Modified Exhaust:
Using RC40 Exhaust Boxes

R H Johnston

The original exhaust system is perhaps adequate for the original 948cc engine, but a tuned engine, or a larger engine needs a much more free flowing exhaust system, otherwise most of the expected performance will not be obtained. I know as I have tried a standard exhaust on a 1275cc engine, and the top speed was about 75mph - the same as with the 948cc engine.

The Competition Silencers RC40 exhaust system, available (in 1988) from Mini Spares Centre, 29-31 Friern Barnet Road, Southgate London N11 1NE (01-368-6292), is said in David Vizard's book "tuning BL's A-series Engine (Haynes), to be the best exhaust system available for A-series engines, and is suitable for engines upto 130 bhp. It is also quiet.

The system is designed to be used on a Mini, so the pipework supplied has to be adapted, extended and modified to suit the A35. There are two main approaches - either using the pipework under the axle, or over the axle. Over the axle is preferable because there is less risk of damaging the exhaust on the road or by damage from the rebounding axle, but the amount of space is limited over the axle which makes all the tolerances tight - the under axle approach is much easier.

This describes my approach to fitting the system over the axle. The front pipework will depend on the manifold used, but the over axle pipework will be common to all systems. I assume the availability of welding equipment, access to curved pipe for dealing with the necessary bodges, and an endless supply of patience!

I use a Marina 1.3 manifold, so it is logical to use a Marina exhaust system to provide the suitable pipework (the Estate Car system gives more curved pieces of pipe for making the pipework), with the RC40 system used to provide the boxes. The front pipe has to be hammered and bent slightly at the front end to clear the flange at the bottom of the crankcase of the engine so that it will also clear the bodywork. Otherwise the pipe follows exactly the same line as the original A35 exhaust. The pipe will be too long and is cut off roughly where the original pipe turns up to enter the original exhaust box. The smaller diameter box of the two supplied is separated from the pipe that joins it to the big box and fitted onto the end of the pipe, with a bend. The angle is similar to that of the original single box. The large box is fitted underneath the spare wheel well (which is hammered up from below to improve the ground clearance. A length of suitably curved pipe, adapted from the over axle curve of the Marina tailpipe, then connects the two boxes, with a separateable joint made some somewhere over the axle (this enables the system to be constructed and removed, but does tend to give leakage problems). This is easier said than done, of course. The exhaust hangings are made to provide flexible support in a number of different places.

More detail instructions on sizes and shapes are difficult as it depends on what pipe is available. The points to watch are: there must be adequate clearance between the axle and the pipework when the axle is at the limits of its travel; avoid getting the pipe too near the rubber rebound stop (they burn and smell terribly); the system must not foul the propellor shaft; the system must not touch, or be very close to the fuel tank.

The distance between the boxes is supposed to be important. With this modification tpo go over the axle, the distance is increased as small amount, but this small increase does not seem to cause any real problems or extra noise. Although the exhaust is the "straight-through" type it is very quiet, possibly even quieter than the standard exhaust.

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(c) R H Johnston, 1998.  Material may not be published for profit without permission.

Whilst great care is taken to ensure that the technical information and advice offered is of the highest standard, neither the author, nor The Austin A30/A35 Owners Club, or the Officers of the Austin A30/A35 Club accept any liability at law for any death, injury or loss whatsoever arising from the use of advice contained in this article.