Maney exhaust downpipe length (headers)

Can anyone tell me what the length of the exhuast downpipes is on a Steve Maney exhaust system. I am about to book my race outfit in for downpipes, and need to know what length to have them made. I thought starting with the same dimensions as Steve would be a good starting point.

tonybsa said:

Can anyone tell me what the length of the exhuast downpipes is on a Steve Maney exhaust system. I am about to book my race outfit in for downpipes, and need to know what length to have them made. I thought starting with the same dimensions as Steve would be a good starting point.

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@Brooking 850 makes updated Maney race exhausts (more equal pipe volumes on both sides), he likely has some he’d sell you.

gortnipper said:

@Brooking 850 makes updated Maney race exhausts (more equal pipe volumes on both sides), he likely has some he’d sell you.

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These are for a racing sidecar, solo pipes wont fit.Hence why I asked for the length, then I will ship it off to Tony Laws to have them made.

I have a set on my Seeley (the very first Maney's one with the left one not as long as the later or the brooking one ) will take measurement tomorrow ;

Dumb question time:

These pipes are quite a complex shape. How do you measure the length of a pipe with a complex shape like this ?

Is the Maney exhaust a 2 into 1 which goes down the side of the bike ? My exhaust system goes under the motor and the header pipes are the ones which are used to make exhausts for a Kawasaki 900. The tuned lengths are similar.
My tail pipe is the same length as a header pipe, but obviously resonates at twice the frequency. It has the same cross-sectional area as the sum of the areas of the two header pipes. I suggest the exhaust pulses from the two header pipes need to interact constructively in the tail pipe. If they are out of phase, there might be more back-pressure.

marinatlas said:

I have a set on my Seeley (the very first Maney's one with the left one not as long as the later or the brooking one ) will take measurement tomorrow ;

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Thankyou.

Fast Eddie said:

Dumb question time:

These pipes are quite a complex shape. How do you measure the length of a pipe with a complex shape like this ?

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The way I usually do it, and I dont know if its correct is to take a tape measure, and start at one end, run it around the outside of the bends, until I get to the other end. I guess you should probably measure the opposite side of the same pipe( inside the bends) as well, and take the average of the two?

Mensuration maybe ?

Hi Tony I have a set on the shelf waiting to go back on the bike. It's the 2 into 1 section that is the work of art. I will measure them tomorrow.

tonybsa said:

The way I usually do it, and I dont know if its correct is to take a tape measure, and start at one end, run it around the outside of the bends, until I get to the other end. I guess you should probably measure the opposite side of the same pipe( inside the bends) as well, and take the average of the two?

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I reckon that’ll give you a measurement that’s longer, esp with big pipes.

The average might work.

I‘d have thought a piece of string, or cloth tailors tape measure, carefully placed as close to the centreline, little by little, would do it?

If you wanted to be really fancy / accurate, then, as the diameter is known, filling them with water would facilitate a very accurate calculation on length.

But it is a Norton, so the nearest inch will probably be plenty accurate I guess !

It’s worth mentioning that Steve’s pipe works great with Steve’s cam. Using any other cam really throws it all open again. My own playing around showed that Steve’s pipe works with long duration cams, I reduced the duration (on the followers) on a cam that worked great with Steve’s exhaust, and the benefit of using it disappeared.

Have you considered Nigel @ NRP? He has done many Norton exhausts and has good data and opinions on pipe length and design.

Fast Eddie said:

If you wanted to be really fancy / accurate, then, as the diameter is known, filling them with water would facilitate a very accurate calculation on length.


That would be the mensuration then ^^^

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Chris said:

Hi Tony I have a set on the shelf waiting to go back on the bike. It's the 2 into 1 section that is the work of art. I will measure them tomorrow.

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Thankyou

Fast Eddie said:

I reckon that’ll give you a measurement that’s longer, esp with big pipes.

The average might work.

I‘d have thought a piece of string, or cloth tailors tape measure, carefully placed as close to the centre, little by little, would do it?

If you wanted to be really fancy / accurate, then, as the diameter is known, filling them with water would facilitate a very accurate calculation on length.

But it is a Norton, so the nearest inch will probably be plenty accurate I guess !

It’s worth mentioning that Steve’s pipe works great with Steve’s cam. Using any other cam really throws it all open again. My own playing around showed that Steve’s pipe works with long duration cams, I reduced the duration (on the followers) on a cam that worked great with Steve’s exhaust, and the benefit of using it disappeared.

Have you considered Nigel @ NRP? He has done many Norton exhausts and has good data and opinions on pipe length and design.

