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which megaphone #407505
12/06/11 9:32 pm
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Wiebe Offline OP
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Which Megaphone replica comes closest to the one originally fitted to the all sports comp an some Catalinas, ah and could be considered road legal.....?

thx

Wiebe

BSA Gold Star eBay items

BSA Gold Star forum This board is dedicated to BSA Gold Star motorcycles.

Re: which megaphone [Re: Wiebe] #407510
12/06/11 10:03 pm
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I don't know about the UK, but here in the States I don't think there is any mega that would be considered road legal.


Boomer
Re: which megaphone [Re: Wiebe] #407513
12/06/11 10:26 pm
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Judging by the some of the Harleys running around here I don't think noise ordinances are enforced very well.


When given the choice between two evils I picked the one I haven't tried before
Re: which megaphone [Re: Wiebe] #407531
12/07/11 12:10 am
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Wiebe Offline OP
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well, as i now understand it, isnt there a pre 83 law in place in the uk, or something like, if it was loud in 59, it is allowed to be loud now? Some exhaust systems are sold as pre 83 only fitment....

Wiebe

Re: which megaphone [Re: Wiebe] #407585
12/07/11 2:02 pm
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Unity sells what appears to be a decent replica...but I would add some perf tubing if you want to actually ride the bike. Particularly in combination with a big carb and clubmans cams, megaphonitis can be a PITA.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
Re: which megaphone [Re: Wiebe] #407607
12/07/11 4:43 pm
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Wiebe Offline OP
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megaphonitis? Youve lost me there....

Re: which megaphone [Re: Wiebe] #407615
12/07/11 5:24 pm
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kommando Online content
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megaphonitis?

A hole in the power band usually mid range caused by a megaphone, difficult to tune out and creates bikes that when you change up a gear the drop in revs hits the hole and the wait for the power comes back looses the race.

Re: which megaphone [Re: Wiebe] #407650
12/07/11 8:33 pm
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Hence the term "keeping it on the boil". Usually around 3 to 3.5K RPM.


Boomer
Re: which megaphone [Re: Wiebe] #407653
12/07/11 8:48 pm
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Wiebe Offline OP
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so the perforated tubing is like bafflers? unity does sell the short megaphone with bafflers installed....

Re: which megaphone [Re: Wiebe] #407743
12/08/11 10:00 am
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Wiebe Offline OP
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No baffled megaphone at unity anymore, some yanks bought it, as well as the last catalina pipe thank you very much! Hopefully the dollar will stay where it is and we will buy all the goldstars!!

All kidding aside, question about the megaphonitis. Does a Catalina with regular open pipes without silencers as per standard (or at least for the eastern or western part of deliveries...) have the same power band issue? If not, how could fitting a megaphone cause it?

thx

Wiebe

Re: which megaphone [Re: Wiebe] #407771
12/08/11 2:43 pm
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Wiebe, straight pipes do not send as "focused" of a reversion (reflected) pulse back to the carb as megaphones and, hence, tend not to suffer from the same problems. The idea of a megaphone is to reflect a pressure pulse back to the combustion chamber at the time the inlet is just closing to improve charging of the cylinder. The problem is that this only works in a narrow rpm range and at lower rpm, the pulse actually makes it THROUGH the combustion chamber and into the inlet tract to decrease charging of the cylinder. The more overlap you have, the worse so, again, it's usually not a problem with touring cams and smaller carbs. What a simple piece of perf tube will do is spread out the reflected pulse and mitigate its impact. It can make a significant difference. It's not hard to add to a megaphone after the fact and can be made removable. The other way to reduce megaphonitis (and I hope Dave will chime in here, he's described this very well in detail) is to insert a step in the pipe at the inside of the bend where it enters the cylinder head.

I didn't want to scare you but this is something to consider when putting a straight mega on a tuned motor.

