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MG Midget and Sprite Technical - Exhaust change advice needed please

Hi all,
My 1275 midget has the following mods, a Peter Burgess large valve cylinder head, Piper BP 270 fast road cam & 1.25" su carbs that have been "Vizarded" by Kim Dear at magic midget.

Prior to the su carbs being re fitted a previous owner had a weber carb fitted & the exhaust system upgraded to suit...A large bore Maniflow lcb with 2" exit pipe connected a 2" thro pipe & single large bore silencer, again from Kim Dear.

The car runs well, but is LOUD, I bought it with the intention of fitting a new exhaust to quiten it down.

The advice I have recieved from Maniflow exhausts is that the twin box system with 1 5/8" pipes would best suit a car of ths spec & make it a little less loud, they also advise that it would be best to change the lcb to a smaller bore type with a 1 5/8" exit pipe... For cost reasons I was hoping to keep the large bore lcb....But I would also not want to loose a lot of power by fitting the wrong exhaust system....What do you think ?

Alan.
Alan Cotterill (1972 standard 1275 )

Alan
Do you have the repackable system?
If so repack it.
Make sure you first wrap the perforated pipe with wire wool and then add a dens packing of glass or rock wool.

You might not need a new system then ;)
Onno K

Alan,
you've asked the Maniflow so ...

you could check with Kim to see if he has an alternative

I've always found when I try to save a bit of money on the car it ends up costing me more later

I changed the unknown make LCB to a Maniflow LCB big improvement as the Maniflow was better made

my car is a '73 but I run on a standard pipe with single box which makes the exhaust noticable but not overloud
Nigel Atkins

Onno,
Thanks for the reply, I did re pack the silencer & this did make it less loud, but still to loud for me.

Nigel,
I will check with Kim.

Alan.
Alan Cotterill (1972 standard 1275 )

sorry sentence got mixed up, my fault not computer's (this time)

- I meant you've asked Maniflow so they should know what they're talking about

Kim might be able to offer an alternative within what they've told you

I hope it makes sense now
Nigel Atkins

I've got a Maniflow LCB system on mine - engine is an Oselli fast road unit running 11/4" su's - updating to HIF6 shortly.

I had them use a larger 'across the back box' instead of the two box system - nice sound but not excessively loud when on a long run.

No the colour match is not by design - its their standard colour !

Maniflow are probably the very best for exhausts - I would be cautious of going too big a diameter on a fairly standard tune.

R


richard boobier

Just clarify - I meant silencer is larger not the int bore.

R.
richard boobier

Pipes are too big, and you will probably have more usable power at road speeds with smaller. The LCB tubes are probably too big as well, but fixing the pipe out of them may help noise and power. Use 1 3/4 OD/1 5/8ID pipe off the LCB, and RC40 silencer if they are still around. Tested by Vizard as best to over 135bhp. I've not seen an RC40, as they are rare & costly here.

There are changes in silencer technology. I recently fitted a Borla straight through to my Mazda because I had one (and the old OEM one fell apart). Car is about the same (1839cc/102HP) as a very well sorted A or even B series. The pipe starts out at 1 3/4OD after the cat, but is stepped up to 2"OD into the silencer. Silencer has a 15" long 2 1/2" core, offset (bent) through the silencer, 2"OD straight tailpipe, 18" long. I expected it to be way loud, but it is disappointingly quiet, near the OE system which you couldn't hear at all. New silencer is half the thickness, half the length, a third the weight, all stainless, and my gas mileage went up from 31 to 34 MPG US, at 75+mph, with a noticeable increase in "snap"!
I have a Magnaflow round muffler that looks exactly like the Borla internally, though it is round outside - haven't fitted that yet, but it is going on my daughters Mazda 1600. The Magnaflow is 6" round x 14"
L, all stainless, offset in/out, lifetime guarantee, list $125, $65 online including shipping!

Sometimes odd small changes can totally change sound - try a length of pipe across the back of the car as an extension of your silencer if it is good. I once fit an MGB centre box to a Deutsch-Bonnet, which has a very odd exhaust signal (2cyl opposed 850cc engine). It sounded sporty but good, Then I fit about a 18-24" pipe out in front of the rear wheel, started it, and thought the building would fall down - unbelievably loud, even at idle. So I tried about 5 ft straight 1 3/4OD pipe out the back and all was well again.

FRM
FR Millmore

Hi
Have you thought about using a 'Supertrapp' I used to use them on open race pipes for Hillclimbing to get the noise db to legal limits. They bolt on to the tip of the pipe and you .aspeither add or remove plates to adjust the noise. Ita an option where you don't have to replace what you've got.

http://www.supertrapp.com/product_sections/cat.asp?CatID=27

Ed
Ed H

Excuse the typos bl**dy smart phones !!!

