engines and shows you the results side-by-side. If you don't have the "Intake Valve
Closing Angle", there is also a calculator for that included.
I prefer this to online calculators. I can save my results and review them later, can't
do that with the online versions. You can only look at one calculation at a time
when online, not so with this Excel spreadsheet...you can see all 5 versions at the
same time !!!
You will need Microsoft Excel 2007 or you can download "Open Office" for FREE here
http://www.openoffice.org/. Open Office can open and work with Excel spreadsheets.
Don’t worry if you don’t know every number the calculator is asking for. Some of them
are technically there, but so small they won’t make much difference. Such as the
space between the ring land and the cylinder wall (Line 10).
.
- DCRCalculator-1_Closeup02.jpg (36.02 KiB) Viewed 290 times
Tab -1 is the main calculator.
.
- DCRCalculator-1.jpg (117.76 KiB) Viewed 290 times
Tab -2 is a calculator for determining the IVC if you don’t know directly. Always use the
seat timing, don’t use values at 0.050 inches.
.
- IVCAngleCalc-2.jpg (96.82 KiB) Viewed 290 times
Tab -3 is for your information only, these values are used in the calculator on Tab 1
.
- IntermediateCalc-3.jpg (66.32 KiB) Viewed 290 times
Tab -4 is to record more details about each engine if you can’t get it all in the short
description on Tab 1.
.
- FullEngineDescription-4.jpg (35.2 KiB) Viewed 290 times
As an example take the 4 engines below. Pretend you have two camshafts on your short
list and want to see what size combustion chamber size you would need to purchase.
You want a DCR of ~8.0. You are also thinking about retarding the cam timing by two degrees.
To get our DCR of ~8.0, I’m going to play with the Combustion Chamber size (Line 4) and
the Intake Valve Closing Angle (Line12). With Cam#1 and retarding the cam timing, the
combustion chamber with decrease from 72.0cc to 70.8cc. If you decided on Cam#2, then
your chamber size would be 70.1cc or 68.8cc.
.
- DCRCalculator-1_Closeup.jpg (167.01 KiB) Viewed 290 times
The DCR and SCR will not change with a change in altitude, but the cylinder pressure will
most certainly change. If you live at a higher altitude, then you might want to consider
using a higher compression ratio.
Let's look at the example below. With a 2000 foot change to a higher altitude, you have to
adjust the atmospheric pressure by 1 psi. (See the table below from the Engineering Toolbox
website.) That means you could decrease the combustion chamber volume by 4.7 CCs to
return to the same cranking pressure.
So at 2000 feet, a SCR/DCR of 10.65/8.34 is equivalent to 10.07/7.91 at sea level.
.
- CrankingPressureExample01.JPG (89.97 KiB) Viewed 290 times
http://www.engineeringtoolbox.com/air-a ... d_462.html
.
- AtmosphericPressureVsAltitude.JPG (78.57 KiB) Viewed 290 times
I only have actual cranking pressure data from two engines, so don’t take these number too
serious. If you have some real world experience with the above please post your experiences.
Download the Excel file below.
.