Engine Advice on engine swaps and general useability - 84 CJ7

[Citizent3]

Hello, long time lurker first time poster.

After lusting for a project car for too long I recently purchased an 84 CJ7 . Overall it is great condition. It runs well and has very little rust. I've been making my way through it; replacing seats, addressing oil leaks, replacing the plastic valve cover on the AMC256 with an aluminum one, etc.

The jeep sits on 35s with a 4 inch lift. My main concern is increasing the drivability. I don't plan on off-roading it but do plan on taking it to the beach, lake, camping, hauling small sail boats, and general cruising around town on nice days. I have a Tundra daily driver.

To that effect I am considering an engine swap. As it is now, it cruises well on the highway maxing out at ~65mph. In final gear (5th) it loses speed significantly on any type of hill or strong gust of wind such that I find myself driving it in 4th at slightly higher rpm than I'd like for extended periods or constantly shifting between 4th and 5th.

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[Manic Mechanic]

Just regear it. My assumption is who ever did the lift and larger tires never geared for them. Almost any engine swap will cost you thousands maybe even 10s of thousands depending on what you go with and how much your capable of doing yourself.

A few simple upgrades to help with power would be a GM hei distributor for the AMC 258 i6 / 4.2l and a sniper EFI fuel injection. Both will help over stock without digging into your wallet like an engine swap.

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[Citizent3]

Yeah, they absolutely didn't regear it after the lift and new tires. I guess my question is will I be satisfied with the drivability of a properly geared AMC256 on 35s or will it be better but still off? As it stands now it drives great on surface streets but on the highway it can barely get out of its own way such that its borderline hazardous to drive on the interstate. My best bet is tucking in behind the slowest 18-wheeler I can find and hoping I can keep up. I'm not looking for it to perform like a modern car but I assume basic highway road worthiness isn't out of the question.

 

[Manic Mechanic]

It's a AMC 258 i6 / 4.2l not 256. And yes a regear will help out as well as the other upgrades. I run 33s and I can do 80mph on the highway. I do have to down shift and move over going up steep inclines on the mountain but typically I'm rolling with the traffic.

I'm geared for my 31s that I typically run year round (only use the 33s for off roading) but I can still hold highway speeds. Start off by figuring out what axles you have and what gear ratio you have and we can go from there to determine the best setup.

Original should be a wide Trac Dana 30 in front and wide Trac AMC20 in the rear
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[Citizent3]

You're right, it's the AMC 258 i6 / 4.2l I6. Not sure where I got 256 from. I check and get back to you. Thanks for the help.

 

[Manic Mechanic]

Your welcome. I'm sure others will chime in as well.

D.U.I. is pricey but they make a good distributor. I've also run A Team performance as well with good luck. I'm thinking about adding the Holley hyper spark to my sniper EFI setup

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[Belizean]

I went from the AMC 150 4 cylinder and could do usually 60 - 65 mph except in hills or wind with 31s with 3.54 gears in the axels. Now with the AMC 258 i6 / 4.2l with EFI with 31s or 33s and same gears with a 4 speed I have plenty of power. A 5 speed would be better but I’m good enough. I actually like a 2 1/2 inch lift and 33s driving around.

 

[CJ]

An AMC 258 i6 / 4.2l is a pretty strong torquey six cylinder. Geared right you should be able to cruise.

What is your current gear ratio?

How to tell what gear ratio is in your CJ.

There are several ways to determine your gear ratio. Look for a tag on the differential. Pull the differential cover and look for the # of teeth stamped on the ring and pinion. Count the number of teeth on the ring and pinion. Lift the wheels...

jeep-cj.com

Here is the best online gear ratio calculator for final and all gear ratios.
Grim Jeeper gear ratio calculator

 

[Patrick]

Rule out a V8 if you have a T-5 . You will have to keep it a cruiser with that size tire by regearing which is not cheap either. The Jeep smiles start at the 300+ hp mark. Stay green.

 

[Patrick]

Look at KRUXR’s recent content.

 

[NP435]

I had 2.73 gears in the last CJ rendering 4th gear useless on long hills or around town, that jeep was on 31's. The current CJ has 3.73 gears and works well on 33's. No Overdrive in the NP435 it slows on long grades anyway wind enhances the slowing. Were I to do this again I would have a 302 Ford set up for low to mid range torque and 4.10 gearing. If I had 35's lower gears would be a must Imo and some trimming of sheet metal to avoid my tires being nibbled when flexed out.