Cheers.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
Re: which megaphone [Re: Alex] #407794
12/08/11 5:43 pm
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Wiebe Offline OP
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what puzzles me is that some catalinas were delivered with a megaphone, claiming it inceased torque accross the rev range (i am quoting a 60 or 61 brochure) Would this have to do with the overlap being smaller (scrambles engine) and the carb being smaller (Monobloc rather than GP) than on an Goldstar all sports competition for instance?



rgds

Wiebe

Re: which megaphone [Re: Wiebe] #407800
12/08/11 6:23 pm
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Yea...I can't speak to the validity of the advertising department's claim, but yes, the smaller carb would porbably help some. The overlap, however, AFAIK from the specs is little different in the scrambles configuration than the clubmans or race spec (only about 2 degrees difference).


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
Re: which megaphone [Re: Wiebe] #407802
12/08/11 6:25 pm
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Wiebe Offline OP
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can of worms....

did some reading and came accross some interesting things. Not sure how to combine everything to something workable but anyway....
See my intention is to make the catalina road legal and with straight through pipes without any silencing thats not going to work. Enter the megaphone as it was part of standard equipment, well certainly for some years and some parts of the US. Than I am acquiainted with megaphonitis which makes absolutely no sense as BSA claimed the megaphone actually helped increase torque over the whole rev band.... So enter this article http://victorylibrary.com/brit/mega-c.htm .

Left me totally clueless about what to do.

Re: which megaphone [Re: Wiebe] #407806
12/08/11 6:34 pm
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If my worn out memory recollects, the mega was fitted to the 1 7/8" pipe and this exhaust system was the set-up for the "Clubman" head with GP carb and 2442 intake cam. The Catalina with the Monobloc carb would run the 1 3/4 straight pipe that curved out and was not swept back. The Bruce Main-Smith book has a chart that shows different set-ups with different lengths of inlet and exhaust tracks.


Boomer
Re: which megaphone [Re: Wiebe] #407813
12/08/11 7:07 pm
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Wiebe Offline OP
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[img]http://www.classic-motorcycles.com/galleries/bsa_scrambler_ad.jpg.html[/img]

This is one of the brochures I found with a Catalina with mega.

Re: which megaphone [Re: Wiebe] #407820
12/08/11 8:23 pm
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Well, as it says "larger carburator and full race cams". Those brochures are artist renditions and are sometimes published before that production year and as we have discussed on other threads, IMO, what was actually sold wasn't always what was advertised. The GS megas that I have seen are 1 7/8" and the scrambler header pipes were 1 3/4". I wouldn't think a mega would be practical on a scrambler that is relying on low RPM torque versus a road racer or 1/2 to 1 mile flat tracker that is using the upper range of RPM for power. They are easy to make if you know a metalsmith. I believe in BM-S's GS book, there is also a dimension detail of the mega. I don't espouse to be an authority as I'm going by experience and failing memory.


Boomer
Re: which megaphone [Re: Wiebe] #407821
12/08/11 8:27 pm
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Some comments on megas... I have a 'factory' 1 7/8" headpipe and mega we've used on our GS tracker when there's no noise restrictions. The 'big' pipe and mega were sold by BSA during The Era and then was fitted OEM on the '62-'63 Competition model as mentioned by Boomer. It's debated by many tuners if this combo is useful in normal competition vs the 1 3/4" pipe setup. We use the 1 3/4" headpipe modifiied for AR with a silenced mega built by a gent in Texas for most racing.

On my road GS 'special' I use a AR modified 1 3/4" pipe with a modified 'twitter' that's been cut open with the forward perfed pipe section removed and a reverse cone added with a SS 'pot scrubber' packed rear section. A tidy silenced mega.

With suitable ant-reversion pipe modifications AR is not an issue even with the 1 7/8 pipe. Exhaust Reversion is present in all exhaust sytems and will be a problem with a short/tuned length straight pipe no megaphone required.

In their techy book on Intake and Exhaust systems, Smith and Morrison mention reversion being a problem on the earliest engines way back into the late 1800s. One guys cured was a ~28 foot long exhaust pipe! Race car tuners have long fought reversion by merely mismatching headers to the exhaust ports making a 'dam' to stop the reversion pulse.

Exhaust Reversion is merely a pulse of ambient air flowing back into an exhaust system to fill the vacum caused by the expelled hot gases, even flowing back out the open intake valve and back out the carb. This can and will cause double and triple fuel loading of the incoming charge. This why AMAL supplied a extra lean 'mega needle' for the GP carbs.

