The Chummy's nearside rear wheel is always dirty thanks to the exhaust fumes coming out near it. Also with the exhaust coming out at the back of the car there is less likelihood of the fumes being swept back into the car.

David

Chris,

I run my Pearl Cabriolet with a short pipe out the side just in front of the rear wheel as you describe, but then turned it in towards the centre of the car to prevent my wife getting covered in smuts when she entered/exited! Coupled with a straight through (reliant, I think) silencer, this system made a marked improvement on low down torque and pick up.

I ran the RN with a similar system - it too ran (slightly) better than with the longer tail pipe.

Both systems are slightly noisier than the original set up.

The new SWB silencers I have bought more recently have an integral tail pipe that points straight back and down (slightly, see photo below or here) - I understand this is more in keeping with how they were supplied originally, they work very well and may be just what you are after.

Thanks David and Ruairidh for your comments. I like the look of the silencer but sadly I've already bought a bog standard one which will probably see me out. I think I will try a side exit exhaust - after all it won't break the bank - and I'll encourage 'er indoors to wear dark trousers so the smuts don't show!
Regards
Chris

Location: Windy Sheffield

I recall a certain person telling me that the updraught carburettor required the short exhaust pipe and the side draught required the long small bore tail pipe when I commented that the stock long small bore tail pipe strangled my RN to death. I'd bought one of those infernal things cut it into 2 to make 2 RN tailpipes, it was like I'd got the handbrake on. These tailpipes slid inside the stub on the silencer so I then made my own which fitted over the silencer stub and produces a pleasing burble.

Looking at the diameters of the inlet and exit of my new silencer I was a little surprised to find that they are 1.5" and 1" respectively. This means that the inlet is 2 1/4 times the area of the exit and hence the exhaust has to speed up 2 1/4 times in its journey through the silencer.
What is the reason for this? To my simple mind it seems illogical to put a restriction in the flow of exhaust gas by narrowing the pipe. After all, the aim of the exhaust system is to get waste products out of the way as quickly as possible and a narrowing could lead to back pressure which would slow things down. Would my exhaust system work better if I opened up the exit end of the silencer to the same as the entry end? Or have I missed a trick?

i don't know the theory behind it but have always understood that some back pressure is a good thing.

I would like to know if this is true and also if that is the reason for the smaller exit hole.

Until recently I'd always run the RP with a full-length oversized tailpipe that ran dead-straight under the axle and it performed very well. It also made a very nice fat burble. Replacement with another large-bore pipe that curves over the axle still makes a pleasant noise, but appears to have taken a few mph off the top speed

The PD, with a standard, narrow pipe, is faster, but then it's a lot lighter. At speed, it sounds like the fart of an angry wasp!

Location: Herefordshire, with an "E" not a "T".

Whilst I understand 'the best thing to do with the exhaust gas is to get rid of it', back pressure has no benefit whatsoever, except as a fuel saving measure in 2-strokes.

However, The further a gas has to pass down a pipe, the more it cools. Cool exhaust is denser than hot exhaust and causes more 'pumping loss'. By restricting the diameter of the exhaust, the gas is accelerated thus exiting faster and also causing a pressure reduction (think airflow over a wing).

That's what was explained to me. Seems those Austin designers may have known a thing or two.

The tailpipe on this car was anything but long and did run pretty hot...



Made the girls smile though!

https://www.youtube.com/watch?v=de0u8hOdcOU&feature=youtu.be

When gas is flowing it causes a lot of turbulence if it has to slow down. This means that if the pipe gets bigger at some point there will be a considerable restriction.
Speeding the gas up is not nearly so problematic.