89 Jeep 258 With 4.0 Head Build Update!
Posted: April 4th, 2025, 2:12 pm
Havent been on the forums in awhile but now that the jeep is running I thought I would tune in!
Would like to say thank you for all the info and advice I have read and revived directly from everyone here. It has been a huge learning experience and am excited to drive it until the bottom end enters orbit.
Current Settup:
- 1989 Jeep Wrangler 258, 150k miles, Rebuilt AX15 (syncros went out at 142k)
- 4.0 7120 head: new mopar valves, valve seals, spring retainers, springs, and small shims on the springs. Blocked off coolant ports using the mythical packing peanuts and JB Weld setup.
- 4.0 Banks Manifold. I knew they're known to crack but it sounds great, and whats a jeep without a little exhaust leak?
- TeamRush Upgrade: TFI coil, Ford 300 cap adapter, cap, rotor, wires, stock ignition box (stock box is actually going out, but a new one is 89 dollars vs 260 for a MSD)
- Amazon special MC 2150 Carb. Required some tuning out of the box and lots of vacuum rerouting, but has been pretty solid
- Nutter Bypass
- About 5 different mechanical fuel pumps until I bit the bullet and got an old stock Carter off ebay and has been running great for about 1000 miles.
The power band difference is truly shocking with these upgrades. Better response and power across the entire rev range really woke it up to a different level. The TeamRush upgrade + head work has made the top end of the rev range amazing. It feels like it wants to sing past 4000 RPM, but I haven't and probably will never take it there as it still sounds pissed off to be at that rev in the first place.
When compared to a 4.0, I would say the torque makes it a way more fun weekend warrior and rock crawler. As for highway speeds, its definitely still a 4.2 from 1989.
I can say I have learned a lot and acquired quite a bit more fab skills than I originally had. If you guys have any questions, I'm here! Ill be back when its time for a stroker
Would like to say thank you for all the info and advice I have read and revived directly from everyone here. It has been a huge learning experience and am excited to drive it until the bottom end enters orbit.
Current Settup:
- 1989 Jeep Wrangler 258, 150k miles, Rebuilt AX15 (syncros went out at 142k)
- 4.0 7120 head: new mopar valves, valve seals, spring retainers, springs, and small shims on the springs. Blocked off coolant ports using the mythical packing peanuts and JB Weld setup.
- 4.0 Banks Manifold. I knew they're known to crack but it sounds great, and whats a jeep without a little exhaust leak?
- TeamRush Upgrade: TFI coil, Ford 300 cap adapter, cap, rotor, wires, stock ignition box (stock box is actually going out, but a new one is 89 dollars vs 260 for a MSD)
- Amazon special MC 2150 Carb. Required some tuning out of the box and lots of vacuum rerouting, but has been pretty solid
- Nutter Bypass
- About 5 different mechanical fuel pumps until I bit the bullet and got an old stock Carter off ebay and has been running great for about 1000 miles.
The power band difference is truly shocking with these upgrades. Better response and power across the entire rev range really woke it up to a different level. The TeamRush upgrade + head work has made the top end of the rev range amazing. It feels like it wants to sing past 4000 RPM, but I haven't and probably will never take it there as it still sounds pissed off to be at that rev in the first place.
When compared to a 4.0, I would say the torque makes it a way more fun weekend warrior and rock crawler. As for highway speeds, its definitely still a 4.2 from 1989.
I can say I have learned a lot and acquired quite a bit more fab skills than I originally had. If you guys have any questions, I'm here! Ill be back when its time for a stroker