1973 304, rebuild, replace or upgrade

I've picked up another project before I've even gotten my M38 build really started, a 1973 CJ5 with the 304 V8. It is currently blowing smoke like a mosquito truck, but it does run and has been driven.
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I've come up with 3 options:

1. rebuild the current engine
2. rebuild a 78 304 that is supposed to be in running condition
3. buy a 401!

The guy with the 78 304 wants $350. I haven't found any used 401s for sale locally (NE Atlanta, GA). I've found that I can buy an ATK 401 longblock for ~$2200.

I plan for the Jeep to be a simple trail rig, with occasional street use, no highways. I wanted to go with a few hop up parts, Edelbrock Performer with a Holly Truck Avenger 4bbl, mild cam and fenderwell headers.

I've read that 304 and 401 are the same exterior dimensions, but are there any gotchas I should be are of? Like differences in some mounting boss or such? Are there any differences between the 73 and 78 304s? Any years more desireable?

Thanks,
David

 

If you are going to rebuild a 304 why not yours? Why buy another when you are going to rebuild anyway. 401? Only diff that I know is you have to use the 401 flywheel because of balance defferences. I've got a 304 with some mods (head work, bigger cam). Still have a motorcraft 2100 though. Watch some other 4x4 and here web sites for a 401 if you go that route. Can usualy be had for a lot less. Have even seen 360's and 401's free up here. With the power mine has, I can't see me putting one in, unless I was bogging or racing it. Rebuild yours for about $800 for everything including bore job. Rebuld kit with pistons, and everthing but intake gasket is $551 here. Have used them alot and never had a problem. If you want a diff cam or pistons etc, they charge you the difference.
http://naparts.com/ProductDetail.cfm?ProductId=184
304, 360 401, I would spend the $200 for a new timing cover, it could save your new motor. Oilpump is in it and the galley wears out.

 

Well a 401 is uber cool...but way overkill in a CJ. That's why I want one. But the cost of them has gotten silly.

You could drop in a 360 for way less money and get more power than the 304 but not as much as a 401.
Course the 304 is plenty.

BUt I want a 401 too.

 

This guy wants $2500 and you get 2 Ramblers with the 401
http://www.racingjunk.com/post/1150709/AMC-401-complete-w-extras.html
This guy wants $650 but it costs you a trip to Cali.
http://moeslist.mybisi.com/product/6755/Jeep-AMC-401-Engine_12202.html
There is more, google is your friend,
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rlz=1T4DKUS_enUS205US206&q=amc+401+for+sale

 

that 401 looks more like it's been in a fire...

 

Vortec V8? AMC 304 with EFI? Ford 5.0L?

 

Just because the current engine smokes doesn't mean it can't be rebuilt. For a complete rebuilt, it's very unlikely there would be any cost difference between rebuilding the engine you have and rebuilding the '78 engine. Since you aren't driving the Jeep, to me spending the extra $350 seems like a waste. Certainly don't buy the other engine until you disassemble your current engine and measure the block and journals.

The first thing to do is to measure the compression, wet and dry. Also you need to assess the oil pressure, hot idle and hot running. What are your plans for this Jeep? How many miles do you plan to drive it during the next decade? How long do you think you'll keep it?

How much do you want to spend? Is it important to save money on the rebuild? The 401 is a great engine, but good cores aren't cheap and bad cores often have to be sleeved ($$). Nominally they should not be overbored more than 40 thou. Have you rebuilt engines before? Do you plan to do the teardown and assembly yourself?

Sorry for so many questions, but your scenario has a lot of variables.

 

Also, swapping in a 401 couldn't be easier. You must use a 401 flywheel though - you cannot use the 304 flywheel. Otherwise it bolts in. The exterior dimensions of a 304 and 401 are exactly the same. There may be minor differences in the carb linkage.

 

Flipping your CJ onto its tailgate with a 401 couldn't be easier. You'd surely need to upgrade the radiator for cooling. They are toasty motors.

 

I've heard that 401s that have been bored to 60 thou will overheat. This is because the cylinder wall of a 401 is thin to begin with, and at 60 over, they sometimes have thin spots in the bore. A thin spot will cause the coolant to boil locally, and steam has a low heat capacity.

Some blocks can go 60, some can't. You can have a block sonic checked to see if it can be bored more than the allowed 40, but because of core shift, not all blocks can.

No personal experience - but this is what I've learned hanging out at the FSJ sites. In the day, I was there, and I never heard of factory-fresh 401s having heating problems. Chuchua would put 401s in new CJs, with the 304 radiator, and they would be fine.

 

Well, the $350 304 was gone when I went back to look at it yesterday. The CJ5 is going to live 250 miles away from me at my dad's house. I thought it would be a good father/son bonding project. Dad was a service manager at an AMC dealership in the mid 70's, I figured he would appreciate the AMC V8.

I plan on just playing with the CJ5 when we go down to visit, I can't thrash the Commander since we need it to travel home in. Light trail riding, some street use.

I guess I just got 401 fever, it sounded like fun. I'm going down in a few weeks to have a look at it and start the shopping list. I know it needs new shocks and springs, it will need new tires, the gas tank is under the passenger seat with the fill in the middle between the front seats. I've got a 79 CJ front axle with disks, I'm hoping I can just swap out the knuckles and not have to swap the entire axle.

Dad had already planned the compression test to evaluate what needs to be done. He is thrifty, he thinks we should just do a re-ring job. I of course am trying to figure out if I can keep a straight face while telling him I only paid a $1000 for a Big Dawg 401.