Doc

with bathtubed heads is the extra time(advance)needed to ignite the greater volume (especially at idle)

if yes, would extra dished pistons also benefit? (eg 10 -18cm)(turbo league)
from more advance at idle?
and finally if yes
interesting dilemma for turbos who need to dial back advance once going.... sensibly a case for MJ etc

It is not the volume, it is the chamber shape. My 1360 is running 11.0:1 C/R now. Pistons are stock 9.75 Hypatecs, the head has had a lot off it.
http://www.flickr.com/photos/31275265@N05/9389133396/

With a bathtubbed head there is little or no squish area left. So the flame propagation from the spark plug is slower (which I read somewhere).
In comparison, the stock 1275 chamber shape is very good in this respect.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

What about these? It says it has 16 programmed advanced curves. Otherwise I might have to go searching for a pulsar dizzy. What's the megajolt one

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If its yours, customize it !

As the Doc said it's the shape of the chamber is the reason for more advance.
The flat section on 'normal' head is call squish or quench (depending on whether you're English or American. It was first understood by an Englishman) and this is what allows for late or retarded timing. It allows the engine to run smoother with less heat and stress.

The 123 dizzy was one of the first programmeable ones for a Mini but there are others now that are more friendly.
Mick (or somebody else) put a link up here recently, but the search function is fubar'd and I cbf looking for it by scrolling each page....

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

hi 1380k

the megajolt is a distributor-less system.- infinitely programmable curves based on crank timing. ( see how tos for lots more info)

A number of programmable electronic distributors have a set number of maps (curves) you pick the one the best suits ( CSI, 123, Amethyst etc)

Single curve (typical) distributors are mapped for the masses , so tend to be conservative, however get one mapped for your spec by Performance, etc and it is customised exactly for your needs.

Horses for courses

Mg and doc , thanks for the info -

Dr mini has done well to realise what I'm talking about. Whoops

The 123 dizzy is appealing to me ATM. Just for ease of purchasing and installing. That is assuming it has an advance curve suitable.

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If its yours, customize it !

Did a bit of research and think I might just bite the bullet and get a 123 distributor. Even if later down the track I go megajolt or something ill chuck the 123 in one of my other minis I'm sure ill have more than one mini to muck around with.

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If its yours, customize it !