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I had looked at NRP, nut, the outfit is the first frame I built(on with number 3 now for a TZ750 Yam),and I want to do it again.Bearing that in mind, I just want a reasonable set of pipes shorterm that will get this one on track. Then I will build a better chassis, using the knowledge,and experience I have gained since I built this one, and look to spend good money, on a good set of pipes for that bike.Also I live near Croft, and Tony Laws is in Leeds,a lot closer than most of the other eputable exhuast guys, and he has done excellant work for me in the past. BTW, I am looking at using a JS2 cam. I think you are probably right with the string idea.

tonybsa said:

I had looked at NRP, nut, the outfit is the first frame I built(on with number 3 now for a TZ750 Yam),and I want to do it again.Bearing that in mind, I just want a reasonable set of pipes shorterm that will get this one on track. Then I will build a better chassis, using the knowledge,and experience I have gained since I built this one, and look to spend good money, on a good set of pipes for that bike.Also I live near Croft, and Tony Laws is in Leeds,a lot closer than most of the other eputable exhuast guys, and he has done excellant work for me in the past. BTW, I am looking at using a JS2 cam. I think you are probably right with the string idea.

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Sounds good.

And BTW it was a JS#2 cam I was referring to earlier, they work great with a Maney pipe (like 5BHP plus in the middle and top). So definitely worth getting the dimensions right Tony. Same with the collector and mega shapes BTW…

Fast Eddie said:

Sounds good.

And BTW it was a JS#2 cam I was referring to earlier, they work great with a Maney pipe (like 5BHP plus in the middle and top). So definitely worth getting the dimensions right Tony. Same with the collector and mega shapes BTW…

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Thanks for that. I still haven`t had any measurements for the downpipe lengths yet. As for the mega, with Englands overzealous niosemeter men, it will probably need a 2ft long can, like something off a Honda SP2.

tonybsa said:

Thanks for that. I still haven`t had any measurements for the downpipe lengths yet. As for the mega, with Englands overzealous niosemeter men, it will probably need a 2ft long can, like something off a Honda SP2.

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My Brooking 850 made Maney repops are on my bike, so I measured from the outer edge of the head, along the outside of the bend and to where I estimated they ended in the collector. Both of them right about 92 cm. Then you would need to add the depth into the head minus the gasket.

tonybsa said:

Thanks for that. I still haven`t had any measurements for the downpipe lengths yet. As for the mega, with Englands overzealous niosemeter men, it will probably need a 2ft long can, like something off a Honda SP2.

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Indeed. But that’s normal these days sadly.

The mega is critical to the design if you want the added oomph.

Are you convinced you need a 2 into one? I run single pipes, I am biased, but I can show you a graph that says it's better in the mid range than a Maney system with a PW3 profile cam (JS2 is PW3ish)!

And I reckon mid range is what you need on an outfit? And don't say 'a 2 into 1 makes better mid range and single pipes make better top end' that is a popular myth which the comparison of my system and Maney's shows to be wrong on both points. Search some threads on here, it has been discussed, you might want to look for inputs from 'Snotzo'.

Anyway, Nigel at NRP made it. And he has made many more. Nortons well catered for, just tell him the cam you are using.

On the noise front, the Maney system has always been noted as 'noisy'. Single pipes have the benefit of two cans to help with that. Nigel is pretty close to the racers and knows all about meeting UK noise regs.

From my perspective, NRP is 'on your doorstep'!

A word on primary length for a 1 3/4" ID pipe, you will measure '73/'74 works Nortons as 28", I used that on my '75/'76 build 850, and it works fine, but.....you need Norman White to tell you that the pipe you could see was indeed 28" long, but a further 2" went inside the megaphone

I can tell you Nigel's pipes on my 750 short stroke are longer than 28", however there isn't a clear start point for a Mega as in the old days, the pipe gets bigger in steps until it gets to the silencer.

So there you go, you now have 'anything from 28" to 37"' Bet you are glad you asked!

When you fit a 2 into 1 pipe to a motor in a featherbed frame, the down tubes stop you from going under the motor. My 500 Triton had unequal length header pipes, and I never liked that. The exhaust system needs to resonate properly. Unequal length header pipes might cause more back pressure when the high points in the sound waves do not work constructively. My system goes under the bike. The header pipes get a straight run into the collector. If you think about it - when your motor is running at 7000 RPM, the gas in the tail pipe resonates at twice the frequency of the gas in one of the header pipes. A tail pipe of the same length as one of the header pipes provides the same tuning as occurs in the header pipes. But experience tells me that if the teil pipe is too small in diameter, you lose too much power off the top end of the rev range. If you do the exercise and start with a small tail pipe, then cut the collectot back and fit larger diameter tail pipes - best power comes whrn the crossectional area of the tail pipe is a big as the sum of the two pipes entering the collector. I do not use large diameter tube for exhausts.
From photos, the Maney exhausts use large diameter tube for the headers. My exhaust system probably runs at a higher pressure. I have also advanced the cam 12 degrees to make the system work harder. You could not do that with a road bike. It is too loud.
If you gain more torque from a Commando motor, you often do not know it until you raise the gearing, and the corners arrive faster. It is probably no easier with a dyno