[2741]

I\'m taking the 401 plunge

I came across a great deal on a complete 1975 AMC 401 the other day. Since my 304 is tired, leaks every fluid it holds and is generally slow, I thought, why not? I'm a grownup I should be able to have the bigger engine if I want it. Now the engine is at the machine shop in pieces, it is being balanced, blueprinted and the compression will be upped to 9:1. I've got a couple of questions though before I go too much further.

Cooling: Am I going to have cooling issues going from a 304 to a 401? I plan to replace my existing radiator, which I think is a 3 core and also replacing the tired clutch fan but will that be enough? I have a good shroud. I'm also considering an oil cooler and I want to keep my A/C.

Intake and Carb: The engine came with the stock low-rise 4bbl intake and a motorcraft 4300. I'm considering a couple of options here; 1) I could port the existing intake and help it to flow a little better, and keep the 4300, 2) Switch to an Edelbrock performer with a little AFB or Rodchester (something around 500 to 650 cfm), or 3) I've thought about keeping my 2bbl intake and getting one of those 500 cfm Edelbrock 2bbls that are set up like the Motorcraft. I've heard that they are simple, clean and dependable.

Exhaust: Will my 304 exhaust manifolds fit on the 401? The engine was complete except for exhaust manifolds. My plan here is to port and match the manifold to the heads and keep my single exhaust. I just put a new exhaust system under it this past fall and went with 2¼" pipe and I'm not interested in it being loud. I know single exhaust will cost me a little horsepower but I can live with it.

Any help or opinions here would be appreciated. My Commando is not really a trail ride. I'm certainly not opposed to going off road; I just do not get the opportunity very often. I use the four-wheel drive mostly in the summer at the beach and in the winter in the snow. The rest of the times I just enjoy the classic ride. My goal here is to be smooth and dependable, being fast is just big plus.

 

[Caver Dave]

Re: I\'m taking the 401 plunge

The 401 should drop right in and the ex. manifolds will fit too. You'll need to find a new flexplate for the 401 as the balance is different from the 304 part. If you don't "need" the 4bbl., swap your intake & 2100...it doesn't get any simpler than that. OTOH, is the 4300 any good? Seems it'd be right up there with the 2100, just 2 extra bores?

Oh, and congrats! The last Commando I rode in that was 401 equipt was a monster! Might have needed "de-tuning" for safety!

 

[uglyjeepoffroad]

Re: I\'m taking the 401 plunge

The driver needed the detuning, not the Commando.

 

[645]

Re: I\'m taking the 401 plunge

do as much for the cooling system as you can. rebuilt, and espically bored out, 401's have a bad habit of overheating afterwards. the origional radiator should be enough with a good clutch fan and a shroud. for some reason edelbrock carbs are finiciky on AMC motors. i think you will be happy with the 2bbl intake and autolite 2100 carb (550 cfm version), espically since you are not going to run headers. all in all, a sweet VERY tourqey motor, just remember, that skinny pedal is going to get fun to push, choose the places you do it well, or you'll find yourself with many points on your license. enjoy!

 

[2741]

Re: I\'m taking the 401 plunge

Thanks for the tip, I'll keep an eye on that heavy right foot.
I figure with a 401 I can have the best of several worlds, it's a classic car, it's a four wheel drive Jeep, it's a convertible, and it's a hot rod.

 

[1082]

Re: I\'m taking the 401 plunge

look at pg. 18 of the January issue of Jp. It shows the danger of a RamJet 502 powered CJ-7.
Michael

 

[Guest]

Re: I\'m taking the 401 plunge

are your 304 exhaust manifolds dogleg style? had to ask - as you may know AMC flow very well on the exhaust side - every thing will be hunky dory there
I would recommend an Edeldbrock air gap and a Quadrajet, mainly cause I run this same combo on both my 401's - Quadrajet has small primary bores for excellent throttle response and good gas mileage, you'll also have the huge secondaries if you ever feel the need to use them and since the secondary air doors ( the things that are usually mistaken for choke plates and mistakenly wired open ) are vacuum operated thus maintaining a high air speed for better fuel atomization - the QJet is highly underated carburetor mainly because people don't know how they work ( see secondary air door thing ) and are one of many good choices, good luck

 

[2741]

Re: I\'m taking the 401 plunge

-Jeff
Why do you like the Edelbrock Air Gap over the Performer? I'm not sure what the difference is, but I've used a Performer in the past on several Fords and have been very happy.

 

[1108]

Re: I\'m taking the 401 plunge

Poke around on the net through Jeep tech web sites - i just recently found a PDF'd copy of a car mag rebuild of a 401 - where it got over 500 Hp with not a lot of extra work - and yes becareful on boring it out - 30 over is max - unless you really like overheating on the trial .... if i can locate the article i'll update this post ...........

 

[1022]

Re: I\'m taking the 401 plunge

KEEP IN MIND THAT THE 401 TAKES A DIFFERENT FLEX PLATE OR FLY WHEEL THAN YOUR 304.

