Engine More Power for my CJ7

[oldcj7guy]

1979 CJ7 . I want to replace the AMC 258 i6 / 4.2l with something more powerful. Less than 100 hp and less than 200 lb/ft doesn't do it for me. I want to drive 35's on it and have plenty of torque for off-roading and speed for highways.
I've looked at Golan's 4.6L Stroker. It seems to have the level of power and torque I'm looking for (<300 lb/ft and 275 HP). That one is interesting because little modification should be needed for a swap. But... it costs 10K.
I'm not interested in the LS1 because I don't need that much power and I don't want to have to do a lot of mods.
I'm wondering how much trouble it would be to modify my present AMC 258 i6 / 4.2l to get what I want. Is there a kit? Has someone documented a similar project? Suggestions?

 

[Manic Mechanic]

You could build a stroker motor for much less at your local machine shop. All you need is your AMC 258 i6 / 4.2l crank and rods and then snag a 4.0 from the junkyard. You will need to modify the fuel system or better yet make it EFI work in your Jeep. Machine work and parts should come in around 4ish depending on location and labor rates. There will be other associated prices for parts to make everything work.

On a side note you mentioned about not wanting to do a lot of mods I can tell you even with a stroker and 300 HP that you mentioned your Transmission won't hold up at least not very long.

 

[CJ]

As @Manic Mechanic said, building the I6 is the easy part. It's all the support hardware that you will need to upgrade also. .
You said you want to roll on 35s so you must already have that in mind.

 

[TSB8C]

C'mon - go all the way with V8 power. You can get a brand new under warranty Crate carbureted SBC 350 with 330HP and over 300 ft lbs of torque for about $5K. A set of headers and tranny adaptor for another $1K and you're ready to play. Now EFI on an LS swap or ZZ6 will add a lot more, work and cost, to the equation as you stated.

Regardless of the route you take, a higher HP and torque motor will lose some oomph on 35's if you don't re-gear the axles. I'm running 35's and had 3.54 gears. Hated it. Swapped to 4.56 gears and can now spin those 35's and get off the line quick when needed in Houston traffic.

 

[oldcj7guy]

Sounds like you're saying that I'm going to end up with a 4.0 block if I take this route?
Looks to me that the Golen stroker uses the same AMC 258 i6 / 4.2l block. Check out golenengineservice.com

I do plan to upgrade the whole power train.

 

[Manic Mechanic]

Sounds like you're saying that I'm going to end up with a 4.0 block if I take this route?
Looks to me that the Golen stroker uses the same AMC 258 i6 / 4.2l block. Check out golenengineservice.com

I do plan to upgrade the whole power train.

4.0 block and heads along with your AMC 258 i6 / 4.2l crank and rods would be the cheapest way to get a stroker. Otherwise you have to get a whole new rotating assembly for the AMC 258 i6 / 4.2l to build a stroker adding to the cost.

A V8 would be fairly cheap power added.

BTW stock AMC 258 i6 / 4.2l is rated @AMC 150 . horsepower and 240 lb-ft of torque

Just looked at what they're offering. It's really over priced for that. You could build your own using your block plus an aluminum head for less than 10k and have a better engine. Parts around 5k 3-4k at the machine shop and can be done locally to save on shipping.

 

[oldcj7guy]

Good info. BTW, I'm not sure why we have different power/torque specs. I'm looking at a chart from ProfessCars supposedly based on factory data. Showing peak HP at around 98HP at 3000 RPM and peak torque at around 190 ft-lb at 1500 RPM. What are you looking at?

 

[Manic Mechanic]

The Novak Guide to the AMC Jeep I6 Engine

Information on the AMC Jeep I6 engine

www.novak-adapt.com

 

[oldcj7guy]

Interesting. Looks like the numbers I found are for the AMC 232 i6 rather than the AMC 258 i6 / 4.2l . Given this revelation, I think I'm looking at an LS1.

 

[Manic Mechanic]

LS 1 are getting harder to find id suggested an LS 2 or 3 both can be found in cars and trucks and a lot more plentiful these days. Or even the LS 4

 

[oldcj7guy]

Looks like i'm headed toward an LS swap. Now I need to know the best way to acquire an LS. There's an overwhelming number of options on the internet. Suggestions?

 

[Manic Mechanic]

Is buy a totaled vehicle. That way you get the motor wiring harness etc. then you can sell and scrap what you don't need to recoup some of the money