Help with Dynamic Compression Ratio
12-08-2005, 10:39 PM
#1
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Help with Dynamic Compression Ratio I'm trying to figure out if I should have my heads milled and what cc to shoot for for the combustion chambers.
Cam is:
Valve Timing @ .050
OPEN CLOSE
INT: 6 BTDC 38 ABDC
EXH: 46 BBDC 2- ATDC
LSA 110 ICL 106
DURATION @ .050 224/224
Using this calculator:
http://www.kb-silvolite.com/calc.php?action=comp2
with a Stroke of 3.622
rod length of 6.098
and a ABDC = 38+15 or 53 (some say +25?) Which is right...it makes a big difference
CR of 10.19
Gets me Dynamic Compression Rato of 8.802. Does that sound right? That means if I goto a static compression ratio of 10.7, I get 9.235. Aren't you supposed to stick to about 8-8.5?
Thanks,
Dennis
Cam is:
Valve Timing @ .050
OPEN CLOSE
INT: 6 BTDC 38 ABDC
EXH: 46 BBDC 2- ATDC
LSA 110 ICL 106
DURATION @ .050 224/224
Using this calculator:
http://www.kb-silvolite.com/calc.php?action=comp2
with a Stroke of 3.622
rod length of 6.098
and a ABDC = 38+15 or 53 (some say +25?) Which is right...it makes a big difference
CR of 10.19
Gets me Dynamic Compression Rato of 8.802. Does that sound right? That means if I goto a static compression ratio of 10.7, I get 9.235. Aren't you supposed to stick to about 8-8.5?
Thanks,
Dennis
12-09-2005, 01:24 AM
#3
Calculating DCR: Calculating the DCR requires some basic information and several calculations. First off, the remaining stroke after the intake closes must be determined. This takes three inputs: intake valve closing point, rod length, and the actual crank stroke, plus a little trig. Here are the formulas: (See the bottom of the page for a way around doing all this math.)
Variables used:
RD = Rod horizontal Displacement in inches
ICA = advertised Intake Closing timing (Angle) in degrees ABDC
RR = Rod Distance in inches below crank CL
RL = Rod Length
PR1 = Piston Rise from RR in inches on crank CL.
PR2 = Piston Rise from crank CL
ST = STroke
1/2ST = one half the STroke
DST = Dynamic STroke length to use for DCR calcs
What's going on: First we need to find some of the above variables. We need to calculate RD and RR. Then, using these number, we find PR1 and PR2. Finally, we plug these number into a formula to find the Dynamic Stroke (DST).
Calcs:
RD = 1/2ST * (sine ICA)
RR = 1/2ST * (cosine ICA)
PR1 = sq root of ((RL*RL) - (RD*RD))
PR2 = PR1 - RR
DST = ST - ((PR2 + 1/2ST) - RL)
This result is what I call the Dynamic Stroke (DST), the distance remaining to TDC after the intake valve closes. This is the critical dimension needed to determine the Dynamic Compression Ratio. After calculating the DST, this dimension is used in place of the crankshaft stroke length for calculating the DCR. Most any CR calculator will work. Just enter the DST as the stroke and the result is the Dynamic CR. Of course, the more accurate the entries are the more accurate the results will be.
Variables used:
RD = Rod horizontal Displacement in inches
ICA = advertised Intake Closing timing (Angle) in degrees ABDC
RR = Rod Distance in inches below crank CL
RL = Rod Length
PR1 = Piston Rise from RR in inches on crank CL.
PR2 = Piston Rise from crank CL
ST = STroke
1/2ST = one half the STroke
DST = Dynamic STroke length to use for DCR calcs
What's going on: First we need to find some of the above variables. We need to calculate RD and RR. Then, using these number, we find PR1 and PR2. Finally, we plug these number into a formula to find the Dynamic Stroke (DST).
Calcs:
RD = 1/2ST * (sine ICA)
RR = 1/2ST * (cosine ICA)
PR1 = sq root of ((RL*RL) - (RD*RD))
PR2 = PR1 - RR
DST = ST - ((PR2 + 1/2ST) - RL)
This result is what I call the Dynamic Stroke (DST), the distance remaining to TDC after the intake valve closes. This is the critical dimension needed to determine the Dynamic Compression Ratio. After calculating the DST, this dimension is used in place of the crankshaft stroke length for calculating the DCR. Most any CR calculator will work. Just enter the DST as the stroke and the result is the Dynamic CR. Of course, the more accurate the entries are the more accurate the results will be.
