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Exhaust pipes. #773092 05/09/19 12:36 am
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Mark Parker Online Content OP
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The exhaust I'm using on my modified A65 uses header pipes that are 41.2mm expanding to 44.5 part way down going into a 51mm twisted X connector with 51mm tail pipes into mufflers that are straight through at 38mm. Ben's similar system has a pair of mufflers that are straight through at 51mm, they are a bit noisier but sound very nice. I'm wondering if my small bore mufflers are restricting power, and maybe if I should try some of the 51mm bore mufflers. Is there likely to be more power available with the bigger bore mufflers?

[Linked Image]


mark
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Re: Exhaust pipes. [Re: Mark Parker] #773119 05/09/19 6:39 am
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JER.Hill Offline
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Hi Mark

I think you might want to get hold of some of these exhaust people who can run all your engine spec into their computer programme. They should then be able to come up with the proper length and diameter of the front pipes and mufflers etc, this should help obtain the maximum power output of your engine.

my tuppence worth

John

Re: Exhaust pipes. [Re: Mark Parker] #773121 05/09/19 7:19 am
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+1

Re: Exhaust pipes. [Re: Mark Parker] #773122 05/09/19 7:21 am
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First time I sleeved my tail pipe down it worked really well, the first tube took the ID of the pipe to being the same size as the inlet, the next pipe I bolted inside of that was 2 sizes smaller so there was a gap around the outside of the most inner pipe and what it was bolted in to, it worked, ran and sounded a beaut.
Being happy with that I cut the exhaust up, removed the original tail piece and welded in a length of that smaller pipe but the full length. It was a bit too much for the bike, seemed it needed the extra volume that the gap was providing. It accelerated fine and gave the bike plenty of torque, but most noticing was the bike would feel like it was choking up if held at the same revs/speed over many miles (we were touring to Denmark and back at the time covered over 500 miles over 2 days on the motorways) it would sound like the bike was running rich, a bit of acceleration for a bit cleared its throat but that was the product of the pipe being too small. I’m convinced though that had I spent some money and bought some 1 3/8” OD pipe, so the perfect fit inside the down pipe size then it wouldn’t have been a problem.

I’ll try and find some pictures and post, but I’d say that if your not getting the feeling that it’s running over rich then it’ll probably be fine as it is. You could also fit inserts into Bens silencer or put yours on his and see how his performance changes.


beerchug
Re: Exhaust pipes. [Re: Mark Parker] #773189 05/09/19 10:44 pm
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Mark Parker Online Content OP
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I have tried quite a few varieties of exhausts, this set up is the best so far, its just a matter of weather the 38mm mufflers are much of a restriction, I knew they were smaller dia than 51mm but didn't know it was by so much till I measured them yesterday. A couple more hp I don't need may not be worth the extra noise, I could probably borrow Ben's mufflers some time and see what it's like.

https://www.aliexpress.com/item/51M...ml?shortkey=IzIZZzI3&addresstype=600


mark
Re: Exhaust pipes. [Re: Mark Parker] #773192 05/09/19 11:23 pm
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NickL Offline
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Most 'old school' types would look at that system and say you have too many pulses in the pipes.
IE. they are too long.

But they work for you and as it's only on the road, so it hardly matters too much as your'e not likely
to come across another similar bike to race.

Re: Exhaust pipes. [Re: Mark Parker] #773450 05/12/19 11:14 am
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Aussie riding footwear...Blundstones [or Redbacks] lol

Re: Exhaust pipes. [Re: Mark Parker] #781697 08/17/19 3:41 am
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Mark Parker Online Content OP
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Answering my own question; is there more power available with the bigger mufflers? Considerably. Especially noticeable in the midrange, makes changing down less necessary, can use a higher gear and low revs in a corner and drive out really hard. I had a T150v bored to 880cc with 32mm carbs, big valves, big bore 3into1 and it was never like this. The question is what hp it might make around 8,000 how much more than the previous 85rwhp it may have. Winding the throttle on around 3000rpm it just goes and goes, very unrelenting.

The new mufflers fit well and are lighter than before and less than $200au for the pair. Right hand turns are the best because the nice noise these pipes make is reflected up by the road.