Ed
Ed H

Fit an RC-40 back box, as mentioned earlier. Designed for the A-Series - makes a good quiet sporty sound, and easy to fit. Give Kim a call.

A
Anthony Cutler

I got my Maniflow system and RC40 back box from Kim too.
The RC40 has a deeper sound than the standard rear box which sounds better, but more importantly is a lot easier on the ears for prolonged high speed driving (I still use earplugs on the motorway though).
frogeye Gary

I am going to have to replace my LCB Maniflow, its rusted/ burnt through where it comes through under the car. At around 8 years old I supposed that's to be expected but I see that the price has gone up a lot since I got this one.

Actually it has never been right. You never see any criticism of Manifold systems, but when I first got it the flange plates at the block were not properly aligned. I should have sent it back at that time as being faulty but one gets so used to having to make minor adjustments on new stuff. I did a bit of filing so that it went onto the studs and then by tightening the nuts it seemed to pull it straight.

Seemed OK for a while but it was clearly under tension as later if fractured in the fork where the front and rear pipes are siamesed together and I had to reweld it. Now its the triangular plated area where the two pipes join under the car that has become paper thin. As the pipes themselves are still solid I might try fabricating a new junction box but I suspect that welding to the pipe will burn it through too easily for a satisfactory job.

Ho hum! I wonder how much there is in granddaughter's piggy bank.
Guy W

Guy-
I have repaired many such, including Rover 2000TC rusted or cracked. Often replacing the lower bends. Easy to weld, will crack again eventually. Helps to heat a longish section of tubes to let all the stresses settle out. I do gas weld all this sort of thing, no idea what electric welding might do. A big propane torch can stress relieve pretty well (while bolted to head).

FRM
FR Millmore

Thanks FRM, Maybe I will have a go at it. Nothing to loose really, except a bit of free time!
Guy W

>>At around 8 years old...

My A-Series PCB was still going fine after 20 years; and my FL 4-brancher looks almost new after more than 10 years...

A
Anthony Cutler

the size aspect of Alan's exhaust seems to have been lost, at present it's large bore LCB, 2" centre pipe and single large bore silincer (muffler)

Maniflow have said the LCB wants to be smaller with smaller centre pipe and a twin box sysyem

things is Alan doesn't want to change the existing large bore LCB to save money

Alan,
personally I think the existing large bore LCB is literally the start of the problem so needs changing in which case the whole system needs changing along with it - sorry it's bite the bullet and change the lot and reap the benefits in noise and probably performance over the range of road use

I put up with messing about with my previous LCB and system because it was newish but to cut a long story short after messing around with it, luckily at little cost, and putting up with it for a good while I still ended up changing it and wished I'd done so a lot soon and saved the time, money and performance I'd lost

if you change the lot now I'm sure you'll not regret it but the longer you just change bits the more you'll regret not doing it now when you end up with the full change later
Nigel Atkins

Interesting comment on manifold durability, Anthony. So have I just been unlucky with my 8 year old Maniflow? What sort of life span have others had with these systems?
(Incidentally, that's 8 years and around 65,000 miles)
Guy W

Hi Alan, I'm not sure if you've tried to ring as I've been away for a few days, but I hope I can clarify/ help your exhaust dilemma!. Andy Robson, the previous owner of your car, was very particular and methodical about the exhaust system and its development. As the car was producing good power on Aldon's rolling road with the Peco manifold and system he had fitted previously (94bhp and @93ftlbs torque). After several discussions we decided on the Midget challenge Maniflow LCB, which uses the same primaries and secondary pipes as the standard manifold with a larger 1 7/8" collector. This then had a 2" outside dia through pipe and a custom made repackable silencer, which had the 5" outer dia shell. I did mention to Andy that it was likely to be noisy, as we usually use the 5.75" dia box with the 2" through pipe, so to try and counter this we made the box 20" long, as opposed to the normal 18". (20" is about the practical limit on silencer box length to fit between the handbrake linkage and the lip of the rear panel). Andy did say it was still a trifle noisy according to SHMBO, but everybody else travelling behind it thought it sounded great!. As a matter of interest Andy put the car back on Aldons rolling road, and it produced 98bhp and 98ftlbs of torque over a wider rev range. Repacking the box , should bring the noise levels back down, but the smaller chamber of the 5" dia box will struggle to absorb the noise 'slugs' going through the 2"pipe. You could use the larger 5.75" 20" silencer that is used by the majority of the Midget challenge race cars, as it will fit straight onto your throughpipe, but I'm not sure if we would have clearance issues. If you want to get in touch, we could try the larger box to see if it brings the noise down to acceptable limits. Atb Kim
Kim Dear

Kim-
Interesting. Do you happen to have the dyno curves? I am interested in the 2000-5000 numbers. It is my contention that I'll take 6 hp or even 3 over that range for 4 on top every day. I personally have never seen a header/exhaust I thought was right for a hot street engine.
I think the 1 3/4 OD pipe is about perfect for road use in the 75-100+ hp range, at least for about three feet after the collector, when it can get bigger.

