely on spinning up a heavy flywheel and measuring it's acceleration rate. When you measure the torque output of your motor on the dyno, you are also spinning up the flywheel inside your motor - so two flywheels are involved.. How reliable is the torque measurement you get off the dyno and how is the torque measurement calibrated ?

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This little bit above is irrelevant when you are doing comparative runs on the same dyno. Repeatability is relevant and from what I have seen of the inertial dynos, they have all been repeatable.

acotrel said:

The peak horsepower increase is irrelevant unless you are trying to outrun somebody at the end of a long straight.

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This irrelevance is pure rubbish.

Two identical Colin Seeley Mk2s, one with a well tuned Commando motor and another with say a short stroke Commando with the same torque and power as the first motor but continues on with even greater power beyond the first motors redline. Which bike do you think will be the favorite to win every time.

Steve, my point was (and I failed to make it clear) that the 2:1 I was referring to was a Maney system.

Fast Eddie said:

Steve, my point was (and I failed to make it clear) that the 2:1 I was referring to was a Maney system.

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I think Steve is caught up in the symantics where there are two pipes into a collector pipe into something else and then there's the Steve Maney pipes where the two pipes more or less merge into the megaphone with little or no collector. Bottom line is that the Steve Maney system works exceptionally well and has been proven to be rather versatile to the state of engine tune. I have thought about dabbling a bit with primary lengths to see what else is there for the short stroke engines but never got around to it.

Ugh, what yoose guys is hung up on is confusing a separate header system like Many merged at the outlet vs a 2>1 that merges into a single pipe of significant length before the exit. The power curve/characteristic being described by Maney type systems matches separate pipe more than 2>1's.

Here's few min video on power curves expected 90% of the time between separate headers vs merged in true 2-1. Agree's with my remarks and experience, good 2-1 adds power down low compared to separates but should make similar top end power too. Win Win if can get it right enough. I'm a rear spin stunter of cycles and car/truck more than top end, so 2-1's and 4>2>1's, with cross over is my favorite.


Something else to consider is heat transfer differences between mostly separate headers vs 2-1 with shared length of single pipe. 2>1's help keep more heat=speed=ease of flow going, which is mainly significant at lower rpm - more cooling time between heat pulses. This difference disappears at higher rpms with less time to radiate/conduct heat through the pipe walls. Bends tend to increase this transfer so main reason to minimize bends not for streamlining flow issues.

On Ms Peel 2-1-megaphone in public contests I had in conditions similar to Barbers, I tried to keep rpm over 5000 mostly d/t wide gear ratios and strong pulls over the ton but also learned not to snap throttle off idle in 1st or 2nd w/o bike literally running out form under, which at 1st pissed then depressed me till realized had gained too much response down low for that so just feathered throttle more to stay in seat. Ms Peel was so responsive up to the ton I'd use THE Gravel and pasture steering methods, throttle snaps to trip Peel down instantly for next instant hi side back up right, pivoting on CoG to be able to make longer turns into series of short up right WOT sprints not smooth low hook up caution d/t limits of forks/suspension. Also tripping a low side steps rear out enough to act as brake to outward tangent fly off - all others must use brakes, not extra power.

Peel's 2-1-mega weighed almost 1/2 less than dual and put more mass opposite the DS primary/chains/clutch/charger for more neural r/l balance. Little details that all add up.

All the theory is great, I make them, supply them and race them and therefore have current data and feed back from customers and my own race bike to prove they improve performance when compared to 2 x single headers and gutted mufflers of any style. The dyno is a tuning tool, why wouldnt you use one to gain the best possible result before going racing, natural changes like weather conditions effect everyone on the day, so at least the bike is in the best possible state of tune at the start of the race weekend.
Guys that produce results year in year out on builds and actual road and or race use are where I look for guidance and help, not theorists who seem to be keyboard warriors and living on memories
Regards Mike

I once did the exercise of making my own 2 into 1 pipe for my previous bike. The first thing that happened was I lost about 2000 RPM off the top of the usable rev range. I then started cutting the collector back and fitting larger diameter tail pipes. I didn't get top end back until the tail pipe was the same cross-sectional area as the two pipes going into it - no restriction.

