401 swap 1991 GW

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TeaBag
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401 swap 1991 GW

Post by TeaBag »

The 360 in my 91 is in need of a rebuild and I was going to take advantage of the opportunity to enhance the performance with roller cam and rockers, raising the compression to 9:1, etc.

My GW has 86k original and is in outstanding condition other wise- No rust and painted about 7 years ago, upholstery redone.

Previously, I added headers, true dual exhaust, eliminated the Cat and added a Flowmaster. In addition, I upgraded to FITECH FI with ignition control.

I am fortunate to have an AMC performance building guru in my area that is going to do the build for me.

He offered to build me a performance 401 for $1000 more than the cost of rebuilding my 360 (reusing my existing exhaust and FITECH). The additional thousand would cover the core for the 401, which he already has ready to rebuild.

Is there any reason why I shouldn't take advantage of this opportunity?

rocklaurence
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Re: 401 swap 1991 GW

Post by rocklaurence »

Sounds Fishy to me. However, if he's willing to give you the 401 plus that addition parts etc to put it in your vehicle for a Grand--do it. Watch out for Project Creep [where all of a sudden you find out that you need this and that plus this and that].
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fulsizjeep
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Re: 401 swap 1991 GW

Post by fulsizjeep »

I put a 76 401 in my 88 GW in 2004. Some things to keep in mind...

- The 88 360 exhaust manifolds use 5/16" AND 3/8" mounting bolts and will not fit the 401 heads that are all 3/8". Also note the Left hand exhaust manifold is different between the 71-78 and 80-91 FSJs. The change came with the introduction of the left hand differential front axle. I installed Hedman headers on mine.

- If the 401 is from another Jeep with T400 tranny, there is a shim "ring" that needs to be removed from the back end of the crank shaft for the 727 torque converter to fit correctly. The shim is usually fairly easy to pull.

- 88-91 FSJ 360s use a Mitsibushi starter. There is no 401 flex plate available for this starter. You have to use a 74-87 V8 Autolite starter and solenoid (along with modified wiring) to fit the 727 style 401 flexplate. I ordered a 727 flex plate for a 74 AMC Matador X with 401.
Flint Boardman
88 GW, 401/727/208, 5" lift, D44s/4.10s/locked up, 35s
https://jubileejeeps.org/quadratrac
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TeaBag
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Re: 401 swap 1991 GW

Post by TeaBag »

Thanks for your response. I had headman headers installed previously and will be using the heads from the 401. They previously drilled out the 5/16 holes on my existing heads when they installed the headers.

I had previously replaced the stock TQ converter with a higher stall-which this guy had built for me. I'll ask him about the shim ring but I suspect he is already aware of it.

will e
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Re: 401 swap 1991 GW

Post by will e »

Some of the accessory holes in the 401 heads are larger too. Specifically the one used by the alternator. You'll need a replacement bolt. I believe it is a 7/16 course (14) 6 1/2 inches long/
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge
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fulsizjeep
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Re: 401 swap 1991 GW

Post by fulsizjeep »

will e wrote: Sun Nov 01, 2020 9:36 am Some of the accessory holes in the 401 heads are larger too. Specifically the one used by the alternator. You'll need a replacement bolt. I believe it is a 7/16 course (14) 6 1/2 inches long/
Ah, yes. I also found that with my swap. Fortunately I had all the original 76 401 accessories to pick through for the project.
Flint Boardman
88 GW, 401/727/208, 5" lift, D44s/4.10s/locked up, 35s
https://jubileejeeps.org/quadratrac

will e
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Re: 401 swap 1991 GW

Post by will e »

fulsizjeep wrote: Wed Nov 04, 2020 9:23 am
will e wrote: Sun Nov 01, 2020 9:36 am Some of the accessory holes in the 401 heads are larger too. Specifically the one used by the alternator. You'll need a replacement bolt. I believe it is a 7/16 course (14) 6 1/2 inches long/
Ah, yes. I also found that with my swap. Fortunately I had all the original 76 401 accessories to pick through for the project.
The bummer is the slightly smaller bolt 'kinda' threads in and you may not realize it isn't the right sized bolt.


Ask me how I know.
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge

MReese Wagoneer
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401 swap 1991 GW

Post by MReese Wagoneer »

will e wrote:Some of the accessory holes in the 401 heads are larger too. Specifically the one used by the alternator. You'll need a replacement bolt. I believe it is a 7/16 course (14) 6 1/2 inches long/
Yep !!
7/16 you will need , then have to ream out the alt brackets and spacer to fit that 7/16


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