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Thread: 401 serious performance/endurance build for a CJ7

  1. #1
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    401 serious performance/endurance build for a CJ7

    Alright guys, i have a 30 over 401 i got awhile back that i have torn down. Going to be sending it to the machine shop soon to be looked over. It was supposedly rebuilt when i got it. But it was definitely by some shoddy machine shop. The bores look like they have some scuffing on them, and the crank looks like it going to need to be cleaned up as well. The current pistons are deep dish cast.

    This is going in CJ7 with an Sm465, on 33's for now. Current gears are 3.54. Which keeps the max speed at about 70 with that old tractor 258.

    I'm thinking 10:1 compression, 500hp?
    -I'm not opposed to a methanol injection system for the high compression either.
    -Big oil pan,
    -Roller cam maybe for the broader rpm range? geared toward a hard midrange. Not worried about torque, its already a 401, in a lightweight jeep with a granny gear 1st
    -Holley Sniper Efi
    -Can i get/do 6" rods without stroking it?
    -I'd like the best performance/endurance i can get, making it happy to spin at 2500-3k all day on the highway. With the occasional slam to 7k rpm.

    I drive it like i stole it, and frequently scare passengers going through the local twisty back roads.


    I've daily driven my CJ for 8 years, been to Canada, Arizona, the Outer banks, etc.. The 258 gets 17 mpg but is no fun on the interstate.

  2. #2
    Thank you from BT ULTIMUS MAXIMUS STATUS tufcj's Avatar
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    Bigger isn't better, and a Jeep isn't a sports car. What do you use it for mostly? Mud bogs, drag racing, rock crawling? Different use means different builds for different power bands. You can't have it all, HP usually sacrifices some torque, more torque loses some HP.

    You're going to be disappointed in performance with 33" tires unless you go to at least 3.73, if not 4.10 gears. I ran 4.27s in my CJ with 35s, went to 4.88s when I went to 37s.

    I'd keep the compression down in the 9-9.5 range to run premium pump gas. Roller cams are nice, they do require machining the block for a cam walk plate, then you need to watch the lifter bores for diameter and uncovering of the oil slot. Higher lifts with roller lifters sometimes require bushing the lifter bores. Rollers are usually for bigger HP (higher lift and quicker valve open/close). Big oil pan is good, but don't get something so low that it gets smashed on the ground. Watch for clearance from the sump to the front diff. The jury is still out on the Sniper EFI. I haven't heard a lot about it yet. 6" rods will require machining the rod journals to 2.0" or 2.1", which is a perfect time for a stroke. It will also require custom pistons with the right compression height and pin diameter. Spend money on Aluminum heads or have the steel ones ported. AMCs like to breathe. It's money well spent.

    Read this article: http://www.hotrod.com/articles/amc-brute-engines/

    Bob
    tufcj
    Last edited by tufcj; 01-09-2018 at 07:27 PM.
    1969 AMX
    1967 Rambler Rogue

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    With 3.54s and 33s, I'm turning 2800rpm at 80mph. Going any deeper doesn't seem logical unless i had an overdrive 5speed. I suppose the 401 is happier spinning at higher revs with the shorter stroke though, which is why i was thinking and read longer rods reduce sideloading of the pistons on high/sustained rpm. Instead of using longer rods to increase the stroke? My experience is somewhat limited, but I like short stroke/high revving. I was thinking more along the lines of the engine builds in Trophy trucks.

    For reference my brother had a 327sbc in his CJ. Same transmission as mine. But he had 4.10 gears with 33s, and it was scary fast. And when he put the 36" tires on it. It was still scary fast and would bury the speedo.. 98 mph in a CJ with 36s.. was an experience. :)

    With my current setup i have plenty of power off idle and can cruise decently. With the 401 it would be a rocket. If i went bigger on tires I'd regear for sure. Honestly, i use it for pretty much all those in Virginia, mud, trails, crawling and cruising hard on the road. With the 6.5 first gear in the trans i have all the torque and gearing i need. Which is why I'm looking to build this with a broader/higher rpm range than most would. A low lift RV cam just seems like a waste in a 401, and puts so much torque down low i imagine it makes it even easier to break parts.

