stock rebuild vs 4.6L Low-buck, low CR "rockcrawler"

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i82much
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Joined: July 9th, 2022, 5:08 pm
Vehicle Year: 1997
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stock rebuild vs 4.6L Low-buck, low CR "rockcrawler"

Post by i82much »

Hi all,

I have a 97 TJ with a 4.0, 3.07 open diffs, and 32rh. Engine has 210k. I am thinking about the merits and costs of a stock rebuild vs a very basic stroker. If I intend to completely rebuild the 4.0 anyway, how much more will it cost to go with a stroker?

Apologies if this is covered elsewhere. Also curious about durability of the strokers, do you see these lasting 100k plus miles?

Thanks!
Randy Bobandi
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Re: stock rebuild vs 4.6L Low-buck, low CR "rockcrawler"

Post by Randy Bobandi »

i82much wrote: July 9th, 2022, 5:13 pm Hi all,

I have a 97 TJ with a 4.0, 3.07 open diffs, and 32rh. Engine has 210k. I am thinking about the merits and costs of a stock rebuild vs a very basic stroker. If I intend to completely rebuild the 4.0 anyway, how much more will it cost to go with a stroker?

Apologies if this is covered elsewhere. Also curious about durability of the strokers, do you see these lasting 100k plus miles?

Thanks!
Minimum cost difference is the price of a crankshaft, fuel system and tune. You would probably have the stock crank journals touched up at the machine shop so you can subtract that $120 from the 3.895" stroke crank cost. "Low-buck" is what Jeep straight 6 strokers are all about. I'm not sure if there is any other engine platform that makes more power per dollar. Low dollar LS truck motor builds are long a thing of the past.

The only issue with the "low buck" mentality is when you get to fuel and tuning. There are way too many good folks spending all this time building a sweet motor just to run it with tiny injectors and a stock tune. Folks get their stroker Jeep on the dyno just to see it make 180 HP. The tuner says "bro what did you expect with 24# injectors, a stock fuel pump and a stock ECU?" So if your willing to change a fuel pump, injectors and have the Jeep tuned; build the stroker, pop wheelies and burn 35" tires to the ground. If not, nothing wrong with the stock displacement engine, excellent engine. You have a strong transmission that can handle much more than stock power. You don't have a Dana 35 in the rear do you?

Durability? If the engine is built properly, the only difference from the longer stroke is piston speed. The golden rule for reliability is to stay under 4000 Ft/M at 6000 RPM. The stroker pistons at 6000 RPM reach 3895 Ft/M. Pretty safe and really, how often will you have the engine ripping at 6000 RPM. Whether stock or otherwise, the engine will be as reliable as the build quality. You'll hear stories about every engine platform failing after a rebuild. There's a reason for it. It's either a poor understanding of engine building/machining or parts failures.
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Cheromaniac
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Re: stock rebuild vs 4.6L Low-buck, low CR "rockcrawler"

Post by Cheromaniac »

Randy's covered it pretty well.
Yeah, the only extra costs associated with the stroker are the 258 crank, custom pistons, and higher flowing injectors. The good news for you is the JTEC PCM in your '97 TJ is programmable so you can have the fuel and timing curves optimized to make maximum power. [email protected] (real name Chris Jensen) is THE man to contact for that task.
A properly built stroker with good quality parts should last over 100k miles. Many have failed prematurely either because of poor machine shop work, poor quality or mismatched parts, mistakes made during assembly, or improper cam break in. As long as you avoid those pitfalls the engine will live a long and happy life.

