static vs dynamic compression ratios

[David Redszus]

Did you ever ask him how he defined DCR? It's probably not what most think.

Exactly.
There's a lot of good information you can compile, looking at pressure waves in a running engine.
None of it has any relation to the output you receive from a "DCR" calculator.
How can you input static parameters, and get a Dynamic result ?

Very easy. DCR is a comparison of volumes. It does not matter whether the engine is motored, firing,
or simply measured. Volumes are volumes, period. The volume ratios do not change.

If you believe DCR has limited value, then you must agree that SCR has negative value.

Which DCR calculator do you use? Why?

[PackardV8]

Just yesterday a guy building an el cheapo BBM told us of a new cam grind he was going to use, marketed as a crutch for the low SCR OEM pistons and heads; supposedly, it closes the intake fast and early to trap more DCR while still having overlap to give the required fairgrounds idle lope. Anyone know of this deal?

That's the Comp Thumpr series.

Thumpr™
Benefits:

Great sound (early exhaust opening and more overlap)
Great power (new lobe designs give great area and air flow)
Great mid-range response (early intake closing traps more air)

Important Considerations:

Minimal engine vacuum – requires mods for any vacuum accessories such as power brakes
Designed for use only with valve train upgrades including COMP Cams® Beehive™ Valve Springs and roller rockers
Works best with looser converters, more rear end gear and other performance engine modifications

They idle like crap, and make no top-end power.
I'm sure some people love them.

Hi, Mike,

Figures. Of course, we've been aware of the Thumpr for many years. I guess the Mopar guy wasn't and was telling it as the latest new thing, just came out.

[CamKing]

Figures. Of course, we've been aware of the Thumpr for many years. I guess the Mopar guy wasn't and was telling it as the latest new thing, just came out.

Well, it seems some of the other cam companies have come up with their own version, so maybe he was talking about one of those

[rebelyell]

Computational Fluid Dynamics CFD
Perhaps a clever software engineer might meld a CFD program with DCR programming?

Top flight CFD suites are rather pricey but free programs available as well.

[Mark O'Neal]

An engine with a SCR of 8.5 would typically have a DCR of about 6.5. A this should produce a cranking
pressure of about 186 psia...if there is no leakage. I might look for a valve and/or ring leak. What was the leakage?

Is there a mine field warning here I missed? Should there be? Popcorn?

How does a 8.5 SCR engine produce 186PSIG cranking pressure?

Mine has a SCR of 10.5 and cranking pressure is 180psig.

Same way gas mileage motors ran 15.0:1 static back in the 80s.

The only thing DCR causes is me to hang the phone up. Altering static compression is a function of cam design...but almost everyone does it backwards.

B303 FTW!

[RT Machine]

I worked with a Ford Engineer in Australia who used to be in charge of prototype engine calibration in the UK.
He told me many things that went on in the dyno test cells etc
They always measured DCR and combustion pressures etc with transducers in the combustion chamber.
The OEM,s monitor every parameter possible to get that engine as perfect as possible.
If DCR is important to the OEM,s then its important to the rest of us.

Did you ever ask him how he defined DCR? It's probably not what most think.

Hi Hoffman900, no I did,nt ask him, it was along time ago, i recall him showing me a pile of graphs on a PC, and explaining a few things that I thought impressive, at that time we both were working on building durability test machinery for OEM steering components.