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hot rodding a 258?

hot rodding a 258?
R

rr41mag

Full Time Jeeper
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Location
Panama city florida
Vehicle(s)
04 dodge truck, 1966 chevy truck, 2012 rav4
And finally a 1981 jeep cj7 258 hardtop
Any of yall built up a AMC 258 i6 / 4.2l ? I know it would be a lot easier getting a V8 but I've got this extra AMC 258 i6 / 4.2l that I'm toying with. I also have a 1976 350 out of a truck. Which direction should I go? This is a very, very long term project so I'm in no rush. I know I could get some serious HP from the V8 but the challenge of getting some HP from the six is right up my alley. Once again I'll emphasize the fact my AMC 258 i6 / 4.2l is in excellent condition and my jeep is a daily driver.
 
find ways to increase torque below 2500 rpm.:D
 
IOPort51 said:
find ways to increase torque below 2500 rpm.:D
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Unless you plan to install a Dana 60 or something equally stout, concentrate on the AMC 258 i6 / 4.2l and build it out for torque.

Your Jeep is a BRICK. Brick's don't need horsepower. If you want to compete with boggers in the mud, sure build a HiPo 366 or 383. But for an all-around DD and fun Jeep, build the AMC 258 i6 / 4.2l . There's more than enough kick.
 
The AMC 258 i6 / 4.2l was based from a tractor engine(why it's 'redlined' at 4500rpm).
It builds torque, from idle on up.
What are your goals etc.
LG
 
gutthans said:
Unless you plan to install a Dana 60 or something equally stout, concentrate on the AMC 258 i6 / 4.2l and build it out for torque.

Your Jeep is a BRICK. Brick's don't need horsepower. If you want to compete with boggers in the mud, sure build a HiPo 366 or 383. But for an all-around DD and fun Jeep, build the AMC 258 i6 / 4.2l . There's more than enough kick.
Click to expand...

I completely agree. It's a jeep. I love chevy motors, but I'm getting a little tired of seeing them in.......Everything. I thought about it for a minute (sbc) and I'm doing research right now to build the spare AMC 258 i6 / 4.2l I have to the best I can make it. I've been buying some parts for awhile now, got a brand new offy dual port intake last week for AMC 150 .00. :) The wife knows she cant stop me but I'm getting some rough looks. I'm trying to learn on here so I don't have to ask too many of the same ol questions. I think it will be fun to build a I6. for a CJ7 . It wouldn't be fun to build a I6 for a 55 Belaire......:eek:
 
im working on a 264, i like what was said about chev is everywhere, any monkey can do a chev.
My plan is port work slyitly oversize valves and a cam. i have a split header and ive reworked a stock intake with open pelinum and rediuing into the runners.

I think daul exhast with a cross over sounds fickin cool, mite run both pipes out the pass side daytona style.
muli spark ignition, im still looking at a holley economaster for carb. would tig weld a adaptor on top and die grind it out.

I like the idea of a a Lunati 256/262 cam i need a little lope at idle and they say its best for torque.
 
danray48 said:
I completely agree. It's a jeep. I love chevy motors, but I'm getting a little tired of seeing them in.......Everything. I thought about it for a minute (sbc) and I'm doing research right now to build the spare AMC 258 i6 / 4.2l I have to the best I can make it. I've been buying some parts for awhile now, got a brand new offy dual port intake last week for AMC 150 .00. :) The wife knows she cant stop me but I'm getting some rough looks. I'm trying to learn on here so I don't have to ask too many of the same ol questions. I think it will be fun to build a I6. for a CJ7 . It wouldn't be fun to build a I6 for a 55 Belaire......:eek:
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Me too It's not a hotrod if its a hotrod you want then go buy a hotrod and sell the Jeep to someone who will use it for what it was made for.
 
mtnwhlr said:
Me too It's not a hotrod if its a hotrod you want then go buy a hotrod and sell the Jeep to someone who will use it for what it was made for.
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Anything with a motor that you soup up constitutes a hotrod or having been hotrodded.
If someone buys a hotrod it does not make them a hotrodder it makes them a hotrod owner.
My Jeep has been souped up so it is a "Hotrod" I know my jeep was made for a porpuse and by hotrodding it ive made it more capable of doing that and more.
 
Last edited:
OK let me get a little more specific. My present AMC 258 i6 / 4.2l has:

HEI distributor
Dual collector header
Rebuilt original carb

It runs great has plenty of torque. I might add I don't do any fourwheeling so it's 99% road driven daily driver. Since I have this other motor I'm thinking of doing something to the head first.

Port/polish
valves/seals
intake?

If I do the head I'd like to change cam/lifters at the same time.

This is a very long term project so it's not like I'm gonna tear it down any time soon.
 
I dropped the head off today and should pick it up Thursday. I'll get it home check it for cracks then start the porting and polishing.
 
I netted approximately 300hp out of my AMC 258 i6 / 4.2l with the 4.0 head and a boat-load of torque.

So it is possible. The limiting factor is the 4500rpm redline.
As far as torque, the AMC 258 i6 / 4.2l is built perfectly for it and can expand on it with a little engine modification.
 
mtnwhlr said:
:eek: 300hp how did you come up with that # have you had it on a dyno?
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I did have it dyno'ed. It was just under 300hp (299hp if I remember) and the torque was through the roof.
I wish I had kept the spec sheet, it was years ago and pretty much forgot everything about it when I started on the 401 :(
 
CJim7 said:
I did have it dyno'ed. It was just under 300hp (299hp if I remember) and the torque was through the roof.
I wish I had kept the spec sheet, it was years ago and pretty much forgot everything about it when I started on the 401 :(
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Hey can you remember what cam you were running?
it would be real nice to know not a lot of cam talk out there for the AMC 258 i6 / 4.2l
was it a comp? or lunati?
 
Yea really I'd like to know what you did too. The guy at the machine shop gave me a mans phone number who is building up a AMC 258 i6 / 4.2l for his jeep
 
The fact that this tread is recieving zero response tells me that people just arent into rodding these motors, a search of the net yields little more, im afraid your pretty much on your own buddy.
Whod-na thought doin up a AMC 258 i6 / 4.2l would be trail blazing, well on this site anyway, its sleepy time zzzzzzzzzzzzzzzzzzzzzz
 
You might want to look at the spec sheets that Golen Engine Services posts on their website. They have a good breakdown of reliable Hi-Po parts for their 300HP and 4.6 builds.

I am currently running one of their 270 hp/4.6 motors, and it runs within 20 ft.lbs of the MUCH MORE expensive 300hp version.

Only thing I'll do different this year is install roller rockers to shut the valve train up...just waiting for time to do a head refresh at the same time...When I ran the 4.0 on the AMC 258 i6 / 4.2l block I had the head cut for Chevy springs and ran Z-28 springs on a Comp-cam Extreme 4x4 cam with SBI intake and exhaust valves. Popped the Mopar .017 steel gasket on...ran about 10.3 compression.
 
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