Quote Originally Posted by tomtaylor View Post
Thanks for the feedback on fuel types

In reading here about Dynamic vs Static compression ratio the conversation sounds more like cylinder pressure than compression ratios. Isn't Dynamic CR only affected by cam profile?

if that is true then DCR is cool to understand but wouldn't really matter since we can't change it unless we are out grinding custom cams as we don't have a plethora cam options like a SBC 350?
Compression Ratios, static and dynamic directly correlate to cylinder pressure ratios. Which when combined with Combusting fuel correlate to cylinder pressure. In a naturally aspirated induction system, your DCR will always be less than your SCR.

With Forced induction you can increase the DCR over the SCR with the added benefit of having more Oxygen available for the fuel to use to combust.

DCR can be controlled as the calculator More power posted by increasing the level of boost. or mechanically altering your SCR Via increasing the combustion chamber volume size which is commonly done by shaving pistons down, using thicker gaskets, or using pistons which have the wrist pin placement raised on the skirt thereby shortening the stroke of the piston.

Custom cams and grinds for diesel motors are not very prevalent because almost always they will move the power band further up into the rpm range given the same timing correlation of the valve events to a stock motor. Retarding or advancing the cam to bring it back into a useable RPM range is often not practicle With the relatively small piston to valve clearance in a diesel motor. Due to the sheer mass of the components and already high cylinder pressures within a diesel motor RPM's are typically 3/4 to half of what a gasoline motor operates off of so any work to adjust the level down to an area where it is most useable becomes fruitless as parts will start contacting.

With forced induction this becomes even less important as you are increasing the engines ability to intake air which is where most of your power over stock grinds comes from with custom camshafts in Gas motors.

All of that being said If you were able clearance the pistons around the valves and change the overlap and allow the exhaust valve to hang open a bit longer it seems that some more power could be made. But would it increase your DCR and therefore your Pressure ratio to a point where things start breaking?

A simple way to visualise it assuming that a compression ratio is Adiabatic (Thermal dynamics phrase which doesnt take into effect heat introduced outside of the heat of compression as that math is overly complicated for this example). Your pressure ratio with a Compression ratio of 10:1 would be 25.12:1 CR of 15:1 would be 44.31:1 CR of 20:1 would be 66.29:1 CR of 25:1 would be 90.61:1 and a CR of 35:1 would be 145.11:1

Actual cylinder pressure when taking into account the combustion is hard to figure accurately without measuring it as so many different factors effect it. If you could figure the PSI of a metered amount of diesel combusting you can than get a general ideal of the cylinder pressure and its relatationship to compression above by using a simple formula.