Maximum Reliability For Harsh Environments and Cheap Fuel

[Musktrat]

My 1996 OBD-II XJ burns oil and needs more power for steep, sandy hill climbs and passing people on the freeway. It's heavy and even with 4.88's/35's it struggles in loose, sandy soil, which is a problem because I live in a desert. A high desert specifically, where temperatures range from 0F in winter to 110F in summer and altitudes range from 3,500 feet feet to 10,000 feet. I'm usually somewhere around 5-6k feet in elevation, and I'm out year round regardless of temperature, but I'm out more often in the freezing cold. The most readily available fuel here is 85 octane, and I need this Jeep to reliably run 85 octane year round because sometimes small gas stations in the middle of nowhere only have 85.

Most stroker recipes these days call for 4.0 rods and forged pistons, but sometimes it takes 30 minutes for my engine to warm up in cold weather, and sometimes it never warms up because I'm running the heater full blast in freezing cold 40mph wind. Letting it warm up before driving isn't an option, especially when I have 200+ miles between gas stations.

I found a recipe for 4.2 rods and off the shelf pistons in an old forum post, but the quench and compression have me hesitant when it comes to running 85 octane in the middle of summer:

Jeep 4.2L 3.895" stroke crank
Jeep 4.2L 5.875" rods
Sealed Power 677CP standard bore pistons
9.2:1 CR
Stock 4.0 camshaft
Ported HO 1.91"/1.50" cylinder head
Mopar/Victor 0.043" head gasket
0.088" quench height
Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines
247hp @ 4900rpm, 300lbft @ 3500rpm

Are there any other recipes out there that aren't terribly expensive? Are there any off the shelf pistons that retain the D shape/squish pad and keep a tight enough quench/low enough compression to run 85 octane in the summer? KB424C sounded good until I realized it's a circular dish. The Silvolite 2229 pistons dished to around 22cc sound viable, but I don't know where to have them dished that won't cost me $750 in machine work, giving me roughly $1,000 pistons to go with my 4.2 rods. Are broken piston skirts with 4.2 rods a genuine concern if I rarely, but do sometimes (ie sandy hill climbs), exceed 4,500 rpm? Will modern forged pistons knock in cold temperatures?

I currently have an extra 1998 short block, 1989 4.2 long block, rebuilt 7120 head, and Comp Cams Xtreme 4x4 197/201 sitting in my garage. I'm getting ready to send out the 4.0 block for machine work and need to know what to tell the shop.

[Cheromaniac]

You could go for the slightly taller Speed Pro H802CP pistons and have 0.020" milled from the block deck. These measures will reduce the quench height but will also raise the compression ratio. Therefore I suggest you polish the piston dishes and combustion chambers to gain as much volume as possible.
Running 85 octane fuel isn't a problem at higher elevations since the lower air density reduces the risk of detonation.

[Russ Pottenger]

You’re welcome to reach out to me and I’ll be happy to send you information on my rotating assembly in recipe of parts.

I offer a Forged Piston and Bushed Steel Connecting Rod Package for just over $1000.00
The benefits of my package is multiple dish volumes to choose from for a Piston with a 1.895 Compression Height you have cost saving option of not having to surface the deck of the block, and with my Bushed Rod you’re able again to save machine shop labor costs of not having to rebuild your cast rods and not having to pay the machine shop to press fit your pistons on your stock rods where with my rods you can hang them yourself.

You’re welcome to reach out to me in an email or phone call and I’d be happy to send you some information.

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]

[75SV!]

One thing I wonder about is, instead of milling the block down 0.020 is to go with a thinner head gasket. Cometic goes down to 0.027 on their site. I know they do custom head gaskets. Also, I look at the build, and I wonder about 9.2 to 1 CR with a .088 quench.
I forget what pistons I used on my mini stroker. I had to grind out to a 59cc combustion chamber and use a 4.00 head gasket.

[Russ Pottenger]

If your piston is .088 from the cylinder head at TDC you’re not affectively utilizing the benefits of a quench