 

[TSB8C]

Just for reference, I also have an '84 sitting on 35" tires. I also don't do any serious mudding or rock crawling. Mine is a daily driver in Houston traffic. My offroading is similar to what you described: beach, camping, hunting trips, etc. I easily do 80 mph with no issues. I regeared with 4.56, but I also have a 700R4 auto which has Overdrive . At 65 mph I'm right about 2000 RPM. I have plenty of torque and can accelerate into traffic with ease. I had the I6 AMC 258 i6 / 4.2l and swapped to a fuel injected SBC 350. Easy swap, but as Manic said - a bit pricey, but not what it could have been. I homemade the engine mounts, did my own exhaust, used a Novak adaptor for the Dana 300 ; but had to purchase a new radiator, electric fans, have drive shaft lengths changed, etc. And as usual, such an overhaul got me doing other "add-ons" like a twin stick kit on the Dana 300 , scoop and vents on the hood to deal with extra heat, etc. Of course there was also the cost of the engine and tranny themselves as well. If you're happy with the power output of the AMC 258 i6 / 4.2l , do the upgrades others recommended (EFI, HEI, etc) and regear (have to do that anyway for the tire size). IMO ditch the T-5 .

 

[Manic Mechanic]

I have the T-5 behind my AMC 258 i6 / 4.2l . But when it gives out. (When not if) I'm putting an AX15 in it

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[melman]

Hello, long time lurker first time poster.

After lusting for a project car for too long I recently purchased an 84 CJ7 . Overall it is great condition. It runs well and has very little rust. I've been making my way through it; replacing seats, addressing oil leaks, replacing the plastic valve cover on the AMC256 with an aluminum one, etc.

The jeep sits on 35s with a 4 inch lift. My main concern is increasing the drivability. I don't plan on off-roading it but do plan on taking it to the beach, lake, camping, hauling small sail boats, and general cruising around town on nice days. I have a Tundra daily driver.

To that effect I am considering an engine swap. As it is now, it cruises well on the highway maxing out at ~65mph. In final gear (5th) it loses speed significantly on any type of hill or strong gust of wind such that I find myself driving it in 4th at slightly higher rpm than I'd like for extended periods or constantly shifting between 4th and 5th.

My understanding is that AMC256 is a great engine and very reliable and as such an alternative option would be regearing it instead of doing an engine swap.

What would y'all recommend? My preference would be for it to be a little bit more agile on the highway such that I don't feel like an obstacle people are constantly driving around, reliability, an efficiency and assuming the recommendation is to pull the trigger and do a swap, my preference would be for the most straight forward and reliable swap.

Thanks for the help.

 

[melman]

My 84 CJ7 has a 4.0 in place of the AMC 258 i6 / 4.2l with some bolt on horsepower I run 33" and it has 331 gears with the T-5 Transmission , Only the steepest freeway hills require downshifting to 4th gear.
33" tires got me across the Rubicon so why do you need 35" tires when you have a HP issue? mine is mostly stock and does very well on the road

 

[Manic Mechanic]

HP is not what turns the wheels that is what the torque does. It's lack of torque that requires the down shifting in lew of steeper gears

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[TSB8C]

HP is not what turns the wheels that is what the torque does. It's lack of torque that requires the down shifting in lew of steeper gears

But HP sure is fun!

 

[Manic Mechanic]

But HP sure is fun!

Sure is and the long skinny pedal brakes things as well

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[flyn hawaiian]

My 85 CJ7 w/ AMC 258 i6 / 4.2l cid that I had. 4:56-1 gears detroit locker in the rear, true trac up front. 35" tires, 5 speed manual, dui ignition, clifford reshearch headers, clifford reshearsh 4bbl intake, holley 500 cfm 4bbl.. Best damn all around jeep I ever had. Had to sell when wifey got pregnant. Should have sold the wife instead. Bought me another jeep. 30 years later fo my retirement. 78 CJ5 383 stroker and other goodies. mostly fo street use.

 

[flyn hawaiian]

My 85 CJ7 w/ AMC 258 i6 / 4.2l cid that I had. 4:56-1 gears detroit locker in the rear, true trac up front. 35" tires, 5 speed manual, dui ignition, clifford reshearch headers, clifford reshearsh 4bbl intake, holley 500 cfm 4bbl.. Best damn all around jeep I ever had. Had to sell when wifey got pregnant. Should have sold the wife instead. Bought me another jeep. 30 years later fo my retirement. 78 CJ5 383 stroker and other goodies. mostly fo street use.

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