View Full Version : AMX engine

01-24-2005, 03:37 PM
Hi. I recently purchased a 69 amx. It has mostly everything besides the two main parts, the engine and trans. It was originally a 390 go pack, but i am having a difficult time deciding what i want to do. Some people say to find a 390/401 and just pay the money where as others are saying find a 360 and i will get almost the same performance if its worked over. Please give me your opinion on the subject. Thanks

Big Bad AMX
01-24-2005, 04:45 PM
Being an original X code I would lean heavily toward finding a 390. All 390s (and 401s) came with forged steel crank and rods whereas the 360s didn't. So the larger engines have stronger bottom ends. Depending on what you plan to do with car that *may* be a consideration. The 360 is a good engine and it'll certainly hold up well to mods. And yes, you'll get plenty of hp from a 360, though it'll be tough to match the torque of the bigger cubes.
Also, you probably only want to do an engine build once, so why not try find a 390 as it originally had? Just my 2 cents anyway.

01-24-2005, 05:16 PM
Since I recently rebuilt both engines, one in a 70 AMX and the other in a 71 Javelin, I would definitely lean toward the 390. Both engines were bored .030 over and new higher performance cams put in, the 390 runs circles around the 360. Although the Javelin weighs more (about 450 lbs more) and less cubes, I was somewhat expecting something a little more exciting than what I ended up with on the Javelin.
I put the same carbs on, Edlebrock 650 CFM 4 BBL, MSD Electronic Ignition and the such. Almost everything that went inside the motor and some of it's accessories are the same. The only difference is one is mated to an automatic and the other is mated to the factory 4 Speed (AMX has the 4 speed).
Bottom line, if you are after performance and you can find the engine, either the 390 or 401 is the one you want. My final costs for both of my engines were about the same, but the performance stuff that I did do worked far better on the 390 than it did on the 360.
Good luck in finding your engine

01-25-2005, 07:26 AM
I also agree with all of the above. Also would like to add the if you end up with a late model 360 block the overall strength of the block is suspect. AMC did alot of metal removal on the lower end of the blocks, I guess to reduce some weight, not sure. But if you put a later 360 next to the 390 or 401 blocks you will see the difference.

01-25-2005, 02:42 PM
Thanks for all the input. I will try to find a 390/401 block. Any andvice on a stick trans. Aftermarket or Original.

Big Bad AMX
01-25-2005, 06:46 PM
That's a tougher decision than the previous, I think. There's certainly some appealing benefits to going with an aftermarket 5 or 6-speed tranny. If originality is of concern you've got one choice, the four-speed. If you want the versatility of the extra gears than it's the 5 or 6 speed.
Personally I lean toward the 4-speed with a 3.54:1 rear-end (which was standard with a four-speed). Even with a 3.15:1 rear-ratio you'll have a better gear for highway which, with the torque of a 390, isn't a bad choice either depending on how you plan on driving the car. Of course the 5 or 6-speed gives you the best of both those worlds.

01-27-2005, 01:59 PM
Thanks again. You have been a big help.