guimond47

im pretty sure dynamic is ACTUAL. dynamic means that this is the compression ratio the engine will see at any condition. I got theses numbers by imputing my cam specs, and engine specs in a calculator.

BUT if u want the information

Bore : 4.030
Stroke: 3.75
Gasket thickness: .028
Piston to deck : .028
Piston dome : -16 CC
Heads : 64cc
gasket bore : 4.166"
CAM IVC : 64 degrees

SB

iTrader: (1)

no.

Actual (static)is actual (static). Cam events have no effect on actual (static)(physically measured) compression ratio. Actual (static) compression is how much physical volume at BTDC vs TDC,

Dynamic includes cam specs. overlap and intake valve closing event. As I noted, this confused more people that not and is pretty useless anyway.Looks like it confused you too. I wish dynamic was never invented.

Bummer.

94sylvan

A flattop KB piston with (2) valve reliefs would be -6cc dish, not -16cc

SB

iTrader: (1)

And piston to deck of .028" ?

beaver 3

but dynamic is what the engine sees when its running.. and cam choice definitely changes this. it could be detonating under load with one cam but not another even though the static is the exact same.

SB

iTrader: (1)

No. It is not that simple, this DCR thing. Throw it away.

If you have too much cylinder pressure while running, you have too much static compression.

If you have too much compression, you need to add higher octane fuel or reduce your static compression.

Certain cam specs complement certain compression ratios...which is all picked out for rpm too...when building an engine. A DCR calculator does nothing good for any of this.

Why would the cam choice be so far out that it is the issue for detonation ? Ifyou have detonation issues and can't/won't change the detonation issues, you lower the compression. But, why would you run into these sort of issues anyway ? The sbc and the cams and heads and compression and today's fuel have been around forever. Pick the rpm range and power, and any parameters that may be special (like wet exhaust and what kid) and etc and things like the cam become quite easy. Don't let others make you think it's voodo or anything. It's not.

Engine Rules racing, trying to gain 3hp over your competitor is a whole different deal.


I'd love to meet the person who came up with this dumb DCR thing and pull him by the ear and givem a good spanking. LOL.

Case in point; This thread is like the 3rd or 4th this year where the OP tried to do things by dynamic compression ratio and went much too high with static compression and screwed up their build.

DCR....lol.......intake valve closing (IVC) is not the only thing that determines (running compression - better termed cylinder pressure before ignition) and such can't be calculated really unless using an in cylinder transducer (you can't afford it) and not needed at our level with normal perfomance boats.

SB

iTrader: (1)

Added a lot more to the above. ^^^

cyrus77

iTrader: (4)

Good job on the wm12.5 wot afr . 58 mph at 4800 I would go down on the prop pitch. Detonation can be heard if you are by the engine, get it a driver. I think you will be pleasantly surprised.

guimond47

I have 93 oct in the tank which i will be running out of soon. and the engine bay is completely open right now. so i can hear it really well. i have a good ear for this kind of thing. it defiantly does not sound like its falling on its face tho.

guimond47

Just to put an ending to this thread a few years later. I bought a 496 HO and dropped it in, max speed is 59-60 MPH. The stroker was close. Lighter if anything. I am assuming the haul is not built for speed or it needs more push. I may drop in a 900 hp Build this summer. its a 597 Cu in, Whipple. That should push the b*tch out of the water LOL