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MG MGB Technical - Exhaust

After much thought and research (including reading Peter Burgess' book), I'm going to do the following to my mgb gt to attain an bit more power. I intent to rebuild and fit HIF4 carbs (replacing the HS4s currently on the car), a Burgess econotune/fast road head, electronic ignition and K+N's. (the engine is in good condition showing good oil pressure and running as smooth as a B series engine can).

I realise I also need to fit a free flow exhaust system to realise the full potential of these improvements. I was wondering if anyone could share their experiences and suggest the best option, to increase efficiency while not making it too loud. I would prefer to fit a stainless exhaust if possible. Cost is also a consideration of course.

I would also appreciate opinions on my suggested improvements.

Cheers Ian
Ian

Ian,
If I'm not mistaken doesn't Burgess recommend the Peco header and large bore exhaust. I asked a like question about a month ago. Most respondents said that the stock manifold is a good design and the cost of changing isn't justified. But since you are upgrading your head also I would be interested in what the true experts have to say. I am in the process of having my head rebuilt and will have it ported and polished for a little boost, but since the manifold is off I have been doing a little thinking and a Peco would look good in there, now to find the money. As for noise factor I have a Peco exhaust (not large bore) on now and it is not as loud as the Monza type.
Lewis

When my exhaust system rotted out, the manifold was still in good condition. I bought the Peco system sans header. It was no trouble mating the two. I did have to use a reducer between the two systems, and I had to cut about two inches off the end of the downpipe of the manifold (aft of where the two pipes join). I've been quite happy with the result. No leaks, not too loud, nice rumble.

Some say a header and big bore flows too freely for this motor, and so may rob low-end power. I hope that using the stock manifold, with its smaller tubes prevents some of this problem. But I've never had the car on a dyno to test the theory.

Just wanted to mention the possibility. Especially since you said cost was a factor.

Best wishes.


Matt Kulka

To my 1950 engine I have fitted a manifold LCB and a exhaust system, one box, big bore Maniflow. Very, very good.
Regards.
http://www.maniflow.co.uk
michel

Hi Ian

My car has a stage 1 head and cam and a 4 branch mild steel system that needed replacing. I didn't want too much noise but wanted to keep the good performance so had a look round.

I went for B013 system from MGOC which is all stainless standard bore with the B012 4 branch manifold and 2 boxes. There was a choice of small bomb or full size front box. I went for full size, both boxes are straight through daylight and it sounds good to me, not tiring, no buzzes or resonances, but still with that distinctive B sound and just a touch of manifold rasp :-)

I can't say how well it performs as a solitary item - can any of us? - but it revs well and I've no reason to think it's not similar to many others as they are mostly similar in design. The fact it sounds sweet and is stainless is worth quite a lot to me in practical terms.

It was easy to fit with the car on diy ramps and a jack for a bit more clearance to get the header on. Fit and alignment are spot on.

Two small mods were needed. The centre pipe of the branch is full bore and not flattened like some. This causes it to need 1/4" dent putting in the heatshield to clear. Also needed was to make 4 of the manifold washers into step washers by welding on pieces of 4mm steel as the flange is 10mm and the inlet 14mm. Worth taking a bit of trouble getting these washers level then it won't blow. Use the later metal foil gasket. Lifetime g'tee, £219 plus vat, very pleased.

Rich

Rich

My setup is the same as Matt's... Peco on a stock manifold and header. I'm quite happy with it. The sound is aggresive but not loud.
Steve Simmons

I had the Ansa system on my car ('71) and it wasn't any good for power. Depending on the distributor I was running, the exhaust note took on very different tones, mostly pleasant. I seriously beleive that a 2" system will provide more power than this 1 7/8" system. The exhaust side of the B cylinder head is notoriously restrictive, so it only makes sense that a larger than stock exhaust could help improve performance of a better-than-stock B.
The new system is going in this weekend (I hope). Custom 2" stuff. We'll see if my theory is right!
Jeff Schlemmer

Some thoughts on stainless: The pipes won't rust out as fast, but the fibreglass in the muffler (silencer) will still deteriorate at the same rate as the one on a mild steel system. When that happens, will you be able to just replace the silencer? If so, how much will it cost vs. the cost of an entire new mild steel system?

I don't mean to say that you *won't* save by buying stainless, just suggesting you do the math to ensure it's a good investment.
Matt Kulka

Hi Ian
Went back to the std CI manifold and a large bore Falcon exh with large single back box, from a 3 branch S/S club exh with bomb centre box. Made a huge difference, the car seems a lot more responsive, almost as though it was being choked before. Beware of poorly designed 3 Branch manifolds where pipes 1 & 3 are not the same length, (they should be). The Falcon has a very nice deep sound, but is louder than std, ours qualifies for rallying at 91 dB (4500rpm).
Also if you go with the CI manifold, its very easy to change to different exhausts in the future, without modifying different sized pipes.
Good luck
Graham
Graham Cherry

Also have the Peco big bore exhaust on my 80B with a chrome bumper manifold. Fit flawless with original hardware. Looks nice. Sounds nice. Plus there is no muffler on it..just a rear resonator. Stainless to last (virtually) forever, and no internal baffles, etc to break down. Best of both worlds. Reasonably priced to boot.

I was going to use a LBC header..but could not find a Stainless steel one of decent quality. Been trying to locate a Double-S brand, but not easy to find in the states

Paul
Paul S

Hi

Cheers for your input guys, is it nessecary to go for a bigger bore or is the standard peco with just rear box sufficient? Also anyone tried the 1 7/8" moss single rear box performance system option?

