Dauntless 225 V6/Buick 231 Oddfire

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Buick V6 FAQ

Is a 225 interchangeable with a 231?

Yes, the engines are interchangeable with no modifications to the frame or body.

Is the 231 a better engine than a 225

Actually the 225 has better rockers than the 231 motors, the 231 used stamped rockers instead of cast units that are found on the 225. The oiling system on both motors with the exception of the rockers are the same on both motors until you get to the even fire motors. When all things are equal as far as being in good shape the 225 will always run cooler with less chance of overheating than the 231 simply because it has more water passages in the motor and a higher capacity in the block. The later rods on the 231 oddfire are stronger but can be swapped to the 225. The 231 can run higher lift cams due to the lifter area having more material then the 225 and the 231 also also has gussets to strengthen the lifter valley. The 231 uses cam bearings that are all the same size rather than progressively smaller bearings like the 225. The 231 should have hardened exhaust seats for running unleaded fuel, the 225’s while it can be installed never had it from the factory. Most differences are minor and for a low speed Jeep engine wouldn’t make much difference

Buick V6 Development in the early 60’s timeline:

Jamie Carter writes a brief timeline of the Buick V6 History

As I understand the timeline, the 215 was used as standard in ‘61, became an optional engine in ‘62 and ‘63 with the Fireball 198 V-6 as the standard engine. So, when use of the 215 V-8 stopped, the iron 300 V-8 was used and the 198 was “changed” to the 225 V-6, so that the two engines could share assembly line duty (same cubic inch per cylinder sizing). In essence, the Fireball “disappeared” sometime 1963 and the Dauntless appeared. Sometime ‘71 to ‘74 Buick bought the 225 V-6 back from AMC Jeep and rebored to 231 cu in. The engine stayed odd-fire until sometime in early or mid ‘77, when the engine was changed to even-fire by revising the crank throws (and other modifications). The odd-fire V-6 was gone forever.

I have no info of Buick using the “new” V-6 in ‘74; first use seems to be in the ‘75 models. I haven’t seen any info that shows these engines in production for ‘72, ‘73, or ‘74 (of any firing order or displacement).

198 versus 225 Identification

The 225 cylinder bore size standard is 3 3/4″. The 198 is 3 5/8″. So unless the 198 cylinder has been bored 125 thousandths over size (ye gads! is my math right? 3.750-3.625=.125) then it must follow that a cylinder that measures that much less than 3 3/4″ can’t be a 225. For further reference, bore on a 231 is 3.800″, bore on the late ’70’s 196 is 3 1/2″ AND I have block casting numbers on the 198 beginning with 125 or 126 listed (like the 231) but this part we already covered. I believe the 198 had a 6-digit ID number or two stamped in the crankcase, probably in the traditional places just under front/side head mount areas. So measure the cylinder, that’s the ticket! And find any stamped numbers. Also see 198 versus 225/231 V6 Bellhousing and Tips on Identifying Chevy Bellhousings

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Important Information for 231 Odd Fires

The way to find out exactly what kind of engine you have is to look up the serial number cast on the engine block near where the bell housing bolts to the engine on the top, you might be able to see it looking down the firewall of the engine compartment to the top rear of the engine. The valve covers style make the engine look like a 1976 or later Buick V6. The Buick V6 changed from odd-fire to even-fire in mid-year 1977. You might have the very latest odd-fire that had the external appearance of an even-fire engine. The 1976-1977 odd-fires are the strongest Buick V6s ever made, stronger connecting rods, single piece cams, large wrist pins.

When ever in the junk yard and you find a Buick V6 with an odd-fire HEI check out that engine it might be the last and greatest odd-fire of them all If it has freeze plugs in the heads it might be a super duper 1976 odd-fire. These odd-fires have a very strong bottom end because the odd-fire crank combined with stronger Oldsmobile V8 style connecting rods. The oil stick even enters the block like an even-fire everything looks even fire until you see the casting on the drivers side under casting says “76″ on the block, you must pull the oil pan, see the odd-fire crank shaft. This was the transition series of engines.

Is Fuel Injection for an odd fire V6 Possible?

Yes! Several members of our forum have retrofitted Holley Projection kits and some more enthusiastic members have retrofitted other types of factory available fuel injection to their V6. Megasquirt is also a possible option.

For more on this please refer to the forum search option.

Is the 225 V6 an Odd Fire Engine?

Yes!

What makes an Odd Fire Engine an Odd Fire?

For more on this see Merl Howell’s excellent illustrated explanation please.