4.6L Low-buck, low CR "rockcrawler"

Jeep 4.2L 3.895" stroke crank
Jeep 4.0L 6.125" rods
Custom forged +0.030" bore pistons, compression height 1.380", dish volume 32cc
8.8:1 CR
CompCams 68-115-4 192/200 degree camshaft
DIY ported HO 1.91"/1.50" 57cc cylinder head
Mopar/Victor 0.043" head gasket
0.043" quench height
Bosch 0280155703 injectors for '96-'04 engines
242hp @ 4600rpm, 317lbft @ 3000rpm

The build you're contemplating is pretty simple really.
To get the most out of it you'll need external bolt on upgrades to help those bigger lungs inhale more air i.e. true cold air intake, 62mm TB, header, 2.5" high flow cat, 2.5" cat back exhaust. An '00+ intake manifold will also deliver a slight improvement in midrange torque and fuel economy.
FWIW my 4.563L poor man's stroker with a 9.3:1 CR put down 200rwhp & 258rwtq, equivalent to 246hp & 311lbft at the crank.
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:
i82much
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Re: stock rebuild vs 4.6L Low-buck, low CR "rockcrawler"

Post by i82much »

The additional costs do not sound prohibitively expensive. I've read about a lot of problems with the strokers but for the most part they sound like the kind of issue that can be mitigated by finding a good engine builder and paying careful attention to compression ratio, quench, clearances, that sort of thing.

I would run a cam with very gentle lobes, I think the one suggested above is a high energy grind and those are usually pretty mild. I am not at all concerned with making lots of power, just curious whether a stroker makes sense if a rebuild is in order.

I run open diffs and 235/75r15 tires. I just futz around on forest roads in north Idaho, I'm not going to run lockers or be hard on the throttle. So I think the D35 will hold up fine. I'm more interested in setting up trail cameras than climbing over rocks.

The only other concern I can think of is cooling. I could imagine creeping along uphill at 5 mph on a 105 degree day with the sun beating down might tax the cooling system with the bigger engine. Do people usually need to upgrade the radiator or fan clutch to keep these things cool?
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Re: stock rebuild vs 4.6L Low-buck, low CR "rockcrawler"

Post by Cheromaniac »

A thicker aluminium radiator plus an electric fan with shroud that's big enough to cover the radiator should keep the engine cool and happy.
275/350 I-6
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Re: stock rebuild vs 4.6L Low-buck, low CR "rockcrawler"

Post by 275/350 I-6 »

When I built my engine I used a water pump from the local
FLAPS, nothing special at all.

I had my OEM radiator repaired at the local radiator shop, he pressured testing it, fixed a couple leaks, and repainted it. Nothing special here either, it didn’t absolutely need a re-core, so we didn’t do it.

I replaced the clutch on my OEM clutch fan. My Jeep has the HD cooling system and an automatic transmission. I run 31’s on the stock suspension and 273 gears.

My engine runs as cool or cooler than my old 258 inline six.

Based off my experience, these engines run fine for daily driving, even in the heat of summer idling at the drive through window, my engine runs cool in the heat.

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i82much
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Re: stock rebuild vs 4.6L Low-buck, low CR "rockcrawler"

Post by i82much »

great, thanks all! now i need to go blow the 4.0 up so i have an excuse!
275/350 I-6
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Re: stock rebuild vs 4.6L Low-buck, low CR "rockcrawler"

Post by 275/350 I-6 »

Get the compression and quench right so you can run 87 octane pump gas.

You will be happy with the results.

I suggest you call Russ and work out a plan. His rods and pistons are nice, and they got my compression and quench where needed for 87 octane. My engine has instant throttle response, and makes the Jeep a joy to drive.

If you are going to rebuild your worn out 4.0, I recommend you definitely stroke it, you will not be sorry.
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Torqsplit
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Re: stock rebuild vs 4.6L Low-buck, low CR "rockcrawler"

Post by Torqsplit »

I ran the original D35 w/ my stroker w/ 165k miles on it for another HARD 35k before the spider gears let go. It was 3.07 open diffs then, w/ 31's & AX15. You'll have a great time with 235's and almost no concerns for durability if you're driving easy. put some fresh gear-oil of your liking in diff and cruise on 👍 Like 275/350 mentioned, very little issues with cooling, even while wheeling in the mtns. If you're current cooling system is healthy, i wouldn't spend any extra $ until you see how it does. Might not need anything - 🍻
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