Looking @ Some 304's...

[poppatello]

My jeep currently has the AMC 150 and its serverly under power now running 35's with 3:54 gears. So I started looking for a stronger heart and I first started with the 4.0, then went to the AMC 258 i6 / 4.2l then found a AMC 258 i6 / 4.2l EFI. Well I sold all those engines to get the next one in line until I bought an 88 waggy woody that needed the AMC 258 i6 / 4.2l EFI that I had last. I installed that AMC 258 i6 / 4.2l EFI in the waggy and I gave that jeep to my father in-law since his blew up.

So I then moved to try and nab a diesel. Well that just isn't working out for me so I started looking @ the Dodge 360's. I was told I would be best to look @ AMC motors as parts are easily available. So I started looking and came across quite a few AMC 304 's in my area and a few @ a decent price.

All but one are from the early 70's. I looked at the AMC specs and the early 70's seem to be the best HP/Torque range I'm looking for.

I don't see to many write ups or threads on the AMC 304 's. Is this a decent option? Are parts easy to come by?

Are the AMC car AMC 304 's the same as the Jeep's AMC 304 's? If not would it work?


I am in the process of upgrading to one piece axles, and re-gearing from 3:54's to 4:56's. My rear axle is already trussed. I also plan to drop out the T-4 and install a T-176 , SM 465 or the NP 465.

So I have a plan in place no matter what engine I use just still trying to figure out what route I want to take. (NO SBC's) I'm sticking with AMC's or jeep. If I go outside the brand it will be a diesel...

 

[Incommando]

The Jeep AMC 304 /360/401 IS the AMC 304 /360/401. There are minor year and application differences like exhaust manifold type and maybe accesory drive locations but the basic engine is the same AMC engine. From '71 model year through 1987 the Jeep was an AMC. Well it was technically a Renault for the last few of those years but I digress.... The earlier AMC engines did have a less efficient head design.

One truth is that there is no replacement for displacement. Every dollar spent on a AMC 304 will yield better results in an AMC 360. AMC 360's are not uncommon nor much more expensive than a AMC 304 . They share the exact same external dimensions and as long as you have the correct flywheel/flexplate to match the CID of your engine there is no difference in putting a AMC 304 or a 360 in your jeep. 401's are pricey because AMC people consider them the holy grail of AMC motors... For pure performance you can modify a 360 to outperform a 401 for less than the asking price of most running 401's.

To be honest you probably will still not like a V8 cj with 35's and 3.54 gears. That is not on anyone's "recommended" list with 4.10's being about the bare minimum for that tall of a tire. 4.27/4.30, 4.56, or 4.88 are all choices which will make you happier in the long run. In fact you may be better off swapping to 4.88 gears with the I4 than a V8 and 3.54's if your current engine is in good shape.

 

[IOPort51]

the man^^ is right.

If you are going to spend money for the 8 go with a 360. there are a lot more of them around. Make sure you get the flywheel for the engine, they are balanced engine specific. If you don't get the one for that engine you will be best off to have the crank assembly balanced as a unit.

He is also right about the tires and axles. I will not argue the replacement for displacement line but the fact is that our game is centered around gears.
You don't see a lot of Jeeps street racing or even going over 60 MPH for that matter. It's going to take gears and torque to turn those 35s.

The way I see it you need to have the gear combo that will give you low speed crawl power in 4 low and cruse at 60MPH @ peak HP/torque RPM in 2 high.

If you can get those numbers right you have what you were looking for.

 

[poppatello]

Thanks guys.

I plan to install the 4:56 gears when I do the axle upgrade. I also plan to replace the T-4 as it is an extreme light duty tranny and I know it won't hold up behind a V-8.

I was thinking the AMC 304 because of the cooling issues. I've read where many cooling passages are just to thin on the 360 as it's the AMC 304 bored out so makes keep her cool harder. I don't need much more power so figure the AMC 304 would suffice.

My engine spits up oil out of the breather when I push her hard and I always thought it was do to the fact I have to rev it up high to get her moving with the 35's. It only has 40,000 on it. I was planning on running it then working it up. I think it would be cool to keep the original motor, work it up a bit and see what it can do. I talked to a machine shop and they told me they can make a sweet, dependable torque monster out of it which I want. I still may go that route.

But with the oil issue it seems I may need to do something sooner then later and if I go this route I guess I'll just scrap the 4 banger since there is a lot of mods to swap up.

I know one AMC 304 doesn't have a fly wheel so I would need to tear down the motor and have the crank balanced to the new one? I'm not interested in that idea if so. I just want a running motor and drop it in for now...

 

[poppatello]

Also, I'm guess the AMC motor are the same weather they came from a car or truck? I thought the cams and intake would be a bit different no???

 

[Incommando]

There may be minor application differences that probably have more to do with year than original application. As you are doing a complete swap anyway it wouldn't be an issue. The factory Motorcraft 2100 2v carb is a dandy if you get one equipped with that.

