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First you can use sheet 1 of ECcalc to get ballpark figures for the right lengths of header, diffuser, and belly so that after fine tuning with header and belly lengths on sheet 3 the combined return waves shown will sync with the port timing at peak powerband RPM like what you see here:  Here is sheet 1 where you will enter the basic engine data. Data entry boxes are in light blue. This section is also useful when porting an engine and trying to decide on the exhaust and transfer duration. I like to have around .5 milliseconds as the blowdown time which is the same as the "transfers open" time (time from exhaust opening to transfer opening). Row 6 continues at row 19, row 7 at row 20, etc. Notice how I scaled down the mid header temperature with decreased RPM.  Enter exhaust port duration at A6, transfer port duration at B6, RPM at C6, and mid header temperature at E19. Take notice of the blowdown time at E6.  Now you have to change the header length till F19 matches F6. Then change the diffuser length to be close to what makes G19 equal to L6. Change lengths in 10mm increments so that the final number can be divided by 10 without any fraction left over. This is so that the length will be usable in sheet 3. Then change the belly length so it is close to what makes H19 equal to L6. It does not need to be perfectly divisable by 10.  Each set of rows can either be a separate engine/pipe, or all of them can be of the same engine/pipe which would require a lower RPM for each row, say 500 to 1500 less for each row. The purpose of making them all of the same engine/pipe is to make the graph at the bottom right hand of the page which can show you at what RPM the pipe starts to have a positive effect on power output. The top of the numerical columns should read the same RPM that you entered in C6 to C13, but instead it read 2300 to 9300 before a friend helped me figure out how to fix that error. But the next two graphs were made before the error was fixed. The crossover of BDC and end of diffuser return wave marks the beginning of the pipes beneficial effects.  Here's the same graph with annotations and corrections. TO="transfers open", BDC="bottom dead center", TC="transfers close", EC="exhaust close", RW="return wave"  Next Page |