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megaphones #650783
04/30/16 2:51 pm
04/30/16 2:51 pm
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ohio, usa
kevin roberts Online content OP

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i have just switched from an old two-into-one muffler on my T120 to stock pipes with reverse cone megaphones. i've seen some really interesting stuff that i don't understand.

i'm at the 2016 ECTA LSR races at wilmington. i'm running a 1972 five-speed triumph with a 740cc morgo bigbore kit. megacycle 1000 street cams at the stock clearances and timing, 3/32-oversize intake valves, mild port work from MAP, 34mm mikuni vm carbs on stock length stubs, no stacks, no filters. 21/47 sprockets, an avon road rider tire with a circumference of 84.8 inches. twin plug head using NGKB8ES and NGKD8ES plugs, gapped at 23-25. timing is 30 BTDC with a Boyer.

the pipes i've run for years are a set of old alphabet street pipes that have long had the fibrglas blown out, leaving a perforated straight through tube:



yesterday the best times with this setup gave me 114 mph, at 6500 indicated rpm on my old smiths tach, probably closer to 6000, based on tire diameter and a calculator. the AEM A/F O2 sensor in the front of the muffler read 10.2-- rich-- for the fastest run. wouldn't pull higher than that rpm with more track still to go.

today i ran with a set of pipes i've never used-- haven't even ever had them on the bike before i took them down the track. stock 1.5-inch pipes with eBay reverse cone megs:

Quote:
Outlet at widest point: 100mm.

Overall Length : 420mm ( 16 1/2 Inches )

Reverse point of inlet: 75m
m.

i bumped the main jets from 220 to 240 based purely on guesswork. the bike seemed to carburate cleanly, and ran 117 mph at an indicated 6900, probably 6500. seemed to have horsepower still left on the table by the time i hit the lights. one run, i didn't notice any reversion, but i was kind of busy. had to disconnect the A/F gauge because i didn't have time to put a bung for it in this pipe.

i didn't have time to paint them before i brought them, either, and the pipes colored in a really interesting way after the single 117 mph run:









what's going on? i'm guessing that the heat is accumulating at this section of the pipe because of the intersection of a pressure wave going out with a pressure wave coming in, but i don't know how exhaust gas temperature might correlate with sonic waves in the pipe, or why.

i'm also guessing that this zone of increased heat (due to pressure?) can be relocated up and down the exhaust system by changing the length of the header pipe or messing with the megaphone, given constants on the other stuff. for instance, a shorter pipe could extend the zone out the end of the megaphone into the atmosphere, maybe. a steeper taper on the megaphone could make the zone narrower?

what am i looking at here? what might be gained or lost by moving this really interesting zone up or down the pipe?


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Re: megaphones [Re: kevin roberts] #650784
04/30/16 3:07 pm
04/30/16 3:07 pm
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Bolton Lancs UK
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It could be due to turbulence when the gasses exit the pipe into the megaphone


1955 BSA B31 400cc "Stargazer"
1962 Greeves 200cc "Blue Meanie"
1962/67 Greeves 350cc
1967 Greeves 360cc Challenger
1984 Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc grasstrack
2003 Aprilia RSV Mille "Lo Stregone"
Re: megaphones [Re: kevin roberts] #650787
04/30/16 3:24 pm
04/30/16 3:24 pm
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could be, andy.

the end of the pipe is about one inch into the meg, with about 1/4-inch step due to several reducers and a roll of beer can aluminum to make the clamp hold.

does a zone of turbulence like that obstruct flow? shortening the pipe would have no effect on a turbulence zone, but would alter where a zone of changing pressure occurred in the exhaust.

rather than a wave of doubled amplitude, could it be standing wave instead?

i'm going to be experiment with trombone sections on this setup, and i'm curious about what i might looking for.


