Vehicle exhaust extraction.

[Spectric]

An engine is a pump. It has a displacement and an rpm. The flow rate can be calculated from that.

Petrol two strokes are not quiet the same as they also use the crankcase so often have lower volumetric efficiency.

Yes that full racing one from 1981 would give many modern bikes more than a run for there money, just the £47,000 price tag. But you get a bike capable of 180 mph and a 0 to 60 time of less than 3 seconds but where can you do that now.

 

[paulrbarnard]

That bike is a sad reminder of just what could have been for the British motorcycle industry and british engineering overall as we often had the technical expertise but lacked the marketing and production side. The ariel leader came first and then the arrow, both used one of the first two stroke two cylinder engines to hit the market and it has been said they were a forerunner to the Japanese invasion of two strokes, so why did we not keep up ? Also don't forget Ariel also had a four stroke overhead cam square four engine back in 1930, this would have been years ahead of any major competition from the japanese or Italians.

If you want a really quick two stroke bike then look for an RG500 Suzuki 4 cylinder but in race trim, the acceleration is mind blowing.

My brother had one when they first came out. It was incredibly fast but couldn’t make it between motorway service stations when at full throttle. I did Lands End to John O’Grotes with my brother in a day and had to resort to pushing him (bikes leaning into each other sharing footrests) twice on the way up the motorway. Then again we had to stop at Birmingham to replace my rear tyre…

 

[paulrbarnard]

When I was working with wood, I had my dust extractor in an mdf box with baffle and exhaust to outside - so we could put the fan/ extractor in a box by the wall, and have a pipe run to the exhaust?

eta - I'd not thought of a monitoring device, we'll definitely do that. Thanks.
He won't be running it inside for long, just short periods - he can take it outside to warm up etc, and just start it up inside once he's ready to make any adjustments.

I was luck enough to have access to a rolling road so could load the engine up. It then also had to have fans to cool the engine. That was a fantastic thing to have access to as you could get the power curves and compare before and after on any changes. I tuned a CBX1000 six cylinder, six carb, bike at one point and balancing all six carbs are a nightmare.

 

[ChaiLatte]

Petrol two strokes are not quite the same as they also use the crankcase

The engine sucks air in through the air filter. It expels every millilitre of that air through the exhaust. It has one way in and one way out. The crankcase is merely part of the road from in to out.

The OP is asking about what capacity (flow rate) of extraction might be required. The simple pump analogy is more than good enough for that purpose.

 

[Spectric]

It expels every millilitre of that air through the exhaust.

Not all the air entering the air intakes continues into the crankcase, you also get backflow depending upon the port timing and secondary compression ratio so a simple calculation of displacement will not yield an accurate rate of volumetric flow. All we used to do was keep the doors open when running because you cannot run them to long without having a fan to mimick airflow for cooling.

 

[paulrbarnard]

Not all the air entering the air intakes continues into the crankcase, you also get backflow depending upon the port timing and secondary compression ratio so a simple calculation of displacement will not yield an accurate rate of volumetric flow. All we used to do was keep the doors open when running because you cannot run them to long without having a fan to mimick airflow for cooling.

To add: one of the characteristics of the expansion chamber is to create a standing wave that lowers the intake pressure to suck in more air.

All that said for the intended calculation it’s near enough if you apply a significant margin.

 

[Spectric]

To add: one of the characteristics of the expansion chamber is to create a standing wave that lowers the intake pressure to suck in more air.

With really ported engines the pressure wave will also in effect push the fresh charge that has entered the cylinder via the transfer ports and heading outthe exhaust back into the cylinder but only within a narrow RPM range.

 

[Homeless Squirrel]

That's exactly the kind of shenanigans he's obsessed with! As I write, he has the RG running, it's a great sound. I'll get him to have a look at Alf Hagon. I think there are now programmes that calculate volumes etc, and even adjust them as you drag to pipe to the shape of the bike.

check on You tube Tinmans saw's and Iron horse they build them for chainsaws and they explain along with timing and porting jugs! and creating/keeping the back pressure.
And were not talking 30cc there doing 70cc plus they had a 125cc!
This guy's totally mad but they build saws for him and see some of the Cans he has on them,
https://www.youtube.com › channel › UCsIFvStf9Oz99GMitW4vD_g

Buckin' Billy Ray Smith - YouTube​

Visit my website here: http://www.buckinbillyray.com

 

[Homeless Squirrel]

Re Extraction if garage/shed has a gable roof put an extractor fan up there like many paint shop garages and has fumes rise that sucks it out.
As long as the airs moving through garage you should be good to go so often won't need a kit that will suck the neighbours cat off the floor!
You can get a hood type like an ex shop one from skips etc or these places that make for kebab shops etc as often replace ones and so on or ones that didn't work out right.

