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WS6 VERT
11-06-2002, 12:22 PM
What is the difference between an odd fire engine and an even fire engine? I have seen for the 4.3L engine,there is an "odd fire", "even fire" and "semi-even fire" engine. Also, how can you tell what you have? Like if I popped the hood of somebodies vehicle, how would I know?

Jaysz28
11-06-2002, 02:08 PM
I would hope it would be specified on the emmissions label, or even old school like on the air filter assembly, valve covers, etc.

What worries me about this post, is the person who is asking the question! :eek: Our illustrious leader and our subject matter expert! :eek:

86IROC
11-06-2002, 03:10 PM
My guess would be the firing order Bernard. But, I've never seen any of those terms used to describe a 4.3L I know the 3.8L Buick V6's had ood & even fire variants. My dad says the odd fire ones ran like they had a couple of plug wires off - very rough.

WS6 VERT
11-06-2002, 09:33 PM
Originally posted by Jaysz28:

What worries me about this post, is the person who is asking the question! :eek: Our illustrious leader and our subject matter expert! :eek: Hey, ya just can't know everything... tongue.gif

I think it has something to do w/ the throws on the crankshaft, but I don't know exactly what. I'm thinking that odd fire cranks have two rods per journal, and even fire cranks have a seperate journal for every rod. Somebody must know for sure here...

SportCoupe
11-06-2002, 10:57 PM
Here's the best description I could find "semi-even fire" engines.

Distributor. Production 1978-84 V6/90 Chevrolet (229ci) engines have a "semi-even fire" sequence which alternates between 132 and 108 of crankshaft rotation between sparks. This electronic distributor for semi-even fire V6/90 engines has a lightweight machined aluminum housing, a hardened shaft, and a ground and hardened centrifugal advance cam. Its high-output magnetic pickup will trigger GM Performance Parts heavy-duty ignition amplifier P/N 10037378. This distributor uses a small diameter cap and rotor, and it will clear most competition induction systems. A selection of advance springs and bushings are included to allow you to tailor the spark curve. Technical Notes: Do not use with even-fire 4.3-liter engines or heavy-duty common pin crankshafts. This distributor does not have a mechanical tach drive; use electronic tachometers P/N 10038474, P/N 10185001, or P/N 10185002.

WS6 VERT
11-06-2002, 10:59 PM
John, you took that from the very source that got me confused. You'll have to do better than that ;)

SportCoupe
11-06-2002, 10:59 PM
Here's the best description for "odd fire" engines.

Distributor. Competition V6/90 Chevrolet (229ci) engines with common pin crankshafts have an "odd-fire" sequence which alternates between 15 and 90 of crankshaft rotation between sparks. This odd-fire distributor is highly recommended for V6/90 racing engines equipped with heavy-duty crankshaft P/N 14044838. It has a lightweight machined aluminum housing, a hardened shaft, and a ground and hardened centrifugal advance cam. Its high-output magnetic pickup will trigger GM Performance Parts heavy-duty ignition amplifier P/N 10037378. This distributor uses a small diameter cap and rotor, and it will clear most competition induction systems. A selection of advance springs and bushings are included to allow you to tailor the spark curve. Technical Notes: Technical Notes: Do not use with even-fire 4.3-liter engines and semi-even fire 1980-84 production 4.3-liter engines. This distributor does not have a mechanical tach drive; use electronic tachometers P/N 10038474, P/N 10185001, or P/N 10185002.

BTW, this distributor is $757!!!!

SportCoupe
11-06-2002, 11:02 PM
The "King of Internet Lookup", yours truely, has found ALL the details for even, odd and semi-even fire engines.

http://home.golden.net/~appster/text.february.html

WS6 VERT
11-06-2002, 11:16 PM
There ya go. Much better. So I was kinda right. :D

So basicly, the SBC V8 is an "odd fire", but it doesn't matter since there are 8 cylinders to balance the power pulses. And most later V6's should be "even fire".

[ November 06, 2002, 08:17 PM: Message edited by: 92 DropTop T/A ]

SportCoupe
11-06-2002, 11:25 PM
I'm good, huh? :cool:

88WS6TA
11-07-2002, 12:53 AM
Darn, I knew the answer to this one :D

WS6 VERT
11-07-2002, 12:56 AM
OK, rob, give me your version

88WS6TA
11-07-2002, 01:16 AM
Small block chevy are even fire. The fire every 120 degrees.
Odd fire v6's fire very irregular like 15 or 90 degrees between fire. This makes for a not so smooth motor.
Semi even was close but no cigar. They fire with either 108 or 132 degrees between.
Then we have the 4.3. even fire. Fires at 120 degrees between.

GMC-YA
11-07-2002, 01:22 AM
http://www.chitownsyty.com/tech/odd.htm

This is another good info site.

DONT FORGET TO BRING MY CABLE TOMORROW

TheGreatJ
11-07-2002, 01:44 AM
One thing: although the SBC is an even-fire engine, it does not fire once every 120 degrees. It fires once every 90. Each cylinder fires once for every 2 crank rotations...so you get 4 fires per rotation which computes to 90* of rotation between cylinders. If you ever pull your heads and watch the pistons you'll notice that for every 90* you turn the crank, 2 cylinders will hit the top of the bore (at exactly the same time). One on compression stroke and one on exhaust stroke.

88WS6TA
11-07-2002, 02:29 AM
OK you caught me. My bad SBC's do fire every 90 degress, must have had v6 on the brain.