As to kickback, it's all about EFFECTIVE cylinder pressure.
What is a 10/1 engine?
This is a ratio of cylinder volume comparing it between when the piston is at the bottom to when it is at the top. By itself it is not very meaningful.
Why is that?
Because compression cannot start until the intake valve is closed and not leaking. With a small cam, this starts early enough, that the Dynamic compression ratio can be fairly high. But the later the intake valve closes, the less the Dynamic ratio can be.
What is Dynamic CR?
It is the same as Scr except the swept volume does not begin until the intake valve is closed. Dynamic CR can vary wildly in the came engine, at the same Scr, with different cams, but rarely gets closer than 1.5 point less than the Scr.
There is a third Compression Ratio for throttled engines namely Effective CR or ECR. When the throttles are closed, very few air molecules can actually find their way into the chambers. So even tho you have a 10/1 engine, that big cam of yours might bring the Dcr down to say 8.2 (just guessing) but worse is that your 10/1- 440, has a total volume of say 900+100=1000cc with the piston at the bottom, But, maybe only 300 cc worth of air, when measured outside the chamber, actually gets into there during cranking ,with the throttles closed, So your ECR might be 1000/300= 3.3 to 1.
But say during cranking, you open the throttle some, and now 500cc of air gets in there. And so, now, 1000/500= 5/1 ECR.
So now you can kindof see why 20* initial is not that big a deal.
But it gets worse.
When you start the fire, at some early number like 20*, there is way more than just 100cc of minimum chamber volume,above the piston; So your actual ECR at the time of ignition might be even lower than 5/1.
But it gets even worse.
When the engine is cold; of the fuel that gets into the plenum, most of it is gonna puddle on the cold intake floor. Some of it is gonna stick to the various cold port surfaces like rain sticks to your windshield at 60mph. And some of the drops, when they get into the cylinder are too big to burn and they are gonna go right out the tailpipe, unburned. So what do you do? You put a few pumpshots into the intake, in the hopes that there will be enough fuel in suspension, that maybe it will catch fire.
But it gets even worse!
With 1000 ccs of total chamber volume,the finally inducted elements of gasoline and oxygen have to wander around in there and find each other, cuz if the gas don't find oxygen, it cannot chemically react to produce heat, which is the author of the motive force that eventually moves your car.
And that is why you start the fire so darn early in the low-efficiency mode of starting.
A soon as the engine is warmed up, you don't need the early timing any more, but AFAIK, nobody has ever made a stand-alone self-switching system.
For your time and knowledge
