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MG Midget and Sprite Technical - LCB and two box Maniflow or STD

Evening,

What with all the other issues of the Sprite I had decided that for my slightly warmed engine - head ported, 1mm bigger valves (Peter Burgess), lightened flywheel, Kent 276 camshaft and high ratio roller rockers, I would not be bothering with an LCB and sports exhaust as Vizard seemed to indicate an LCB and fancy system was circa 7hp if lucky.

However, having got it running the engine seems twice as loud as it was ( worn out std engine ) my car was a 1098cc - so has the single back box, I see that changed to the twin system at 1275.

The question - does anyone think it's worth the £600 ish to go maniflow or £250 ish to go AH Spares std twin box stainless system ?

I am more likely to go AH Spares, but would like to hear from people with experience of both

Ta
Malc Gilliver

The 1275s retained the single box until they changed to slim bumpers and black sills in 1970.

How old is your silencer? If it’s getting on a bit, a new one might be quieter. I do like the sound of the single box.
Dave O'Neill 2

I have switched from an LCB with a bomb box on the back (essentially straight through!) to a std 1275 manifold and single box.

The wife and I had to shout at each other at anything over 30mph (even in 4th) with the bomb box, but now we have a gentle burble. Does make engine sound more noisy and rattly though, and I do hear other clicks, clonks and whines from other components, but prefer the std system.

No obvious impact on performance, but have fitted a 3.7 diff so not expecting the earth.
Tim C

I have a Maniflow ‘across the back’ system but only the one box which is an oval shape heavy duty job - being oval if fits well and helps ground clearance.
It’s a heavier unit than the standard single box - the sound is deeper but not overly loud and not an issue on any longer trips.
richard b

Dave,

The exhaust was new a few years ago, definatly not many miles, but I'll dig through the mot's to find an accurate mileage.

Tim,

I have the std manifold and system, but the 3.9 diff ( I am considering a 3.7 in time) I have written off an LCB and sports system, so thanks for confirming that and the fact you can't really feel the difference.

Richard,

Do you have an LCB or just the bigger back box ?
Malc Gilliver

If the rest of the system is in good order you could see if a single RC40 back box will fit. I have this on mine, gives a pleasant sporty burble without being overly loud.
AdrianR

I have got a Maniflow LCB straight through pipe to a Mini RC40 which are quite inexpensive and agree with Adrian it’s not loud at all and a pleasant sound. I think the HP gain is more likely through the LCB.
Mike Fairclough

Just my opinion:

I have a standard 65bhp 1275 in the Frogeye. I decided against an LCB manifold and fancy exhaust because I like the "original" exhaust note you get with a standard manifold and exhaust (single box). For me, it's what a Sprite should sound like but it depends what you prioritise.

(Of course, I realise if you've a "warmer" engine with a higher lift cam etc you want better gas flow).
Bill B

Yes I have a LCB manifold - it seems to assist gas flow/ free reving.
Maniflow didn’t recommend a stainless version when I bought it years ago as they said the sound was more tinney.
My system is now getting a bit old and rusty and I may well have to replace the main pipe and possibly the box- I will get a stainless one but retain a mild steel manifold.

When I had my first unmodified 1275 F reg back in the day !! the Janspeed manifold I fitted back then certainly made it rev quicker and it felt a little more powerful.
richard b

If you want to keep the cost down but have some gain then an option is a mild steel rather than stainless LCB and standard pipe cut down and standard box.

Trev
T Mason

Adrian,

Thanks for the RC40 suggestion, I have enough projects on at the moment not to want to be making an exhaust system, and I'm worried that the standard single box, with the changes I have made is way too noisy.

Bill B,

The car is already distinctly quicker than it was, the only reason for warming it up was the fact the engine in it was worn out and I figured that while I was rebuilding that, I might aswell tweak it a bit for the occasional motorway dash. But the tweaks have been it way to noisy.

Richard,

It's my understanding that stainless sounds tinney cos they use thinner metal - which as it doesn't rust they can.

Trev,

Maniflow want £280 for the Manifold alone.