 

[Fergie 307]

That bike is a sad reminder of just what could have been for the British motorcycle industry and british engineering overall as we often had the technical expertise but lacked the marketing and production side. The ariel leader came first and then the arrow, both used one of the first two stroke two cylinder engines to hit the market and it has been said they were a forerunner to the Japanese invasion of two strokes, so why did we not keep up ? Also don't forget Ariel also had a four stroke overhead cam square four engine back in 1930, this would have been years ahead of any major competition from the japanese or Italians.

If you want a really quick two stroke bike then look for an RG500 Suzuki 4 cylinder but in race trim, the acceleration is mind blowing.

MZ were the leaders in two stroke technology after the war, courtesy of Walter Karden. He had worked on the V1 pulse jet engine, and applied his knowledge about gas flow to design the expansion chamber exhaust. I believe he also invented the disc valve for two strokes. Suzuki effectively stole this technology by sponsoring the defection of one of the MZ team riders, Ernst Degner, who was also an engineer who had worked with Karden on the design of the engine and exhaust. Many people don't realise that the BSA Bantam is actually one of their designs, the RT125.
In the late 20's they were the biggest motorcycle manufacturer in the world. The original company DKW were one of those that combined to create Auto Union, and so are still represented as one of the rings in the Audi logo.

 

[Chris152]

MZ were the leaders in two stroke technology after the war, courtesy of Walter Karden. He had worked on the V1 pulse jet engine, and applied his knowledge about gas flow to design the expansion chamber exhaust. I believe he also invented the disc valve for two strokes. Suzuki effectively stole this technology by sponsoring the defection of one of the MZ team riders, Ernst Degner, who was also an engineer who had worked with Karden on the design of the engine and exhaust. Many people don't realise that the BSA Bantam is actually one of their designs.

The lad has a 1953 D1 Bantam that I bought a couple of years ago, thinking he'd be able to work on it as a starter (which he has, all good) but foolishly thinking he'd be able to ride it on the roads - turns out you can't keep up with the flow of traffic on it, so it's all a bit hazardous. I believe BSA got the plans from Germany as part of post-war reparations, something like that? He was also recently given nearly all the parts of a 1942 Flying Flea [eta - Royal Enfield motorbike, not the plane!] - I'd not heard about them, fascinating stuff. He needs to make up front forks as they're missing, but apart from that, seems to be good.

 

[Chris152]

Apparently the 8" Clarke fan I linked to above runs at 65dB, which isn't bad, especially if we put it in a wooden box.

 

[paulrbarnard]

The lad has a 1953 D1 Bantam that I bought a couple of years ago, thinking he'd be able to work on it as a starter (which he has, all good) but foolishly thinking he'd be able to ride it on the roads - turns out you can't keep up with the flow of traffic on it, so it's all a bit hazardous. I believe BSA got the plans from Germany as part of post-war reparations, something like that? He was also recently given nearly all the parts of a 1942 Flying Flea [eta - Royal Enfield motorbike, not the plane!] - I'd not heard about them, fascinating stuff. He needs to make up front forks as they're missing, but apart from that, seems to be good.

The Bantam engine can be tuned to a very significant level. Plating, porting, gas flow, head skim, shortened piston, balancing, methanol and an expansion chamber and they can easily achieve 100mph.
throw down the challenge to your lad

 

[Fergie 307]

The lad has a 1953 D1 Bantam that I bought a couple of years ago, thinking he'd be able to work on it as a starter (which he has, all good) but foolishly thinking he'd be able to ride it on the roads - turns out you can't keep up with the flow of traffic on it, so it's all a bit hazardous. I believe BSA got the plans from Germany as part of post-war reparations, something like that? He was also recently given nearly all the parts of a 1942 Flying Flea [eta - Royal Enfield motorbike, not the plane!] - I'd not heard about them, fascinating stuff. He needs to make up front forks as they're missing, but apart from that, seems to be good.

