4.0 on a 4.2 Options
Rescue Diver
Full Time Jeeper
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- 1979 CJ-7 with a fiberglass body and 1982 wide track axles, 258 I-6 with a 1995 4.0 head, HEI distributor, Motorcraft 2100 Carb, T-18 wide ratio tranny, Super Lift Springs and 33s, a 1997 BMW 328i, and a 2010 REDLINE CONQUEST TEAM Cyclocross Bike. :)
Everyone says there is significant HP gains to be had by putting a 4.0 head on a AMC 258 i6 / 4.2l . What years will fit, and what intake and exhaust manifolds will work?
I have a pre 1981 AMC 258 i6 / 4.2l and I've been told that a 1994 4.0 head is a direct bolt on for my shortblock with just a few issues with the power steering bracket. In keeping with my keep it as simple and cheap as possible theme, I'm still wanting to stay in the stone ages with a carb instead of fuel injection. I know my pre 1981 intake and exhaust manifolds won't bolt up to a 4.0 head, but will an intake from 1982 or newer AMC 258 i6 / 4.2l work on a 4.0 head?
What kind of HP gain can I expect with a 4.0 head swap that's still carbed? My stock 1bbl AMC 258 i6 / 4.2l is rated at 110 hp. I've read that I can expect about 140 hp with the 4.0 head. Can anyone back this up with real experience?
I'd like to install a later model 4.0 head with a 2 bbl carb and intake.
For gas mileage I want to keep my stock 354 gears and I'm running 33" tires so it's currently a little gutless on the highway. I can maintain 65 or 80 mph with my foot on the floor depending on which way the wind is blowing.
I have a pre 1981 AMC 258 i6 / 4.2l and I've been told that a 1994 4.0 head is a direct bolt on for my shortblock with just a few issues with the power steering bracket. In keeping with my keep it as simple and cheap as possible theme, I'm still wanting to stay in the stone ages with a carb instead of fuel injection. I know my pre 1981 intake and exhaust manifolds won't bolt up to a 4.0 head, but will an intake from 1982 or newer AMC 258 i6 / 4.2l work on a 4.0 head?
What kind of HP gain can I expect with a 4.0 head swap that's still carbed? My stock 1bbl AMC 258 i6 / 4.2l is rated at 110 hp. I've read that I can expect about 140 hp with the 4.0 head. Can anyone back this up with real experience?
I'd like to install a later model 4.0 head with a 2 bbl carb and intake.
For gas mileage I want to keep my stock 354 gears and I'm running 33" tires so it's currently a little gutless on the highway. I can maintain 65 or 80 mph with my foot on the floor depending on which way the wind is blowing.