Maniflow exhaust system with MGA manifold
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.
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Installation at Maniflow
David was reasonably confident of completing the system within a day, however I
would have to swap over from the standard Magnette manifold to the MGA one when
I arrived. So I made an early start from Surrey, and got to Maniflow's workshop
on an industrial estate outside Salisbury at about 9am. Most of their business
is making standard exhaust parts for sale via various distributors, and there
are several employees doing metal fabrication, pipe bending and welding. There
is just a corner of the workshop kept for fitting, where I parked the Magnette,
removed the carbs and fitted the new manifold. This took about half an hour
(trying to avoid burns from the still-hot exhaust), then the car was raised up
to start removing the old system. The fitting work was mainly done by Chris,
after David had established exactly what was required. With my 1600cc engine and
ported cylinder head he advised that pipe with 1 5/8" inside diameter should be
used all the way through
At this point I couldn't really contribute much more, so went off to explore
Salisbury. The industrial estate is about 20 minutes walk from the city centre
and cathedral, and fortunately it was a nice day for sightseeing...
The fitting was eventually completed about 4pm - this included disassembling and
painting all the pipework once the trial-fitting and welding was completed. I
think the section from the manifold to under the gearbox took a bit more trial
and error than David and Chris expected, but it all looks beautifully made, with
joints either welded or swaged. Custom mounts were made up for fixing to the
engine backplate and boot floor (the original tailpipe clamp was for smaller
diameter). The total cost was £375+VAT - I believe David has a standard figure
for the Magnette system with original manifold, to which he added the extra work
on the front-pipe. Since the fitting involved more than four hours of their time
I thought the price was quite reasonable, and David and Chris were helpful
throughout my visit even though they seemed to have plenty of other work that
would have kept them busy.
Was it worth it ?
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 are at http://www.maniflow.co.uk Finally, I expect to be at the
Magnettes+Steam event in April, so you're welcome to have a closer look/listen
then.
Stephen Tickell, Surrey UK
