A puzzler 304 to a 360?

[Hedgehog]

So I have absolutely NO idea as to the shape of the AMC 304 engine I got with my '75 CJ5 . It starts well, doesn't seem to smoke, but it has had the stock manifold changed to an Edlbrock, the carb is a Holly 4 barrel, the air filter is an Edlbrock, the emissions stuff is missing, the altinator is suspect, oil pressure isn't great but what you'd expect. Why do I mention emissions? Arizona requires emissions to be in place starting in '75. At least if I'm going to drive in the City's and I live in Tucson.

I have an oppertunity, but I'm not a gambling man, to get a 360 in good shape, from a professional, with all the bits and pieces in place for about $550.

The Witch has had a hard life with questionable maintenance. Everything I've touched had to be fixed or replaced. The only thing left is the engine. With all the performance and the fact that it came with 35' tires and a lift, stock gearing and completely warn out drive shafts I can't help but wonder about the health of the engine. I starts easily and idles acceptably with no real smoke, but how many times has this thing been down the drag/mud/rock strip at full throttle? I just don't know. Of course I don't know about the 360 engine either.

 

[Scooter402]

If it were mine, I'd at the very least pull the engine and go through it. If you have the budget available, i'd also say go for the 360 for the added grunt. But of course, me being me, I'd take it apart too just to hear what stories it's got for you. I did that with the TH350 Transmission that's in my CJ now that I knew who I got it from, what car it came out of, and how it shifted when it was pulled. I just wanted to make sure everything was still good and tight.

 

[Hedgehog]

I'm fairly handy, but not confidently handy enough to tear into a V8 engine without someone who knows what they are doing right there with me. A Harley now that's another story. It would be interesting to go through the engine though......

Horse power doesn't draw me like it does others, but it can lead to an adiction.... I simply don't know the best route to take and yes I am on a close budget. When I got the Jeep my harley was sold to finance the project, but the harley went into the initial cost of the Jeep, brakes, power steering gear box, winch, tools, seats, Transmission repair, clutch, paint, wheels and tires. I'm sorry to say the easy money is gone.

 

[Deerejeep]

What's the biggest concern?

A) not having emissions
B) engine condition AMC 304
C) budget.
D) performance stuff

If the performance stuff is concern and emissions. Then what do you think about purchasing the 360 for the stock intake with EGR and swapping it over. This would give you the ability to take care of the emissions issue and have a 360 to tinker with as funds become available and you learn your way through it.

Then the 360 is a back up to handle any AMC 304 condition issues.

 

[Saddle Tramp]

The 360 will be a direct bolt in for the AMC 304 and are more plentiful than the AMC 304 ; most everything except some of the internals are interchangeable. You could swap the AMC 304 tag from the valve cover (or just swap the valve cover) so to the Smog guys it will code as a AMC 304 (unless they are on it enough to check the side of the block under the motor mount for the engine size but I wouldn’t think they would). Remember that the AMC 304 flywheel is not interchangeable with the 360. These motors are externally balance and only a flywheel balanced specifically for the motor size will work.

Having said that have you done a leak down or compression test on the AMC 304 ? It will give you a lot of info on the health of the engine.

 

[Hedgehog]

I'm an idiot when it comes to compression and leak down type tests. I suppose there is no time like right now to learn though.

Deerejeep - After working on the Witch for a few months I am worried the motor is in the same condition the rest of the jeep. I know the oil pressure is 16-18 lbs. at idle and 360 is showing 32-35.

 

[Scooter402]

Low oil pressure issues are common for the AMC V8 family. I've heard 10 psi per 1000 rpms is acceptible, but I always thought 10 psi at idle was waaaay too low. But that's what my 360 did when I first had it.

Saddle Tramp is right though -- a compression test will tell you a lot.

 

[Hedgehog]

Is the 360 a significantly greater gas hog than the AMC 304 ?

 

[CJim7]

Is the 360 a significantly greater gas hog than the AMC 304 ?

Not really...and with your AMC 304 already being equipped with a 4bbl, probably pretty close to the same.

 

[johnbilt]

Hi - Sounds like you have a nice jeep and that you are learning as you go. I certainly have done the same over the years.

1) Do you have to pass a tailpipe test only, or do you need a detailed underhood inspection? Sometimes you can request a judging station to review an older vehicle.

2) The AMC 304 is a good engine. However I do like my 360 better for the low end torque. Checking compression is easy and would give you a better idea of overall engine health. You may find that a fresh set of plugs and ignition components along with a timing adjustment will freshen up your AMC 304 . The 4 bbl manifold and carb should be fine, but I would carefully adjust the idle circuit and possibly change the main jets to get proper tuning. I used to adjust the idle circuit at our test station to get it to pass the tailpipe test at idle.

3) Oil pressure doesn't sound bad. As long as you have proper pressure at speed, it may be fine. I did lose all oil pressure in a AMC 304 once due to failed cam bearings.

4) If you are still running 35" tires, you probably want to get some lower gears eventually. Especially with a Dana 20 tcase with the 2:1 ratio. Hard to gear down enough for 35's with a 3.73 ratio. Maybe you're lucky with the stock 4.27's ?

Good Luck

 

[Hedgehog]

Johnbilt - Thanks, yes I'm learning as I go thank goodness I'm a quick study on this sort of thing.

Answers:

1) Since I live in a population center a '75 Jeep has to pass an under the hood visual inspection. Bummer, if it was a '74 the tailpipe is the only thing that matters. With these visual inspections a lot rides on the inspector, some are close counts types, others are sticklers, you really never know until they hand you the paper. Waivers are available, but all the fuss that goes along with them is a hassle I really don't want to bother with on a yearly basis.

2) My AMC 304 seems to run well enough, but honestly I haven’t had it out on the open road. Until recently it simply wasn’t safe enough to play with.

3) After asking around, it is startling to see how low acceptable oil pressure is on an AMC engine.

4) I am not into lifts or big tires or hot rodding around so the lift and 35” tires went down the craigslist road long ago. Unfortunately the springs still provide 3 or so inches of lift and I’m running 31x10.5x15’s on wagon wheel rims. A little bigger than stock, but not much. I mentioned the original setup to show that the PO worked the driveline hard, evidence says VERY hard.

Over-all this has been great fun and a relatively inexpensive proposition. Boards like this are a god send. Back in the mid ‘80’s I put a 231 V6 Buick and a T-18 ford truck Transmission in my ’80 CJ5 . Talk about learning by the seat of my pants. It did turn out great though.

 

[johnbilt]

Great - Sounds like you have things in hand. I like the 72-75 CJ series. They are a somewhat unique model from the early AMC years. I've owned mine for 30 years now and have wrenched and rebuilt just about every part over the years.

A 3 inch lift should work good for you. I have run Rancho springs and Superlifts. They both were the easy-ride with the tapered ends and soft spring rates.

I wish you the best of luck getting your jeep set-up as you like it.

John

 

[Mick]

Hedgehog... Move up here around Kingman/Bullhead... We don't give a about stinkin' emissions in this part of the state... LOL...