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MG MGF Technical - more exhaust questions

is the standard f exhaust 4/2/1,are the two pipes combined in the muffler,or are they separate as 4/2/2? has anyone made up a 4/2/2, would the cat then work ok in one section only and would that cause different loading in that half of the system,also does the fitting of a sports system remove heat a little better? thanks bruce
b dix

The std one is 4/2/1 but the 2 part is very very short, about 3". The after market 4/2/1 have longer primary and 2s. However, they are a tight fit with the alternater. In addition they are normally combined with a new shorter flex section.

Have a look at:
http://www.mgf.ultimatemg.com/group2/exhaust/exhaust_menu.htm and http://www.mikesatur.co.uk/fx01.html

I have the JanSpeed 4/2/1 and I am very pleased with it.
Steve Ratledge

H Bruce,

the standard exhaust manifold is actually a 4-2 design, with the final 2-1 occuring in the downpipe that incorporates the flexi pipe as it passes under the sump. A figure showing the design of the MGF exhaust system can be found here: http://www.mgf.ultimatemg.com/group2/exhaust/exhaust_differences.htm

I think that the idea of incorporating a cat in only one arm of a 4-2-1 manifold would be pretty diasterous in terms of power output, exactly for the reason you suggest: uneven back pressures.

Not sure why you'd want to do this?

One idea Roger and I had for a catalyst with a built in bypass would be to take an old catalyst, drill a hole through the centre of the matrix, run a pipe through it, and have a butterfly valve guarding it. When the butterfly was open, all the exhaust gas would flow through the bypass tube, but when closed, the exhaust gases would flow through the catalyst matrix. Unfortunately, this idea is severely compromised by the available size of matrix... oh well!
Rob Bell

Well Bruce a quick peek under yer car would answer the first part and for the second part no it wouldn't work see the excellent books by Alexander Graham Bell on exhaust tuning and design. Check out Mike Satur's or Janspeed's web sites for exhausts for the F. As for the heat no they wouldn't but exhaust wrap would reduce radiating heat.
Blue Pocket Rocket

Sorry for the missleading info - I was thinking of the 1st piece of the exhaust and forgot about the longer 2 pipe section below the join. Durrr.

Need more coffee...
Steve Ratledge

LOL Steve - mind you, I guess you could regard the down pipe as part of the manifold, insofar as the downpipe does include the 2-1 pipe union...

I agree with you though: definitely a "coffee morning"! :o)
Rob Bell

thanks for the feedback what i had in mind was to keep 2 separate pipes from the 1st junction right through 2 separate mufflers( like coby)and out, this comes from a system i had on a healey 100/6 years ago peformed well and sounded awesome in those days there wasnt all the paraphenalia found in todays vehicles eg cats in some of thew systems ive seen online i think they do away with the cat,but that may be on the highly modded engines ,the dark side beckons,of course here in nz we cant just go downtown and pick something off the shelf,unfortunately or i would be broke permanently cheers bruce
b dix

Ah, okay - you you're looking at two 2-1 manifolds, two catalysts and two back boxes? Would certainly sound different - but I am sure that a properly designed 4-2-1 manifold will perform better due to gas extraction set up by negative pressure pulses being reflected back to the head...

You could probably get a good 4-2-1 manufactured locally - and the ideal primary and secondary lengths are not a industrial secret (surprisingly!) since these have been found by enthusiasts and published for use by enthusiasts. Can't recall what they are off the top of my head, but a quick search of the internet sound reveal some answers. :o)
Rob Bell

thanks rob yes the idea is evolving and a balance pipe between two separate pipes may possibly give the effect the negative pressure pulses have on the system more research thanks bruce
b dix

This thread was discussed between 23/03/2005 and 25/03/2005

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