AMC V8's are externally balanced. You would need to get a AMC 304 flywheel to keep the engine balanced. They are out there new and used. If you wound up with a 360 or whatever flywheel you could have a machine shop re-balance it to AMC 304 specs. Having the correct harmonic balancer and flywheel is the key.

 

[derf]

The 4.56 gears may be too short once you get a V8 in there.

With 35's, you'll be running 3K RPM on the freeway. I have 4.56 gears and 35" tires on my truck and it's miserable on the highway. But I'm going to be starting the 70R4 swap on Saturday so I'll have Overdrive to bring the RPMs down.

If you were sticking with the 4 banger, the 4.56 gears may make more sense.

With a V8 in a CJ, you probably don't need much over 4.10s with 35s. If you go with a deep first gear Transmission like the SM465 or NP435, you can get away with more highway friendly gears and still have plenty of crawl ratio.

 

[poppatello]

Hmm, that is one factor I didn't allow for. I guess I need to narrow down what tranny I want to install. One thing for sure the T-4 is outta there. So your saying if I run a V-8 with the NP or SM tranny I only need to go 4:10's?

I'll check and play around with the gear charts later after work...

 

[derf]

It all depends on how you plan to use the Jeep. If it will never see the highway, there's no need to be concerned about highway RPMs.

It's all a balancing act.

How are you going to use the Jeep? Street? Highway? Mud? Rocks?

If you're never going to go over 40 MPH, you can use a different axle gear than if you were going to drive it on the highway. If you have Overdrive , you can get shorter (numerically higher) gears and still have a reasonable RPM range at the higher speeds you plan to run (whatever those are). If you plan on making a trailer queen for rock crawling only, you can bump up to 4.88s easily and not worry about freeway RPM.


My example:

I have a truck with a 360. I'm going to tow with it some but it will end up on the freeway more than a little bit. It came with 29" tall tires and 3.31 gears with a 3 speed automatic. It ran OK but the 31" tires gave it a better freeway RPM. I knew I was going to run a lift and 35" tires so I could do some mild to moderate wheeling so when I did the axle swap and lift, I planned the whole package.

The options are more Limited with the 3 speed automatic. If I wanted a balance for towing and highway cruising, I was looking at 4.10s or 3.73s depending on which way I wanted to favor. With the 4 speed automatic, I get a slightly deeper first gear but I also get a significant Overdrive . Because of that, I can run 4.56 gears and still cruise down the freeway at 70 pushing just over 2100 RPM. Right now I have the 4.56 gears and 35" tires and I'm pushing over 3200 RPM at 70. I can't break into double digit gas mileage with this combination. That's why I'm putting in the Transmission with the lockup torque converter and 0.70:1 Overdrive .


If you're looking at a Transmission with a 1:1 top gear but a 6+:1 granny low, you're going to want to consider going with different axle gears than you would if you had Overdrive . You can run 3.73 gears in the axle to get 2500 RPMs on the freeway at 70 but still have the low first gear to give you some serious crawling ability. You might even consider staying with the 3.54 gears so I could drive it on the highway with even lower RPMs and still have the granny low there to give me a decent crawl ratio. It might be worth doing the V8 swap with the granny low Transmission before you do anything to the axles and see how you like it before dropping the money on new gears. It won't be any slower than you already have with the 4 banger while you save up for the gear/locker swap that you really want.

Of course, that all depends on what you're going to use your Jeep for.

 

[Incommando]

Go to Grimm Jeeper and click on their conversion chart. It let's you pick different tranny, t case, axle ratios, and tire heights to check various rpm's at various speeds for different combos

 

[derf]

Go to Grimm Jeeper and click on their conversion chart. It let's you pick different tranny, t case, axle ratios, and tire heights to check various rpm's at various speeds for different combos

That's a fantastic website! Whoever wrote that was a genius!

 

[Incommando]

Allow me to thank you! Your website has been invaluable to me in my various builds. I also use it when "daydreaming."

With my 360/T18a/Dana 20 combo I went with 4.56 axle gears and 38" tires. It gives me a decent crawl ratio of 58:1 which ought to be adequate with the torque of the 360. If I had a low-output I4 I would have gone with a much steeper axle ratio and/or a different Transfer Case to get the near triple digit crawl ratio that such rigs require. At 65 MPH my RPMs should be about 2,600. That is maybe a little more than is ideal but as it will spend much more time at 5 mph than 65 I slanted the gear ratio's to that. 4.10's only drop the 65 mph Rpm's by 250...

 

[CJ]

That's a fantastic website! Whoever wrote that was a genius!

LMAO! Yep! Pure genius!

Allow me to thank you! Your website has been invaluable to me in my various builds. I also use it when"daydreaming."

Couldn't agree more - invaluable information, provided for free, by derf!