Morris Minor Owners Club

hi all

i dont know much about all this yet ..... but ive been wondering about the practicalities of putting two exhausts on one engine ? - i have two stainless steel exhausts for my morris 1000 and rather than sell one it might be worth trying this to help my moggy breathe better

would it be possible ? - is it worth it ? .... is there any particular manifold i would need to get?

cheers
grainger

Hi Grainger,

Your moggy will breathe better with one. If you connect two up (even with a linking mixer box) then the overall effective diameter is increased dramatically, which means that you will loose the cylinder scavenging effect due to the reduced particle inertia and it will be more difficult for the engine to remove it's spent charge. This is a point that a lot of 'boy racers' are unaware of when they put a 'big bore' system on their 1.2 vauxhall novas and then wonder why it performs worse than before!

If you are hell bent on doing it (which is cool ) then you will need a large bore LCB manifold and a front box with two outputs, or a Y-adapter and the 2nd exhaust (right hand one) will need more pipe than the left because of the bend to get it into the right place. A LOT of work!!

It may be better to get an exhaust company to make you a complete system up. My mate did this with a 250BHP escort RS Turbo van and it looked and sounded very good but it was symmetric, wheras the moggy one would not be due to the side exit from the engine. This would mean that the effective length of the two pipes would not be equal and so tuning the length(s) would be a nightmare.

It would not be very free flowing either due to the bends, junctions & unequal lengths!

There is another possibility of making a custom manifold by connecting one pipe up to the centre siamesed head port and the other pipe to the outer two, but to ensure that the car would run correctly you would need a front mixer box to join the two pipes together and then apart again (2 in 2 out), so work wise you are back to square one!!

LOTS of hassle!! Performance wise and money wise I certainly would not recommend it!!

Might look cool though!!

Cam.

message received though not quite understood there cam !

as i say i dont quite understand all this business yet - one of the reasons i went from a new car to an old moggy is to learn about cars and engines ... concerning exhausts - i just thought that giving it more exhaust area to get rid of its gases must be a good thing


whats all that particle scavenging thing mean, cam ?

we discussed me good mpg in the other topic, im thinking now its been set to run very lean .. one thing ive noticed is iv got a bit of an embarassing noise when i take myfoot off the accelerator at high revs, or rolling down hill in gear about 40 mph it starts to fart through the front of the exhaust (which is stainless with no holes i can see - though its that kind of noise like a blowing exhaust) ..... to my mind that may indicate a lean mix - what do you think ?

anyway cheers m8

cu
grainger

Hello there!

Grainger, if you don't like the "exhaust parp" you shouldn't have bought a Minor! They all do that!

Changing gear at high revs, will make the exhaust parp, as will travveling down long hills. If it starts snapping and popping at this point, you've either got some nastiness goin on with the valves, or a leak in the exhaust.

I had that happen. There was a leak around the manifold - a new gasket sorted that, and later, a leak where the exhaust is fitted. The latter is a very common problem, as it is tricky to get the exhaust fitted correctly. IF the noises are coming from the front, then it could be either of these two areas.

Failing that, it is most likely to be the "parp" from the back.

Wouldn't running very lean reduce the overall power of the car? Of course, you don't go over 50, so you might not notice that...

Just kidding.

As for the exhaust. There has to be a happy medium. If there is too much freedom for the gases (as you may discover should your exhaust fall off...) then the car won't run happily at all!! If there is not enough room for all the gas, then the car will similarly not run well, and in some cases the build-up of gases can cause the car to stop.

Anyway, twin exhausts might make it look like a Beetle!! Ohhh, I don't feel well!

Grainger,

With regard to the 'particle scavenging', what happens is:

as the exhaust gasses move down the pipe length they move at a particular speed, and as they are made up of tiny particles (which have mass) the faster they move the harder it is for them to change direction quickly, so the particles rushing past the entrance to the pipe leading to the closed valve (in the manifold) cause a small vaccum which helps remove the charge when the valve opens (obviously the piston pushes the majority of the charge out) but this slight rhythmic 'sucking' helps to evacuate any remaining charge from the cylinder.

If you increase the size of the pipe dramatically, then the particles travel slower, which allows them to change direction easier and the amount of vaccum at the next cylinder is reduced, thereby reducing evacuation effeciency, so the next induced fresh charge is reduced in size by the previous spent charge still in the cylinder, which reduces power.

And, as Gareth correctly stated there is a trade-off. If you make the pipe too small, then a slightly different problem occurs, whereby the piston cannot push enough charge out in the first place due to the fact that the particles cannot be forced to accelerate fast enough to escape through the small diameter pipe in the given the time and for the given power. Thus the next induced fresh charge is reduced in size by the previous spent charge still in the cylinder, which reduces power.

Many skilled engineers have spend many years developing 'tuned' exhaust systems to optimise the cylinder scavenging efficiency. It is an exact science, and not just a slap it on and that will do job.

But the car will run with mostly any exhaust system you care to bolt on to it just not very well in terms of both power and efficiency.


The farting noise sounds very much like the characteristic Moggy parp, as Gareth says, which I think is quite endeering!

If that noise is coming from the front then you may have a leak from either the manifold to head joint or the manifold to exhaust joint. Try getting someone the 'blip' the engine while you go around listening for exactly where the noise is coming from. Also check the tightness of your manifold nuts.

A lean mix should not cause this noise, BUT if I thrash my engine (and get the exhaust hot) and then rapidly decelerate then unburnt fuel is allowed into the hot exhaust where it explodes causing the characteristic 'popping' that rally cars get. Cool eh?

I have never seen this on a standard engine, but I suppose it's not impossible, if the engine is lean enough to cause a very hot exhaust. But I very much doubt that this is your problem.

Oh and by the way Gareth, Beetles are cool.......just no where near as cool as a Moggy!!!! Ha Ha!

Cam.

Hi
Mostly caused by an air leak on Manifold.
Great write-up on exhaust. There is a previous comment on "Twin exhausts".
I have found that if the Ignition contacts are Too close, gap small, this will cause the unburnt fuel to ignite at the wrong time in the exhaust. If possible the more accurate Dwell method is prefered. It does exaggerate the "Natural" sound of this system.
"Back-firing" on de-celeration another sign of this problem.
..............Ivor..................