Thanks all, I will try the AH Spares standard two box and see what happens, from what I can tell the LCB robs a bit of bottom end in exchange for a bit of top end, just hope it doesn't throttle the car or sound tinney !

Malc Gilliver

Appreciate you've made your choice Marc but for the record, my vote goes for Mike's set up which is the same as on my Midget.
It was a gob smacking moment when the engine was first fired up after fitting.
A rich, bass sound more akin to a B then a Spridget. Big fan of LCB and RC40 even on a standard (+30 over bored) engine.
I still have the standard two box (one across the back) in the shed somewhere...kept it just in case.
Jeremy MkIII

My experience says an lcb, single box, and k&n plus stub stack and filter, does definitely boost performance. Also 1275 +30 over, and hif44.


anamnesis

Jeremy,

My concern is the noise, with the changes I have made to the cam and head, the car sounds about twice as loud as before and has a hard "blat" to the sound - maybe a function of the higher lift and duration cam, with higher ratio rockers.

I have asked AH Spares to keep the exhaust for me, while I wait for the new cranksshaft pulley to come into stock and figure that will do for the next year, but with so many recommending the RC40 for noise quality, and at £45, it has to worth a second thought.

Anam,

It's the noise, not the power, at the moment I feel it should be doing 3 times the speed for the racket it's making !
Malc Gilliver

Just found a page on the RC40, the box is IMO much bigger than the std silencer
Malc Gilliver

I fitted a 2 box RC40 system to my Sprite with a LCB and was happy with it, I had previously used a single box from a Mini 1275 GT IIRC and found it a bit loud and tiresome on long journeys. The RC40 was a good improvement with a nice note and not loud. The small box fitted along side the tank and the larger box behind it across the rear, some making of pipe bends was required.
David Billington

David,

Thanks, I am beginining to wonder about a two box RC40 system, using two of the larger boxes, if I can suppress the racket I would consider an LCB.

Your thoughts ?
Malc Gilliver

Malc,

I believe the 2 boxes in the RC40 system, 1st small 2nd large, are designed to work together to deal with the A series exhaust characteristics. I can't find my scan of the exhaust at the moment so I'll dig out the photo tomorrow and scan it again and post it.
David Billington

Don’t think there would be room for two large rc40 boxes !
Original was one large, one small !
As it is for a mini it will require a lot of work to get to fit.

Hence the midget across the back two box system which will fit !

Why make work and probably stress trying to get it to fit ?

I like my single h/d across the back solution and will replace eventually when it finally rusts out - every one to their own !
richard b

Just remembered my exhaust thread in technical from last year.

I repaired and modified my two piece as a spare. But decided I preferred the single.

Thread: Exhaust pipe. One piece or two?

Last Post 13 June 2025 at 08:54:11

https://mg-cars.org.uk/cgi-bin/or17?runprog=mgbbs&access=&mode=archiveth&subject=97&subjectar=97&thread=202506050952462915398

And check out Rob Armstrong's system. Very nice.




anamnesis

Richard,

https://maniflow.co.uk/product-category/mg/road-performance-systems-mg/

Maniflow no longer offer your system, according to the website, I do believe is ( subject to heat shielding the fuel tank ) the best option


I am going to get all technical now, first job is meaure the actual size of the current box and do some more research from there
Malc Gilliver

I spoke to them a while back regarding a replacement and it was available - if you look at the picture the small silencer is a separate item fitted with clamps.
As I understand it they just supply a bent tube in lieu of the box.

R.
richard b

Malc,
Try this link.

https://maniflow.co.uk/?s=Ls031atb

Simon


S Holt

so I fitted the s/s twin box system from AH Spares and I am really happy, before the car was noisy at idle and got worse, at 50 mph and above it was all exhaust noise, now the idle is a bit quieter but from 40 mph I can hear the engine now !

So much less tiring than it was, I would love to have tried/heard the large box maniflow system.

But thanks !
Malc Gilliver

This thread was discussed between 28/04/2026 and 10/05/2026

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