Even vs Odd fire engines December 30, 2009, 09:21:19 AM Since there are some smart folks here my question is:What the heck does it mean when an engine is refered to as even fire or odd fire?I just don't understand what it means. It's typically only when discussing V6 or V12 engines so that has to be a clue. It also seems to relate to the bank angles of the engines e.g. 60*, 45* and 90* bank angles.So, who understands this? Quote Selected
Even vs Odd fire engines Reply #1 – December 30, 2009, 10:14:48 AM In a 90* V6 engine (3/4 of a V8) with three crank rod journals, firing will be at 90*, 90*, 90*,180*, 90*, & 180* so you wind up with a rough idling engine that's pr0ne to vibrations at various RPMs... The original V6 Buicks that were introduced in the early 60s is one such example(those had a V8 sized distributor with two spark plug wire towers missing on the cap)... To correct the problem, crankshafts were developed that have offset crank pins that give six different positions and allow for 120* firing between all cylinders, so they run much smoother(actually I believe some of the earlier "even fire" V6 didn't allow for totally even firing, but were far better than the early Buicks)... The 60* V6 will have 120* firing with the three journal crank, so was not necessary to redesign the crank... Same applies to a 90* v12 as it does the V6, just that cylinders will fire every 60* of crank rotation... Quote Selected
Even vs Odd fire engines Reply #2 – December 30, 2009, 11:43:51 AM Quote from: TurboCoupe50;304393In a 90* V6 engine (3/4 of a V8) with three crank rod journals, firing will be at 90*, 90*, 90*,180*, 90*, & 180* so you wind up with a rough idling engine that's pr0ne to vibrations at various RPMs... The original V6 Buicks that were introduced in the early 60s is one such example(those had a V8 sized distributor with two spark plug wire towers missing on the cap)... To correct the problem, crankshafts were developed that have offset crank pins that give six different positions and allow for 120* firing between all cylinders, so they run much smoother(actually I believe some of the earlier "even fire" V6 didn't allow for totally even firing, but were far better than the early Buicks)... The 60* V6 will have 120* firing with the three journal crank, so was not necessary to redesign the crank... Same applies to a 90* v12 as it does the V6, just that cylinders will fire every 60* of crank rotation...So, does this mean that the "normal" firing of 90/90/90/190/90/180 is EVEN? and the other is odd? I'm just confused about the terms odd and even. Quote Selected
Even vs Odd fire engines Reply #3 – December 30, 2009, 12:30:36 PM No that is a odd fire engine, which is basically a V8 with two missing cylinders, a truly even V6 is evenly spaced at 120* for each cylinder... Quote Selected
Even vs Odd fire engines Reply #4 – December 30, 2009, 01:02:14 PM I'm having trouble picturing that in my mind but I understand the concept now.It's all in the crankshaft, not which cylinder fires when.Let me restate:Even firing engines the crank journal travels 120* to complete a full stroke. Meaning that all are cylinders are EVEN. This means that the rod journals on the crankshaft all have the same offset from center. Right?In my simple mind then in the odd firing engine then some rod journals on the crankshaft are offset twice the degrees from the others thus odd and it's only two of the six that have double the offset and this serves to dampen the inherent vibration? Quote Selected
Even vs Odd fire engines Reply #5 – December 30, 2009, 01:15:29 PM A even fire V6 engine will fire a cylinder every 120* of crank rotation, engine has to rotate two turns(720*) to fire all six... It'd probably be easier for you to read this...http://home.off-road.com/~merls_garage/oddfire.htmlBTW I was incorrect on my 90* & 180*, it's actually 90* & 150(see article)... I'm not a six cyl person regardless of firing pattern, gimme a V8... Quote Selected
Even vs Odd fire engines Reply #6 – December 30, 2009, 01:27:46 PM The V8 sounds simpler. Kinda like my inline six. Simple...all lined up in a row.:DThanks for the article. Quote Selected
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