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Odd & Even fire V8

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Old 07-20-2009, 08:42 AM
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Smile Odd & Even fire V8

I know the 928 engine fires every 90 degrees of crank rotation, so it would be 90,90,90 270 right? I was also told that the Ferrari engines are even fire motors? I'm very ignorant on the matter so someone please shed some light.
 
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Old 07-20-2009, 04:42 PM
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Every piston fires every 720 degrees of engine rotation (once every two revs), so on a V8, you get 4 cylinders firing per revolution, which averages out to one combustion every 90 degrees of rotation.

If the crankshaft journals are offset - those for opposing cylinders are split a bit so that firing cycles are evenly spaced -- the split adjusts for the fact that the V shape is 90 degrees off (or in some V8's 60 degrees off -- then you get cylinder firings at evenly spaced 90-degrees of rotation times per revolution. Almost all American, German, English, and Japanese V8s use this type of crankshaft. It results in "even" firing.

Ferrari uses a "flat" crankshaft - the journals for opposing cyliners are not offset and in fact the journals are al 180s out of phase. As a result in a V configuration the cylinders fire four times per resolution but with a timing somewhat uneven. These crankshafts are used for a variety of reasons/excuses. They make more vibration but are stronger (some say) and lighter (probably true). I have not heard the term "odd" used for this firing cycle (this is not an even-odd thing, but an even-uneven thing).

If the difference seems confusing, think of the sound a Harley engine makes -- it is a V twin with no offset in the crank journals (like Ferrari) only just two cylinders, so the cylinders fire unevenly in time -- pow-short delay-pow-long delay- pow-short delay-pow-long delay . . .and so forth. Some big Japenese V twins don't make that uneven rythum because they use an offest crank journal for their two pistons. A Ferrari V8 is sort of like four of those Harley's bonded together, each pair having that uneven staccato sound. It doesn't sound like a Harley because of some other differences and because there are four sets of pistons feeding into two headers and it revs alot higher, etc.
 
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Old 07-21-2009, 09:00 AM
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danka schoen. I'm studying an A.S.E. book but it doesn't have anything about this in it.
 
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Old 07-22-2009, 05:18 PM
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Well, there is a lot you won't get by reading any one book. This is covered in several engineering books I have, and you certainly see it when you take apart, say, an GM LS6 V8 vs. a Ferrari 430 V8. (the Ferrari, by the way, isn't the better engine, just the more expensive. I actually like the Chevy more - a bit lighter, fewer parts, and with more stock HP and torque)
 
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