Newbie Stroker Advice AKA over my head

Performance mods and Advanced Stroker discussion.
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Skyguy2897
Posts: 3
Joined: January 28th, 2025, 12:27 pm
Vehicle Year: 1991
Vehicle Make: Jeep
Vehicle Model: XJ Laredo

Newbie Stroker Advice AKA over my head

Post by Skyguy2897 »

Hi Everybody, Skyler here. I'm a long-time reader, a first-time author. Anyway looking for some friendly advice, I'm mid-rebuilt on my 1991 XJ 4.0 HO been doing lots and LOTS of research into stroker recipes. let me break it down this might take a while.

I've Had this Jeep since I was 15, did basically no maintenance and didn't know anything about cars till I was 21, this jeep was parked in my yard for 8 years while I owned other vehicles, but I've spent the last 2 years and thousands of dollars bring her back from the brink. she had oil leaks and an overheating issue when I got her running again (disappointed but not surprised). Did a full rewiring on all the ignition and battery cables and a full new fuel system except injectors, rebuilt the cooling system, swapped her to 4 corner disc brakes, and replaced all fluids in both diffs, tranny, Tcase, and engine. The system was rewired to take LEDs on all 4 corners and rerouted the power load off the headlight switch. got running good...... till a week later I drove her 10 miles and she puked all the coolant out and overheated like crazy.

Damage report...
Yanked the 4.0 out to diagnose and fix, the head gasket was cracked into the water jacket. I thought it would be a new gasket and good to go, BOY WAS I WRONG! On a hunch, i tore her all the way down to see if there was anything else needing some TLC. The camshaft was shot, lobes eaten up from lifter wear, 2 pushrods clogged with sludge, 1 pushrod very slightly bent, valves pitted from water jacket moisture, and the crankshaft starting to show bearing wear pretty bad, pistons showing bad wear marks. :frustrated:

Build data
Had the idea to just go ahead and do a full stroker rebuild with all new internals, I have an MLS head gasket that I'm cutting for more water passages into the head instead of the stock 2-hole HG. The camshaft I got is a COMP CAM 68-235-4, Pistions are KB 424C.040 with a 27.5cc Dish, I also have the complementing COMP CAM Dual Valve Springs and hardware, and fresh valves. I plan on getting a set of blue top 24#/h injectors, 4.2 crankshaft, Hesco adjustable fuel pressure reg, ALLOYWERKS 3 row 3 electric fan radiator, ARP head studs and stock pushrods.

Advice needed
should I get 4.2l or stock length 4.0 connecting rods? my goal is reliable power and highway drivability in the TX panhandle while still running 87 or 89 octane. I'm trying to stay away from premium fuel so that I can save a little money for the fast car. I've tried using the CR calculator on here and it keeps saying 10:1 is that correct, would that be too much for a port and polish HO head? Any other things I'm not thinking about that I should keep in mind? Any and all advice is greatly appreciated. :cheers:

TLDR: lots of research done but still feeling a bit overwhelmed and cautious.
Lemme get a hell yeah :rockout: - SKYLER
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amcinstaller
I love JeepStrokers.com!!
I love JeepStrokers.com!!
Posts: 623
Joined: May 22nd, 2008, 11:57 pm
Stroker Displacement: 4.6L
Vehicle Year: 1980
Vehicle Make: AMC
Vehicle Model: Spirit
Location: Red Deer, AB, Can

Re: Newbie Stroker Advice AKA over my head

Post by amcinstaller »

Couple things:
Your piston choice dictates your rod choice. If you got stock style pistons, use the short rods. If you got stroker intended pistons, use the long rods. Double check part numbers. If you are using short rods, you will have to deck the block down to get the quench better.