...Well never mind, what I need from you is either your degrees IVC abdc @ the lobe base OR the advertised intake duration, so that I can figure this out for you.
See this thread for more info (Thanks to Mr. J-Rod)
https://ls1tech.com/forums/advanced-engineering-tech/102153-math-figure-out-if-your-car-will-run-pump-gas.html
Last edited by NO-OPTION-2002; 12-09-2005 at 01:37 AM.
12-09-2005, 01:35 AM
#4
I'm trying to figure out if I should have my heads milled and what cc to shoot for for the combustion chambers.
That means if I goto a static compression ratio of 10.7, I get 9.235. Aren't you supposed to stick to about 8-8.5?
Anyone else have opinions for him????
Last edited by NO-OPTION-2002; 12-09-2005 at 01:21 PM.
12-09-2005, 06:18 AM
#5
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Originally Posted by NO-OPTION-2002
As an exaple using your parameters...
...Well never mind, what I need from you is either your degrees IVC abdc @ the lobe base OR the advertised intake duration, so that I can figure this out for you.
See this thread for more info (Thanks to Mr. J-Rod)
https://ls1tech.com/forums/showthread.php?t=102153
...Well never mind, what I need from you is either your degrees IVC abdc @ the lobe base OR the advertised intake duration, so that I can figure this out for you.
See this thread for more info (Thanks to Mr. J-Rod)
https://ls1tech.com/forums/showthread.php?t=102153
Valve timing close @ .050, Intake ABDC = 38
There's not much more info on the cam card. Duration @ .0066 is 277/277
Lobe lift is .334/.334
12-09-2005, 06:20 AM
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Originally Posted by NO-OPTION-2002
It seems (to me at least) that the jury is still out as to the ability to run pump gas on more than 8.0-8.5 dcr. I definately wouldn't chnce my motor without seeing some more definitive research on the subject.
Anyone else have opinions for him????
Anyone else have opinions for him????
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12-09-2005, 09:21 AM
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The problem is that the Silvolite site's calculation is based on very aggressive cam lobes, more like drag race solid rollers than hydraulics. If you notice, it adds 15 degrees to the 0.050" IVC point, implying a cam with only 30 degrees more duration at the relevant 0.006" lift points. Yours is 277 - 224 or 53 degrees more. Therefore, your actual IVC is 38 + (53/2) or 64.5 degrees ABDC. This gives a DRC of ~ 8.5:1 from a SCR of 10.7:1, which shouldn't get anyone's shorts in a knot.
12-09-2005, 11:03 AM
#9
Ok, here goes...
(277/2 +106) -180 = 64.5 IVC ABDC
DST = 2.93473 (as per above formula)
Now go back to the KB calculator and DO NOT use the DCR section. When it asks for the stroke input the 2.93473 DST instead of your actual stroke. This will give you the DCR for your motor.
*CORRECTED*
(AT ME!)
(277/2 +106) -180 = 64.5 IVC ABDC
DST = 2.93473 (as per above formula)
Now go back to the KB calculator and DO NOT use the DCR section. When it asks for the stroke input the 2.93473 DST instead of your actual stroke. This will give you the DCR for your motor.
*CORRECTED*
(AT ME!) Last edited by NO-OPTION-2002; 12-09-2005 at 01:15 PM.
12-09-2005, 12:22 PM
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Ha ha, that's my old cam. Trust me, you're not going to have any knock issues with it, I had that cam in my car for about 1 year or so and had no issues, except frying the tires from hella torque. Good luck.
12-09-2005, 05:19 PM
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Originally Posted by DAPSUPRSLO
Ha ha, that's my old cam. Trust me, you're not going to have any knock issues with it, I had that cam in my car for about 1 year or so and had no issues, except frying the tires from hella torque. Good luck.
12-12-2005, 09:50 AM
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Originally Posted by Teutonic Speedracer
That's what I'm looking for! Cool! I'm pairing it with TEA S1 Heads, LS6 Valves, Kooks Headers, LS6 Intake, Ported TB, etc. Plus the car is in the 2900 lb. range! What other mods did you have with that cam?
Basically full boltons (tb, ftra, intake lid, 85 mm maf, headers, asp pulley, etc.). Used the stock water pump and did not have a lsx intake as it was not available that far back.
