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MG MGB Technical - Exhaust types

I have got the engine in car at long last. It is a standard 18GG(gold seal equivalent).

I am looking to replace the exhaust with a stainless steel system. Looking around a few of the suppliers websites they offer standard, bomb and big bore varieties either to fit the standard manifold or with a stainless steel tubular manifold.

What are the advantages / disadvantages of each and does the tubular manifold give any benefits?

Cheers Tony

Tony Brough

The standard manifold is perfectly adequate. It flows well and will outlast a tubular manifold by a considerable margin.

If you are unlucky enough to have one break, they are readily and cheaply available secondhand.

I bought a standard system for mine.

Big-bore is not necessary on a standard engine.
Dave O'Neill 2

Thanks Dave

Standard it is.

Is yours back onthe road yet?


Tony Brough

'Bomb' is more about noise than anything else, I think. I've had stainless on my roadster for many years, and was very disappointed with the sound originally - 'farty' is a good description which apparently occurs with stainless systems in general. It wasn't until I partially crushed the centre box on a Kimber Run at Chatsworth that it started sounding anything like decent. I can't see it failing any time soon, but if I had to replace it I'd prefer to do with an original mild-steel - IF I could be sure it would sound like they always used to.

The car came to me with an 'extractor' tubular manifold and down-pipes but I had to replace that with cast as at the time there were issues in mating a stainless system to it. I doubt anyone would notice the difference for road use. The only potential for problems are the studs for the down-pipes. These should have brass nuts which limits corrosion, but the studs can still fail. Nevertheless having to replace the clutch some 20 years after the pipes were last attached they all came undone OK, albeit some if the studs unscrewing from the manifold which was a bit of a surprise.
paulh4

Tony

Unfortunately not. Very little progress has been made since you last saw it.

Are you retaining your steel wheels, or changing them for something else?
Dave O'Neill 2

Tony I am in the process of sorting out a new exhaust for my car, at the moment I have a SS 2 box system, but as you can see in the photo, I keep catching it, I am thinking about doing away with this box and running with just a back box,

Andy Tilney

The OE exhaust was a 2 box and was welded up solid from the manifold back. It produced a very distinctive "hollow" boom at around 3000 rpm.
I think it was welded so it stayed in one piece when you clouted the centre box. I put a mild steel LCB on my car in the 90s because the OE cast one had a broken and seized stud and I damaged the thread drilling it out from under the car. I then put a stainless system with a single bigger box at the back which has a skid welded to its front. That has saved the system a few times and has the witness marks to prove it. I had to have an adapter made from a stretched short length of s/s tube to join the 2 parts. Ive never had a bomb silencer but i think they would be better at surviving being grounded.
I've always liked the sound of the s/s systems on both MGs
Stan Best

I went with the bell stainless in standard setup. I like it. No real sound change from original.
Bruce Cunha

There's stainless and stainless. Some of the poorer SS systems use really cheap mild steel internals which of course still corrode. ASK the vendor..
The centre box takes some of the harsher and tiring "rasp" away. "Bomb" boxes are quite small diameter efforts, quite often tapered at the ends, and are therefore a bit less prone to being caught by dozing PC's.
Allan Reeling

Tony-
Tubular steel exhaust manifolds radiate more heat into the engine compartment. They're also noisier, sometimes producing a 'ringing' sound at certain engine speeds. They can also be more prone to warpage, making re-installation all but impossible. The Original Equipment cast iron exhaust manifold flows just as well and doesn't have these problems, so why bother? Big-Bore tubular steel exhaust manifolds are good only for larger-displacement engine (like, for example, a 1950cc engine).
Stephen Strange

Tony,
I did away with my centre box for the same reasons. Got this company to make a tube (in stainless ) to fill in the gap.http://www.everyexhaustpart.com. Ring them up an they will make it whatever length you need
A J Dee

About 25/30 years ago somebody sold me at a discount a new Peco HDR mild steel tubular manifold which has worked fine on car ever since. Didn't notice any performance difference, to be honest, but equally haven't had all the faff with the exhaust rings/sheared studs etc that I can recall with the standard arrangement. When I remove the head or fish out the engine, I just tie the manifold to side of the bay.

After my impecunious years of connecting this manifold to bits of mild steel pipe leading to the standard rear silencer, I eventually bought the Peco HDR single box mild steel system aft of the manifold. This was OK, but I could never get it quite right on ground clearance, and the system seemed to hang low forrard of the axle. The silencer eventually failed around the front flange due to corrosion. Bought another system, with all the same issues as above. However, it did look nice when you first bought it, as it's painted Post Box red.

Then more recently thought about stainless steel, but for a big bore system to align with the manifold, it all seemed rather expensive for what it was. What I did in the end was buy proprietary stainless sections off ebay(from the likes of the firm mentioned by A J Dee), they swage ends as you specify, so it all goes together neatly. Mine now is a straight length to the battery boxes, a couple of supports along the way, then a length of polylock flexible tubing, then more pipe to a proprietary stainless big bore silencer. Quite fun putting it all together and did it all for not hugely over £100. Works well and IMHO sounds good too with a throaty, but not too loud tone.
Peter Allen

Thanks for the replies and opinions. I have gone for a bomb system so that hopefully wont be as vulnerable to bottoming as the standard. If it is then I still have the option of a straight through pipe. It is made by Bell Systems and they offer a lifetime corrosion warranty.

Dave I am keeping the steel wheels as I prefer them to wires or rostyles.
Tony Brough

Tony

Yes, I also like the steel wheels.

I think I have located a set.
Dave O'Neill 2

Have the manifold ceramic coated inside and out. It will flow better and radiate much less heat.
Steven Rechter

This thread was discussed between 31/12/2017 and 12/01/2018

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