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| Dynamic compression calculation confusion. https://slantsix.org/forum/viewtopic.php?t=50074 |
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| Author: | wjajr [ Sun Oct 14, 2012 9:24 am ] |
| Post subject: | Dynamic compression calculation confusion. |
I have tried to calculate dynamic compression of my engine using the following quantities using this [url=http://kb-silvolite.com/calc.php?action=comp]calculator[/url]: COMPRESSION RATIO CALCULATOR Static and Dynamic Compression Ratio (Considers Cam Timing and Rod Ratio) ENTER YOUR DATA CALCULATED DATA Cylinder Head Volume 44(cc) Cylinder Head Vol (cubic in.) 2.684 Piston Head Volume (cc) Piston Head Vol (cubic in.) 0.000 Gasket Thickness (in.) Swept Volume (cubic in.) 38.116 Gasket Bore (in.) T.D.C. Volume (cubic in.) 4.485 Cylinder Bore Diameter (in.) Gasket Volume (cubic in.) 0.387 Deck Clearance (in.)Note: Neg. nubmer above deck, Pos. number below deck Deck Volume (cubic in.) 1.414 Stroke (in.) STATIC COMPRESSION RATIO 9.499 OPTIONAL DATA Rod Length (in.) Adjusted Stroke (in.) 1.061 Intake Closing Point (degrees)ABDC @ 0.050 lift plus 15 degrees DYNAMIC EFFECTIVE COMPRESSION RATIO 3.186 Based on a graph generated from degreeing cam last year that looks close to this at bottom of [url=http://tildentechnologies.com/Cams/CamBasics.html]page[/url] I come up with a ridicules value; 3.186:1 compression ratio When closing intake closing event at zero lift of 290 degrees is used I get 7.2:1 compression, a reasonable number. 9.5:1 Static compression ratio is correct. What am I missing? My graph: [img]http://i294.photobucket.com/albums/mm87/wjajr/Dart%20Engine/100_1373.jpg[/img] At 0.050†lift I get 219*, and at fully closed at 290* 219 + 15= 234* at 0.050†lift per calculator instructions |
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| Author: | DusterIdiot [ Sun Oct 14, 2012 2:55 pm ] |
| Post subject: | Rod Length |
The last entry field looks to be screwed up...seems to be OK if you think of the closing event ATDC and subtract 180 degrees....So 219 is what you figured - 180 = 39 + 15 degrees....ballparks my variables and guesses at your build somewhere in the 9-10 DCR range.... http://cochise.uia.net/pkelley2/DynamicCR.html This one is easy to download and seems to be fairly accurate for most users. -D.Idiot |
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| Author: | wjajr [ Sun Oct 14, 2012 3:59 pm ] |
| Post subject: | |
DI, Previously I found that page you directed me to, all that comes up is some file stuff that I can’t open. I think the calculator I was using assumed cam card info only available, not actual event from degree wheel, and adding 15* to 0.050 lift was a fudge factor. Calculating closing event before it takes place yields a bad number. The ramps on this cam are long where a roller cam probably has much shorter steeper ramp; just guessing. My engine does not ping on 87 octane, so its DCR must be well below 8:1. I looked for the cut depth to remove one cc from a head, but can’t find it. I think if I reduce the cc of head from current 44 giving 9.5:1 SCR to 37cc it will move DCR to 7.95 and SCR to 10.3:1 35 cc produces 8.17:1 DCR, and 10.64:1 SCR From what I have read 8:1 DCR will run on pump gas well, is this correct? Bill |
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| Author: | DusterIdiot [ Sun Oct 14, 2012 6:10 pm ] |
| Post subject: | THe subjective DCR... |
Quote: Previously I found that page you directed me to, all that comes up is some file stuff that I can’t open.
You should be able to right click on it and save the file to the desktop and open it from there...if not, your internet security settings may be high enough that you can't access them...Quote: From what I have read 8:1 DCR will run on pump gas well, is this correct?
This is a largely subjective saying:Rule of Thumb DCR 8:1 87 regular pump gas, 9:1 super pump gas, 10:1 race gas... That being said, there are some different characteristics of chambers, spark plug location, and timing curve that can make it work in one way or another...my 10:1 slant is in the mid 8:1 range and runs fine on 87...but I can dial a few more degrees and get a bit better ET and mileage if I run plus or super. The 12:1 motor I ran I broke in and drove on pump super, has a mid 9:1 DCR... can run on 87 but I took a load of timing out and mpg suffered...on 92 it ran OK on the street...fearing detonation I gave it a nice shot of 110 at the track... Be wary of cutting the head under about 45CC...if the cut is approaching the slope of the chamber the cut will greatly reduce the chamber size and you may over shoot a bit more than planned... -D.Idiot |
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| Author: | wjajr [ Sun Oct 14, 2012 7:19 pm ] |
| Post subject: | |
[quote]my 10:1 slant is in the mid 8:1 range and runs fine on 87...but I can dial a few more degrees and get a bit better ET and mileage if I run plus or super.[/quote] Will stock steel head gasket live in 10.5:1 environment? If so I can pick up a little more compression over Fel-Pro head gasket by reducing proposed cut by 0.020â€. Currently I’m at 0.075†off of peanut head. I know that using steel gasket SCR moves to 9.9:1 without any more cuts. |
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| Author: | kielbasa [ Sun Oct 14, 2012 10:03 pm ] |
| Post subject: | |
I have been trying to figure out dcr for my vw, not sure if its any different for american motors. Ill have 11: 1static and 7.5: 1dynamic. I was told i want to stay between 7.5-8. Its air cooled so it will run hotter. |
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| Author: | hantayo13 [ Mon Oct 15, 2012 6:34 am ] |
| Post subject: | |
Bill my 120 ci harley engine is 10:1 compression,runs a steel gasket and on high test pump |
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