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258 Engine Replacement |
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19592 |
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The head swap alone doesn't add enough power to be worthwhile, unless you need to rebuild the 258 head anyway. Adding the EFI and manifolds along with the head is worth it! Throw in a bit better cam (at least a stock 4.0L cam... a little better than the stock 258 cam) and it's REALLY worth it! Stock injectors work well, the newer four nozzle injectors improve economy just a bit, probably not worth in unless you need new injectors anyway though.
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Frank Swygert
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DaemonForce
AMC Addicted Joined: Jul/05/2012 Location: Olympia, WA Status: Offline Points: 1070 |
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You already know I'm going to say the 258 is a waste of time. It's easier to do a 4.0L swap or if you want something involved, do a stroker MPFI build like I did and wake that car again. Be careful with cam selection, especially if you have no interest in regearing. Despite final engine displacement, anything with extra tall gears like we saw in the early 80's like 2.72 should handle well on anything mild like the Crower 44242/44243, Comp 68-231-4 or Lunati 63500. If you have 3.08-3.31 gears a Crower 44311, Lunati 63501 or Crane 753941 will do fine. Anything deeper and you're looking at some WILD Crane cams like the 750591 and 751121. You will most likely need to remachine the spring seats if you pick a cam greater than .460 lift but at that point it's the least of your pricing and labor concerns since you'll be on new springs and rockers.
I don't subscribe to single pattern cam logic for these engines so I tend to focus on a narrow selection outside the usual Comp and Isky list that literally everyone else here recommends. There are a TON of cam options for these engines. This 6 is probably the most highly optioned/supported engine in existence to the point that it's a legitimate problem. Since this build concerns a Concord that I assume will be daily driven, all I can say is make sure all of your components get along with one another. No worries.
The stock grey Chrysler-Bendix injectors I've encountered are always leaky laser streaming junk, most likely from a harsh 180K+ life as a neglected daily driver and weekend wheeler. I piecemealed my stroker, going to 238cc Bosch 280155703 injectors commonly found in the Dodge Neon and Plymouth Breeze. They are a 24LB 4-pintle design that runs +4cc over stock but atomizes MUCH better, making this the most responsive engine I've ever seen outside of F1. My injection harness was from a 96 and had the JTEC connectors but I can see some 12-pintle 240cc Ford Focus injectors being used if you have CARS connectors. Probably not much better since the law of diminishing returns is quickly reached when engineering injectors to atomize better but we can all agree that nothing is worse than unresponsive leaky misfiring garbage. An overhaul kit is mandatory. This guy helped me out. Edited by DaemonForce - Feb/06/2018 at 8:22am |
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1971 Javelin SST
American 304 2v | FMX | AM20-3.31 1983 American Limited Jeep 4(.7)L S-MPFI | 1982 NWC T-5M (4.03/.76) | Dana30IFS/35-2.72 |
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vinny
Supporter of TheAMCForum Joined: Jan/05/2012 Location: Calgary Status: Offline Points: 2837 |
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Any difference in coolant or oil levels? Maybe you will get lucky with just a blown head gasket.
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19592 |
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I agree with DF -- the original injectors in a 10+ year old high mileage XJ probably need replacing. I'm running Ford 5.0L injectors in mine -- you can get a set of 8 or about the same price as 6 replacements for the XJ, and they are a little bigger. But if I needed injectors today the Neon four hole injectors is what I'd get. Mine runs great, so will leave them alone. Note that I have a bored out throttle body and a bit bigger cam also...
Isky makes a dual pattern cam, the 256/262. It's a great one if you want dual pattern, and lift is under 0.50" -- the max for stock springs. I caution against anything much over stock for a street engine. You need to use oil additives for a flat tappet cam if much over 300# on valve springs. Mopar performance springs for the 4.0L are good, and I think the Crower AMC I-6 springs are like 330#, about the max you can go and use regular oil with no additives. |
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Frank Swygert
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