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MG MGB Technical - exhaust choice.....Long thread

Hello one and all

I know this has been documented many times in the archive but i don't feel the threads fully answer the questions i have.

At the moment i am running a stock 1968 bgt with uprated suspension. I am now at the stage where i want to up the performance and will probably go for a burgess fast road head. Before this i am looking at replacing the air filters with K&N, new needles and replacing the exhaust whilst keeping the stock CI manifold.....here lies the problem

At the moment i have a Stainless system from MGOC (twin silencers) which souns pants. Reading the info on here i will go for a straight through exhaust made of mild steel with one rear silencer.

My dilema is what to choose - Do i go with the Peco normal system on stock manifold or the Peco Big-bore on stock manifold and have an adapter made or do i go with a maniflow exhaust?

I would like to have any performace gains from the switch that are going. Peter Burgess recommends the Peco - i'm assuming the big bore but i have only got a stock 1798cc engine (some to have fast road head). Is the big bore warranted - and will i lose low rpm grunt for grunt higher up the rev band? I deally i want lower rpm grunt up to say 4000rpm. Will the standard peco or maniflow give any performace enhancements?

thanks


Matt Kearns

Matt-
From what you've posted, it sounds as if you're seeking and exhaust system that will equally suit both a stock and a Peter Burgess Fast Road head. There is no such creature. You need to understand that a performance exhaust system merely facilitates the power increases that stem from other modifications. Taken alone, a performance exhaust system will do little other than transfer some power from the lower part of the powerband to the upper part of the powerband when used with a stock head and camshaft. Peter Burgess recommends the use of the Peco Big Bore exhaust system with his Fast Road head for good reason: the increased volume of exhaust gases require an appropriate flow capacity exhaust system in order for the potential of his modifications to be fully exploited. A stock exhaust system would choke the power output. That having been said, if your formula is a stock camshaft, K&N airfilters, Fast Road head, and stock exhaust manifold, then Peco gray system is the way to go. Installing the red Big Bore system onto a stock exhaust manifold would be pointless as the smaller size of the exhaust manifold runners would negate any advantage of the larger size exhaust pipe. The only time that the larger Big Bore exhaust header and exhaust system should be used on a small bore B Series engine is when the camshaft is a fairly hot one, such as the Piper 285.
Steve S.

Why do you want to keep the standard manifold, but upgrade the exhaust to a large bore?

Is there a problem in changing the manifold as well? It would certainly help the money spent on the modified head seem more worthwhile if changed.

Why not give Peter or Sean a ring and ask them what they recommend for your proposed engine spec.

Tony
T Crossley

Read Peter's book again - the standard manifold is regarded as an efficient design - the only benefit Peter ascribes to the Peco tubular manifold is is ease of fitting to the rest of the Peco system.

Just go for the single large rear box and whether it is stainless or mild matters not except on initial cost (but you will be replacing the mild system more often.

Interestingly Peter suggests using a custom manifold similar to the MGA's with three pipes into one instead of the usual three into two into one design - adds another 2 to 3 bhp to mid range power.

Matt,

I would just remove the front silencer on your present system and replace it with a straight pipe.

Run it that way till you upgrade the head and then think about the PECO system or go for the MGOC Big Bore system and manifold in SS - I use this system on my V8 and I can recommend it.
Chris at Octarine Services

This thread was discussed on 20/07/2004

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.