Custom 850 Commando Exhaust dimensions help needed. I'm currently building an 850 special and it's exhaust manufacture time.

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Paul (850 Commando.)

Paul (850 Commando.)

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I'm at something of a financial pause at the moment, so concentrating on making petrol tank/belly pan etc.
The design of the belly pan in part is dictated by the exhaust.
The header pipes are to run under the engine. but I now need ball park lengths for them + 2 into 1 manifold dimensions (Length/diameter etc.).
Also another option is for two silencers using an H or X pipe, again under the engine, IF I have room. Looks like the chain run might limit my options for this though.

Anyone that has dimensions for the Steve Maney 2 into 1 would help a lot. TIA!
 
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I recently tried nine or ten header and silencer combos on Dyno hill. One of the systems tested was the Dunstall 2-1-2 that advertised " a full 1.25 second reduction in 1/4 mile et when fitted to an otherwise stock machine."
In fact, it slowed the hill times considerably.

The best combo for midrange grunt was standard skinny non balanced separate headers with open fluted type peashooters with the large exit hole .
 
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worntorn said:
I recently tried nine or ten header and silencer combos on Dyno hill. One of the systems tested was the Dunstall 2-1-2 that advertised " a full 1.25 second reduction in 1/4 mile et when fitted to an otherwise stock machine."
In fact, it slowed the hill times considerably.

The best combo for midrange grunt was standard skinny non balanced separate headers with open fluted type peashooters, large exit hole type.
Click to expand...
I'm pretty well committed to running them under the engine TBH and probably with non standard silencers.
I LOOKS like I'm going to run out of room for clearances etc.
Never say never though!!!!
 
Are you going to leave clearance for draining the sump and gear box?
 
Eddie Paul won't unveil anything until he's finished lol. It will be worth it.
NRP for a custom exhaust system. I know Rayson has a good name & Al
 
The exhaust system depends on the intended use for the bike and noise rules, A 2 into 1 exhaust usually makes the bike more rideable, but separate pipes usually give more top end go. If you use a 2 into 1 which offers no restriction at the collector, the tail pipe will be big . And when you adjust the cam timing to suit the exhaust , the noise levels will probably be too high if you intend to use the bike on public roads.
My 2 into 1 system uses header pipes which were originally intended for an aftermarket 4 into 1 exhaust for a Z1 Kawasaki, The tail pipe is the same length as one of the header pipes. It works very well, but it is too loud.
 
The dimension at the outlet of the collector is critical, If the tail pipe is too small in diameter, any restriction can adversely affect top end power.
My left header pipe has a slip joint with springs halfway down it, to help fit the system to the cylinder head.
It is better to have system go under the bile, rather than down one side. The header pipes need to be of equal length. The exhaust system does not simply dump exhaust gas. It is part of the tuning.
 
Chris said:
Eddie Paul won't unveil anything until he's finished lol. It will be worth it.
NRP for a custom exhaust system. I know Rayson has a good name & Al
Click to expand...
I'm at something of a hiatus financially Chris, so shock/horror I might post before it's finished.
Long story but selling my old workshop I HOPE, slumming it in my garage at home!
 
acotrel said:
The dimension at the outlet of the collector is critical, If the tail pipe is too small in diameter, any restriction can adversely affect top end power.
My left header pipe has a slip joint with springs halfway down it, to help fit the system to the cylinder head.
It is better to have system go under the bile, rather than down one side. The header pipes need to be of equal length. The exhaust system does not simply dump exhaust gas. It is part of the tuning.
Click to expand...
Did god knows how many dyno runs while making my Weslake exhaust, so that's why I'd really like some "Starting point" dimensions.
 
Paul (850 Commando.) said:
Did god knows how many dyno runs while making my Weslake exhaust, so that's why I'd really like some "Starting point" dimensions.
Click to expand...
If your bike is to be used for racing, I can help a bit. But you could never use an exhaust system like mine on public roads. I do not even start my bike as home because of it's loudness. It is silly, because I have always believed a good fast bike is often quiet. Mine goes like buggery. I think Exup is about getting more power without more noise. Valve timing can be more extreme with Exup.
 
Paul (850 Commando.) said:
Did god knows how many dyno runs while making my Weslake exhaust, so that's why I'd really like some "Starting point" dimensions.
Click to expand...
When you were doing dyno runs to optimise your exhaust system, were you also varying your valve timing to find what best suits the exhaust system ? The cam in my 850 has nearly standard timings but probably has slightly more lift. My inlet valve opens at 65 deg. BTDC, exhaust at 92 deg. BBDC.
I was at WInton Raceway a while ago, there was a bike there with 750cc Triumph motor which had a 2 into 1 pipe. Out of interest, I asked the owner what his exhaust valve opened at - he said 90 deg BBDC.
There is a reflected wave which returns up the pipe. If the exhaust valve opens earlier, that wave probably becomes stronger My cam sprocket has two more keyways broached into it.
I suspect that within reason, it does not really matter what configuration the exhaust system is, when you optimise the cam timing to suit it. The result is probably nearly always the same.
 
When I was building my Seeley in 1978. I took the cam to a reputable cam grinder and asked to have their best Norton grind. I did not know about this forum and it probably did not exist anyway. Whatever cam I bought, I would probably be buying a pig in a poke anyway. I knew from experience approximately where the valve timings had to be, and whatever the cam and exhaust system was, I could get it to work well. After I built my 2 into 1 system I made an educated guess about the cam timings - it all worked. All I had to do was tune the carbs and ignition timing. But with my previous race bike I had spent eons playing with the same stuff. I think if I had not been using methanol, I would have ended up in trouble with heat.
I know this does not sound very scientific, but there is a lot of margin for error when you use methanol fuel. If the bike coughs when you ride it - stop immediately.
 
Chris said:
Eddie Paul won't unveil anything until he's finished lol. It will be worth it.
NRP for a custom exhaust system. I know Rayson has a good name & Al
Click to expand...
I have an NRP exhaust, single pipes, high level. And he has made Maney style 2 into 1 systems for the likes of Dave Watson. So he has all the dimensions needed for a race exhaust matched to your cam timing!

Nigel will put the pipes where you want them, and it will give you the performance. He uses pre-made stainless bends and really pretty welding.

But if you want old school sand bent mild steel, ready for your choice of finish, Raysons Exhausts is your man. Look for him on Facebook and you will see him working.
 
worntorn said:
I recently tried nine or ten header and silencer combos on Dyno hill. One of the systems tested was the Dunstall 2-1-2 that advertised " a full 1.25 second reduction in 1/4 mile et when fitted to an otherwise stock machine."
In fact, it slowed the hill times considerably.

The best combo for midrange grunt was standard skinny non balanced separate headers with open fluted type peashooters with the large exit hole .
Click to expand...
Was this done with a 750 or 850 or maybe it doesn´t matter?
 
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