AMC 401 Build Options and Questions

[jeepsr4ever]

We can accomodate pistons for you with rings. We are setting up for H13 tool steel pins and have forgings available for virtually any compresison. Give a shout when your ready to pull the trigger on pistons.

[fifesjeep]

IMO... go with the forged pistons... and make sure the garage doing the work zero decks it or slightly has the pistons in the hole .005" to .007"... for quenching reasons... Definitely check out the Bulltear stuff... as well as everybody elses... compare and then look for the best deal(s) etc.

[Mudrat]

JeepScrambler that is a seiously fine looking CJ-8!! And I can see why your are looking for an ideal build.

Taking into account what you plan to do with it - which sounds like mostly road work, you can build a 401 on the mild side and still have enough ass to do what you need to without the super expensive high-tech parts. Little touches like bushed pistons, the cam oil mod, and I agree with Ironman on the push rods and with AMX69 on the 7/16 studs with 1:6 rollers if you think you need them - a wee bit less friction, but like he said make sure your shop understands about angles and binding. The little things to reduce friction, add to HP and economy.

Pistons are personal If your wanting to stay with 87 octane and a 8.5-9.5:1 CR, cast will probably serve you well. Look at the hundreds of thousands of miles on stock motors as evidence they work. If your pushing the envelope with routine hi-RPM passes, race fuel or Nitrus then super-whamadyne high tech is the only way. I think any of the cams mentioned would work well with a Performer - not sure about any future EFI set up, I'm still mulling that over myself. You won't find a cheap R4B anywhere (cheap is a relative term to some folks though ). The major thing to keep in mind, and that was mentioned, is vacuum. If your going to tow ANYTHING you'll need the brakes to stop you and the load, and if you don't have them already put in a vacuum assist brake system (dual diaphragm 7' or 8') will do you nicely. So the cam and intake need to provide at least ( and BARE MINIMUM is) 16 in, better is 18-20 inches. The Torker intake is a misnomer in my opinion - had one on a 304 and hated it. Even tried one on a 327, 4-bolt SBC and it sucked!! Stay to the high side on the carb 650-700 CFM. It's easier to restrict air flow than it is to open.
The HD oil pump from MC gets me 60psi cold, 30-35 warm without a mid-plate on my 360 (bored, balanced, yada, yada, yada), but I'm looking to do that later as insurance against wear.
Engine work should include trueing both block and heads, line bore mains and cam. If your doing the work balance the rotating assembly best you can (or pay the shop to do it ). And if your reusing your con-rods, gett'm refurb'd! In the oil valley, clean up the flash around the oil drain holes and any casting flash that will keep oil from flowing back down. I try and chamfer the holes a little to help the flow. Not a big deal, but one of those 'little things' to get the oil back to the pump as fast as it will go. I've seen guys paint the inside of the oil valley to help as well - but I've not tried it.
Heads - THE most critical part of your build. It allows the air/fuel mixture into the cylinder and holds it all together while it explodes several thousand times per minute, then lets the gases out. Where ever you can improve flow, do it. Port match to the intake , smooth but don't polish the intake path (you still need some swirl to mix the air and fuel) and polish the exhaust to reduce carbon build up. You need some back pressure on the exhaust so you don't suck burnt gases back in when the piston starts to move downward. This is the balancing act on the guzz-out side and takes some research to get right. While it's combusting you need to have good valve seats to hold it all together. You've heard of 3 and 5 angle valve jobs to provide good valve seating and a 3 angle would suffice. And make sure all your valve springs are matched (and not binding). This will apply an even load on the cam and make your motor much happier Valve diameter is also something to consider. Stock 401's have a 2.025 intake and 1.68 exhaust diameters, this should be enough, but you can always open them up if you have the $$$.
If your not going to go too extreme in running this rig off road or trying for a 10 sec pass in a straight line, you shouldn't need a crank scraper or stud girdle. A good oil pump, properly spaced pick-up tube and windage tray will get you through.
The exhaust needs to handle all the air flow leaving the engine of course, and the design is all theoretical. Long tube headers get low end, short tube headers get better high end, just as small primary tube with 1 5/8" diam to a 2 1/2 collector will do better for low-medium end grunt than a 2 1/4 to 3" collector - unless your running flat out down the strip. So you'll have a trade off of hi/low power based on road/off-road manners and the desire for where you want your torque band. What that trade of is depends on you. I would go with the 1 5/8 to the 2.5 collector with a cross over pipe (improves cylinder scavenging in a dual exhaust set up) before it gets to the muffler - after that a 3" pipe will do ya

Good luck on the build and we DO expect pictures and progress reports

[JeepScrambler]

Mudrat, thanks for all the info and advise!

