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MG MGB Technical - Timing degree discussion, please

After reading about the blown head gasket here and the comments about too much advance I would really like to know what all of you think advance should be.

I was told 34 degrees at 3500 or all in at 3000 rpm. However with the fight to find the low oil pressure culprit I changed all the rod and 3/5 of the main bearings. When someone looked at the bearings they said it showed of too much advance.

Here's the set up:

GK block at 10:1 compression. No blower. When build 40K miles ago new billet VP-11 Cam (276 Deg. Duration, 0.280" Lobe Lift, 224@0.050" LCA 106 Deg.). +.030 pistons. All new bearings throughout naturally. Rebuilt Harmonic Balancer.

1967 head PP’d with larger valves, 25D dizzy recurved and rebuilt, standard SU’s.

What is the concensus of what is optimum advance degrees?



Max71

Max
The other variable in the max advance is what fuel you use (we have 91, 95 & 98 octane in Oz) - high octane will allow more advance. A lot of the experts say 32 BTDC @ 3000 (no vacuum advance) for compression below 10:1
The MGAguru has a good article on the subject.
http://www.mgaguru.com/mgtech/ignition/ig116a.htm
Mike
Mike Ellsmore

Max
The other variable in the max advance is what fuel you use (we have 91, 95 & 98 octane in Oz) - high octane will allow more advance. A lot of the experts say 32 BTDC @ 3000 (no vacuum advance) for compression below 10:1
The MGAguru has a good article on the subject.
http://www.mgaguru.com/mgtech/ignition/ig116a.htm
Mike
Mike Ellsmore

I think I would start with 28 degrees max, time acceleration runs then increase max advance to see how it goes. Only problem is if dizzy curve does not match requirements of engine and gives you false runs.
Advance should be minimum needed to do the job.
Peter
Peter Burgess Tuning

"What is the concensus of what is optimum advance degrees?"

Whatever allows you to accellerate smartly in 4th from 30-50mph and it just does not quite pink/pre-ignite/detonate. That's for your set up-all others will be different.

Unless you have programmable ignition, it will by definition be a compromise, as the only adjustment is rotating the dizzy. The curve is determined by the springs/weights-right or not so right, as Peter mentions.
Michael Beswick

Agreed for high compression, if it pinks then retard it till it doesn't, although Haynes says just perceptible is OK.

For low compression you are likely to stall the starter before it pinks, so you can really only go by the 'seat o'pants' meter, or go by the book. The most likely thing to vary is spring tension - losing it, which will mean you get more advance sooner as the revs increase, so check the max figure and its rpm. Probably shouldn't exceed the book figure for that rpm, so you may have to retard, even though it may not be over-advanced lower down.
paulh4

Thanks everyone!

Wish I could easily find more than 91 here. I do set it without vac advance.

Its worth exploring more to find what's optimum. I'll start lower and go from there. I recall telling the dizzy guy what the cam guy said ie 'all in by ??RPM so I have an email in if he answers. Otherwise I'll just start at 28 as suggested and go up from there.
Max71

This thread was discussed on 19/05/2017

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