4.2L vs 258

[mwood65]

HA, I know everyone came on here to tell me "it's the same engine knuckle head"

I know that but have a question.


I had an 80' AMC Eagle SX/4 with the 258, T4 (?) and the full time T-case.


The car was almost what I would say was quick'ish


Now my 74' Cherokee with the 258, T-18, Dana 20 will not get out of it's OWN way.


Question is: Besides the 80' having a BBD 2 barrel, is there a difference in the engine?


Is the performance difference due to vehicle weight & gearing or did the newer 258 have better power?

[Heavy_Metal_Thunder_81]

Is the Cherokee a 2 or 1 bbl carb?
Weight and gearing do have a lot to do with it, too.

[tgreese]

The watershed year for the 258 was 1981, when the engine was lightened with a new crank, lighter block, new manifolds, etc. Your '80 should have been the older engine (same as '74) with the heavier parts.

As mentioned, lots of factors contribute. Wind resistance is a big factor - the FSJs are pretty sad in this respect. Vehicle weight, final drive ratio, etc etc. The first year for the 2V BBD in a FSJ was 1977. It would be most informative to compare the listed power for both 1976 and 1977.

[joe]

Is the Cherokee a 2 or 1 bbl carb?
Weight and gearing do have a lot to do with it, too.

+1
All three make quite a difference! Toss in aerodynamics it's almost an apples to oranges thing. I put an 84 258 in an 4cyl 82 CJ8 and once the goofy carb issue was sorted it performed as well as a stock 258 in an earlier CJ7, both running 4.10's in the diffs but CJ7's and 8's are much more similar then are Eagles and FSJ Chero's

[Carnuck]

Cam timing on later motors and compression ratio as well as gearing plus weight and aerodynamics stuff changes it a lot. I had the Mexican 282 in my ‘83 Cherokee SJ from a CJ which had more get up and go than the remanded 4.2L due to carb emissions stuff. And the high miler 282 beat the rebuilt motor hands down.

[yossarian19]

Look at the rated horsepower vs curb weight for each vehicle, as well as gearing.
I bet the Eagle saves 1,000 lbs
Hotrodder's addage is 100 lbs saved = 10 horsepower gained at the drag strip, right?

[Carnuck]

I put the 282 into my ?83 Cherokee (FSJ) and got 17 mpg and it held 90 mph on the I-5 from Seattle to the Canadian border the day my father had a heart attack.

[FSJunkie]

It's big, it's heavy, and it's square. It's going to be slow.

You can make sure that engine is running at full strength. AMC I6's are very good at having a lot of things wrong with them that sucks their power and yet still seem to run fine aside from being piss slow. Worn timing chains and lean carbruetors neuter them.

[mwood65]

The Cherokee is a 1 bbl.

I guess the best way to compare straight across is HP / weight for each to see what the LBs. to HP is.

I sure would like to have the performance in the Cherokee I had in the Eagle.

[FSJunkie]

I sure would like to have the performance in the Cherokee I had in the Eagle.

You need 170-200 horsepower under the hood of the Cherokee to do that.

I have a 1977 AMC Hornet powered by a 232 1bbl I6, 100 HP. Probably slower than your SX/4. It has about the same performance as my 1972 Jeep Wagoneer with a 2bbl 360 V8 of 190 HP. Both are 0-60 in the 10-12 second range.

So you basically need either a 4.0L or a 360 V8 to make a Cherokee perform like a 258 SX/4......or a 258 that is a 4.0L above the head gasket.

[mwood65]

Sorry I made a boo boo, My Eagle SX/4 was a 1981...not an 80'

1981 SX/4 / 258 / 4 speed had a power to weight ratio of 29.1 lb. per HP

74' Cherokee / 258 / 4 speed had a power to weight ratio of 34.5 lbs. per HP

--------------------------------------------------------------------
The Eagle:

Gear ratios (overall):


I
3.5 (9.56)
II
2.21 (6.03)
III
1.43 (3.9)
IV
1 (2.73)
rear diff: 2.73 (wow!)

Curb weight: 3205 lbs.

----------------------------------------------------------------

1974 Cherokee:

Gear ratios (overall):


I
6.32 (22.37)
II
3.09 (10.94)
III
1.69 (5.98)
IV
1 (3.54)
Rear diff: 3.54
Curb weight: 3790 lbs.

Jeep: 110 HP & 195 ft-lb
Eagle: 110 HP & 200 ft-lb

So power difference is not worth noting between the two vehicles......
Jeep has lower gearing and lower final drive
Eagle is only 585 lbs. lighter
(thought it would be a larger weight difference but the Eagles were built like tanks not that the Cherokee isn't)

So the Cherokee has 585 lbs. more weight and the aerodynamics of a steam locomotive. A lot of info for nobody that cares probably...lol
I was just curious about it that's all. Crazy thoughts of a senile man!

Maybe I need to run a compression test on the Cherokee to see if the engine in it is just a worn out dog. The Wagoneer 360 is on the stand now and I can barely handle one project at a time.

[FSJunkie]

I know what the numbers say but I'm telling you as someone who has a Jeep similar to your Cherokee but with a V8 and two AMC's similar to your SX/4 that the numbers don't show it all. Jeeps take a lot more power to move, especially at high speed.

The 258 in the Eagle made more power than the 258 in your Cherokee because the Eagle had a 2bbl carbruetor. AMC didn't account for that in the published horsepower figures. 1bbl 258's make 110 HP, but 2bbl 258's are 115-120 HP.

You will need to get that Cherokee to at least 150 horsepower if not more like 170-190 to match the Eagle. Just how it is.

[babywag]

80's aluminum intake & exhaust manifolds
2100 2bbl carb (adapter required)
Compcams 260H

Made a very nice improvement on my dad's '79 258.
He was a happy camper afterwards

[mwood65]

80's aluminum intake & exhaust manifolds
2100 2bbl carb (adapter required)
Compcams 260H

Made a very nice improvement on my dad's '79 258.
He was a happy camper afterwards

You JUST HAD to go and add the Cam didn't ya?!?!


More work than I wanna get into right now....


Intake....sure
Carb..... yeah
Cam..not now

[brielly]

The carb and intake along with an ignition upgrade will give you a noticeable improvement.