Stock 4.0 vs. 4.2 w/ 4.0 head

[MasonMcK]

First off I'm not quite sure if this is the right place for this or not so I'm sorry if it isn't.

Secondly, this may seem like an interesting question, but how does the performance compare between a stock HO 4.0L vs. a 4.2L with a high output 4.0L head with fuel injection? Basically my delemia is I need to replace the motor in my 1995 Jeep Cherokee Sport since it overheated and I would like to gain a bit of power while I'm at it. Would it produce more HP if I were to swap the bottom end of a 4.2L into my jeep topped with the top end of a 4.0L with the stock jeep MPI? Or is there something seriously wrong with the 4.2L blocks that would make it not an upgrade over the 4.0L?

Thanks guys,
-Mason

 

[cal]

No.

The 4.2 is a small bore long stroke motor. All torque, no horsepower.

The 4.0 is a big bore small stroke motor. A lot more power, a little less torque.

Your swap would be a net loss - also not a strait forward swap - the water passengers don't all line up correctly, so there is some epoxy work involved.


You *could* do your 4.0 block, 4.2 crank and rods, 4.0 pistons, and 4.0 head, and get a little bit more - but without doing a full engine rebuild, cam, etc etc there's not enough gain to make it worth what you would go through.

Start here:

https://www.jeepstrokers.com/forum/viewtopic.php?t=645

If you think a stroker option might be for you, call Russ Pottenger at Bishop Buehl racing engines and talk to him about his low buck DIY stroker kits.

Bishop-Buehl Racing Engines
531 N. Lyall Avenue
West Covina, California 91790
Work (626) 967-1000
Fax (626) 967-7836
Cell (626) 673-2203
Email/PayPal: [email protected]

 

[Ben824]

I second calling Russ. There is no cheap way to dive into an engine I will say. When my engine gave up May of 2015 I was determined to do a stroker. But after all the research I did and spending about 2 hours total on the phone with Russ, I realized in order to do a reliable build, more money would have to be spent on it that I was able to drop on it. I got an amazing deal of $850 on a fully rebuilt no mileage engine from someone in one of my local Jeep groups. You would be better off picking up a decent used 4.0 locally for a few hundred bucks and then take your old engine and slowly rebuild it using Russ's low compression stroker recipe. He said with the recipe he has put together for a low compression stroker, you can still achieve around 285 HP and 300+ torque.

 

[MasonMcK]

For some reason I was under the impression that the 4.0 and the 4.2 had the same size bore and just different strokes. But that makes sense. I'll prob give him a call and see what he has to offer. This won't be my first engine rebuild so I will probably pull my engine and do a 4.7L stroker build on it since the #1 cylinder is more than likely worn. Since I will be going through the trouble of pulling the motor I may as well build it right and make it last at least another 165k miles. Plus the added power is definitely welcome. Btw, what other CID stroker kits are available for the 4.0L btw? Are they equally reliable? Because I am all for almost 300hp in my Cherokee. Thanks for the clarification guys.
-Mason

 

[Ben824]

For some reason I was under the impression that the 4.0 and the 4.2 had the same size bore and just different strokes. But that makes sense. I'll prob give him a call and see what he has to offer. This won't be my first engine rebuild so I will probably pull my engine and do a 4.7L stroker build on it since the #1 cylinder is more than likely worn. Since I will be going through the trouble of pulling the motor I may as well build it right and make it last at least another 165k miles. Plus the added power is definitely welcome. Btw, what other CID stroker kits are available for the 4.0L btw? Are they equally reliable? Because I am all for almost 300hp in my Cherokee. Thanks for the clarification guys.
-Mason

Call Russ for sure then! He has been reliably making power with the Jeep straight six for over a decade and even longer building engines. He was one of the pioneers of using bigger LS valves in the Jeep cylinder head to get more air flow! He has a perfect low buck low octane stroker that you will like. All the other kits out there are off the shelf combination of parts and most bump the compression up and require you to run premium fuel. Russ takes Keith Black Silv-O-Lite pistons and mills the dish out to 28cc to bring the compression down to run 87 octane fuel. Other kits will just supply a thicker head gasket to knock down the compression ratio if you want to run 87 octane. But doing that increases the quench height and kills all your power potential. Russ knows better so he dishes out the pistons more. Some people aren't a fan of Keith Black pistons but he has had good success with them on street motors and he likes them because they are made with a lot of extra material in them that allows him to mill them out without compromising the structural integrity of the piston.

 

[cal]

There are definitely other builders and kits out there, but Russ puts more thought into his, and every engine is custom to your needs, instead of telling you to pick template A, B or C. He's built strokers from the mid 200 horses to the mid 400 horses, and from commuter to full race style builds.

If you've built your own engines before, he sells kits where he sends you a head and rotating assembly, you get a block machined locally and build it yourself - and it is surprisingly affordable.

We have raced on IIRC 5 different engines of his, and can't say enough good things.

 

[MasonMcK]

This sounds great! I emailed Russ last night to see what he has to offer. With any luck I will get the engine pulled this coming weekend but we will have to see how that goes. Now with a 4.7L stroker producing 250-300+ hp will I have to beef up my clutch, transmission, or transfer case any? I have the AX-15 5 speed with the NP231 T-case. Not worried about my axles though because the sooner they blow up the sooner I have an excuse to swap better ones in. Lol.

-Mason

 

[cal]

Not unless you plan on getting really stupid, no. Other people aren't having problems with them.

 

[David_Bricker]

I'm running a 4.6L stroker Russ built for me a few years ago. He will build what you need. The motor in my heep couldn't be more different than the motor in Cal's, yet both built from the same stock.

I've got the LS1 valves, ported, polished, CCed, balanced, etc. No clue as to overall power, but as one person who has driven it, it is "unstallable". So, Russ can build the low end torque motors, or the high HP, high RPM motors.

My son just bought a DYI kit from him. Not built yet, but I expect great things from it as well.

David Bricker / SYR