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MG MGB Technical - Stub Stacks question

Yet another question from someone new to the MGB - I have K&Ns, a free flow tubular stainless manifold and exhaust, and richer needles in the SUs of my '69 B. I am going to fit stub stacks - will this necessitate any retuning, further richening or carb balancing etc?
S R Ellawala

SR,
Any change which alters the rate of air flowing through the engine would ideally be partnered by a full retune to maximise the advantage of making change.

The balance should remain as before but changes will need to bo done to both carbs simultaneously.

My thoughts would be to find a reputable rolling road dyno facility and have them do it.
Properly set up you should see an increase in performance and possibly a reduction in fuel consumption as well.

Perhaps some other listees in London may be able to help with a recommendation here, or more corrrectly there.
Cheers, Pete
Peter Thomas

Been round this loop recently on the board, check out the archive.

To summarise, yes definately worth it (IMHO), yes definately need a re-tune, but not necessarily new needles. If you've got K&N pancake filters already the bulk of enrichement has been done already. You can use the existing stacks from inside the old filter housings. The advantage is a small, somewhat tenuous one, but the idea is to give the air entry to the carb mouth a smooth radius. Without a stub stack or ram pipe the air forms it's own radius round the square edged air entry of the carb mouth. This leads to a narrowing of the effective area of the intake, a refraction (sp?) ?? Sod's law says this occurs at the jet bridge and effectively makes your 1 1/2" SU flow like an 1 1/4". I think......... that'll teach me to drink at dinner time !!

Anyway, hope this helps.

Phil.
Phil Hill

This thread was discussed on 16/05/2002

MG MGB Technical index

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