In answer to the question about motors which rev higher to get more horsepower, when that is achieved it is often at the expense of mid-range. A motor which has higher torque output is usually geared higher. My question is how good are torque measurements off your average dyno ? (Because you get a number, how do you know it means anything ? ) Peak horsepower is not midrange torque, the optimum inlet port diameters are different in both cases.
Sensibly you would expect a short stroke 750 motor revving to 9000 RPM to be faster than a long stroke 750 motor revving to 7,500 RPM. But in effect they both suit different parts of a race circuit and you adjust your riding to suit, The short stroke motor would probably be slower getting around corners but faster at the ends of the straights, whereas the long stroke motor would be better getting around the corners. The same situation occurs in every road race where there are old bikes and moderns. You meet two-thirds of the way down the straights. I try to never get myself into the situation where I come out of a corner at the same speed as the opposition, side by side, then try to out-drag them. With a Commando engine , you must have the run on them or they will beat you every time.

One thing I have noticed while watching on-board videos on Youtube, is that many guys shut off half way around corners. With my bike, I usually never have to do that. It is always full bore, all the way round. Perhaps my bike is underpowered ? - but the last time I raced, I was beside the leader when it stopped.

acotrel said:

the last time I raced, I was beside the leader when it stopped.

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Were you both on the same lap...?

I watched the video that Hobot posted up there and my results were directly opposite to what the video mentioned. My 2:2 had a much flatter torque output than the 2:1. The 2:1 had a big hole in the torque in the mid range.
Maybe it was a badly designed system, but at least when you're working on separate pipes, there are far fewer variables to work on.

acotrel said:

One thing I have noticed while watching on-board videos on Youtube, is that many guys shut off half way around corners. With my bike, I usually never have to do that. It is always full bore, all the way round. Perhaps my bike is underpowered ? - but the last time I raced, I was beside the leader when it stopped.

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Watch the videos posted by guys who win races, not people on track days who don't even have a competition licence. There's a good chance that the race winners got it right.

acotrel said:

In answer to the question about motors which rev higher to get more horsepower, when that is achieved it is often at the expense of mid-range. A motor which has higher torque output is usually geared higher.

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Hardly an answer but certainly an expression of a preconceived notion on your part. It is only "often" for someone who is 1.) clueless as to what they are doing or 2.) is deliberately targeting a different engine performance characteristic. Again, if you refer to the comparable bike scenario I cited which is based on direct real world experience on the track (not conjecture, supposition or preconceived notions), the engine which can extend power and torque further up the rpm range without giving up the mid range and low range torque will win every time - with or without a 2 into 1 exhaust.

acotrel said:

My question is how good are torque measurements off your average dyno ? (Because you get a number, how do you know it means anything ? ) Peak horsepower is not midrange torque, the optimum inlet port diameters are different in both cases.

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Fair questions but misplaced on this thread/topic. As stated earlier, with repeatability one can directly measure and then compare for changes and express as a percent change. Really handy on engine development.

acotrel said:

Sensibly you would expect a short stroke 750 motor revving to 9000 RPM to be faster than a long stroke 750 motor revving to 7,500 RPM. But in effect they both suit different parts of a race circuit and you adjust your riding to suit,

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See above. It may take some getting familiar with a bike with more rpm and power but suitability seems to be even across the board with a short stroke having a distinct advantage across the board. That is a properly set up and tuned short stroke.

acotrel said:

The short stroke motor would probably be slower getting around corners but faster at the ends of the straights, whereas the long stroke motor would be better getting around the corners. The same situation occurs in every road race where there are old bikes and moderns. You meet two-thirds of the way down the straights. I try to never get myself into the situation where I come out of a corner at the same speed as the opposition, side by side, then try to out-drag them. With a Commando engine , you must have the run on them or they will beat you every time.

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Again, this must be some sort of cartoon (preconceived notion). You may have had this experience with your short stroke (other) bike but from my experience, your preconceived notion is far from the truth.