DCR & Pressure
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From: Frozen Tundra, WI
DCR & Pressure I could use some help on determining if my numbers are too high. Most of the (Google) information out there is about "traditional" old school chevy's. I have done some searching on here and got conflicting information. The calculator puts me at 9:1 DCR and 185 psi cranking pressure. Is this too much for 91 or 93 octane??
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From: Frozen Tundra, WI
Would cranking pressure be a more accurate (real world) number to follow than DCR??? Can cranking pressure and DCR vary...in other words, could a 8.8 DCR equal more than 185 pressure with a different set-up??? These are the calculators I used... http://www.csgnetwork.com/compcalc.html http://www.wallaceracing.com/dynamic-cr.php
Last edited by Paul57; Dec 9, 2011 at 09:56 PM.
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From: Frozen Tundra, WI
Bore 4, Stroke 3.622, Rod 6.098, SCR 11.31, ABDC 64.5, Gasket .051 4.020
63 cc chambers with -.006 Piston (deck)
Am I on the right track???
63 cc chambers with -.006 Piston (deck)
Am I on the right track???
Last edited by Paul57; Dec 10, 2011 at 11:44 PM.
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From: Frozen Tundra, WI
I wonder if the .005-.007 comes from figuring a loss of .003 due to cylinder pressures?? We are measuring with zero load. Maybe .001 for wrist pin, .001 for rod bearing and .001 for crank bearing load???
Last edited by Paul57; Dec 11, 2011 at 08:37 AM.
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I am beginning to think the calculator needs to be recalculated. 
Has anyone found these calculators to be inaccurate on the pressure?? I have seen a couple posts that stated factory LS1's are 190-200.
Has anyone found these calculators to be inaccurate on the pressure?? I have seen a couple posts that stated factory LS1's are 190-200. I just checked my Maverick's engine ('03 Corvette 350 HP) two days ago and got from 175 - 205 with a torquer v.2 cam...
Static compression ratio of 10.25:1.
Effective stroke is 3.21 inches.
Your dynamic compression ratio is 9.20:1 .
Your dynamic cranking pressure is 190.33 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 9.20 :1.
V/P (Volume to Pressure Index) is 175
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From: Frozen Tundra, WI
The cranking pressure on the calculator is right in the middle of your actual/real world check. Obviously, the calculator doesn't need recalculating then. Thanks for taking the time to check...that was appreciated. I feel a lot better about my numbers now especially when I have heard that many LSx's are 190-200 (like yours) on pump gas. I take it you are running 93 pump gas??? Are you using the .051 head gasket???
Thanks for taking the time to check...that was appreciated. I feel a lot better about my numbers now especially when I have heard that many LSx's are 190-200 (like yours) on pump gas. I take it you are running 93 pump gas??? Are you using the .051 head gasket??? The cranking pressure on the calculator is right in the middle of your actual/real world check. Obviously, the calculator doesn't need recalculating then. Thanks for taking the time to check...that was appreciated. I feel a lot better about my numbers now especially when I have heard that many LSx's are 190-200 (like yours) on pump gas. I take it you are running 93 pump gas??? Are you using the .051 head gasket???
Thanks for taking the time to check...that was appreciated. I feel a lot better about my numbers now especially when I have heard that many LSx's are 190-200 (like yours) on pump gas. I take it you are running 93 pump gas??? Are you using the .051 head gasket???
just checking my math here, but using the 98-00 stock cam and the factory 10.1CR I get intake closing at 37* and a dynamic compression of 9.44 and 196psi.
I am doing a heads only build and am using E85, compression will be close to 12.4 or so. With the same 37* IVC and 12.4 I get DCR of 11.5 and 255psi, which is about what I wanted and will make a pile of tq.
I am doing a heads only build and am using E85, compression will be close to 12.4 or so. With the same 37* IVC and 12.4 I get DCR of 11.5 and 255psi, which is about what I wanted and will make a pile of tq.
Sorry, your using the wrong numbers. To get 37abdc you would need a cam with an advertised base duration of 200-210 degrees depending on advance. Not going to happen... Your abdc at base duration is more like mid 60's with a healthy cam. Use base duration ....not .050 abdc....
Also, with the stock cams i've seen. Stock compression LS1's are way below 8 to 1 DCR. Very slow closing intake abdc.
