Emma the 'M' model.

[teazer]

Nice pipe. And lots of good comments. I agree totally that a big old softy that the GT is, doesn't need 150HP and couldn't handle it on the street anyway. More to the point, as someone mentioned, that's not why we like these old bikes and now really how we ride or enjoy them.

Some of us prefer a different sound to stock and some of us like less weight or more power and most people just want to ride their old shiny bike at a safe and moderate pace and enjoy that experience. And that's all good.

[PaulD738]

Oh, trust me - it's nothing like a Piper - I have one of those that will be going on my next resto.
You have to realise that most folks nowadays realise that we don't need maximum power & speed out of a '50 year old' bike anyway.
Bottom end and a good mid range is enough to annoy modern bike owners. A 3-1 weighs a helluva lot less than a standard GT exhaust, so performance where WE prefer it is great. Anyway, most modern multi cylinder bikes have siamese exhausts, but no-one seems to complain about those do they? If you need 200hp, get something new.
Running a Piper on my GT550K on the IOM a few years ago didn't seem to lessen performance anyway - over 100mph is fast enough.
You need performance? Get a modern bike - my 15 year old GS1400 was fine in that respect.
Big torque, lots of mid range and fast enough to lose a licence.

That’s because they’re four strokes yer plank

[Alan H]

And only fire every other stroke, so as they rev higher than proper 70s 2 strokes, there will be a similar amount of stuff trying to get of the back of the exhaust.
Who's the plank now?

[750ynot]

but a 4T doesn't rely on back pressure to push fuel air mix back into the cylinder that would otherwise be wasted, and this is where the 3 into 1 falls short, the return pulse is not timed correctly with the port timing to do so, with a 4T after the tuned length has done its job you can do almost anything with the pipes, as long as you don't restrict the flow that is, 2 very different animals.

[PaulD738]

And only fire every other stroke, so as they rev higher than proper 70s 2 strokes, there will be a similar amount of stuff trying to get of the back of the exhaust.
Who's the plank now?

You because you obviously don’t understand the difference in how two and four strokes work as explained by 750 ynot

[Alan H]

The return pulse would be split into 3 wouldn't it? Then as there would only be 1 pot that was in the 'correct' position, it wouldn't affect the other 2 and so long as the stinger bit on the end was a sufficient diameter - (and it appears to be in the pic) - the exhaust gases would get out fine. The Piper I had on my 550k worked fine on the IOM a few years ago anyway. Not as if the 550s mild port timing would be affected at all really as far as I can see.

[750ynot]

The return pulse would be split into 3 wouldn't it? Then as there would only be 1 pot that was in the 'correct' position, it wouldn't affect the other 2 and so long as the stinger bit on the end was a sufficient diameter - (and it appears to be in the pic) - the exhaust gases would get out fine. The Piper I had on my 550k worked fine on the IOM a few years ago anyway. Not as if the 550s mild port timing would be affected at all really as far as I can see.
November 2015 a.jpg

That is the problem, the return pulse being split into 3, the effect is less because it is split, but also hits the other cylinders early or late, and at certain times the fuel air mix will be forced out the back of the carb on the other cylinders because of the port timing, that is all taken care of by the valves on a 4T, but the 2T uses the exhaust to do this, this is why you can get such big gains with well tuned expansion chambers, they act like a turbo charger so to speak, but forcing fuel mix back in via the exhaust port instead, you can't alter the speed of the return pulse, but you can alter where it hits in the rev range with an expansion chambers tuned length, or in this case 3 into 1 has no control over the return pulse, its almost all lost, you have to be careful with the stinger diameter, too small and you will end up with a hole in the piston, too large and no back pressure, 2T tuning is all compromises, this is all if you are looking to gain power, if not happy days with the awesome orgasmic sound of the 3 into 1.

Though I do agree with such mild porting on your 550 and my 750, there should not be a great difference, which is why I was shocked at Pauld saying he lost 20MPH, I would not expect that much lose through the pipe, the Suzuki standard pipes are not highly tuned, sorry If I am teaching you how to suck eggs so to speak, but I thought it would be good for others to see and help them understand the system a little, if they want to know that is.

[PaulD738]

To answer the question of the 3-1 two stroke exhaust system as opposed to the one exhaust per cylinder you only have to look at the sadly extinct two stroke GP bikes of a “few” years ago. How many factory two, three and four cylinder two strokes used 2-1, 3-1 and 4-1 exhaust’s
Yes you sound like your doing 100mph everywhere but the reality is two strokes need one exhaust per cylinder to work properly. A certain Mr Kaaden worked it out in the 60’s
And yes my Dunstall kettle just stopped accelerating when it reached 80mph, very embarrassing

[750ynot]

To answer the question of the 3-1 two stroke exhaust system as opposed to the one exhaust per cylinder you only have to look at the sadly extinct two stroke GP bikes of a “few” years ago. How many factory two, three and four cylinder two strokes used 2-1, 3-1 and 4-1 exhaust’s
Yes you sound like your doing 100mph everywhere but the reality is two strokes need one exhaust per cylinder to work properly. A certain Mr Kaaden worked it out in the 60’s
And yes my Dunstall kettle just stopped accelerating when it reached 80mph, very embarrassing

2 into 1 is popular in Japan on the RDLC, not for the performance though obviously, have you seen what they are doing to them out there


Yes sound is but then someone on an X7 comes flying past to say the least, or for that matter at 80mph the X5 and RD200 would have come flying passed too at around 85 top end, and even a few tuned 125s too, now that's

[teazer]

Dead at 80mph sounds drastic but not totally surprising. a 3 into 1 loses quite a bit of power above say 5,000 or so. 750Ynot is right that the pulse arrives at a most inconvenient time on 2 of 3 cylinders and the longer the exhaust duration the worse that becomes.

As we all understand, a two stroke exhaust port opens and positive pressure wave is sent on its merry way down the pipe. As the diameter of the pipe increases, that wave is reflected back to the exhaust port as a negative wave. When a pressure wave is reflected by an open end, the reverse wave is not only traveling back towards the port but is now a negative wave or a suction wave. That helps to empty the cylinder and also pulls gas out from the transfer ports.

As the pressure wave continues down the pipe it eventually gets to the convergent nozzle which acts like a closed end and reflects the pressure wave back only this time as a positive wave. That pressure if timed nicely will push any fresh mixture back into the cylinder just before the exhaust port closes. With a 3 into i those positive and negative pressure waves arrive at the wrong time for the "other" cylinders. And if the collector design is poor, and they mostly are, not only do pressure waves suffer but so does the mass flow of gas trying to get downstream to be free.

On a 4 stroke, the same pressure wave dynamics exist but the time and effectiveness are different. In fact anti-reversion exhausts and raised exhaust port floors are designed to minimize the amount of exhaust gas that gets pushed back into the head before the valve shuts. Stepped headers and collectors and siamese pipes are all designed to evacuate exhaust gas from the combustion chamber in much the same way as a two stroke, but that's where the similarity ends.

There's a whole lot more going on including the fact that the waves travel down and back 5 or six times per cycle losing strength with each reflection.