Exhaust- early vs late

[Zimm]

Is there a difference in the fitting of exhaust pipes between the iron head A10 and the later alloy head? 

I have a 54 Golden Flash with the iron head.  I also have access to a very nice 2 into 1 set of pipes that was originally purchased to fit a 59 with the alloy head. 

Obviously the answer is to give it a try, but the motor is currently out of the bike for a rebuild and I am researching exactly what I want to put on it when it goes back together.

Your best advice is appreciated.

Zimm

[Topdad]

Hi Zimm, I've got Siamese pipes on an iron headed bike, bought them from Cake St and don't recall being asked what head was fitted and they fitted great, Bob.

[bikerbob]

They are different I had a 1957 Gold Flash and bought a set of exhausts and silencers  and had to exchange the exhaust pipes  the supplied ones were for the later model, the brackets are different and maybe the bends. not sure about that though. I don't think it has to do with either alloy or cast head it has to do with year of production 54-57 then 58 onwards.

[Topdad]

Yes did inform what year my bike was , Bob

[worntorn]

Did the 2 into 1 add a bit of power or was a more of a cosmetic preference for some? I suppose it eliminates a fair bit of weight by jettisoning  one muffler.
Does the 2 into 1 as delivered as a factory option (on some years of Super Rockets at least) utilize a standard muffler of the dual type, or was it a special muffler?

Thanks
Glen

[groily]

Reckon that is a very good Q Glen.
I have three machines including my A with Siamese pipes because I like the access to the primary side (and don't want too many bits - any bits really - to clean).  So that's cosmetic, but probably for the wrong reasons!
Two of them have run with twin pipes & silencers as well for long periods, and I haven't really noticed any great difference. Maybe a tiny bit less good at large throttle openings with the siameses - the routing on the A in particular, with a sharp bend inside the downtubes from the left hand exhaust port - could conceivably stifle things a bit I suppose? But then again, those pipes went onto Super Rockets, as you say. (I suppose we should also note that the pipes are slightly different lengths, which some would be 'against'.)  Probably have to thrash things to within an inch of their lives to get a true feel for any difference, I think.

Things can sound a bit busier with all the noise coming out of the one hole (hardly surprising) but in terms of normal road-going performance, if there is anything much in it, I haven't discovered it. I've heard it said that Siamese pipes improve the mid-range feel (or even the reality!) but can't say I've noticed that either.

As to silencers/amplifiers I don't know what is correct on anything, but I've run with megas, pattern Goldies (pair and just one) on the A, and standard-type BSA silencer(s) various, and again, apart from the sound I can't tell much difference - except with a megaphone. With that on, this bog-standard siamesed A seems to rev very freely (and frighten the horses), but is less good at the low end. Some of the 'gain' will be an aural illusion though (overgrown teenagers spring to mind); the perceived shortfall may be down to not having done enough tweaking of the carburation to compensate for reduced back pressure.

Whether the picture with a siamesed A is significantly different with higher compression and a lumpier camshaft than mine, maybe others can say. But running the other bikes I have, with compression ratios up to 10:1+ in some past configurations, I can't say there were any obvious differences between separate and siamesed. So I'll be sticking with siamesed when it's a choice.

[muskrat]

Yes I think groily hit the nail on the head. Normal or even spirited road use won't show much difference. Any pipe change will require a little carb adjustment to make it work.
Cheers

[worntorn]

Thanks for the info groily and muskrat. If  performance is similar then I would also gravitate toward the siamesed exhaust. A bit less costly , a bit lighter and,as groily pointed out, less area to polish.

Glen

[bikerboy]

I was under the impression that the siamese pipes were mainly introduced for bikes that had sidecars on them?

[Topdad]

I never got  to sell new A10 's only second hand ones as I started selling in '65/66 but if the sales form for a new bike sale back then was anything like the one we used ( we were BSA/TRI main dealers so it was the official form ) I'd say it'd be an "optional extra " like the  tacho, dual seat and I seem to remember  pillion pegs. I used to be embarrassed when I had to point this out . Bob.

[worntorn]

The ad from 62 offered the Siamese exhaust as a high performance option. It is named "the Power Jet Exhaust" and the claim is  more horsepower through the extractor (cylinder to cylinder scavenging) effect.
Glen

http://www.bsansw.org.au/catalogs/1962/T3.jpg