Got my pistons on order from Jeepsr4ever last weekend, they should be here in two weeks or so. The pistons are forged, are set up for a 4.195 bore and chevy piston rings (1/16, 1/16, 3/16) and a CR of 9.5:1. Anyone have any recommendations on what type of piston rings I should order (cast, chrome, moly, plasma-moly)? I have been looking at these sets from summit:
http://www.summitracing.com/parts/TSR-CR2455-30/
http://www.summitracing.com/parts/TSR-CR2455-35/
http://www.summitracing.com/parts/TSR-CM2455-35/

[fifesjeep]

I used chromoly rings in my 360... I didn't have any issues with the rings seating...
Another thing you can do is go with Chevy valves... they're a lot lighter but, machine work will be needed... (this is probably overkill for what you plan on using the motor for but, it's another Idea)...

[JeepScrambler]

Still collecting parts for the build, but I do have one more question about the piston rings. One set I have looked at are file fit http://www.summitracing.com/parts/TSR-CR2455-35/ and have a slightly larger bore of 106.680mm. The other set are not file fit http://www.summitracing.com/parts/TSR-CR2455-30/ and have a bore of 106.553mm. The are both the same price but I was needing to know which would benefit my build. Are the file fit rings much more work than the non fileable ones? Or should I just go with the non-fileable ones and be done with it? Thanks again for all the help.

[Mudrat]

All rings are fileable for fit, except the spiral type and they are self-adjusting

[JeepScrambler]

Progress has been slow on the 401 build since I am currently living and working in Houston, TX and all of my Jeeps and the 401 are back in Kansas. But I have been able to get most of the parts ordered that I am needing to complete the build, including some forged 9.5:1 pistons from bulltear along with the oiling pump kit with some of the upgrades.

I do have one more question regarding rocker arm studs. I am having the head machined for 7/16"-14" base and milled down 0.375" for the guide plates and ARP studs to run Harland Sharp 1.6:1 roller rockers. I know this is a pretty common procedure for those wanting to run roller rockers on the later model AMC's so does anyone have the ARP part number for the rocker arm studs I will be needing?

I have searched and all I have come up with is that I should use SBC or BBC studs, but there are several different options for that as well. Can someone give me a part number so I can get these ordered!

I was able to go back home to Kansas for two days around Thanksgiving so I figured I'd better get the Scrambler out and snap some current photos!

[JeepScrambler]

Got my Harland Sharp 1.6 ratio roller rockers orders as well as the ARP rocker arm studs. The studs I am going with have an effective length of 1.75" with the threads being 7/16-20" and the base studs threads being 7/16-14". They are ARP part number 135-7101 . That's all the progress I have for now!

I still haven't decided on what cam and an intake I will be running. I'm leaning towards an Offenhauser intake http://www.summitracing.com/parts/OFY-5917/ since I already am running the Edelbrock performer on my 360, and I have an old school set of offy valve covers I will be using. And for the cam, possibly an Engle, part number 5052H or the 5054H, or a custom grind; still not sure yet.

I'm definitely open to suggestions since I won't be ordering these parts for a month or so.

[AMX69PHATTY]

ARP 135-7101 are the studs I used with HS #S4004-7 Rockers in 1970 AMC heads.
The ARP #134-7103 studs were too short, not enough thread ingagement.
Sounds like you've got the right studs for the 7/16 HS rockers.
Might want to remove the locking set screws from all the Poly Locks and run them all the way down onto the studs to make sure they're all smooth with no burrs in the threads.
Would suggest using a pair of adjustable length pushrods and a pair of solid lifters temporarily to determine correct pushrod length once a cam is chosen. Keep an eye on bottom of rocker arm to rocker stud hex clearance where they screw into the heads, as well as rocker geometry throughout the entire valve travel range.

A little pricey, but like the Lunati part #31702 grind #SPT1-285-300.
It's a dual pattern cam, allows about 10:1 or a little more CR, and still should work with pump gas since the Intake Valve closing angle bleeds off some CR.

Need to pick a cam and slide it in the completed short block and use a pair of solid lifters and adjustable length pushrods to determine correct pushrod length before ordering the puchrods, and check piston to valve clearance. Have the new hydraulic lifters on-hand so any pushrod pocket depth differences between the solid and hydrauilc lifters can be compensated for when determing and calculating correct pushrod length. Each cam can be different, they may have a different base circle radius dimension which will affect correct pushrod length. I used Comp Magnum Pushrods. They're available in a lot of off-the-shelf stock lengths. If a stock length can be used it might save some money on pushrod cost over a purely custom length pushrod.

Cam I guess depends on desired RPM range and the Lunati is listed as good from 2500 to 5600, and the rpm range will help determine what Intake Manifold for the same range. I'm a believer in the Torker Intake on an AMC as long as the gearing and such lets the engine get up to about 2500 before loading it up, so depends on rear end gears, tire size, and converter stall speed if an auto.