Differences Between Dauntless 225 And Buick 231 Odd Fire?

I have a 1971 Jeepster Commando. Being a Noob, I originally thought I had a Dauntless 225. After some research (I know, I was lazy), I found out that my Jeepster has a 231 Odd Fire. The HEI distributor, front inlet Rochester 2G carburetor and Blue paint should have alerted me that the engine was not a 225 but a 231. So now, I might rebuild the 231 OF but I was wondering what the differences are between the 225 and 231 besides more displacement, HEI, carb inlet, camshaft bearing sizes and etc. My assumption (and I am usually wrong) is that the engine came from a 75 - 77 Buick Skylark (or something similar).

Does the 231 have hardened valve seats for unleaded fuel? Do the push rods oil through the rods or outside the rods like the 225? Is the compression lower on the 231 and if so are there any higher compression pistons available. Are there any performance parts, especially camshaft, intake manifold and etc. that are also available?

If I was to re-power I guess I could go with a GM 4.3 or Camaro / Firebird 3800 but I don't know if I want to tackle that path either financially or physically.

I could make a list of questions but maybe someone has some clear insight on the differences or point me to a good link. Most of the Google links cover the 225 and jump to the even fire 231s without giving some information if Buick made some or any improvements to the engine from the 225 engine to the 231 Odd Fire engine.

BTW my block casting number is: 1254083. According to Google, this casting covered a lot of years, or so it seems.

TIA - Mark

 

Welcome Mark -

We have some documents that describe the 225 and 231 differences, and the casting numbers. One of them is here - http://nmr.mgh.harvard.edu/~reese/BuickV6CastingNumbersandInternalSpecs.pdf

You can also use the Wayback machine to look at the old tech sections from the previous site - Early CJ5.com > Tech > Engines > 225 V6

I know more about the AMC era than the Kaiser era (when Jeep offered the 225), but more knowledgeable members will join in. Meanwhile, look at the links above and some of your questions will be answered.

 

According to your block casting number, you have a 231 Buick V6, but the year range is from 1975 through 1986, so it could be an odd-fire (75-77), or even fire (77-up). As mentioned above, check your distributor.
-Donny

 

Photo of distributor:


So, the original question(s), what are the significant differences between the 225 a 231 odd fire besides displacement and HEI? Are there any practical upgrades?

Oh, and thanks for the great links.

 

Warlock, thanks for the information and link. This link and what Keys5a referred to is that this block casting number was used on a wide variety of applications, so I understand the confusion (to me also). I'm pretty sure that this is a 75-77 OF engine. I just wanted to know if I should keep this engine with some minor upgrades (if available and recommended) if and when I do a rebuild. Thanks - Mark

 

Warloch, that is exactly the input I was looking for. Thanks for the information. - Mark

 

Fuel Injection!!!!!!!!!!!!!!!!!!!!!!!!

 

Chuck's motor is fuel injected!

 

That would be a great reason to go even fire. Odd fire engines are not so easy to FI.

 

Sure they are, so long as you do it without timing control.
Mega squirt and several other companies offer odd fire fuel injection.

 

When you add the cost of a manifold and a carb, that might be competitive pricing for FI. I did read that Posimoto had trouble FI ing his odd fire though.

 

Odd fire has a rather distinct sound! Almost old Harley Davidson like. I have a 75 odd fire 231 from Buick skylark pretty sure 75 was last year of odd fire it was split both even and odd fire that year. I've heard arguments of odd fire until 77 but I don't think I believe that until proven otherwise. Your commando was probably 225 factory. The 231 is a surprisingly powerful engine does not disappoint. If you go 4.3 great power also but you'll need to spend 600$ on adapter plates as it doesn't share bellhousing with Buick odd fire

 

1977 was the split. I have a 77 odd-fire 231 in my '69.

 

Almost 6 yr old thread..

 

The split is certainly 77 and

Not 75? Good to know. I have only come across engines 1975 and older. It's hard finding Buicks that old in junk/scrap yards.