Odd Firing

["B Benson" <delornut@xxxx>]

This has been on the list a couple of times but again, the reason an engine
is odd or even firing is because of the crankshaft design as related to the
number of cylinders and their degree of opposed separation. In the case of
the DeLorean engine it is six cylinders with two groups of three cylinders
opposed at 90 degrees. The most economical design for crankshafts in a 'V'
configured engine is to have a pair of opposed cylinders sharing the same
journal of the crankshaft. When you oppose six cylinders at 90 degrees and
have each opposing cylinder share a common crankcase journal the math works
out to the fact that one of these cylinders rotates the crankshaft more
degrees than the other. The firing order is configured accordingly. A more expensive
approach is to utilize a crankshaft with individual journals for each
cylinder which equalizes crankshaft rotation throughout all cylinders.
Unfortunately that creates more expense for the manufacturer and many have
adopted a less expensive approach with a counter rotating balance shaft
designed into the engines total configuration to counter the odd firing
scenario . This works out very well and results in a smooth running odd
firing engine. Since many V-6's were derived from 90 degree V-8's
(8 cylinders at 90 degrees do result in an even firing scenario) they ended up as odd firing. Newer V-6's have been been designed in 60 degree configurations
to allow the math to work out to even firing.

Bruce Benson