Looking to build my 1989 Jeep 4.2. Any info is appreciated

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H3lping
Posts: 9
Joined: June 24th, 2022, 7:34 pm
Stroker Displacement: 4.2
Vehicle Year: 1989
Vehicle Make: Jeep
Vehicle Model: Wrangler

Looking to build my 1989 Jeep 4.2. Any info is appreciated

Post by H3lping »

Hey guys, super new here and after looking through the forms I still have some questions. What I've seen everyone is talking about boring their 4.0 block but I'm interested in keeping the 4.2 block since it's what I already have.
What are the differences between the 4.2 and 4.0 block?
Why not use the 4.2 block as a base?
Seeing that others are using a 4.0 head or summit racing head on their 4.2 block. What are my other options? Boring out the 4.2? Custom pistons ?
Would it just not be worth it and go seek out a wrecked 4.0 and use the block?
Any info is appreciated thanks!!
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Cheromaniac
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Stroker Displacement: 4563cc
Vehicle Year: 1992
Vehicle Make: Jeep
Vehicle Model: Cherokee
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Re: Looking to build my 1989 Jeep 4.2. Any info is appreciated

Post by Cheromaniac »

The difference between using the 4.2 block (3.750" bore) and the 4.0 block (3.875" bore) is the maximum displacement you can achieve with the 4.2 crank. The other drawback with the 4.2 block is the smaller bore causing intake valve shrouding when you bolt on a 4.0 head.
The 4.0 blocks are dime a dozen and cheap as chips, so it's definitely worth using one as a basis for a 4.6/4.7 stroker build. A TJ or YJ block would be preferable as the engine mount bracket bolt bosses would be in the right place to make it an easy swap into the YJ chassis.
1992 XJ 4.6 I6 - 5MT - Stroker build-up, Stroker "recipes" Sold
1995 Mustang GT - 4AT - Modded Sold
2006 Mustang GT - 5MT - Modded Midlife Crisis Car :mrgreen:
H3lping
Posts: 9
Joined: June 24th, 2022, 7:34 pm
Stroker Displacement: 4.2
Vehicle Year: 1989
Vehicle Make: Jeep
Vehicle Model: Wrangler

Re: Looking to build my 1989 Jeep 4.2. Any info is appreciated

Post by H3lping »

Thanks Cheromaniac, just the info I was looking for. Sounds way more worth while just using a 4.0 block ranther than trying to trole out and work with a 4.2 block.
For reference, I'm doing some wheeling but mostly street driving
As for a build I'm sure it's all over the fourms but just to make sure. A 4.0 block and head with 4.2 rods and crank would be a good starter stroker build?
As for doing anything else do you recommend a summit bored head or bore out 4.0 head? Forged pistons? Howell fuel injection or bigger injectors on a 4.0 intake ?
Would it even be worth it to send out the block for surfacing or even a .030 over bore ? Looking for 300 or less hp range
Thanks again for that info
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Cheromaniac
I live here
I live here
Posts: 3180
Joined: March 8th, 2008, 12:58 pm
Stroker Displacement: 4563cc
Vehicle Year: 1992
Vehicle Make: Jeep
Vehicle Model: Cherokee
Location: Cyprus
Contact:

Re: Looking to build my 1989 Jeep 4.2. Any info is appreciated

Post by Cheromaniac »

1. The block deck will definitely need to be checked for flatness and decked if necessary. Same goes for the cylinder head.

2. A cylinder overbore and hone is advised to ensure there's no ovality or tapering of the bores. This will also ensure good ring seal. A 0.030" overbore of the 4.0 block (3.905" bore) combined with the 3.895" stroke of the 4.2 crank would yield a displacement of 4587cc (4.6L).

3. I advise that you use the longer 4.0 rods with custom pistons. Our resident stroker guru Russ Pottenger can supply you with a set of custom.pistons at very reasonable cost.

4. For driveability, fuel economy, and best emissions under all conditions, I'd recommend multipoint EFI. The '99+ "horseshoe" 4.0 intake manifold is best as there's less airflow variability between runners than with the earlier log style manifold. Horseshoe manifolds are dime a dozen and cheap. You could have the 62mm plenum opening bored out to 68mm to accommodate a 68mm throttle body.

5. For performance, a ported #7120 ('91-'95) or #0630 head ('96-'99) would represent best value for money. Therefore try to find a complete engine from a '91-'99 Wrangler ('96-'99 would be better) so you'd have the block, head, and connecting rods that you'd need for your stroker build.
1992 XJ 4.6 I6 - 5MT - Stroker build-up, Stroker "recipes" Sold
1995 Mustang GT - 4AT - Modded Sold
2006 Mustang GT - 5MT - Modded Midlife Crisis Car :mrgreen:
Russ Pottenger
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Stroker Displacement: 4.7
Vehicle Year: 2000
Vehicle Make: Jeep
Vehicle Model: Cherokee

Re: Looking to build my 1989 Jeep 4.2. Any info is appreciated

Post by Russ Pottenger »

Welcome aboard H3,

More than happy to send you out information and pricing on my Stroker Kits and related components.

Hands-down as Dino mentioned a 4.0 based stroker for all the reasons he mentioned is the way to go.

The good news is you could cannibalize your 258 for its crankshaft that will certainly save you a few bucks and get you off to a good start.


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