440 Engine tuning suggestions
Not understanding what you mean here.
I mean you can have a static compression ratio of…I’m just picking a number here 11:1 and by changing the IVC you can end up with an effective compression ratio from 8:1 to 11:1. Well maybe not to 11 because you’d be shutting the intake valve at BDC.
Following that line of thinking you can’t build compression until the intake valve is shut.
You can do the math using stroke length, IVC and I think r/s ratio but I don’t have the math right in front of so I’m not 100% sure on r/s ratio.
Let’s say (I’m going to make up numbers here for discussion) you have a stroke of 4 inches and the IVC is 65 degrees ABDC.
Doing the math you calculate how far the piston is up the cylinder by IVC and that is your effective stroke length.
Your effective stroke length will be the distance in inches (or mm if you like that better) from IVC to TDC.
Stroke length directly affects compression ratio. But, it doesn’t change your static compression ratio because we calculate that without regard to intake valve closing.
I’m going to run 12:1 or a skosh more SCR on pump gas with iron heads. It won’t rattle (the timing curve will be a bit of a challenge for sure) and I won’t have to retard total timing any more than if the SCR and the ECR are the same.
Wallace has a calculator for this. I can’t remember my IVC or I’d run the numbers and post them.
Let me see if I can find it.