If the length of the exhaust system is short enough, the engine RPM is low enough and the exhaust cam timing is long enough, the pulse of ambient air flowing up the pipe will push the lingering exhaust residue with it back into the combustion chamber, preventing proper exhaust scavanging and fuel problems.

The low speed Exhaust Reversion pulse MUST NOT be confused with the high speed Sonic pulse utilized in a tuned length exhaust system!

Are we having fun yet? I hope so!!


Last edited by dave - NV; 12/08/11 8:30 pm.

dave - NV
Re: which megaphone [Re: Wiebe] #407829
12/08/11 9:19 pm
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Dave,

I knew we could rely on you for a better definition. I think Wiebe is looking for something across the counter. He may need to seek out a exhaust specialist to fabricate what he needs.

Weibe,

What cams are you planning on using?


Boomer
Re: which megaphone [Re: Boomer] #407843
12/08/11 10:09 pm
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Is this a trick question? I thought all of this was going to be very clear and easy to find out and implement. I now remember that the catalinas at one point were issued with a slightly larger monoblock, only to go back to the smaller monoblock a year later. The funny thing is that I can only find the Catalina with a Mega in one year, in 1961. I am sure some of you will be able to prove me wrong, but all of the above would suggest that BSA did find that putting a mega on a catalina was not the best of ideas (though I am still puzzled by the fact that BSA claimed to have increased the torque accross the range). As the replys to this thread do not come in every minute, I have had plenty of time to read some other thoughts about the subject on other forums etc and what I found interesting was that the shape of the exhaust pipe alone could cause issues, with the catalina pipe most likely being the smoothest and best.... any way, cams, As I understand that the regular setup of the catalina gave it good torque accross the rev range that is what I will be going for. But I also need a silencer and no way am I going to put something on there which doesnt look like it belongs there..... hence the megaphone and all my troubles. And I have already bought an unbaffled mega from unity today!! My idea was to somhow put a baffle in or to Perforate the end of a catalina ex pipe and slide it over.... what was I thinking....

Re: which megaphone [Re: Wiebe] #407904
12/09/11 8:21 am
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Weibe, I own a '61 and a'63 Catalina and both are original, East Coast bikes. Both bikes came with megaphones and the swept back pipes. The Feb. '62 issue of Cycle World has a road test of the '62 Catalina (West Coast bike) and it also shows the swept back pipe and megaphone. I believe that all of the '61-'63 Catalinas came that way, even though the dealer brochure "renderings" show the smooth curved pipe with the mega. Both of the '62 and '63 brochures have actual pictures of the Competition model (instead of renderings) and it is equipped with the swept back pipe as well. I can't speak to the megaphonitis, but I can tell you that a megaphone equipped Catalina will make some serious sound when you twist the throttle!

Re: which megaphone [Re: jimm] #407915
12/09/11 11:03 am
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ah, would you mind sending me a picture of the megaphones you have with an idea about their length? By the way before i read your post I found a baffle for a saight pipe. made by khromewerks in the us called hp-plus baffles. its supposed to help harleys through mot, so why not a bsa? It would take a lot of guessing out of the way, and the 59 catalina would be looking original. However Id still be very interested in a good picture (or a couple from different angles) of the original megaphone as my all sports comp does not have the original mega fitted...l tyx Wiebe

Re: which megaphone [Re: Wiebe] #408748
12/15/11 6:17 am
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Hey Weibe, here are a couple pix of the megaphone. It is about 14" long, with a 1 7/8" inlet and a 3" outlet. Hope this helps.





Re: which megaphone [Re: jimm] #408920
12/16/11 2:32 pm
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super!! So this is also the one used on the all sports competition, given the inlet size of 1 7/8 I presume.

thank you for posting the pics!

Wiebe

Re: which megaphone [Re: jimm] #409395
12/19/11 10:20 am
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and a day later one appeared on eBay here in the UK. Now mind you, sizes are a bit different, inlet inside diameter is 2" outlet was 3 1/8" length 15", but it was there....

Last edited by Wiebe; 12/19/11 10:22 am.
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