Calculation of compression ratio

[Muppet]

from what I've read up to now;
Corrected 6.5 is widely regarded as a good figure but for which style of combustion chamber and squish band ratio 60/40 55/45 50/50;? Uncorrected depends on port height; pick the wrong pipe to go with your port timings it will suck or blow; but not when it should; carb choice has an influence but is not the deciding factor; it can be a limiting factor; just need someone to explain all this to me so I can understand it; best that they use crayons and draw me a pretty picture,

muppet,

Didn't MB invent compression ratios in 1982 for our little scooters ?

[Darrell Taylor]

for a bigger shock now try my example with the 15cc volume i quoted giving a corrected 6.5

uncorrected = ...........

the point being that corrected calculations are inconsistant with what fuel can be used

[Darrell Taylor]

16.4,, 15cc is small though lol

15cc is very small but a reader could easily have gone away and done a head thinking 6.5corrected is ok 16.4-1 is about the limit on a liquid cooled 125 grand pix engine on race fuel!!!that uses every trick in the book to keep it alive

ps the head on your motor looks about right ,in fact its a nice little tune youve produced

[Darrell Taylor]

gonzo wrote
On an tuned Lambretta, say a TS1 or RB22 that has been mildly ported running a 34/35mm carb and race pipe what corrected/uncorrected comp ratio would you recommend when taking modern fuels into account? is there an upper and lower figure you would say go no higher or lower than?



10-1 to 11.5 -1 with lots of variables to decide which way to go for the final design

[TS1-200]

Think I`ve started something off here
Well I have assembled the engine now with the addition of sealant to the top & bottom of the cylinder,(might reduce the compression a bit)
I have ordered a (hopefully) more accurate burette, and will have another look when it arrives,before the holed piston the motor was nice, very smooth, liked to rev & easy to ride, so I don`t really want to change the characteristics too much, the worst thing for me to have to do, as I see it would be to enlarge the combustion chamber a bit methinks, to get a couple of more cc`s

[Darrell Taylor]

well it does the business on the dyno and on the road n track with only a couple of ponies down on the latest kit offerings so youve found a nice combination there and all from a std cast cylinder
it is very enjoyable carrying out a mod and checking if its an improvement or loss but then working out why and conducting further tests can be very enlightning and provides an improved understanding.

[Darrell Taylor]

corrected would be worked back from the ex duration that has not been provided
but to be fair for the reasons previously stated is of little relevance,
the next part of the calculation is setting an effective squish clearance and msv but thats another subject