vmapper

iTrader: (8)

I like to use this one..
install the calculator on your windows machine.


bottom of page -
http://cochise.uia.net/pkelley2/DynamicCR.html

The more calculators the better - or more confusing perhaps.
Remember Advertised duration are not the @0.05" lift values. - DMM mentioned this as well!

Cylinder pressure is another animal all together...



Some info that may be useful:
You will also have to find out your piston C.H.
the LS6 block is 9.24"
Deck Clearance = 1.304 - C.H. (Compression Height)
C.H. = Block Deck Height - (Stroke/2+ rod length) - deck clearance
Adding boostdum
DDR(boost) = DR * (14.7+ boost / 14.7)

LS6 Cylinders 64.45 cc
LS6 Piston flat -1.4cc
LS6 Gasket 0.051" -
LS6 Bore 3.898"
LS6 Gasket Bore 3.94"
Deck Clearance -0.007
LS6 Stroke 3.622"
LS6 Rod length 6.098"
LS6 Cam Intake Closing Angle in use 68.5°

Static Compression 10.503:1
Dynamic Compression 8.115:1

Happy New year!

tommycompton

iTrader: (1)

Cool calculator.
You don't happen to have the stock LS2 specs do you?

tommycompton

iTrader: (1)

Based on the caculator and basic estimations with the ls9 cam and 72 cc
heads.
I would have a dynamic compression of 8.9
Might be a bit off with a cometic head gasket

Any thoughts on this?
should I be aiming for a lower dynamic compression with 91 octane pump gas?
Should I aim for lower than 8.25 by selecting a different cam?
The stock ls2 cam is higher in dynamic compression @ 9.8 Dcr with 72cc heads.
According to the calculator the stock dynamic compression for the ls2 is ~10.1 does that sound correct?

vmapper

iTrader: (8)

Those numbers do not sound correct.

Post all your values you are entering.

vmapper

iTrader: (8)

The design is a tad wonky, ideally, one will fill out the middle tab first, then the first tab, then the last tab to get your quench, SCR and DCR.
Being aware piston to deck clearance (-) negative is outside the hole.
Flat or dished (would be a negative value) e.g. -8.6 would be entered as 8.6. OR select the DOME and enter as -8.6

tommycompton

iTrader: (1)

It seemed to work before, now even trying to get stock CPR is going wierd.

Stock 10.9:1

bore 4
stroke 3.622
Rod length 6.098
Deck -0.006
piston dome? stock 0
gasket .051
Head volume 64.5cc

stock cam
adv intake 270
adv ex 275
lsa 116
Intake cl 118


Then I would do the above with 72cc heads on stock cam
Then also 72cc heads with LS9 cam specs

adv int 277
ex 295
lsa 122.5
in cl 122

DMM

Agreed. Those values seem to indicate that you are not taking cylinder pressure (above 1 BAR) into account. DCR is obtained by calculating the reversion back through the intake port...in other words, after the piston reaches BDC (bottom dead center) and begins to travel back up during the compression stroke, a small amount of compression will be forced out of the cylinder, into the intake port. This is why ABDC* are required (number of degrees the intake valve is open after bottom dead center). The longer the intake valve hangs open after BDC, the lower the dynamic compression will be as there will be more reversion through the intake valve.

If you have a supercharger or turbocharger operating over 1 BAR (any boost level), the airmass within the cylinder is already compressed before the compression stroke even begins, so your reversion through the intake valve will be much less than that of a naturally aspirated engine would be operating at or under 1 BAR; and DCR will increase dramatically.

Simply put...DCR can be thought of as controlled leakage, and boost in the cylinder will add to your DCR in much the same way that higher ambient temps contribute to higher IAT values...if that makes sense.

Redo the calculations and make sure that you add your level of boost into the equation.


Edit: Here are some of my calc's. Note that for every increase in boost (above 1 BAR), there is a substantial increase in DCR as the airmass is already compressed before the compression stroke and there is less total reversion through the intake valve. Use the DCR link that I posted. You can do this across the RPM range to gauge what you can run for ignition advance also. One last thing...take note that the DCR steadily increases with boost even though the Static (SCR) compression ratio remains constant.

