'98 Jeep Wrangler 4.0L to 4.6L with AX15

[dragginwagon406]

My 4.0L gave up the ghost but spared me a the block. One broken piston and three others cracked.

Going to need some help with the details but I have a std/std '87 crank and rods sourced from an engine i picked up for $100.

[dragginwagon406]

Thanks Dino in the other post - this is about the combo I was looking for

4.6L modified "poor man's" stroker

Jeep 4.2L 3.895" stroke crank
Jeep 4.0L 6.125" rods
Keith Black UEM-IC944-020 pistons
9.25:1 CR
Stock 4.0 HO camshaft
Ported HO 1.91"/1.50" cylinder head
Mopar/Victor 0.043" head gasket
0.071" quench height
Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, Accel 24lb/hr injectors with stock 49psi FPR for '96 and later engines
248hp @ 4900rpm, 306lbft @ 3500rpm (with old intake manifold and early HO cam)

A set of H825CP pistons plus a set of 4.2L rods won't cost much less than a set of IC944 pistons ($416 at Summit Racing), so you can still use the longer 4.0L rods to build a budget stroker and there's less need to use the shorter 4.2L rods anymore.

but...

What fuel would this run on?

Can you increase the dish on the 944's?

Are you sacrificing performance by not correcting the quench?

On a side note, is there a table somewhere that has all the pertinent numbers for the common cam choices to calculate DCR?

What Comp Cam would you recommend for a zero decked 4.6L to run on 87? 91?

Sorry to be a pain, I'm dropping off the block, 4.2L crank and 4.0L rods tomorrow. I have the 4.2L rods and even though there were no spun bearings on the crank and all bearings were OEM AMC, the rods and caps did not seem to hold the bearing like the 4.0L rods and caps. Maybe it is the fact the bearings are 24 years old compared to 13. Of course, for comparison sake, I like the oiling groves in the 4.0L rods better (and it doesn't hurt that they are longer to boot for a better rod/stroke ratio). But by any rationale, the 4.2L rods must oil just fine if they made it 24 years without failure.

I'm rambling, retort please.

[dragginwagon406]

I wonder if the additional stroke will make up for the lose of crank weight? I would think the engine should rev quicker though.

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Also started looking at the pilot bearing situation. Both OD's appear to be 1.808", but the 4.0L is about .75" deep while the 4.2L is only about .575" deep. Should I have the machine shop machine the 4.2L pilot housing to match the 4.0L?

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[dragginwagon406]

After a little searching, found that the pilot bearing bridge has already been crossed.

"That Mopar part number crosses over to part number fc-69907 at AdvanceAuto. They wanted about $20 at the store but had it listed as $10.98 on their website. I printed a copy of the web page and they honored the price. It worked fine with my '97 TJ AX-15. Here's a link:

http://shop.advanceautoparts.com/webapp ... 8776582___ "

[basscat]

Draggin,

I'm running the 944's on a zero decked block and it pings it's ass off when the temp gets above about 88 F. I have to run 93 octane with octane booster to quiet things down. I had some cam run-out issues and had to get my cam straigthened by sending it back to 505 performance. In a rush, we assumed they sent the same cam back and threw it in the block without degreeing it. So, my plans are to profile the cam and degree it sometime this summer or whenever I get the chance. Given the crappy service I got from 505, there's no telling what they sent me so my bad for being in a hurry and not checking behind them.

My point is either I have the cam too addvanced or zero decking raised my compression beyond the supposed benefits of a tight quench.

[dragginwagon406]

Good to know. What cam do you have?

