junkyard jim
Well-Known Member
(this was originally a reply to someone who asked me about the 4.)L swap on a 4.2L)
There is a guy near me who worked over a 4.2L head and is now selling it (I bought my aluminum valve cover from him 2 weeks ago to replace the leaky plastic one)
Plastic valve cover is one of the major reasons to swap heads. Some years of 4.2L head bolts are 7/16" on the 4.2L and the rest are 1/2" like the 4.0L.
I have one Renix head to do for my '82 AMC Spirit which has the 7/16" bolts (one is snapped off already) .The main reason for my swap is the factory header and getting it ready for EFI swap.
HO vs Renix
The whole HO vs Renix is pretty much BS. There is maybe a 10% increased flow with the HO, but the 75 HP everyone talks about is gained from a number of different things Mopar changed.
Same cam on both, but HO cam timing is retarded to do away with the EGR valve (reduces NOx) and it moves the power band up in RPM and that automatically increases the torque as well. Larger injectors (I put HO injectors in my Renix rig and it was WAAAAY stronger, but I couldn't pass as many gas stations so I pulled them)
The HO factory header flows a bit better too than Renix too, but both are better than the cast exhaust (especially pre '81). The Banks header is nice, but I have other things to spend money on to get more bang for the buck and as long as I have both stock trans hangers on the pipe, I haven't had one crack yet.
I'm doing a 2WD AW4 swap at the same time as the EFI in my Spirit. Then the Jeep 4.6L stroker in my garage is awaiting my '84 J10's buildup this summer!
There is a guy near me who worked over a 4.2L head and is now selling it (I bought my aluminum valve cover from him 2 weeks ago to replace the leaky plastic one)
Plastic valve cover is one of the major reasons to swap heads. Some years of 4.2L head bolts are 7/16" on the 4.2L and the rest are 1/2" like the 4.0L.
I have one Renix head to do for my '82 AMC Spirit which has the 7/16" bolts (one is snapped off already) .The main reason for my swap is the factory header and getting it ready for EFI swap.
HO vs Renix
The whole HO vs Renix is pretty much BS. There is maybe a 10% increased flow with the HO, but the 75 HP everyone talks about is gained from a number of different things Mopar changed.
Same cam on both, but HO cam timing is retarded to do away with the EGR valve (reduces NOx) and it moves the power band up in RPM and that automatically increases the torque as well. Larger injectors (I put HO injectors in my Renix rig and it was WAAAAY stronger, but I couldn't pass as many gas stations so I pulled them)
The HO factory header flows a bit better too than Renix too, but both are better than the cast exhaust (especially pre '81). The Banks header is nice, but I have other things to spend money on to get more bang for the buck and as long as I have both stock trans hangers on the pipe, I haven't had one crack yet.
I'm doing a 2WD AW4 swap at the same time as the EFI in my Spirit. Then the Jeep 4.6L stroker in my garage is awaiting my '84 J10's buildup this summer!
