AMC 401 Piston Choice

[happyhoppy]

My AMC 401 block is at the machine shop and after being checked out it can stay at standard bore which really surprised me, a real premium! I've read several posts on engines and oiling and I'm comfortable with that area but I'm not sure my piston choice is the best and would appreciate any advice. Pretty limited on stock piston sizes but I've chosen to purchase the KB 354 - 9.5:1 compression.

Going in a CJ7 with a TH400 Dana 20 - minimal off road use.
Rear Dana 60 from 1992 Dodge shortened to widetrack width, 4.11:1
Front Dana 44 from Wagoneer
Looking for good low end torque

Purchased a bare block and so far I have

Crankhshaft at .010 under
Melling MTA-1 Camshaft
Melling VS280 Valve Springs w High Tempered Valve Springs
Edelbrock Performer Manifold (Plan on 650cfm Edelbrock)
Stock Cylinder Heads (Rebuilt)
Stock Dogleg Exhaust

Is the KB piston a good choice or could I do better with this setup? Love to go to $800.00 forged pistons but I have to draw the line somewhere.

Thanks for any input - wouldn't attempt this build without Bulltear.

[jeepsr4ever]

KB's are an excellent choice but do they have stock pistons available?

[happyhoppy]

I talked to Summit yesterday for about fifteen minutes and they couldn't understand why they didn't carry them. After a phone call to KB he said he could get them in a few days. The 2003 price was $430.00 and I'm to call back today to confirm the current price. 401 stock pistons (except cast) are hard to come by - almost all vendors have .030 and larger.

[happyhoppy]

http://www.flatlanderracing.com/kbpistons_amc401.html

[jeepsr4ever]

I know they are listed there I just didnt htink you could get them anymore in std. I do believe you will have to bush your rod and use a full floating pin due to the hole in those pistons (.927). Their are a couple builds on here and hopefully those guys chime in. Been a while since I have used KB's. And does that price include pins?

[happyhoppy]

I don't think the price included the pins - I'll find out when I call Summit today. Good question on the bushing, not something I would have known until I go to assemble.

I'll check the rod diameter - engine was from a 1976 Wagoneer, not sure where the rods came from. Rods were Ebay item but machine shop said they were fine.

[jeepsr4ever]

Stock 401 is 1.00...what I am getting it is after you pay for pins, pistons and locks you are very close to the group buy on forged pistons/pins we are offering at the bottom of the forum page.

[1980_Cj7]

We just finished a 401 and used KB 354's. We used Ross .030 over forged pistons on the first rebuild, which went south in 300 miles and destroyed the pistons, but that's another long story and was in no way the fault of the pistons. The Ross's were beautiful fine pieces of hardware. I think we paid around $600, pins included, from Maddog.

The second rebuild we used .040 over KB 354's. We had learned about some of the downsides of forged pistons since the first rebuild, and decided to go with the hypereutectics the second time around. The pins and locks came with them, but MC is exactly right in that they use Chevy size pins, and you have to bush your rods and float the pins, which was no trouble, but extra machine shop cost, plus the cost of the bushings (about $40 if I recall). Makes it easier to disassemble the pistons and rods if you ever need to for any reason though.

With the compression ratio, we were worried whether the engine would run on pump gas, but it does. We have never tried anything other than 93 octane though. The Ross pistons had an even higher CR. We were getting pinging with them, but the engine had so many other problems, I can't say if it was the CR or something else causing it.

The KB's are supposedly designed for quench with that step in them. You can read all about it in the tech sections of their web page. We are very happy with them, and their customer support all through trying to decide on what pistons to use was outstanding, even before we bought anything from them. Didn't get nearly the support from Ross who we had paid $600.

[jeepsr4ever]

How much did you end up with for the pistons, pins, bushings, honing the bushings and rings?

[happyhoppy]

Thanks for the input!
After a trip to the machine shop I found that it is $20.00 per rod to rebush plus bushings so I'm looking at $250.00 plus to us KB 354 pistons.
Must do some research and get my numbers together - the group buy on Diamond pistons looks feasible.