Read up on your valve springs, some people like to run a little less spring pressure to help cam lobes live longer

I'm sure Cheromaniac will chime in at some point, he still checks in from time to time :cheers:
1980 AMC Spirit Restomod
4.6 stroker/ax15/Ford 8.8
SilverXJ wrote:Roller rockers won't help that mess you have created. Nor will God for that matter.
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Cheromaniac
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I live here
Posts: 3229
Joined: March 8th, 2008, 12:58 pm
Stroker Displacement: 4563cc
Vehicle Year: 1992
Vehicle Make: Jeep
Vehicle Model: Cherokee
Location: Cyprus
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Re: Newbie Stroker Advice AKA over my head

Post by Cheromaniac »

Indeed I do even though I reluctantly sold my beloved '92 XJ eight years ago.

1. The KB424C pistons have a 1.353" compression height and must be paired with 4.0L connecting rods.

2. According to my calculations, the static compression ratio will be an 87 octane friendly 8.73:1 (assuming 57cc combustion chamber).

3. The quench height comes in at a not good 0.070" since the pistons end up 0.027" down the hole at TDC. I'd recommend decking 0.020" from the block to reduce the quench to a much better 0.050". This will increase the static CR to 9.05:1 which is still 87 octane friendly and provide a slight performance gain.

4. Your choice of Comp cam 68-235-4 is a bit too aggressive for a low compression motor. A milder cam such as the 68-501-5 or even a stock replacement Melling MC809 would be a much better choice, and both can be used with the stock valve springs.
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 :lol:
Skyguy2897
Posts: 3
Joined: January 28th, 2025, 12:27 pm
Vehicle Year: 1991
Vehicle Make: Jeep
Vehicle Model: XJ Laredo

Re: Newbie Stroker Advice AKA over my head

Post by Skyguy2897 »

Cheromaniac wrote: January 28th, 2025, 11:27 pm Indeed I do even though I reluctantly sold my beloved '92 XJ eight years ago.

1. The KB424C pistons have a 1.353" compression height and must be paired with 4.0L connecting rods.

2. According to my calculations, the static compression ratio will be an 87 octane friendly 8.73:1 (assuming 57cc combustion chamber).

3. The quench height comes in at a not good 0.070" since the pistons end up 0.027" down the hole at TDC. I'd recommend decking 0.020" from the block to reduce the quench to a much better 0.050". This will increase the static CR to 9.05:1 which is still 87 octane friendly and provide a slight performance gain.

4. Your choice of Comp cam 68-235-4 is a bit too aggressive for a low compression motor. A milder cam such as the 68-501-5 or even a stock replacement Melling MC809 would be a much better choice, and both can be used with the stock valve springs.
Awesome I appreciate it guys, I was confused by different things I've read up on for rods, I plan to deck the block and head as necessary to make em dead flat. Unfortunately, I already have the cam kit that I got a smoking deal on, what issues would I run into if I go ahead and run it, or should I go ahead and bump up the compression on it? I can't afford to blow it up and get a new block.
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Cheromaniac
I live here
I live here
Posts: 3229
Joined: March 8th, 2008, 12:58 pm
Stroker Displacement: 4563cc
Vehicle Year: 1992
Vehicle Make: Jeep
Vehicle Model: Cherokee
Location: Cyprus
Contact:

Re: Newbie Stroker Advice AKA over my head

Post by Cheromaniac »

If you haven't already bought the pistons, I suggest you contact Russ Pottenger and get a set of his custom pistons. He has various dish sizes and I'd suggest bumping the CR up to the mid 9's. His pistons are taller than the KB units and this would save you the cost of decking the block.
Skyguy2897
Posts: 3
Joined: January 28th, 2025, 12:27 pm
Vehicle Year: 1991
Vehicle Make: Jeep
Vehicle Model: XJ Laredo

Re: Newbie Stroker Advice AKA over my head

Post by Skyguy2897 »

I may have jumped the gun a bit on buying some of the parts, I didn't even know about Russ till after I had started getting deep into this, but I am planning on decking it anyway since it will already be in there for a bore and head work. Now the hard part is finding a machine shop that isn't a fortune, my local shop quoted me $1200 minimum, so it's about time I call around to see if anybody cheaper is around maybe in Dallas or Hobbs. I'm also going to see if I can get in contact with Russ to pick his brain a bit so I can start putting the money pit together. :rockout:
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