AMX Engine Blocks

[ds1970bird]

I am going to buy a 1969 AMX that was an original 290 car. The owner says it now has a 390 in the car. How can I tell if the engine is a 290 or 390 block??? Also if it is a 290 block will all the 290 components bolt up to a 390 block??? Thanks, Dan

[Big Bad AMX]

To confirm the correct cid, the cid number is cast on the sides of the block in approximately 2" high numbers, they’re located behind (above) the engine mounts.
Take a flashlight, you'll need to crawl under the car to see them.

The 290 components will bolt up to a 390. The external dimensions are the same for the 1968, 1969 290, 343, 390.

You'll find VIN and paint, interior code information on the AMX Tech Page
in this website.

[donsjave]

Most exterior components from the 290 will bolt up to the 390 without any problems. The following items will interchange: waterpump, valve covers, intakes, exhaust manifolds, oil pumps, power steering, etc. The interior pieces that make the engine will not interchange and these include the heads (390 valves are bigger) the pistons (different bore size) the crank and rods I am not sure about, however the 390 crank and rods are forged steel versus the 290 being cast iron.
All AMC V-8's are all similiar in design in that AMC tried to use as much interchanability in order to save the money. Their block design in truly outstanding in that they used a very high nickle content in the engines. You could run an AMC engine for 200,000 miles and you would not have any ring wear on the top of the engine. After overhauling two engines, I found neither engine having any significant wear in the bores. Chevy and Ford cannot say the same for their blocks are of inferior design (not meant to run forever I guess).

[Barron]

How about Pistons? I have a 69 390 that was bored 30 over and has some wear on it. It's at between 33 and 36 over now. I need to find some 40 over pistons and rings but I haven't got a source. Where can I find some good interchange data?

Barron

[69amcxtc]

Most piston makers use a generic slug, generally based off of GM standard and popular overbore bore sizes. The best thing to do is have your local machine shop contact a reputable maker of pistons with your current bore size and see how much more you can bore to meet a slug size. Then they can do custom valve reliefs and skirt sizing, wrist pin size, dish to meet your compression based on valve chamber etc... accordingly. Obvious this is not a cheap way out but is this best. I did this with great results for my 390 it ended up 20 over which came from one of the GM 400cid motors cant quite remember. Wiseco did mine and they are awesome.

[donsjave]

Do not forget that you cannot go much over .060 oversize on the blocks for the reason of overheating problems. With the thin casting of the blocks they are really suspect to overheating and you can actually over bore it and end up in the water jacket of the block. Bore taper should not exceed .005 from top to bottom. I am currently working on a 401 for my Javelin and told the machine shop it the block exceeds the bore taper to bore to the next size that will eliminate the taper. Also Sealed Power do make pistons for the AMC engines. They are forged pistons and are constructed using good materials. They are available though Summit Racing, however you have to call them for they are not advertised in the catologue.

[Barron]

I always thought the limit was .030 over. I found a set of .040 over pistons. It's good to know I'm not pushing it. They are Badger brand. I was told Sealed Power only had 70 and up. I'm still looking for a set of .010 over too.
I found a place on the web, Custom Pistons. I have time on that one since it is a spare. I'll check out Wiseco as well.

(sorry for the hijacking)

Barron

[Jimmy]

I learned the hardway that nothing on a 390 block will work on a smaller block. So just watch the internals on it or it will come back to get you trust me I learned the hard way