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Re: megaphones [Re: kevin roberts] #650858
05/01/16 6:28 am
05/01/16 6:28 am
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queensland australia
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ken sak Offline
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Originally Posted By kevin
could be, andy.

the end of the pipe is about one inch into the meg, with about 1/4-inch step due to several reducers and a roll of beer can aluminum to make the clamp hold.

does a zone of turbulence like that obstruct flow? shortening the pipe would have no effect on a turbulence zone, but would alter where a zone of changing pressure occurred in the exhaust.

rather than a wave of doubled amplitude, could it be standing wave instead?

i'm going to be experiment with trombone sections on this setup, and i'm curious about what i might looking for.


any baffling? the Harley and drag race guys would run a line
down the side with crayon and where the line would burn to they would cut the pipe off to get max hp

Re: megaphones [Re: ken sak] #650900
05/01/16 12:01 pm
05/01/16 12:01 pm
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I asked the question on this forum populated by many professional Speed Talk engine builders and tuners....I think the first response makes sense....



650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
Re: megaphones [Re: ken sak] #650979
05/01/16 9:34 pm
05/01/16 9:34 pm
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Originally Posted By ken sak

any baffling? the Harley and drag race guys would run a line
down the side with crayon and where the line would burn to they would cut the pipe off to get max hp


completely open. loud, too. i spoke with a guy who suggested running a chalkline down the pipe. where the chalk turned brown was hot, and an indicator of something he couldn't explain . . .


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Re: megaphones [Re: Hillbilly bike] #650980
05/01/16 9:39 pm
05/01/16 9:39 pm
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Originally Posted By Hillbilly bike
I asked the question on this forum populated by many professional Speed Talk engine builders and tuners....I think the first response makes sense....



what effect would the turbulence have? is there an advantage to, say, making the megaphone short enough so the the turbulent zone extends out the back into atmosphee.

if the heatbuild is due to turbulence then it must be a place where the air isnt moving well. therefore flow is obstructed


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Re: megaphones [Re: ] #650982
05/01/16 10:08 pm
05/01/16 10:08 pm
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Originally Posted By needing
Hi Kevin.
I followed Hillbilly bike's link and the first response makes sense as your A:Fr was already 10.2:1 and you then went to a larger main jet. Low pressure at the header gas expansion point could be acting like secondary air injection into the system.
I'll be interested in what you discover.
Ta.
Owen.


maybe so. i didn't have time to put any bungs into these pipes, so i'm ignorant of what the precise AF ratio was in the pipe. i'll fix that as soon as i can-- the AF information would have been immensely helpful today.

one very interesting thing about these megaphones is that there is zero detectable reversion misfiring-- what people call "megaphonitis."

nothing. i had ten runs today and on the way back to the start i would open and hold the throttle to see if the main jets would falter. the motor always took full throttle instantly with no bogging or hesitation from around 2500 rpm on up, so the jets seemed to be close.

so i carefully would run the motor up and down from 2000 rpm to 5000 rpm, looking for any spot where the mixture would indicate any richness, dull sounding firing, motorboating, whatever, due to the reversion.

nothing. the motor took all throttle positions clean through the entire midrange. this and at wide open were where the AF gauge would really have helped me. i tried several main jet configurations through the day looking for the correct one, and was never satisfied with the information i got. the air density was radically different and unstable all three days, and so it was difficult to find the jetting which would give the correct AF ratio.


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Re: megaphones [Re: kevin roberts] #651002
05/02/16 6:05 am
05/02/16 6:05 am
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Bega NSW Australia
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I'd try bigger dia headers, and leave the megaphones as they are. Reversion may then happen with larger bore pipes because at lower rpm gas will be at lower speed in them and they will not pull the mixture through as well, gas speed in the intake will slow and have less energy to charge into the cyl as the piston rises. You are kind of balancing the pressure of the piston rising against the pressure of the intake charge, which is dependent on its speed. Bigger pipes will flow more and when they do you should get more power and speed, all in the top end. You might get some reversion before the gas speed in the inlet produces enough pressure to win and charge the cyl properly, but I'd aim for that so you get more top end.


mark
Re: megaphones [Re: Mark Parker] #651010
05/02/16 7:29 am
05/02/16 7:29 am
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Based on my past experience I would say the "mild" cams and possibly the Mikunki carbs or their position on Kevin's bike contributes to the lack of reversion...
My 650 Triumph LSR bike with TT type 1-1/2 diameter pipes had reversion with 32mm Amals and a lot less reversion with 34mm flat slide Mikunis. Long intakes and or velocity stacks may make it worse...
Many years ago I put a SS type cam in a Norton 850...the engine had reversion after the cam swap and removing the mufflers helped....
My hot rod BSA A10 of a few years back...."357" cam created a big flat spot at 4000 rpm...


