2.5l

[RandyR]

Does anyone know if an '83 OMC (GM) 2.5 will bolt in place of the 2.5 in a '80 CJ5 ? I know the OMC has intake and exhaust on the same side (driver's) and the CJ has a crossflow design. What I'm concerned about is the bellhousing flange and mounting points. The OMC boat engine is rated at 120hp stock where the CJ is about 85 stock. Seems like a good swap, if it's possible. The boat engine has forged steel rods and a nodular iron crank. The heads may be interchangeable as well.

 

[Tinman22]

Basicly yes. The cross flow head came in in about 79, prior to that hey had a conventional head. Gm did have a serious race effort in the duke though. Look into the SD4 it made around 270 hp in arca cars ive got a gm performance book loaded with parts. Why? You may ask. Well many years ago (30) my father gave me a boat and jokingly said "go as fast as you want". It had a duke and a berkley 12 j jet drive and was 14.5 feet long. Dad never said those words again.

 

[Tinman22]

Sorry i forgot to add. later versions had gear drives (some) distributorless ignition systems ,better cams ,heads, and made 110 hp stock! Many dukes see dirt track service making 200 hp for an entire redline bumping,overheating , season! You can also get factory throttle body for them from the junk yard if you look hard enough. Most people don't see the potential, its not hard if you look.

 

[RandyR]

TinMan,
Thanks for the reply. Sounds like you had one mean boat. The CJ in your description sounds equally awesome.
You said "basically". Does that mean that it will bolt up to the stock engine mounts and bellhousing? The OMC does have the gear drive. Will the heads interchange if necessary? Who makes an intake or tube exhaust for the head with I&E on the same side?
Thanks for all the info. You seem to be a man with a lot of experience and knowledge.
Randy

 

[Tinman22]

There are many good web sights out there I.E.
The Pontiac 2.5L
And
the s10 site : for all people with chevy s10's with the 2.5 iron duke motor
Comp cams has a good selection of cams,headman makes a good header,also jeep 2.5 had a cross flow head although I am not sure of its flow. As a side note if I were looking to buy a jeep a 2.5 would not be my first choice but if it was what I had I would probably keep it .

 

[RandyR]

Thanks Tinman,
I do not have a Jeep, yet. A co-worker has an '80 CJ5 with the iron duke and wants just a little more power. He doesn't want to switch to a I6 or a V8, but just needs a little more power to get down the highway. He says it does just fine offroad. I happen to have a totally rebuilt '83 OMC 2.5 in my garage for a past project boat that no longer exists, so we were wondering if my engine would fit in his Jeep without modification. He says his CJ has about 85hp and my OMC is rated at 120hp. He says that would be more than enough if it fits. I believe the OMC has the standard chev bellhousing mount and did not go to the smaller housing until '84 or so. Not sure about the CJ, but I believe it's the standard size. I believe Pontiac started making the I4 about '84 and it's a completely different engine. I think. Any more info would be greatly appreciated.
Thanks,
Randy

 

[RandyR]

My mistake. Pontiac made the engines from '77 to '93.
Randy

 

[Tinman22]

Sorry for the delay semi decided to break . Anyway if your omc has the big pattern as most do it will bolt up if it's small I.e. front wheel drive bolt pattern it won't

 

[RandyR]

Tinman,
Thanks for all the information. I took a good look at his CJ and my OMC and found that the motor mounts will not work. His right front mount is right where the distributor on the OMC is, so would not work. The driver's side is ok and the bellhousing is ok, but not the right side. The guy with the CJ says he doesn't want to go to the expense of making it fit then having to find an intake and exhaust for it. So, we just let it drop. I'll find some other use for the engine or just sell it.
Again, thank you for all your information Tinman, and good good luck with all your projects. Keep the rubber side down.
Randy

 

[Saddle Tramp]

My mistake. Pontiac made the engines from '77 to '93.
Randy

Actually the GM Iron Duke I4 is a 1980, 1981, 1982, and 1983 model years only in a CJ. The AMC I4 was used in CJs and Wranglers from 1984 to 1991.

 

[Tinman22]

I believe he was referencing the duke as being produced by Pontiac not the amc 4 cylinder used after the duke.

 

[Tinman22]

And even though most people say that the fiero used the small pattern a common swap is a small block in place of the duke 4.