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401 Build For My Rock Crawler |
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Jeep_Guy
AMC Fan Joined: Aug/07/2017 Location: Midland Status: Offline Points: 8 |
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Posted: Aug/07/2017 at 9:23pm |
So i know this is prolly not what most of the guys in here are into but none the less everywhere i looked said all the guys here know their stuff so here i am. So to make a long story short i blew the 360 up in my cj based crawler and bought a cherokee cheif with a running 401 in it. it runs great but there is a slight lifter tap on the 401 coming from the front driver side so im going to pull the the top end of the 401 down. stick a cam in it, redo the heads, reseal it, new oil pump, intake and i have a Vac secondary 650 Holley for it. i have a few questions.... is the 650cfm enough? are the heads on blown 360 the same as the heads on the 401? i plan on sticking one piece stainless valves in the heads, is there anything else i should address while they are apart? what about these oiling mods? are they needed if i stay under 5500RPM? i want to stay out of the bottom end unless i pull the heads and see some issues in the bore or bearing issues when i do the rear main. what it is the best place to source parts? jegs? have i missed anything?? be gentle im new... and used to GM Motors......
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gremlinsteve
AMC Addicted Joined: Dec/16/2008 Location: houston Status: Offline Points: 884 |
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Summit 8600 cam
Carb sounds fine Heads should be the same Being it's low speed rock crawling why the talk about stainless valves? |
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Jeep_Guy
AMC Fan Joined: Aug/07/2017 Location: Midland Status: Offline Points: 8 |
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i was told the factory valves are 2 piece and prone to failure. if that is the case then spending the 300 up front to me is worth it. is that correct info? also what about ignition upgrades? i was going to go with a HEI is that a good choice? and i was told a 650 CFM wan not enough carb but i figured if im not doing 1/4 mile pulls it would be fine.
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gremlinsteve
AMC Addicted Joined: Dec/16/2008 Location: houston Status: Offline Points: 884 |
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Well
It's not a race car so a smaller carb should give you a bit more velocity and better throttle response down low Stock valves will work fine. If you want to spend the coin for new ones that's fine too But your estimate might be off as you will probably need guides and other head work to include a valve job Once your rebuilding the heads your at a crossroads. New guides. Seals. Springs valves a valve job and surfacing can add up. Check your local shops for that Chevy valves as most other stock valves are also two piece friction welded Ignition work is fine. But amc motors are particular about cam gear and distributor gear matching Reused your stock pieces what ever route you go They are matched to each other |
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74Bubblefender
AMC Addicted Charter Member Joined: Jun/29/2007 Location: The AMC form Status: Offline Points: 2589 |
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Get a fuel injection system and stay away from a carb. Virtually all high flow water pump will pump higher volume and pressure at idle to 2000rpms so use one of those. You don't need much more than a stock motor unless you want to rock bounce and join the jumpers. A good build with a small camshaft like mentioned should get you where your going.
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We are just about to forge new AMC V8 crankshafts.. please check here
http://www.bulltear.com/forums/showthread.php?19564 |
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Jeep_Guy
AMC Fan Joined: Aug/07/2017 Location: Midland Status: Offline Points: 8 |
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i would like something in the 400-450hp range. is that obtainable without diving into the short block? my long term plan is to go with a fitech setup. but i have the carb and i wanna get the jeep up and running for this fall. are the 360 heads and the 401 heads the same as far as valve size and runner size? im wondering if i should send both sets of heads to the machine shop to get checked and rebuild the ones in the best condition. if the stock valves are good then i will just replace what is needed. what about the oiling mods?
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gremlinsteve
AMC Addicted Joined: Dec/16/2008 Location: houston Status: Offline Points: 884 |
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What's the casting numbers on both sets of heads?
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Jeep_Guy
AMC Fan Joined: Aug/07/2017 Location: Midland Status: Offline Points: 8 |
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i will have to pull the casting numbers when i get home this evening.
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Boris Badanov
AMC Addicted Joined: Dec/14/2013 Location: NH USA Status: Offline Points: 4209 |
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All 1970 and later heads are so close in flow and runner configuration
that the only things that mean anything are the considerable difference in combustion chamber size and stud vs pedestal mount for the rockers. For a low end grunt motor I would use a small, 390 cfm holley DP or a Carter / Eddelbrock of 500 or 600 crm. Stock cam or something similar and under 9.5:1 compression. Eddelbrock dual plane manifold and small headers. This is if you want all in by 2000 rpm. |
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Gremlin Dreams
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shootist
AMC Addicted Joined: May/24/2012 Location: Triad, NC Status: Offline Points: 1023 |
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I was reading and got a little bit confused on what you are wanting to achieve. For your application I would think you would be less concerned about HP numbers and more concerned with making max torque in a lower RPM range. The good news here is that the 401 by its nature was never really built as a high revving HP monster but was better than most like sized motors for producing power in the under 5k RPM range. That being said, I would maybe use a slightly larger than stock cam with a good low end powerband. Also by keeping the motor under the 5k mark and the nature of rock crawling being very short bursts of pure brute force you really wouldn't need any oil modifications. Bottom end should be fine if it is in good shape. I would inspect bore and bearings but if they look fine re-torque and move on. 650 would be near perfect for your purpose it is all about volumetric flow and efficiency. That does assume that you are going with a mild to medium cam making all your power below 5000 RPM. Now if you raise that RPM range into the 6-7k range the carb would be on the small side. Also keep in mind if you are going to be turning higher RPM then you would add in a need to do something more to the oiling which would add considerable cost to the build. If you decide you want to turn higher RPM get a deeper pan and perform oiling mods. I have seen some just restrict the left galley with a drilled out plug and also seen people add the additional line/lines to improve oil flow. Opinions vary wildly on the oiling mods and I have done both the restriction and the extra line before and both methods seemed to serve me well. Good luck with your build, I think you are in the right place for advice. There are some very bright AMC minds here.
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