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
Re: megaphones [Re: kevin roberts] #651019
05/02/16 8:42 am
05/02/16 8:42 am
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Hillbilly, being 750cc makes quite a difference as its creating more vacuum and pulling the intake in harder than a 650 motor would. A hotter cam will close the intake later so the piston comes up more before the valve shuts and needs more energy in the intake to overcome it and push air into the cylinder. Before it does that you get reversion and flat spot. Big ports and carbs can cause it as well because they slow the gas speed in the head. But in all respects they can pay off in top end when it all starts working. Of those things I do not think the cam is that important, stock cams in these motors are all fairly sporty.

Without changing a cam, pipes can move power up or down the rev range and cause or remove reversion and flat spots. If the inlet side will flow more it could be that the pipes are a restriction.

A head that flows lots through a smallish port seems the holy grail as it limits reversion and feeds the engine lots of air. I noticed on the flow bench I made that opening the valve more on a std A65 head didn't increase the quantity of air going through but reshaping the port with it no bigger in volume, still 30mm at the carb end and through the same std valve same lift it's possible to get an extra 30 or so CFM of air, a cam cannot do that, not to that degree. The std port is that bad BSA put in a very decent cam to get some air through, its difficult to improve on the cam. The Triumph is probably similar.

With this 750 it may be that larger dia pipes, although maybe introducing a little reversion may allow more air through the engine at higher revs and give it more go in the top end. I could be wrong, but that's what I'd experiment with.


mark
Re: megaphones [Re: Mark Parker] #651028
05/02/16 9:16 am
05/02/16 9:16 am
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ohio, usa
kevin roberts Online content OP

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Originally Posted By Mark Parker
I'd try bigger dia headers, and leave the megaphones as they are. Reversion may then happen with larger bore pipes because at lower rpm gas will be at lower speed in them and they will not pull the mixture through as well . . .


i can easily obtain what are called "drag pipes" for triumph hardtail choppers-- 1.75-inches and straight, ideal for trying this out. i'm clueless about what lengths to try, though. clearly it's time for a lot of experimenting.

i didn't have time to mess with intake length, but i have some tubes made up to try out that extend the carb back.


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Re: megaphones [Re: kevin roberts] #651063
05/02/16 11:57 am
05/02/16 11:57 am
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Allan Gill Online happy
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Some time last rear I retarded the cam about 5 degrees on the A65, created a flat spot between 4000-5000 revs, just like reversion. I stronger coil reduced it to a 500rpm flat spot. However still a pain in the tits when over taking something. That said the rest of the range was more spritly than when in its standard position. I guess I just couldn't win with that cam. But as far as A65's go, there are far better cams than the stock spitfire unit. Whilst the stock cam does give a reasonable top speed, it does nothing for acceleration.


beerchug
Re: megaphones [Re: kevin roberts] #651096
05/02/16 3:26 pm
05/02/16 3:26 pm
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ohio, usa
kevin roberts Online content OP

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on these, i'm headed out to the shop after i wash up the dishes and i'll drill out one of the megaphones for the A/F sensor.

i'm interested in what is happening right in the middle of the colored zone, so i'll put it there and see what it reads. maybe i'll have to do another farther up to have something to compare it to.

a fellow on speedtalk.com said this:
Quote:

It's pretty likely that air was being sucked back into the back of the megaphone because of the strong pulses in the exhaust system, and that hot area was where the mixing of that air with the hot (and rich) exhaust reached the highest burn temperature. Closer to the engine the air being pulled back in wasn't getting that far upstream, and closer to the back had more dilution.


however, this is just a 750, and each pipe therefore only expels 375cc for each exhaust stroke. i haven't measured it yet, but the cool zone on the pipe from the reverse cone up to the color has got to be over 375cc. so if the color is due to exhaust gases physically being sucked back into the pipe at overlap, then the pipe is sucking back way more than cylinder capacity. is that even possible?