[Cheromaniac]

Thanks Dino in the other post - this is about the combo I was looking for

4.6L modified "poor man's" stroker

Jeep 4.2L 3.895" stroke crank
Jeep 4.0L 6.125" rods
Keith Black UEM-IC944-020 pistons
9.25:1 CR
Stock 4.0 HO camshaft
Ported HO 1.91"/1.50" cylinder head
Mopar/Victor 0.043" head gasket
0.071" quench height
Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, Accel 24lb/hr injectors with stock 49psi FPR for '96 and later engines
248hp @ 4900rpm, 306lbft @ 3500rpm (with old intake manifold and early HO cam)

A set of H825CP pistons plus a set of 4.2L rods won't cost much less than a set of IC944 pistons ($416 at Summit Racing), so you can still use the longer 4.0L rods to build a budget stroker and there's less need to use the shorter 4.2L rods anymore.

but...

What fuel would this run on?

I run mine on 87 octane when it's less than 95*F outside despite a 0.088" quench, but I made that possible with scrupulous attention to other details to reduce the risk of pinging:

Cooling system: Stock 2-row radiator, 180* t'stat, flowkooler water pump.
Intake system: Genuine cold air intake, insulated intake manifold.
Polished combustion chambers.
Polished piston dishes.
Tune: Proper AFR adjustment with MAP adjuster.

[dragginwagon406]

Comp is recommending a custom cam:

210/218
477/493
114°
IVC @.050" 35°

Without decking, compression will be somewhere around 9.3, 9.7 zero decked. How does this sound?

[dragginwagon406]

I run mine on 87 octane when it's less than 95*F outside despite a 0.088" quench, but I made that possible with scrupulous attention to other details to reduce the risk of pinging:

Cooling system: Stock 2-row radiator, 180* t'stat, flowkooler water pump.
Intake system: Genuine cold air intake, insulated intake manifold.
Polished combustion chambers.
Polished piston dishes.
Tune: Proper AFR adjustment with MAP adjuster.

Sounds like you have a well sorted combination.

[dragginwagon406]

I will go with a new cam, most likely a custom comp cam as mentioned above. Going to call them and get the IVC at the seat so I can better see the DCR. I'm kind of embarrassed asking for a table of cam specs when they are already in the calculator

Sometimes, you don't notice things until you start clicking.

Slowly filling in the blanks...

Mopar Performance Valve Springs : P5249464
Mopar Performance Valve Spring Retainers : P4452032

My engine is pre 1998 and I have the special camshaft bolt, pin and spring so that should be set. Time to investigate these Crower Cam Saver lifters - what's all the fuss?

Anyone document the difference between the pre-98 vs. '99 and later?

[basscat]

I have the smallest roller cam that 505 makes. The specs are in Dino's chart. I do have plans of ventilating the hood, insulating the intake manifold and running an insulated cold air intake from either the cowl area or the cabin area. I also plan to go back to a Mopar camshaft and regular oil pump. When I swap the cam, I will make sure there aren't any sharp edges in the combustion chamber or on the piston tops.

[Mopud]

It's worthwhile grabbing a new bolt, pin and spring rather than reusing the old one.

[dragginwagon406]

Getting cold feet on the recommended springs...

The Mopar Catalog states "P5249464 Valve Spring, 3.9L/ 5.2L/ 5.9L Magnum Jeep/Truck".

The diameter appears to not match the stock 4.0L spring pocket. Is there machining required? It looks like it is off by about .120".

[dragginwagon406]

Realistically, how much am I leaving on the table by sticking with the HO cam over aftermarket?

[Cheromaniac]

Realistically, how much am I leaving on the table by sticking with the HO cam over aftermarket?

Not as much as you might think. In my case it's something like 8rwhp/12rwtq compared to the Crane 753905 I had originally and I could barely feel any difference by the SOTP at WOT. Under part throttle conditions, the engine actually feels more responsive with the stock cam and gas mileage is also slightly better.

Getting cold feet on the recommended springs...

The Mopar Catalog states "P5249464 Valve Spring, 3.9L/ 5.2L/ 5.9L Magnum Jeep/Truck".

The diameter appears to not match the stock 4.0L spring pocket. Is there machining required? It looks like it is off by about .120".

I used those springs in my original stroker build and they went right in. No machining required to the spring seats. That said, you might as well use the stock springs if you're going to keep the stock cam.