Ian
ian

When we are talking about 1 7/8" or 2" exhaust pipes, is this the ID or OD of the pipe?

Jerry
Jerry Causey

BMC Special Tuning goes to Stage 7, past 130bhp, without changing the exhaust yet they had a lightweight tubular free flow available and said it could be used with standard back box and a piece of tube to replace the front depending on noise. That suggests the early cast twin manifold was good and bore doesn't seem to be a problem. The complete book's here,

http://www.1978mgmidget.com/Special_Tuning_for_the_MGB.pdf

A header can be a fiddle to fit properly but I'm glad to be rid of the awkward leaking clamps on a cast twin pipe. I suppose a really bad one could be worse than a cast type but they'd have to try hard. Maybe a cast one sounds smoother.

Aftermarket systems vary and some had baffled boxes, rather than straight through, mostly the mild steel types.

Stainless boxes may suffer packing problems - or not - but if they are g'teed for life you can swap it.

MGOC's are the Double S ones afaik, maybe check with them, good pics here,

http://www.mgocaccessories.co.uk/acatalog/MGOC_Accessories__MGB___GT_8.html

You can see the B012 header looks well balanced though the siamesed centre pair will always prevent all 4 pots being exactly equal. It is well made, the centre pipe is full bore not flattened, and the other bends in the system are full bore not swaged.

Here's the cast one which doesn't look like it would flow as well, #4 pot in partic, but who knows,

http://www.mgbandmidget.com/uk2shop-3.htm


Rich

Don't use stainless steel period.

exhausts lose the wadding after a while - tap the rear box and see if it sounds hollow. You can lose about 8 bhp from this alone.

peco's and maniflows are the ones to go for as a single box system. Beware the peco tends to blow the wadding out so need replacing more often.

mike uk

Sorry Mike but that's rubbish.
The wadding/filling/design has nothing to do with the type of steel used.
Rich.



Rich

I think Mike's comment about using SS was more related to the premium one pays for SS and that the wadding is going to blow out anyway. So why pay SS prices? Pay for the SS only if a lifetime guarantee is offered.
Richard Smith

After many people have put forward sensible discussion in a thread I don't like being told "don't", "period" and then being told to buy one of 2 brands, of which one is known to be poor!

If Mike had thought about it he might wonder which silencer would be more carefully designed - a mild steel one with a short life - or one the manufacturer was offering a long g'tee with?







Rich

Oops, I'll change the thread a bit. I have Double S stainless exhaust on my roadster and the system is 20 year old. It sounds out of character for a B and a bit raspy. I suspect the stuffing is gone in the front box. Any ideas ?
Iain MacKintosh

hey guys no offence was meant by saying don't buy a SS exhaust period.

perhaps i should have rephrased this but surely we all have thick skins after many years of cuts and bruises from working on our beloved machines.

The point i was trying to make is that the wadding in the silencers is vital to their performance. This wadding will not stay in for the lifetime of the exhaust so once this is gone you will stiffle the performance of the engine.

Rich - i have thought about which silencer is better designed or rather i have let the experts and i am very happy with the results. Peter burgess recommends both peco and maniflow and believe he now recommends the maniflow ahead of the peco.
All i can do is offer an opinion, whether you follow it is your own choice. That is my opinion from speaking to various mg garages and also going from a MGOC SS exhaust to a single box maniflow and having the car dyno'd. i am very happy with the results.

mike

Iain

20 years as a daily driver is not bad for a SS system, have you still got the receipt :-) Depends what you want I guess, me, I'd get a new box if you can separate it. Even a bit of pipe may be quieter if it's resonating at the moment.

Mike

Thanks for the extra info. I assume you didn't just change the exhaust, or didn't optimise the old one first anyway, so any result on the rollers means little really does it. Most operators will find a few horses from any car by tweaking timing and carbs. They also find what works for them and like to follow and sell that routine - they are in business and want to give reliable results - and many people need to be reassured.

After, it may or may not be better on the road, eg you might get 3 bhp at the top by richening the mixture only to find you don't like living with a lumpy tickover or the new timing setting may cause pinking on hills etc. Both curable at another price. Like you said we've all been there and paid the bills. 30 years ago with BMC and Fords and 15 years ago with Golf GTIs in my case, do we ever learn :-)

On Bs I was broke and used to pay for a timing and top end mixture set up (£20 from my £40 pay packet), check advanced timing and jet nuts after if it was any good, then work backwards to make it driveable low down if needed. Hardly rocket science with 3 or 4 needles and a nut to twiddle on SUs. My local rollers (same guy!) are £400/day now, maybe worth it if you're a racer or into uncharted territory with a new hot engine, but most of it is known ground isn't it.

5 bhp out on the road is next to un-noticeable (unless it's also cured other faults) - unlike a car which sounds too loud or won't tickover in traffic.

There is another, opposite, problem with many straight though silencers btw and that is the wadding doesn't blow out but gets choked with carbon, oil, corrosion. The silencer effectively becomes a pipe and the noise increases.

Rich.
Rich

Rich, Yes I've got the receipt but I'm not the original owner so the guarantee won't be valid. The car wasn't a daily driver and as far as I can see the exhaust has covered only 30k miles. It's in good nick and comes apart very easily. I'll perhaps try a pipe first.
Iain MacKintosh

Iain, The Burgess aluminised one I've just replaced had done 11k miles in 12 years, fitted by the PO who rebuilt the car. Undrivable over 3000 rpm - sounded like an open pipe, plus a resonance in the first box, it was rattling - yet it passed the MOT as it had no leaks! Rich.
Rich

This thread was discussed between 26/04/2005 and 29/04/2005

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