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MG MGA - MGA Twin Cam Distributor and Advance

I�d be grateful for some expert opinion from someone out there who is familiar with Twin Cam history as I am trying to sort out my distributor spec. on a newly acquired Twin Cam.
Having browsed websites such as MGAguru.com and the various relevant old MG Confidential Service Memoranda (particularly MG/282, MG/288, MG/296, MG/301 and MG/325) it would appear that the latest �correct� ignition arrangement was the 23D4, non-vacuum advance distributor set to a static setting of TDC, for the high compression 9.9/1 pistons, and up to 8 degrees BTDC static setting for the low compression 8.3/1 pistons.
As for the advance curve, this is where my confusion starts! MGAguru quotes a graph/curve taken from the mga twin cam engineering Technical Data Book, dated November 1959, http://mgaguru.com/mgtech/twincam/tc304.htm , which gives very specific advance curve maximum and minimum figures whereas the latest relevant Confidential Service Memorandum on the subject, MG/288, also dated November �59 http://mgaguru.com/mgtech/twincam/csm/MG288.pdf , on page 2 quotes higher levels of advance through the 2000-5000rpm revs range.
Would anyone be able to clarify (i) if the 23D4 distributor set to a static setting of TDC (high compression) or up to 8 degrees BTDC (low compression) is correct, and, (ii) which of the two advance curves is �most correct� and would the same advance curve apply equally to either high or low compression engines.
Grateful for any words of wisdom.
Bruce
B Mayo

Bruce, the factory became obsessed with ignition timing as they were convinced that was the source of the very expensive piston burning warranty nightmare the Twincam quickly became. It wasn't - it was a lean burn situation arising from vibration and float bowls.

If you have a factory distributor, just time it as specced. If you don't, go find a Cooper S competition distributor without vacuum advance - they are a plug in for the Twincam.
Bill Spohn

Bill
Thanks for the response.
Bruce
B Mayo

I're recurved a few twin cam dizzys and they were all orignally set up to be all-in at 6000 rpms. That's a real dud of a curve for power, but as Bill said, the factory was trying to save the engine with a "reserved" curve.
Jeff
Jeff Schlemmer

B Mayo:

If you don't already know or belong perhaps you should consider the twin cam and deluxe group:

http://autos.groups.yahoo.com/group/mgatwincam

It has over 300 owners on line, many archives, files, photos, litereature, and searchable messages.

Regards,
Blake
Bullwinkle

Jeff and Blake
Thanks for your comments.
Bruce
Bruce Mayo

This thread was discussed between 18/02/2007 and 25/02/2007

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