Oddfire systems in Syclones/Typhoons

Many people don't understand what the difference is between evenfire and oddfire.  Simple definition is that the evenfire fires cylinders at even intervals. Every 120 degrees of crankshaft rotation and a cylinder fires, 6 x 120 = 720, or two rotations.  Oddfire fires cylinders at odd intervals, like this:  #1 fires - 150 deg later - #6 fires - 90 deg later - #5 fires - 150 deg later - #4 fires...   and so on, 150deg and 90 deg alternating.  

Why oddfire instead of evenfire?

When the 4.3 V6's were first designed, they based them off the Chevy small block.  The small block chevy has 8 cylinders, fired at 90 degree intervals, 8 x 90 = 720 degrees or 2 rotations.  For this setup, the adjacent cylinders (opposite sides of the block) shared the same crank pin.  When the 4.3 V6 was born, if this arrangement was kept, the cylinders would not fire at the even intervals.  So the crank pin was split, and the journals for the adjacent cylinders did NOT share the same pin.  This allowed for a motor that fired the cylinders at EVEN intervals.

Oddfire forged crank

Evenfire forged crank (this is how stock crank appears, even though this is a forged piece)

So if the engine ran at odd intervals, it was difficult to get an ignition system to operate on this odd firing engine, as well as it did not run as smooth as a regular evenfire motor.  Crank strength was compromised in the evenfire crank design, for this reason, evenfire cranks have a larger pin size so there is more metal to overlap at the offset journals.  This is one reason why you cannot use small block Chevy rods in a 4.3 V6.

Why use an oddfire motor in Syclones / Typhoons ?


What needs to be done to run an oddfire motor in a Syclone / Typhoon?

You need to run an aftermarket ECU that can control an oddfire motor.  For a while, your simplest option was to run an Accel DFI with no timing control (distributor was locked out) and you used it for fuel control basically.  Speedpro can now be run on an oddfire, but it requires use of a magnetic reluctor crank trigger, as well as an MSD or GM oddfire distributor with a magnetic reluctor built in.  The Speedpro can control timing, as well as offering the wideband 02 control benefits.  Motec should be able to control an oddfire as well, and distributorless ignition should be possible.  Motec is very expensive (probably $5000 or so), Speedpro is less expensive (about $3300).  Electromotive can control an oddfire, and is in the $2000 range I believe, with no wideband 02 controls, but has distributorless ignition.  Autronics can work with an oddfire as well, price range of $2000-3500 depending on options.   It is not a cheap decision to make.  Oddfire motor requires an oddfiire camshaft as well.