Exhaust pipe length in peashooter
- Thread starter Diablouph
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That seems way too much, I have only 3-4 inches. That also seems a long length of pipe to remain past the upswept bend in the exhaust pipe as well. Check that the hanging brackets are correctly orientated and not locating the peashooters two far forward, or the next problem will be kickstart and silencer interference. But if all fits nicely I would not be to bothered. Other than that, I'm out of ideas.
I just bought a set of pipes for my 75, they are pipes for a 74' and my aim is to get rid of the crossover piece, these pipes are 7 inches longer and the bend is about 3/4 inch more upward than the set I currently have on the bike. I have the black cap style silencers. I am going to call the vendor tomorrow and get his opinion about cutting them off several inches, I am not sure the silencer will move that much to match up. Hope this makes sense.
porterg said:
I know you didn't buy a MkIII balanced set but this helps explain the difference between MkIII pipes/Beancans and Pre-MkIII pipes/Peashooters. The mounts are different too, I think.
http://www.vikingexhaust.com/getPart.asp?id=17
edit; this pic may help.
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"my aim is to get rid of the crossover piece,"
FWIW, although most people eliminate the crossover and put 750 pipes on the 850, the crossover pipe adds power and reduces noise compared to the straight pipes. So eliminating it is actually a "downgrade" as far as engine performance is concerned.
FWIW, although most people eliminate the crossover and put 750 pipes on the 850, the crossover pipe adds power and reduces noise compared to the straight pipes. So eliminating it is actually a "downgrade" as far as engine performance is concerned.
I'd be cautious about cutting off headers any more than necessary--those black caps may never work satisfactorily--and you may need the extra length to mount and position mufflers to give the nominal exhaust-tract length of 60 inches, which I've found to be about optimal.
In my experience the SS pipes with Dunstalls work best, followed by the balanced pipes, at least on my ancient Combat--the latter are worth one or two BHP and MPG. The SS setup seems to be less sensitive to tract length than any configuration I've tried.
Tim Kraakevik
kraakevik@voyager.net
'72 Combat, '74 RH10 850
In my experience the SS pipes with Dunstalls work best, followed by the balanced pipes, at least on my ancient Combat--the latter are worth one or two BHP and MPG. The SS setup seems to be less sensitive to tract length than any configuration I've tried.
Tim Kraakevik
kraakevik@voyager.net
'72 Combat, '74 RH10 850
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Dunstall found an increase in power available with a crossover in the early '70's and the description/spces for it are in his tuning guide for the 750. The exhaust crossover he made for performance use was essentially copied by Norton and used on the 850. Virtually all automobile engines with dual exhausts have a crossover pipe in the exhaust system for the same reason - it reduces exhaust noise AND it increases power. Currently, X-pipes crossovers have been found to be slightly more beneficial power wise than H-type crossovers. The old 2-1-2 Dunstall header pipe (Viking currently makes a copy) is essentially an X-crossover design though it looks a little different.
Per the Dunstall tuning guide. page 22: "by far the best system for fast road work is separate exhausts joined by a balance pipe up close to the cylinders."
Per the Dunstall tuning guide. page 22: "by far the best system for fast road work is separate exhausts joined by a balance pipe up close to the cylinders."
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Mm got it right, X-over gives more low-mid power d/t less exit resistance via both headers/muffler while lowering and mellowing the note w/o subtracting the top max power, just not helping it like say a megaphone. Norton did it to lower noise ontop of restrictive mufflers. Don't confuse the two factors. I put x-overs on all my V8's and like it better. Extractor Y unions do the same thing but also help suck on exhaust pulses.
You may well be right. I'm always on the quest for more power without going overboard.
As far as I know, Mick Hemmings, Norman White etc. use straight pipes for racing.
This can be argued intill you are blue in the face. Exhaust back pressure on a 4 stroke is very complex, & had books written about it.
Is a 4 into 4 better than a 4 into 1 for instance. Well, yes & no.
As far as I can acertain over the years is that 1 exhaust pipe per cylinder give a better spread of power & converging them might give you more power, but in a narrower rev range.
Then we get onto exhaust lengths, then of coarse, intake lengths, air box volume etc.
I believe Dunstall made a 2 into 1 into 2.
As far as I know, Mick Hemmings, Norman White etc. use straight pipes for racing.
This can be argued intill you are blue in the face. Exhaust back pressure on a 4 stroke is very complex, & had books written about it.
Is a 4 into 4 better than a 4 into 1 for instance. Well, yes & no.
As far as I can acertain over the years is that 1 exhaust pipe per cylinder give a better spread of power & converging them might give you more power, but in a narrower rev range.
Then we get onto exhaust lengths, then of coarse, intake lengths, air box volume etc.
I believe Dunstall made a 2 into 1 into 2.
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In the dunstall tuning book, Dunstall states that with the crossover pipe and Dunstall Decibel silencers, they measured 5.8 more HP at 5500 RPM than a racing megaphone system. He goes on to say that the racing meg had 2 MORE HP than crossover exhaust at 7k RPM. As he points out, the issue for street use, the crossover pipe would outperform the racing system.
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As I've said before, I'd love to put the 2-1-2 Viking copies of the Dunstall pipe on my Commando but the ground clearance reduction and required removal of the center stand makes it a non-starter for me. The ground clearance would be a huge problem here in Mexico. I'm also not sure if the pipe would be as beneficial on the 850 as it was on the 750 due to the RPM difference.
I'm thinking of buying a 750 and keeping it in the US. If I do that, I want to make it into cafe racer with a fairing (yellow, I think) and I would do the 2-1-2 on it. Whether that'll actually happen, I have no idea.
I'm thinking of buying a 750 and keeping it in the US. If I do that, I want to make it into cafe racer with a fairing (yellow, I think) and I would do the 2-1-2 on it. Whether that'll actually happen, I have no idea.
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On Peel I got 2>1 keeping center stand by welding the LH header into RH like
a Vincent sort of. Fender will hit the LH on landings from a few feet high and the Y span was just enough to allow spreading to fit in splayed head ports w/o an adapter like everyone has had to use.
a Vincent sort of. Fender will hit the LH on landings from a few feet high and the Y span was just enough to allow spreading to fit in splayed head ports w/o an adapter like everyone has had to use.
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What's the latest Diablouph.... Have you got access to a Dyno ? You could cut 1" off at a time and see if you like what happens.!!
4-5 inches too much sounds a lot, or you could drill the extended piece like the inside of a muffler. If you do remove it all you
will probably have some jetting to do.
AC.
4-5 inches too much sounds a lot, or you could drill the extended piece like the inside of a muffler. If you do remove it all you
will probably have some jetting to do.
AC.
I love this forum. As the pregnant girl said: "actually, I never intended to go this steady". All I was interested in was why my pipes were almost 8" longer than they needed to be to connect to the peashooters. I sure learned a lot. I don't really care about extra horsepower, I just don't want the exhaust to fall apart. I think I will leave about 3" inside the peashooters. I do however appreciate all the info. I love this forum.
Hobot, we just can't leave you alone with a drill, can we?
Hobot, we just can't leave you alone with a drill, can we?
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So did we establish why they are so long ? Did we establish anything...
AC.
AC.
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