[LINK]Great Dynamic Compression Calculator tool, among other things...
12-09-2002, 02:00 PM
#1
Burning Brakes
Thread Starter
[LINK]Great Dynamic Compression Calculator tool, among other things...
http://cochise.uia.net/pkelley2/
It's a downloadable executable that is zipped up. Installs and opens into a simple windows GUI.
Try out this dynamic compression calculator. Static compression is just a starting point and doesn't really mean squat in terms of power until you calculate the dynamic compression which is wholy dependant on the cam. It was the big fat cams that lowered the 12:1 static compression on factory 60's and 70's (early, obviously) muscle cars into a usable range.
Note: the two boxes at the top are just for reference, don't fill them in.
Start in the "Cam Timing and Overlap Calculator" tab and fill in the 4 input boxes. This will generate the intake duration and closing point. I checked against my cam and it is accurate. Then go to the "Dynamic Stroke Length Calculator" tab and input your crank stroke and rod length to get the "dynamic stroke length" which is the amount af stroke left at the point the intake valve closes. Then go to the "Dynamic Compression Calculator" tab and input the rest of your engine's specifics (stop after filling in the piston dome box) to calculate your dynamic compression ratio.
Then let the discussion of dynamic compression ratio's begin! I will be running my values past my engine builder this week because he advanced my cam 6 degrees which really raises the dynamic compression to the high 8's range.
Chris
PS. I'm an engineer with a thorough understanding of the mathematics involved and these equations hold up. Actually it is pretty simple trigonometry. Compression doesn't start building until the intake valve closes so figure out when that is and then it just becomes geometry.
[Modified by 71roadster, 11:52 AM 12/9/2002]
It's a downloadable executable that is zipped up. Installs and opens into a simple windows GUI.
Try out this dynamic compression calculator. Static compression is just a starting point and doesn't really mean squat in terms of power until you calculate the dynamic compression which is wholy dependant on the cam. It was the big fat cams that lowered the 12:1 static compression on factory 60's and 70's (early, obviously) muscle cars into a usable range.
Note: the two boxes at the top are just for reference, don't fill them in.
Start in the "Cam Timing and Overlap Calculator" tab and fill in the 4 input boxes. This will generate the intake duration and closing point. I checked against my cam and it is accurate. Then go to the "Dynamic Stroke Length Calculator" tab and input your crank stroke and rod length to get the "dynamic stroke length" which is the amount af stroke left at the point the intake valve closes. Then go to the "Dynamic Compression Calculator" tab and input the rest of your engine's specifics (stop after filling in the piston dome box) to calculate your dynamic compression ratio.
Then let the discussion of dynamic compression ratio's begin! I will be running my values past my engine builder this week because he advanced my cam 6 degrees which really raises the dynamic compression to the high 8's range.
Chris
PS. I'm an engineer with a thorough understanding of the mathematics involved and these equations hold up. Actually it is pretty simple trigonometry. Compression doesn't start building until the intake valve closes so figure out when that is and then it just becomes geometry.
[Modified by 71roadster, 11:52 AM 12/9/2002]
12-09-2002, 05:00 PM
#2
Team Owner
Re: [LINK]Great Dynamic Compression Calculator tool, among other things... (71roadster)
It took some digging to find my cam card. But when I used the formula I end up with 8.32 Dynamic compression. I have never got it to rattle or ping on 91 octane with my 10.84 Compression ratio 383.
Quote: It appears that most gas engines make the best power with a DCR between 7.5 and 8.5 on 91 or better octane.
Good link:) I'm going to figure out why my Crane power max pinged all the time without octane booster and retarded timing. It was 10.7 static with iron heads
Quote: It appears that most gas engines make the best power with a DCR between 7.5 and 8.5 on 91 or better octane.
Good link:) I'm going to figure out why my Crane power max pinged all the time without octane booster and retarded timing. It was 10.7 static with iron heads