RYAN

 

[celcius232]

Re: I\'m taking the 401 plunge

I get teary eyed when I think about the 73 Ambassador with a running 401 (still with all the emissions gear) that I let go for $500 6 months before I picked up a '73 Commando with a 304. Since I only paid $250 fo the Commando I don't feel so bad about letting that 401 go. I heard it went into a '64 Rambler. Several others here correctly pointed out that the 401 uses a unique flex plate. I think it is balanced differently from the 360s. I agree the quadrajets are good onece you learn their secrets. I have a Edelbrock performer carb (it looks like an old Carter AFB) on a Performer manifold on a SBC. I think it works great and was easier to tune that Holleys that I have had. Keep up posted on the 401 swap. Cheers.

 

[2741]

Re: I\'m taking the 401 plunge

The original fly wheel came with the engine.

 

[Guest]

Re: I\'m taking the 401 plunge

I like the air gap because it puts the powerband of the engine where you'll use it, when you are cruising down the road driving you are not at idle as i'm sure you are aware, so basically you'll always have a healthy throttle response when you decide to mash the go pedal - plus if you plan to use the Summit k8600 cam which is a very popular choice for the 401 than the manifold and cam will be better matched

the performer would also be a good choice, as would most carb/intake combos - the performance differences between all the different choices would not be all that great maybe 20 hp or so - your choice will ultimately be determined by your needs - and off roader or rock crawler would want the powerband to be as low in the RPM range as possible - street driver/occasional off roader like you're talking would benefit more from a powerband in a slightly higher rpm range

it is kinda misleading when shopping for intakes when the say something like RPM range 1500 - 6000; this is its optimum range while people will try to make it out like it won't even run at any other range - not true at all, it just won't be optimized but no one engine will run at peak efficiency in all situations anyways so it mostly comes down to personal preference, good luck

 

[celcius232]

Re: I\'m taking the 401 plunge

I am still pondering that 304/401 swap. I was thumbing a recent Pacific Automotive Warehouse (PAW) catalog and came across their listing for 401 long block assemblies for right around $2,300 and does not require a core. Not too bad considering all the local wrecking yards around here are bare of 401s. Anyone have experience buying AMC long blocks from PAW? Brian

 

[1858]

Re: I\'m taking the 401 plunge

Too bad were not closer. I've got a good running 401 in a Waggy. I'd sell the whole vehicle for half that.

 

[Caver Dave]

Re: I\'m taking the 401 plunge

Tim, what year Waggy? A bud here is looking for Waggys... details?

 

[jeepsr4ever]

Re: I\'m taking the 401 plunge

If you are going to run a 401 check out this page on AMC oiling

http://www.bulltear.com/forum/viewforum.php?f=25

 

[1078]

Re: I\'m taking the 401 plunge

Not specifically AMC, but I have heard horror stories about PAW stuff. And I believe that the most important thing when choosing an intake is to match the rpm band with the cam specs along with the gear ratios for a balanced package. Having every thing work together is like getting free horsepower. Every seen a kid throw a 750 double pumper on his 305 chebby and wonder why it got even slower??
Or a giant cam without changing the rear gears or convertor? You really can't do just one thing without doing it all to get the balance needed.

Chrysler offers a motor book that tells you what parts to use to make your bracket racer run a given ET. I have not checked, but I heard that they have incorporated the adopted AMC motors in the book. If so, their formulas WORK. Pick the power output you want and use those parts. I followed the 11.0 flat formula for my road runner and it runs 11.30's all day. If I had it in the recommended 3600# car instead of the 4300# pig it is in, I'd be solidily in the 10's. And it was cheap, as I spent less than $2200 on 440's rebuild including maching work, manifold, etc.... 2,200 is not bad for 450 honest horsepower and 570 ft/lb. Of course, if they do not offer the AMC formula's, this was all a waste of time...lol

 

[1858]

Re: I\'m taking the 401 plunge

Caver - I'm thinking '76. It belongs to a cousin of mine who would like to find it a new home. Completely stock. Body is very solid with the only rust I saw being quarter sized on both sides directly behind the rear wheels. Needs a new head liner and some TLC if someone wanted it as a driver. If someone is serious, I'd be glad to get some photos.

 

[2741]

Re: I\'m taking the 401 plunge

My 401 is almost complete and will probably go in next week. I'm very excited. It's bored 20 over, the heads have been ported (mainly in the pockets under the valves) with new mopar 360 valve springs and retainers. I went with a very slightly hot RV cam, it should give good power but still retain a somewhat smooth idle. As a bonus I came across a heavy duty forged crank. Just picking it up it feels heavier then my stock crank and was in very good shape. I found it wrapped in plastic (for 15 years) in the corner of the machine shop.

I'm getting a new stock radiator and a 7 blade fan, but I'm a little worried about the heat. I want to keep my A/C. My question is about oil coolers. I would like to install an oil cooler but have no experence with one. I have heard that they are pron to leaking, is this true. Can anyone recommend a good one?

As far as an intake and carb. I still want to go with a edlebrock performer and a 4bbl rochester q-jet. Will I have any issues with hood clearence?

Thanks for all the recent 401 swap info. I have learned alot from Nate's write in's.