Piston Slap: Is 4.6 Liters of Juice Worth The Squeeze

Phil writes:

My 1988 4×4 4.0L Jeep Comanche needs a ring job and the 2nd gear synchro is weak in its Peugeot 5-speed gearbox (with replacement no longer available). I figured I might as well stroke it and swap to the later Aisin tranny, but I am having trouble finding a shop with experience in this kind of work on Jeep XJs/MJs in the Dallas area.

The truck is a really nice, very original, 105k survivor, but I am not sure about the value proposition of spending this money.

Sajeev answers:

From what I have researched, you should absolutely do the Aisin gearbox swap and the 4.6-liter stroker in your rebuild. The question of it being worth the money is relative to your need to make a profit after you are done with the Jeep, and the time value of money. I don't see either being a big concern for you, as the swaps seem readily available. Correct me if I'm wrong, but reading between the lines, the issue is ensuring you get them done with the right parts and by the right people.

I reached out to Hagerty's own Davin Reckow and Ben Woodworth to discuss their efforts in creating a 4.6-liter Jeep XJ for our Redline Rebuilds video series. The wrap-up video is below.

You should watch the whole video, but the most relevant bits to this Piston Slap question are 64 minutes into it when Davin and Ben share their thoughts about the difficulty of the 4.6-liter stroker rebuild. But since these guys are my co-workers, I figured it'd be wise to ring them up, tell them about Phil's situation, and get their candid feedback. So let's start here:

"Yes its worth it, because we noticed the Jeep will now pull hills in 5th gear. It's crazy, and it's a very noticeable difference."

- Davin Reckow

"It has a noticeable increase in the amount of torque when driving, which is sorta the point of doing a stroker. She pulls hard even in 5th gear. And she's equally at home around town as well as 75mph on the highway."

- Ben Woodworth

I asked Davin about the details (most of which are in the video above) and he verified that the work to install the stroker kit is "nothing special", just prep the block as-is: There is no clearancing needed for the crankshaftas you might expect with a small-block Chevy. The AMC 4.2-liter crank has a different snout, but that's a minor hurdle to overcome. To get 4.6-liters, you must buy the correct formula of AMC 4.2-liter and Chrysler 4.0-liter crank, rod, and pistons, but from there, it's a bolt-in affair. (This is also documented in the above video.)

Davin also reminded me that there are plenty of stroker kits available online to remove the guesswork, but he insisted that everything in the video was purchased from Rock Auto. (A glance at their inventory suggests some items might be out of stock in July 2024, but part numbers are still given and might be sourced elsewhere.)

But wait, it gets even easier: Davin was going to add a higher flow fuel pump, bigger injectors, and an ECU re-tune, but none of it was needed to support their 4.6-liter swap. He did need to drill a small (1/8th inch) hole in the butterfly of the throttle body, because the new engine produces too much vacuum for smooth throttle inputs from idle.

Matt Tierney

One thing I've learned in my 15+ years of restomodding is that the less you need that diverges from factory engineering, the better off you are for a daily driver and/or a mild restomod. So my brief time with Davin on the phone was good news indeed.

While I am many miles from the Redline Rebuild garage in Traverse City, I am confident in assuming this torque monster 4.6-liter would be ideal for your needs in Dallas. The final question is probably at the heart of your concern: can you trust someone to do this for you?

Probably not. Instead, you must consider yourself a General Contractor, farming out tasks to specific businesses and making sure it all comes together in the end. Davin and crew wholeheartedly recommend Thirlby Automotive's machine shop, as they made it work for Redline Rebuilds for multiple projects. They might be game to ship you one of these engines if you can't find a suitable place in the DFW area.

The transmission is another pay-and-ship affair, and make sure you get everything needed before installation. From there a place like RockAuto will have all the ancillary stuff like hoses, clutch, water pumps, and anything else that should be replaced before the motor is installed. (Especially anything made of rubber!)

For me, this is a buy once, cry once type of deal: replace everything you can with high-quality, brand-name parts. If you are a shade-tree mechanic that can get these parts delivered to your home and get it all installed in a few weekends, that's great! If not, you have another step: Performing a Google Near Me search for a good independent mechanic that specializes in older vehicles.

Or find a quality shop that at least tolerates them and works them between their usual rotation of newer, more profitable vehicles to repair. If that last sentence doesn't make sense, going on a few "first dates" with local shops will make it very clear who will and will not be fair and pragmatic with your plan for a stroker motor and a transmission upgrade.

Keep us in the loop on how it goes. And for the Hagerty Community, what advice do you have for Phil and his Comanche?

Have a question you'd like answered on Piston Slap? Send your queries to [email protected]-give us as much detail as possible so we can help! Keep in mind this is a weekly column, so if you need an expedited answer, please tell me in your email.

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