Fitting the MGA Exhaust Manifold and a Maniflow Exhaust System

Details: Written by Stephen Tickell

Recently (March 2007) I had an exhaust system fitted to my ZB Varitone by Maniflow Ltd in Salisbury, and I thought it might be of interest to others as an alternative to the 'standard' system, although it may only be directly applicable to RHD Magnettes.

Talking to Alan Slack at one of the 2006 events, he mentioned that he had fitted an MGA cast-iron manifold in place of the original one, and had Maniflow make a custom front-pipe to connect the rest of the system (I think he kept the standard box and tailpipe). I was interested in this approach for several reasons.
- I've always had trouble getting a reliable seal between the manifold and pipe, as the clamp doesn't provide a positive pulling together of the two parts. The MGA manifold has a conventional flange and 3-stud clamp, with a crushable olive to seal the pipe
- The standard manifold brings the front-pipe out at an angle that avoids the steering column in LHD cars, but this then requires a contorted double bend in the pipe to get past the gearbox. As my car is RHD I could see that the downward-sloping exit of the MGA manifold would make for a much smoother pipe run.
- The MGA manifold looks like a better design than ZA or ZB, although I haven't seen any actual comparative measurements, and the ZB manifold is generally reckoned to be better than ZA. For maximum power at high rpm, a tubular long centre-branch (LCB) is almost certainly the best shape. But from what I've read, a 3-into-1 design can be as good or better for mid-range torque, which is arguably just as important on the Magnette as flat-out power. I had considered an LCB, but thought it was likely to be noisier than a cast-iron manifold.

My front-pipe was starting to develop pin-holes from rusting, so I would have to do something about it fairly soon anyway. Obviously the standard pipe is still available but is quite expensive - probably because of its contorted shape ! Also, I've never particularly liked the sound of my standard system, which has the single stainless silencer box supplied by NTG. At idle it has a metallic 'putt-putt' noise, and at higher speeds is quite rasping.

Following my conversation with Alan, I spoke to Maniflow boss David Dorrington to get an idea of the options.Apart from Alan's system they have also fitted LCBs (fabricated in-situ to fit the car), and a twin-box system mated to the standard manifold. The second box is a cylindrical 'bomb' type fitted between the main box and the tailpipe. Although exhaust flow and maximum power would in principle be reduced by having to pass through two silencers, this is offset by using the same diameter pipe throughout instead of a smaller tailpipe. I was soon persuaded that the twin-box would give me the sound I wanted without sacrificing performance, so booked an appointment to have the complete system fitted at Maniflow. We agreed that a mild-steel system would fit my requirements best, as it has better sound qualities than stainless. It's also cheaper, and because we use the Magnette as our main transport I don't have to worry so much about the risk of condensation and corrosion if the car is left unused for weeks at a time - but this might be more of a factor for others to choose stainless steel.
Trial-fitting of manifold.

I found an MGA manifold on ebay for about £20, in reasonable condition. It was quite rusty but the mounting holes and front-pipe flange were all intact. I did a trial fit on the car to verify that the manifold exit does indeed come out in the right place, pointing towards the gap behind the steering cross-member. The manifold looked better after wire-brushing and spraying with high-temperature paint. I've since discovered that brand-new manifolds are available from Moss, although at a somewhat higher price than I paid.
First impressions are favourable. The sound at idle is definitely more of a throbbing than a putt-putt ! On the move it is also more mellow and bassy than before, although not dramatically quieter, and the engine pulls well throughout the range. Sorry I can't offer xobjective figures on performance yet - I have previously had the car on a rolling road when Peter Burgess tuned it for me, but it's rather a long way to Derbyshire just to check if the peak power changed at all. Anyway, the Maniflow system has met my expectations, and should mean an end to regular re-sealing and clamping of the front pipe. I hope this information is useful to anyone else looking for a new exhaust system, although LHD owners might have to settle for a system with the standard manifold. Contact details for Maniflow here. Finally, I expect to be at the Magnettes+Steam event in April, so you're welcome to have a closer look/listen then.