Paul57 is correct. Most fresh LS1's crank around 190-200psi stock. With an actuall DCR of 9 to 1, look for around 230 psi. So, that calc your using must have a wide window. As an example 8.77 DCR was 230psi on my old combo. I have heard of up to 240 psi at 9 to 1 DCR. But cams are not ground to exact spects. Plus there rated at .006 base duration vice .001 so there's more fudge room. When it comes to stock ls1's there not exactly the same SCR, cam used and timing gears, ect. These would all make small differences in PSI for that 190-200 psi window.
This info for DCR is just for crank psi. In the real world how much actual DCR you can run depends on, cylinder fill (think heads and intake), rh, altitude, cooling, SCR, fuel used and some others that it's too late at night to remember.
Pump E85 your running does have it's limits. Mainly, the crap 87 octane added. Only gets worse in the winter. If you make your own fuel or add Torco you can run some crazy SCR/DCR's. If using pump actual E85 summer blend, I would not go more than 13.5 SCR due to variances in fuel, and the resulting tuning changes caused by this.
Also, with the stock cams i've seen. Stock compression LS1's are way below 8 to 1 DCR. Very slow closing intake abdc.
Paul57 is correct. Most fresh LS1's crank around 190-200psi stock. With an actuall DCR of 9 to 1, look for around 230 psi. So, that calc your using must have a wide window. As an example 8.77 DCR was 230psi on my old combo. I have heard of up to 240 psi at 9 to 1 DCR. But cams are not ground to exact spects. Plus there rated at .006 base duration vice .001 so there's more fudge room. When it comes to stock ls1's there not exactly the same SCR, cam used and timing gears, ect. These would all make small differences in PSI for that 190-200 psi window.
This info for DCR is just for crank psi. In the real world how much actual DCR you can run depends on, cylinder fill (think heads and intake), rh, altitude, cooling, SCR, fuel used and some others that it's too late at night to remember.
Pump E85 your running does have it's limits. Mainly, the crap 87 octane added. Only gets worse in the winter. If you make your own fuel or add Torco you can run some crazy SCR/DCR's. If using pump actual E85 summer blend, I would not go more than 13.5 SCR due to variances in fuel, and the resulting tuning changes caused by this.
Last edited by jimbob; Dec 15, 2011 at 05:39 AM.
I am using the GM stock 98-00 cam specs which were found on a cam doctor to be:
Intake
198.9@.050
0.498"
ICL 119
Exhaust
209.3@.050
ECL 119.8
LSA 119.45
This gives:
IVO .050
-19.6
IVC
38.4
Using this calculator that specifically lists to use the .050" numbers
http://www.rbracing-rsr.com/comprAdvHD.htm
and the specs
Bore-3.9
Stroke-3.622
Rod-6.098
Static Compression-10.1:1
IVC @.050-38.4*ATDC
0 boost
0 Altitude
Results:
Effective stroke-3.33"
Dynamic compression- 9.37:1
Cranking Pressure-194.84 psi
So I cant see what numbers Im using that are wrong to get this value.
Intake
198.9@.050
0.498"
ICL 119
Exhaust
209.3@.050
ECL 119.8
LSA 119.45
This gives:
IVO .050
-19.6
IVC
38.4
Using this calculator that specifically lists to use the .050" numbers
http://www.rbracing-rsr.com/comprAdvHD.htm
and the specs
Bore-3.9
Stroke-3.622
Rod-6.098
Static Compression-10.1:1
IVC @.050-38.4*ATDC
0 boost
0 Altitude
Results:
Effective stroke-3.33"
Dynamic compression- 9.37:1
Cranking Pressure-194.84 psi
So I cant see what numbers Im using that are wrong to get this value.
Last edited by Grr; Dec 15, 2011 at 10:16 AM.
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From: Frozen Tundra, WI
Using this calculator that specifically lists to use the .050" numbers
http://www.rbracing-rsr.com/comprAdvHD.htm
http://www.rbracing-rsr.com/comprAdvHD.htm
Your intake valve has to be closed to build compression, at .050 duration it is still open. The .004-.006 base duration figures are what you need to use. Even these are a little off for actual closed duration but close enough with all the variances found in the cam and valve train. I can't remember the base duration off hand for an LS1 cam but if you search around this site, or the net you'll find it. Plug that number in and the DCR will plummet....