N/A LS6:
Static compression ratio of 10.503:1.
Effective stroke is 2.71 inches.
Your dynamic compression ratio is 8.11:1 .
Your dynamic cranking pressure is 161.81 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of PSI is 8.11 :1.
V/P (Volume to Pressure Index) is 126

LS6 @ 6 Lbs of Boost:
Static compression ratio of 10.503:1.
Effective stroke is 2.71 inches.
Your dynamic compression ratio is 8.11:1 .
Your dynamic cranking pressure is 161.81 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 6 PSI is 11.42 :1.
V/P (Volume to Pressure Index) is 126

LS6 @ 10 Lbs of Boost:
Static compression ratio of 10.503:1.
Effective stroke is 2.71 inches.
Your dynamic compression ratio is 8.11:1 .
Your dynamic cranking pressure is 161.81 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 10 PSI is 13.63 :1.
V/P (Volume to Pressure Index) is 126

LS6 @ 12 Lbs of Boost:
Static compression ratio of 10.503:1.
Effective stroke is 2.71 inches.
Your dynamic compression ratio is 8.11:1 .
Your dynamic cranking pressure is 161.81 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 12 PSI is 14.73 :1.
V/P (Volume to Pressure Index) is 126

tommycompton

iTrader: (1)

True yes I wa doing the calculations with no boost factored in.
I was try to get an aproximate base line before factoring in boost. I can't even seem to get that using the caculator lol.

vmapper

iTrader: (8)

Head gasket thickness should be 0.051.

ALSO


I know the Piston to deck clearance will be different than you have up there.

Also Im sure you need some -x.x number in the Flat / Dome setting.

vmapper

iTrader: (8)

LS6 for example use +1.4cc pistons, and based on the C.D. (compression distance) of the piston, the rod length, this determines where from deck height they sit.
For the LS6 slug on stock rods for example, on a standard LS block 9.245", means the piston will sit 0.007" above. I dont have LS2 info on this workstation.

Also head gasket bore will be bigger, for a more exact value.

tommycompton

iTrader: (1)

Got the head gasket, -0.006 was i'll i could find on deck measurements, and can't find any on the piston.

vmapper

iTrader: (8)

You have 1/2" head gasket in that screen shot.
Should be 0.051 not 0.51

tommycompton

iTrader: (1)

oh lol damn.

vmapper

iTrader: (8)

LS2 gasket 4.060
Deck Clearance -0.007 (same as LS6)

I dont know piston cc ...

tommycompton

iTrader: (1)

Thanks for the measurments, and yes my 1/2" head gasket was throwing things way off. I had i written down corecctly but kept punching it in wrong.

tommycompton

iTrader: (1)

Ok with all the above punched in with 1.4cc pistons I get a static base of 10.9:1
and dynamic of 8.089.

With 72cc heads and stock cam
I'm at 10.01 static
and 7.447 dynamic

With 72cc heads and ls9 cam
10.01 static
6.877 dynamic

So with the 10.01 static and ls9 cam

Camshaft, Rod Length, Boost and Altitude Correction to Compression

Your engine summary is as follows: Bore 4 inches, stroke 3.622 inches, rod c-c length 6.098 inches, with a static compression ratio of 10.01 :1. Your camshaft specifications call for an inlet valve closing of 277 degrees ABDC (after bottom dead center).

Your chamber volume is 82.78 cc's. With this camshaft your dynamic, or effective stroke is 2.30 inches. Your dynamic compression ratio is 6.57 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 122.76 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 6 PSI is 9.25 :1.

tommycompton

iTrader: (1)

or stock cam 6ps1

Camshaft, Rod Length, Boost and Altitude Correction to Compression

Your engine summary is as follows: Bore 4 inches, stroke 3.622 inches, rod c-c length 6.098 inches, with a static compression ratio of 10.01 :1. Your camshaft specifications call for an inlet valve closing of 270 degrees ABDC (after bottom dead center).

Your chamber volume is 82.78 cc's. With this camshaft your dynamic, or effective stroke is 2.09 inches. Your dynamic compression ratio is 6.04 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 109.69 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 6 PSI is 8.51 :1.

DMM

IVC is 200* - 277* ADBC? Is that what you had typed in? That's not right man. Try 89*.

tommycompton

iTrader: (1)

Oh ok got ya
. I'll be back

tommycompton

iTrader: (1)

LS9 cam
Static compression ratio of 10.01:1.
Effective stroke is 2.36 inches.
Your dynamic compression ratio is 6.71:1 .
Your dynamic cranking pressure is 126.25 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 6 PSI is 9.45 :1.
V/P (Volume to Pressure Index) is 90


Stock cam

Static compression ratio of 10.01:1.
Effective stroke is 2.59 inches.
Your dynamic compression ratio is 7.29:1 .
Your dynamic cranking pressure is 140.83 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 6 PSI is 10.27 :1.
V/P (Volume to Pressure Index) is 110

Now what did I mess up My vp is different.