that doesn't make sense to me, so i don't think that is what is going on.

i'm thinking it's likelier a turbulent zone where exhaust lingers and loses heat to the pipe before passing out (and therefore increases in pressure because it is an obstruction), or it's the intersection of outgoing and incoming pressure waves-- not physical gases, but sound-- that intersect and add their pressures and therefore their ability to transfer heat from the exhaust to the pipe.

if the former, then getting rid of the obstruction would be an advantage. bigger headers with less of a step? that's in the plan . . .

if the latter, then there has to be something useful that could be done with that pressure.


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Re: megaphones [Re: Mark Parker] #651105
05/02/16 4:44 pm
05/02/16 4:44 pm
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Mark, what you say makes sense.....I avoided megaphones on my Triumph LSR bike and instead built the engine with TT type pipes and wound up going faster than the guys using megaphones.It's not like it was great planning ... I just used the parts I had....
I found the fastest speed for my engine is from gearing the bike to hit the finish line at the greatest sum of HP and torque..Somehow I got the torque peak at 5100 rpm and at 7000 rpm the engine still has over 90 percent of peak torque available. This makes the bike accelerate very fast and it's easy to ride. One mile LSR on pavement is sort of a long drag race...Reversion bogs down the bike off the line and forces the rider to slip the clutch the using a lot RPM...Better low end or better top, can't have both sometimes...
I do have a set of megaphones and maybe will try them out just to see what happens...


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
Re: megaphones [Re: Hillbilly bike] #651110
05/02/16 5:42 pm
05/02/16 5:42 pm
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this street bike of mine will rev to the sky in 3rd or 4th, with either mufflers or the megaphones. i can get 7000+ in a heartbeat.

but if i run it up to 7000 in fourth and then shift, i drop to 5882, and have trouble getting back up to rpm before the lights. that's a big rpm drop. i go through the lights at between 6500 and 6900, indicated, and the last quarter mile is flat, no increase in speed.

clearly i'm losing torque up there, because the rpm drop is unrecoverable. i suppose i could shift at 7500+, and then the drop would be only to 6500, which would help a lot.

but this is my commuter, and it hasn't been built to take that for long. i'm wondering if i might be better off taking that 21-tooth gearbox sprocket back out and putting the 20-tooth in.

that would give me 120 at 7000 rather than 125, and might be the happy medium with the current breathing.


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Re: megaphones [Re: kevin roberts] #651113
05/02/16 6:01 pm
05/02/16 6:01 pm
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For some inexplicable reason Triumph did not put 4th gear very close to 5th. Your experience highlights why they should have. 1 and 5/8" headers might be better than 1.75" they are pretty easy to make if there is an exhaust place around. An 'X' connecter can help, better results than separate or 2 into 1 in my experience. Allan retarding the cam timing opens and more specifically closes the inlet valve later. But A65s do go better and give more piston to valve clearance.


mark
Re: megaphones [Re: Mark Parker] #651118
05/02/16 6:18 pm
05/02/16 6:18 pm
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Originally Posted By Mark Parker
For some inexplicable reason Triumph did not . . .


^^^that's a concise summary of a whole lot of history right there, mark.

Quote:
1 and 5/8" headers might be better than 1.75" they are pretty easy to make if there is an exhaust place around. An 'X' connecter can help, better results than separate or 2 into 1 in my experience.


leo goff recommended 1 5/8-inch, and http://www.coneeng.com will provide a kit that let's you build it . . .

i don't know enough to have an opinion on exhaust configuration, but i've looked at your BSA's pipes.

why do you like the x-connector?


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Re: megaphones [Re: kevin roberts] #651180
05/03/16 9:59 am
05/03/16 9:59 am
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interesting.

obviously the same thing is going on, but with the 2 into 1 system.

i've never seen anything like this with a muffler on the tube or with straight pipes.

just discovered looking at pictures that blued exhaust pipes have become a fashion accessory-- they come that way new:


Last edited by kevin; 05/03/16 10:09 am.