  4. #4
    Thank you from BT ULTIMUS MAXIMUS STATUS tufcj's Avatar
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    Stroke is determined by the crank, not the rods. A 401 crank has a 3.68" stroke, the SBC 327 has a 3.25" stroke. The shorter stroke will rev higher and quicker. There's less piston acceleration, and with a 4.00" bore, a somewhat lighter piston. The 401 is traditionally a lower revving engine. I think factory red line was 5500. Even with a much lighter piston and a balance to within 1/4 gram, I rarely rev my 390 past 6000. Going to a 6" rod and moving the wrist pin higher in the piston will reduce side loading some. 7000 RPM is close to the limit of what a 2 bolt main cap will handle (did you read the article I posted?) My CJ with 4.88 gears and 37" tires cruised at about 3300 RPM at 75 MPH.


    Bob
    tufcj
    1969 AMX
    1967 Rambler Rogue

    If you need a tool and don't buy it...
    you'll eventually pay for it...
    and not have it.
    Henry Ford


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    Gotcha, I've actually read that article a few times in the past doing research. I do know and understand the stroke is determined by the crank, and that the rods don't change that. But am less clear on how changing the bearing size of the crank and makes a stroker? I know Chevy guys use 400 cranks that are 3.75, in 350s to make 383s. I've never been into the whole stroker deal because i read they seem to accelerate wear/longevity issues.

    I'm not opposed to going with a 4 bolt main kit for strength. I like to do things right and do it once. What are your thoughts on going with a 4 bolt main kit, and ideas on what kind of roller cam to go with? Brand/specs?

  6. #6
    Thank you from BT ULTIMUS MAXIMUS STATUS tufcj's Avatar
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    The stock 401 journal is 2.248". When they cut the rod journal to 2.1", they remove the metal off center, taking as much as possible of the material from the bottom. This moves the center line of the rod journal. Take the 2.248 factory diameter - 2.100 = 0.148". it moves the center line of the crank 1/2 of that (.074"). Now your 3.68 stroke is a 3.754. This is best case, assuming the crank is standard, the stroke will be less if it's already been turned .010, .020, .030, etc. If you remove the material uniformly, the center line of the rod journal doesn't change, and you still have a 3.68" stroke.

    If properly built, a stroker will last just as long as factory. I've got my name on a waiting list right now for a brand new forged 3.75" stroke, 2.100 journal crank and rods (about $2600 delivered). I've got a 390 block to drop it into. The 4 bolt main kit will take a precise drill/tap of the block (they only do the 3 center journals, and the new bolts are splayed out. It also requires a line bore of the block once the caps are installed. It can get pricey.

    I haven't done anything with roller cams, although I might with the engine I have waiting to go into my 67 Rambler. It's built with a 292/302 duration, .525/.540 lift Crower cam. I'm going to put a retro dual quad manifold on it with two 400 CFM throttle bodies. The manufacturer of the EFI system (Howell-EFI) isn't sure that it will draw enough vacuum to avoid a check engine light. I built the engine before deciding to go EFI, so I'm going to try as-is. If it won't work, I'll go to a roller with similar lift, but shorter duration for better vacuum signal.

    Bob
    tufcj
    1969 AMX
    1967 Rambler Rogue

    If you need a tool and don't buy it...
    you'll eventually pay for it...
    and not have it.
    Henry Ford


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    Does anyone currently make an Amc offset 6" rod that isn't intended for a stroker build?

  8. #8
    Thank you from BT ULTIMUS MAXIMUS STATUS tufcj's Avatar
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    Molnar is the only quality rod I know of. Their 2.100" journal has a Chevy wrist pin diameter, so you're looking at custom pistons with pin height adjusted to your stroke.

    http://molnarrods.com/amc-connecting-rods

    Bob
    tufcj
    1969 AMX
    1967 Rambler Rogue

    If you need a tool and don't buy it...
    you'll eventually pay for it...
    and not have it.
    Henry Ford


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