Compression Calculator
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Originally Posted by Edzred72
Which "does it for you" caculator do you guys use for static & or dynamic?? Post links if you can please. 
Eddie
Eddie
I have an adjunct to that:
For those using DCR ... what reference standards are you using to correlate DCR to octane / street use / track use etc? ... and where are those reference standards?
I see alotta DCR numbers bandied about along with "oh your DCR is only x.xx so you can't do that". I understand how to calc both SCR & DCR ... but what is the origin for usage advice based on DCR data?
Thread Starter
Le Mans Master
Joined: Oct 2001
Posts: 5,943
Likes: 3
From: Wildwood IL
Originally Posted by jackson
GREAT Question Ed!!!
OK...lets try an expierement. Here is my engine info. Using your prefered formula/calculator see what you come up with for static & dynamic compression for my 406. I'll post my results & method after a few responses...
Bore 4.155
Stroke 3.75
Deck +.010 (down in the hole)
Gasket thickness .039
Gasket bore 4.200
Head cc 76
Piston Volume -5.4 (flat tops, 2 valve relief)
Intake close 41* ABDC
Rod length 6"
Eddie
Drifting
Joined: Apr 2002
Posts: 1,716
Likes: 4
From: New Baden Illinois
Originally Posted by Edzred72
I have the do it yourself formulas, and have tried two different automatic caculators. Entering the EXACT same data in all, I get quite a difference between them. Isn't there a standard, set formula used by all???
OK...lets try an expierement. Here is my engine info. Using your prefered formula/calculator see what you come up with for static & dynamic compression for my 406. I'll post my results & method after a few responses...
Bore 4.155
Stroke 3.75
Deck +.010 (down in the hole)
Gasket thickness .039
Gasket bore 4.200
Head cc 76
Piston Volume -5.4 (flat tops, 2 valve relief)
Intake close 41* ABDC
Rod length 6"
Eddie
OK...lets try an expierement. Here is my engine info. Using your prefered formula/calculator see what you come up with for static & dynamic compression for my 406. I'll post my results & method after a few responses...
Bore 4.155
Stroke 3.75
Deck +.010 (down in the hole)
Gasket thickness .039
Gasket bore 4.200
Head cc 76
Piston Volume -5.4 (flat tops, 2 valve relief)
Intake close 41* ABDC
Rod length 6"
Eddie
Keith Black: SCR - 10.014; DCR - 8.519
Wallace Racing: SCR - 10.03; DCR - 9.22
I have never had much luck with the Wallace Racing DCR calculator, though. It always seems pretty high.
Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
Static compression is straight forward dealing with swept and unswept volume.
Dynamic Compression gets to be more confusing. Some calculators use the point at which the intake valve is fully closed, some at the point the valve is at .050 plus an additional 15*, etc. Depending how the calculation is done, the results will vary. The results should give an indication if the engine is high, mid, low compression with a certain duration camshaft. If the calculation comes out on the high side, I would not expect the engine to run on 87 octane. One advantage of using DCR is to get the static compression is a suitable range for the cam profile. This is the reason that long duration camshafts require a higher static compression ratio.
Dynamic Compression gets to be more confusing. Some calculators use the point at which the intake valve is fully closed, some at the point the valve is at .050 plus an additional 15*, etc. Depending how the calculation is done, the results will vary. The results should give an indication if the engine is high, mid, low compression with a certain duration camshaft. If the calculation comes out on the high side, I would not expect the engine to run on 87 octane. One advantage of using DCR is to get the static compression is a suitable range for the cam profile. This is the reason that long duration camshafts require a higher static compression ratio.
Thread Starter
Le Mans Master
Joined: Oct 2001
Posts: 5,943
Likes: 3
From: Wildwood IL
Originally Posted by dgruenke
I tried 2 different sites, the Keith Black one that I posted above and Wallace Racing. Here are the results:
Keith Black: SCR - 10.014; DCR - 8.519
Wallace Racing: SCR - 10.03; DCR - 9.22
.
Keith Black: SCR - 10.014; DCR - 8.519
Wallace Racing: SCR - 10.03; DCR - 9.22
.
I too used K Black, along with Cambell Performance and got almost the same results you came up with. Nearly 3/4 of a point difference in DCR is substantial! Eddie
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Le Mans Master
Joined: Mar 2004
Posts: 7,493
Likes: 1,501
From: Little Rock AR
Originally Posted by jackson
GREAT Question Ed!!!
I have an adjunct to that:
For those using DCR ... what reference standards are you using to correlate DCR to octane / street use / track use etc? ... and where are those reference standards?
I see alotta DCR numbers bandied about along with "oh your DCR is only x.xx so you can't do that". I understand how to calc both SCR & DCR ... but what is the origin for usage advice based on DCR data?
I have an adjunct to that:
For those using DCR ... what reference standards are you using to correlate DCR to octane / street use / track use etc? ... and where are those reference standards?
I see alotta DCR numbers bandied about along with "oh your DCR is only x.xx so you can't do that". I understand how to calc both SCR & DCR ... but what is the origin for usage advice based on DCR data?
For SCR I have written a spreadsheet in MS Excell. I also use Pat Kelly's DCR calculator for SCR and DCR calculations as it is easy to switch back and forth. If you do not have this link, you should check it out as it tells you a lot about DCR and has a downloadable SCR/DCR calculator that works great and is FREE!
http://cochise.uia.net/pkelley2/DynamicCR.html
-Mark.