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Re: megaphones [Re: kevin roberts] #651290
05/03/16 8:23 pm
05/03/16 8:23 pm
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Originally Posted By kevin
Originally Posted By Mark Parker
For some inexplicable reason Triumph did not . . .


^^^that's a concise summary of a whole lot of history right there, mark.

Quote:
1 and 5/8" headers might be better than 1.75" they are pretty easy to make if there is an exhaust place around. An 'X' connecter can help, better results than separate or 2 into 1 in my experience.


leo goff recommended 1 5/8-inch, and http://www.coneeng.com will provide a kit that let's you build it . . .

i don't know enough to have an opinion on exhaust configuration, but i've looked at your BSA's pipes.

why do you like the x-connector?


The X connector will allow both silencers to help the headers breath more efficiently than a H section balance pipe.


beerchug
Re: megaphones [Re: kevin roberts] #651315
05/03/16 11:43 pm
05/03/16 11:43 pm
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allan, i can see that if the exhaust pulse for each cylinder leads into two tail sections, it obviously will reduce back pressure, because the power strokes are completely separated and only one cylinder exhausts at a time (in a 360 crank motor).

is the efficiency of the X-section crossover just due to the more streamlined exit passage, or is there something going on with resonance in a X-section that an H-section doesn't have?


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Re: megaphones [Re: NickL] #651328
05/04/16 3:46 am
05/04/16 3:46 am
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Whatever the dramas, that is one beautiful outfit! Would have loved to have met you, Nick.

Re: megaphones [Re: kevin roberts] #651337
05/04/16 6:41 am
05/04/16 6:41 am
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Originally Posted By kevin
allan, i can see that if the exhaust pulse for each cylinder leads into two tail sections, it obviously will reduce back pressure, because the power strokes are completely separated and only one cylinder exhausts at a time (in a 360 crank motor).

is the efficiency of the X-section crossover just due to the more streamlined exit passage, or is there something going on with resonance in a X-section that an H-section doesn't have?


Apart from being a mechanic/mot tester etc I have the fortunate job of making exhaust pipes too, admittedly these are for cars but the smallest pipe size I can work with is 1.5" (and anything upto 3") many pre made performance exhausts if incorporating a cross over use the X type, very rarely do I see a H type unless it's joining two mid boxes together. Other thing to remember is gasses have more of a restriction trying to utilise a H Section than they do with an X.

I suppose you can reduce the outlet of two silencers to retain the same back pressure as one silencer with a bigger outlet but reduce noise output at the same time.

There are too many variables (like with any part of the engine) which can be changed and the key is to make one change at a time and catalogue the difference.

I won't mention who we are a franchise for, however when my boss decided who to go with he naturally picked who's exhausts gave the best performance from the test reports, one of the key differences between what we use and others didn't was that we do not use mandrel bends, ( unless of course it's a very tight bend then we have to buy sections) but when we are bending the pipe they are not of mandrel type.

I do intend to make some standard down pipes and compare them with the off the shelf items, before making the tt pipes for my racer.

.... Now if I had a sheet steel (roller) former then I could make my own silencers as well.


beerchug
Re: megaphones [Re: Allan Gill] #651340
05/04/16 7:06 am
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Posts: 3,260
Running from demons in WNY
Here a photo of Tim Joyce's 750 Triumph. Notice the exhaust systems...This is road racing but Tim's bike made more power than anyone else it seems...Where are the megaphones? Other photos of his bike show a short primary pipe two into one one system..

http://www.worksperformance.com/images/sponsored/tim_joyce/tim_joyce_beaverun_raceway_9_11_04a.jpg




650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
Re: megaphones [Re: kevin roberts] #651344
05/04/16 7:44 am
05/04/16 7:44 am
Joined: Dec 2013
Posts: 3,526
ohio, usa
kevin roberts Online content OP

fefsa
kevin roberts  Online Content OP

fefsa
Joined: Dec 2013
Posts: 3,526
ohio, usa
those appear to the traditional TT pipe length.

his carbs are on 3-4 inch extensions.



i like the swing arm bracing. my street bike at wilmington would start to get uncertain if i lifted off the saddle. i think it's a combination of front and back.


live every day.
die only once.
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