Big pipes look cool indeed!.. The prewar Two Ports also look great but seem to do nothing for performance. Single port breathing was more efficient.
Maybe they were just economical at BSA and simply used the B31 version for the 500 :relaxed:
From Tuning for Speed, Phil Irving:
I fitted the larger Daytona pipe on my Goldie café racer purely because I like the 'fat' pipe look...However, I'm looking for the information now as I have to make a decision on the best pipe size for my sprinter project and that is a more critical application!...
email (option): ian@wright52.plus.com
This is the next page but you will probably have this book yourself:
Seems the shorter the pipe the bigger the diameter, and use of megaphones require an even shorter pipe with even bigger diameter.
Maybe take the M20 pipe and make it easily adjustable in length for testing??
The Husqvarna V twin racers had the end sticking out a metre behind the rearwheel. :slightly_smiling_face:
BR Michiel
Don't know if this helps.
I have a technical book somewhere but it might take some finding. Also I have a calculator for determining optimum dimensions. I can send the working version by email (can't seem to figure out how to attach it here). Below is a print-out - the only figures you would need to enter are along the top row.
email (option): cas.vanderwoude@gmail.com
Here's the carb...The parts I've just finished making are the alloy body top, top locking screw and mounting plate and the upper rubber mount...
I'm not using the flange mounting shown in the photo, the carb will be directly rubber mounted to the inlet stub...The main rubber mounting is an Amal part but the mounting that is at the top/rear of the body is what I've made...That gives additional support to the carb and prevents it 'flapping about' on the mounting rubber...The Mk2 Amal body is drilled and tapped to take a mounting but that has to be produced individually to suit the application...The stud is overly long at the moment as I haven't made the bracket that connects to it yet....
I'll post my conclusions on the pipe sizes when I've finished working it out....Ian:stuck_out_tongue:
email (option): ian@wright52.plus.com
On a website that I cant retrace anymore I read about Roland Pike and a tale about tuning he and others did on a BSA Goldstar.
By accident they found out that a step in the inlet made for a increase in power.
So new Goldstars where delivered with a smaller inlet in the head compared to the carb size.
More then one owner, when finding out that the carb was bigger then the inlet, enlarged the inlet in the head and lost the gain power again.
The article also gave information about this 'step' in the inlet, in fact a venturi. see drawing I made below.
Maybe they were just economical at BSA and simply used the B31 version for the 500 :relaxed:
From Tuning for Speed, Phil Irving:
Valve steels were a massive problem till WWII when sudenly there was no limit to the amount of money poured into researching a lot of things
Remember the exhaust valve runs at yellow heat in a single port but in a twin port that drops down to dull red
Some really high perfomance engines now have valves running white hot and may have ceramic coatings of one type or another to prevent the valve picking up as much heat from the exhaust gasses.
We forget that everything prior to the 69's was designed with slide rules and in most cases engine designers went with what had worked well in the past.
If you look at the bore / stroke ratios you will see BSA used almost the same ones from day one which is why the A 7 and in particular the A 65 were such a radical departure .
And the same applies for just about every other marque that made their own engines
In a side valve you want almost no back pressure because the inlet & exhaust gasses share a common chamber
On an OHV the inlet & exhaust tracts are totally seperate so you can get some big power boosts from tuned exhausts.
The final thing is standard pipe sizes .
Post the great depression the actual mark up on motorcycles dropped drastically so the days of getting custome made tube to make exhausts from was gone so it was a case of using what the mills made .
And finally as BSA made their own exhausts there is production capacity and available tooling .
Remember the M20 came in as part of the redesign to simplify production and standadize parts .
As such the fewer new jigs & fixtures the better as the new B & M range were only 1 year apart .
The M's were the meavyweigh models designed specifically for hauling sidecars around all day every day so ran lower gearing and usually ridden slower so the flow of cooling air across the engine was expected to be lower than the sports B models that were designed for quick green lane recreational riding or short ride to work for highly paid staff .
Remember when they were designed production workers walked to work, foreman rode pushbikes and managers had motorcycles while executives could afford cars .