[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

Last edited by Mark Parker; 08/17/19 8:25 am.

mark
Re: Exhaust pipes. [Re: JER.Hill] #781730 08/17/19 12:44 pm
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Originally Posted by JER.Hill
Hi Mark

I think you might want to get hold of some of these exhaust people who can run all your engine spec into their computer programme. They should then be able to come up with the proper length and diameter of the front pipes and mufflers etc, this should help obtain the maximum power output of your engine.

my tuppence worth

John


I tried that with my Triumph 650 LSR bike...The problem was there war no reliable tuning info to base the formulas on.But it did recomend about the same type pipes used on the T140D two into one system..But on the dyno and track two single pipes performed better for top speed...It was the the often used Pipe Max program...Mark Parker has more info on head flow so it may work for him in a street bike situation...


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Exhaust pipes. [Re: Mark Parker] #781745 08/17/19 2:24 pm
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Mark Parker Online Content OP
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When Aprilia started in superbikes with their 1000cc twin they used a 2 into 1, from vague memory, I don't think it was competitive till they ditched it and ran twin tail pipes. Not sure how they were connected but I expect they were. I've made a few sets of pipes for this BSA, 2 into 1, 2 separate, then I put a balance pipe about halfway down and joined them, then an 'X' connector which is the best of them. I've done 4 versions of 'X' connectors, used 3 versions on this and one big bore high pipes like the '70 and later firebird, tested it on a 750 and it gave very good top end. I sent those pipes for Chris to try on his A65 LSR bike because they are so top end biased. You get the scavenging of a 2 into 1 and the breathing of a twin system.

What I did with these pipes with their stepping up in diam was to sort of copy modern superbike exhausts. The tail pipes and mufflers on the BSA are 51mm and the system seems to work very well. The bigger the diameter the longer the pipe needs to be. There is probably something better, there usually is, but I don't know what it is. Exhausts seem super complex with formulas and theories so I just experiment, you can tell when they work because of the zoom that kicks in, they usually make a way bigger difference than cam changes and other tuning, It's interesting when magazines have a bike and put in a hot cam and compare dyno graphs before and after, they talked in one article about this special high performance cam and they had to stuff around for ages on the dyno till they got an actual power increase, and then it was 1 or 2hp, they raved about this hot cam, much more so than a set of pipes they put on a bike that gave an extra 10hp virtually straight away.


mark
Re: Exhaust pipes. [Re: Mark Parker] #783951 09/11/19 1:46 am
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Beautiful bike Mark.


"Don't trust your eyes if your imagination is out of focus." - Mark Twain
Re: Exhaust pipes. [Re: Mark Parker] #783963 09/11/19 9:15 am
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kommando Offline
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The Aprilla 1000 RSVR was the V twin that had a 5000 rpm flat spot caused by a 2 into 1 exhaust, this is cured by a 2 into 2 setup or 90% cured by adding a X over pipe or pipes (2 versions available) to the collector under the engine. Both solutions need a remap to adjust the fueling at 5000 rpm to exploit the new pipes.

This is the 2 X over pipe added to the collector pipe, the single x over pipe version omits one pipe.

[Linked Image from azz.com.pl]

Before and after

[Linked Image from i687.photobucket.com]


Re: Exhaust pipes. [Re: Mark Parker] #784205 09/13/19 10:14 pm
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kevin roberts Offline
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make em up and test. like you did.

in my opinion, computer programs work best when the parameters they require are predictable and known. things like ambient temperature, relative air density, exhaust gas density, temperature, and pressure, camshaft lift, duration, valve acceleration, and timing, induction density, charge speed, head flow, intake diameter, and pulsing, and so on.

a mathematical prediction is only as good as the data going in, and on a motorcycle, none of that is constant, or mostly even known. making up or installing the mufflers and then going out and testing will give you real world data that skips all the assumptions, constants, and errors in the input to the computer program.

computer simulations are great for a simulated world. they are inferior to and slower than actual testing, in my humble opinion.



every day you do not take a chance is a day of your life that you will never get back.
Re: Exhaust pipes. [Re: Mark Parker] #784209 09/13/19 11:22 pm
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Hillbilly bike Offline
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Mark's exhaust is nice work and apparantly it also performs well...If you go back and read my race bike build from around 2013 you see my commments on building a computer designed exhaust..The late Ron was telling me to forget the fancy pipes and just get on a dyno or accurate track testing...He was correct for me,and Kevin in a limited type of racing but not for everyman I would say...


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: Exhaust pipes. [Re: Mark Parker] #784211 09/13/19 11:41 pm
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old mule Offline
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Your BSA is one of the all time classic machines, I say.


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