AMC Eagle Den Forum
The Mighty 258 => The Engine => Topic started by: Longhunter on July 26, 2020, 01:34:37 PM
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Can you put fuel injection on the 4.2 or can you only put it on the 4.0 head on the 4.2 block?
Sorry for all the questions but as I have stated repeatedly I am not a mechanic. I want to put fuel injection on the Eagle. I am also looking at having the engine and tranny rebuilt. I see several posts here about the goodness of the 4.0 head swap. If I must have the 4.0 head for fuel injection then it is an easy decision.
Thank you.
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Cost of putting a 4.0 head on a 4.2 is realatively easy mod. But it should have a different cam to get more of the benefit; more $. And you should have a 2.25" exhaust system.
Cost of rebuilding a 4.2 and add a 4.0 head and 4.0 cam, compare that against putting a good working 4.0 in that already has a cam for it and fuel injection. Again, 2.25" exhaust system.
You can build a stroker (and a 2.5" exhaust), but how much more would you get over a stock 4.0...
Fuel injection needs a pickup to know the engine cycle position. I don't know if you could get adequate notification for that off a dizzy pickup.
To understand the benefits vs. costs, you're going to have to fully check into 258 rebuild, add 4.0 head, add suitable cam, add EFI, go whole 4.0, go stroker.
start with
http://amceaglesden.com/guide/Technical_Indexes
and under 258
http://amceaglesden.com/guide/How_To_Section
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p.s.
I got an amazing 4.2 rebuild, +0.030, with a 4.0 HO head completely reworked with heavy springs for the valves, and a wider cam, recurved dizzy to match, now a 4.3, hotter coil and ignition module, and its great. Even better with a fake MC2150 but still stock exhaust.
I could have had a 4.0 with a HO head and EFI, for 1/3 to 1/2 the cost of my rebuild, depending on how much of the 4.0 I wanted to replace (timing chain, oil pump, valve job, porting, etc.).
I was just fixated on adding a 4.0 head to a 4.2...
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You can also go with a throttle body style fuel injection. Not as good as using the system from the Jeep 4.0 engine, but a step up from a carb and several options to choose from and it's an easier install. I got a TBI unit from Performance Fuel Injection in my Kammback mated with a 4.0 head and upgraded cam and its much nicer than the stock setup.