About2Bite

Hi all,

Can anyone give me a hand with calculating dynamic compression?

Looking at a 4.00"stroke, 6.125" rod length, and 1.110" piston compression height. With a stock ls1 block deck height that puts the pistons .005" inside the bore.

Cam specs are as follows:
.248/.254 .615/.622 111LSA

Piston options are +5cc or -3cc with a .040" head gasket and 243/799 heads milled .005"

Also, running 93 octane here so any advice on this build is appreciated.

Shooting for a half mile race.

Considering the following:
Decking the block .010" for quench
Direct port nitrous

Thanks!

Blown06

iTrader: (32)

Not enough information.

What is the static compression ratio? If you don't know, give me the bore size and combustion chamber size.

When does the intake valve close after bottom dead center (ABDC) (in degrees)?

About2Bite

3.905 bore, I'm not sure intake closing point. Also I'll be having .010"taken of the deck of the block

Thanks!

G8One2

Need to have your heads CC'd, piston to deck measurement, bore, stroke, rod length, head gasket thickness and IVC @.006"

About2Bite

The combustion chamber of the head was not machined, only the intake and exhaust ports. The deck of the head was milled .005 to clean up. When I tested the volume I found about 64cc volume in the chamber.

Pistons will be out of the hole 0.005" (after the .010" is taken off the deck of the block)

Crank has a 4.00"stroke
6.125" rod length
.040" head gasket

The only cam specs I have are...
248/254 duration with .615/.622 lift ground on a 111LSA

Blown06

iTrader: (32)

Best I can do with the limited cam info is:
Intake Open: 13*
Intake Close: 55*
Exhaust Open: 58*
Exhaust Close: 16*

Also, making some other assumptions and using your figure of +.005 cc piston and ball parked gasket bore size........your static CR will be around 11:1

Again, assuming some things and using these ball park figures, your dynamic CR is 9.43:1.

eaglegoat

And all of this is basically irrelevant...

Exidous

iTrader: (11)

What is the ICL(intake centerline) of the cam? Possible 107? This is rather important for DCR.

Gasket diameter?

Assumptions/setup:

3.905" bore
4" stroke
6.125" rod
1.11" PH -3cc
9.23" deck (decked .010")
.040" 4.1" diameter gasket
64cc heads
Roughly .006"-.050" ramp of 50(averageish lobe) meaning 298/304 duration at .006"
Assumed 4+ advance for a 107 ICL

Results
11.5SCR
.035" quench
8.3DCR

There are sooooo many assumptions that I am certain my numbers are off.

We NEED ICL and .006" int/exh duration.

panic

And all of this is basically irrelevant...

DCR is the modern cliche-du-jour.
The predicted (reduced) CR exists only in the brief window between idle and the bottom of the torque range, at which point the static CR takes over.
IMHO it has little practical use except for predicting knock sensitivity (but only a low RPM, nowhere near your torque range), and it's helpful to compare converter stall speed against a known engine.
I wrote an .xls specifically for the LS engines, where rather than enter numeric values from the keypad you just select from pre-entered values (bore, stroke, and rod length), and use sliders to enter piston oversize, static CR, and intake closing point ABDC.
Results are effective stroke, DCR, and CCP (gauge and absolute), and approximate torque at 1,000 RPM.
E-mail me for a free copy.