What do you make of my observation on the big core straight through silencers I mentioned?

FRM
FR Millmore

Not in my field of expertise, so forgive me if this sounds daft.

What would happen if you brought the 2" bore down by some amount, with a reducer of some kind, over some of it's length? Would that make it quieter? What effect would it have?
Lawrence Slater

Restriction anywhere in the system is the cheapest form of silencing, and usually the worst for performance and economy. Widely practiced by OE, and most inexcusably by "performance" manufacturers. Vizard has cross sections of well known and highly regarded absolute crap from big UK exhaust names, from BMC on down. BMC produced its very own counterfeit "Cooper S" silencers as service replacements in later years. It is usually most obvious at the silencer in/out, but also appears along the entire system length.

Austin 1100/1300 had 1 1/4 OD pipes for an engine that needs/can use 1 3/4 in even stock form - I frightened myself when I replaced the system from manifold back in a hurry, leaving about a foot of the small pipe off the manifold, but stepping up to 1 3/4 from there back, and forgot about it until I left in a hurry; totally different car, in a very good way, for both performance and economy. The Mazda I mention has 1 3/4OD pipes, stepped up to 2" before the silencer - but stepped down to 1 1/4OD or less at both inlet and outlet. Horrible thing!

The theory and at least some practice indicates that having the primaries and collectors small diameter, with some length of pipe fairly small, then stepping up, will give best low end (which you always use)at a very small loss above midrange (which most people rarely use). That is the reason for my suggestions at the beginning of this thread, and I have proved it in numerous cases, and Vizard has documented the same. I cannot say just what effect it has on noise, since the changes always mean new silencers, and I never was interested enough to go backwards.

FRM
FR Millmore

I've got 3 cars with different medium bore systems. The frog has an LCB into a single RC40. Nice on the open road but noisy and sets off car alarms in the village. Then a stainless steel LCB into a twin box system. Less noisy but mild steel has a nicer sound somehow. And lastly a Maniflow mild steel twin box system which is by far the quietest of them all. In your boots I'd keep the LCB and add the twin box system - you can always downsize the exhaust manifold later if you wish.
F Pollock

Main reason "Mild steel has a nicer sound" is that they take advantage of stainless durability to save material and weight with thin wall tubes. I use 16 gauge/.065", which is quiet and lasts forever, at a bit more cost and weight. Also stainless is a terrible heat conductor, so heavy walls mean less heat in the engine compartment and under the floor, so much that people have measured underhood temps the same as ceramic coated systems.

FRM
FR Millmore

Hi all, Thanks for all the advice...I'm still not sure which is the best option, but SHMBO would love a quiter car.

Fergus, I'm leaning towards what you have suggested, keeping the current lcb & adding a twin box system, what spec car do you have your twin box system fitted to ? & what size twin box system, the 1 5/8" or 1 3/4" ?

Thanks, Alan.
Alan Cotterill (1972 standard 1275 )

I have the Maniflow LCB header and Kim's 45mm Fast Road system (see this picture http://www.magicmidget.co.uk/images/Full%20stainless%20exhaust.JPG)

I don't think it is too noisy at all, but sounds very nice, and I am one person who doesn't like very noisy cars. It is nothing like as noisy as my V8 MGB.
Mike Howlett

The twin box Maniflow system is 1.75" onto a 1293cc with 10.5 C/R, MG Metro cam and a single HS6 - it gave 83BHP on the rollers. Here it is
http://www.youtube.com/watch?v=OC8hQX0kmrU
F Pollock

quote " but SHMBO would love a quiter car "

Ear plugs are a very cheap solution!!! ;-)
Ed H

Before you go too far I would suggest adding a bomb silencer where the normal back box fits, followed by a 90 degree bend, then the original back box and a 90 degree outlet. Usually another box makes all the difference. You could also add a bomb silencer after the bulkhead but that may give ground clearance issues, worth a chat with Kim anyhow.

Cheers

Mark
Mark Turner

This thread was discussed between 25/07/2012 and 31/07/2012

MG Midget and Sprite Technical index

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