I used to be able to get 60ish mph out of an MZ TS125, which is pretty much the same engine. They just mirrored all the drawings so everything is the opposite way round to the original German design, gearchange on the right etc.
Stopping it was fun as the drum brakes were pretty useless.
Know nothing about the BSA version but on the MZ the first thing to do was sling the awful carb and use a better one. Mikuni probably the best. Then a better exhaust. But 60 perfectly achievable just with a change of carb and matching everything up carefully in the ports.
I still have a tuned MZ ETZ 125. Will do about 80 at 8000 rpm, very reliable and sounds great.
The MZ road bikes have a mild version of the Karden exhaust, albeit concealed inside a chrome outer tube. There are many tuning companies in Germany and Poland who make all manner of go faster kit for them, including multiple port barrels, much of which would probably fit the BSA.
Interestingly the original race bikes also had a false tube over the exhaust to conceal the chamber shape. The team used to make a great show of covering up the engine so no one could get a look at it, but not the exhaust. All the other teams were convinced their power came from some engine trickery, whereas most of it was due to the exhaust, in combination with the disc valve.

 

[Chris152]

Paul - He's aware! His Bantam is a 125, apparently the one to go for if you're looking to tune them for speed is the 175 D14 (I think) with four gears. We were at Pembrey track recently, some lovely Bantams including one that'd been converted to air cooled and very fast. Among the people he chatted with was an old fella who was advising him on what Bantam to go for and other advice on getting into track racing. We realised he was a successful rider in the past, but it was only on the way home that he looked Alex George up on the net, three Isle of Man TT race wins, and raced loads of Moto GP championships, and if I remember right was well placed in them across the years including podium positions. We were in the company of greatness and didn't know it!

Fergie - He was looking at the MZs at the same event, it seems they can be had for a decent price and again, relatively easy to work on (apparently!). Now you've gone and got him interested again with your 8000 rpm!

Of course, the problem for him with these routes is that to ride on the road, he can't really have any performance modifications - as soon as youngsters mention them, the insurance offers disappear or sky rocket. It's the same with his car - it's remained standard and still costs a fortune.

Thanks for your posts both, he's reading and learning from them.

 

[Fergie 307]

The MZ factory machines exhaust were all tuned to deliver maximum power at around 6000 rpm, primarily for longevity. Playing around with the exhaust, even just the length of the header pipe, can shift the maximum power point significantly. Another thing to change is the ignition. Ideally get rid of the points altogether in favour of optical triggering. If you start going for higher rpm the points can bounce which is unhelpful.
Also well worth looking at the MZ race series. Although this is for the 250 bikes they are very similar in principle. The beauty of the series is that it is intended to be cheap racing, so the modifications allowed are relatively limited. People have come up with some ingenious ways of extracting a lot more power at minimum cost.
Also loads of stuff on the web about tuning both MZ and BSA versions.
If he wants to really have a play then why not prepare a bike just for track days, or "run what you brung" events. Then you can go bonkers, and keep a standard one for the road.
Not sure about the bantam but you can certainly pick up the early MZ bikes for relatively little as a basis for some tuning experiments.
This is one based on a TS 150, very similar engine to the Bantam.

 

[Chris152]

The MZ factory machines exhaust were all tuned to deliver maximum power at around 6000 rpm, primarily for longevity. Playing around with the exhaust, even just the length of the header pipe, can shift the maximum power point significantly. Another thing to change is the ignition. Ideally get rid of the points altogether in favour of optical triggering. If you start going for higher rpm the points can bounce which is unhelpful.
Also well worth looking at the MZ race series. Although this is for the 250 bikes they are very similar in principle. The beauty of the series is that it is intended to be cheap racing, so the modifications allowed are relatively limited. People have come up with some ingenious ways of extracting a lot more power at minimum cost.
Also loads of stuff on the web about tuning both MZ and BSA versions.
If he wants to really have a play then why not prepare a bike just for track days, or "run what you brung" events. Then you can go bonkers, and keep a standard one for the road.
Not sure about the bantam but you can certainly pick up the early MZ bikes for relatively little as a basis for some tuning experiments.
This is one based on a TS 150, very similar engine to the Bantam.

Thanks Fergie - I'm handing this over to the lad, way over my head