Such a sliding scale on engine configuration, mood or state of charge in the starter, air and humidity and phase of the moon at sea level or hurrance eyeball.
Here's a down and dirty rule of thumb to apply to Norton twins in general.
results are typically between 15 and 20 × static compression ratio (9:1 = 135 to 180 psi) 5% difference between cylinders is OK. 100 lbs on a fist kick and a cold motor means compression sealing not your problem.
I found an article in an old Classic Bike magazine on
testing compression which may be of some general assistance.
Here's the gist of it:~
In the absence of manufacturers quoted figures expect the
following pressure from different Compression Ratios:
6:1 88-118;
7:1 103-147;
8:1 125-162;
9:1 140-176;
10:1 162-191;
11:0 176-206.
Dave & Marlene wrote:
On your compression ratio question, Increasing CR has diminishing
power returns (inverse gain) Example;
Increasing from 5 to 6 to 1 gives about 3.5% power increase.
>From 6-7 = 2.5%
>From 7-8 gives 1.4%
>From 8-9 gives 0.7 %
>From 9-10 gives 0.6%
>From 10-11 gives 0.5%
Maximum usable CR depends among other things, compactness of
combustion chamber, speed of burn, more compact, faster burn, can
use more CR.
How much turbulence, swirl in combustion chamber, more swirl or
more compact can use more CR.
Cam timing, the later in the cycle that the intake valve closes
the less cylinder pressure & the more CR that can be used.
A good design rule for small bore engines, around 80mm or less, is
that the CR can be one tenth of the fuel octane number plus 0.5
ratio if everything is optimum. Example, 92 octane fuel = 9.2 CR
plus 0.5 CR = 9.7 to 1 CR.
I am referencing the book "The Design of Competition Engines" by
Philip H. Smith, a well known racing engine designer.
Regards,
Dave Russell