[Mgs] Engine maths...and spare time

[PaulHunt73]

'An' answer to those two:

Because eventually increasing advance will stop the piston going up, enough 
to stall the starter on low-compression engines from what I read.  On high 
compression you get massive pinking way before that.

32 degrees max may be something people with low-compression engines go by, 
but with high compression it has to be by whether it pinks at any 
combination of throttle opening revs and load.  Some MGB configurations had 
a max centrifugal of 36 degrees at 5000 rpm plus up to 24 degrees vacuum 
advance depending on throttle opening.  Others had a max centrifugal of 19 
degrees at 2200rpm plus up to 14 degrees of vacuum.  Some North American 
engines had the vacuum advance disabled if that was the only way they would 
get through the emissions tests.  Others only enabled vacuum advance in 4th 
gear.

PaulH.

----- Original Message ----- 

Okay, let's see if anyone knows the answer to
this one.  Why is it that "You do eventually get
to a point where no more advance will help".  Why
do we stop spark advance at ~32d BTDC at road
speed, and keep the advance the same for all higher engine speeds?