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Kind of depends on your goals. Are you looking for better street performance, or racing, or better fuel economy with decent performance, etc?
I do have to halfway backtrack about not recommending the 3.9 Dakota, Ram truck and Van (locations to find one) engine, I was thinking the first V8 was in 1965, not 1964 (it was the 273), so it would be a direct drop-in, no cutting required, but the only caveat is that I think the 3.8 is a little more fuel efficient. Might be a little different story once the 3.9 is in a car instead of a brick with wheels, 19-21mpg is the best I have ever seen with the 3.9 in a Dakota, I know the minivans with the 3.8 are in the mid 20s easy, and I think your Valiant is a little more aerodynamic and lighter, which helps.I would recommend the Dakota 3.9L and either a 5spd MT or 4 Spd AT, would be an easier swap because it's going to share more with what's already there.. It's already based off the 318; and the entire harness and computer can be grafted in and powered up with quite a bit less work than the newer Jeep parts.. Just my opinion though..
I still need to know what will fit in my engine compartment. Also, does anyone know what Crank bolt patterns the 3.5 and 3.6 have? I need to figure out a flywheel.I have a '64 Dart conv. that I want to update with a v6 and 5 or 6 sp. manual. Where can I get dimensions, weights and vehicle models using the various engines. Also any engines with specific problem areas?
I decided to go with a 318 Magnum from a 1998 Grand Cherokee. I'm giving it F-A-S-T injection and a Keisler 5speed. I'm also changing to a Magnumforce K-member with power r&P, coil-overs and 4 wheel discs on an 8 3/4 with 2.93 gears. Like I said, I don't want fast, just a good cruiser for the canyons. Right now the poor thing is stripped down and we're just ready to trial fit the tranny. By the time we're done the only original pieces will be the sheetmetal and glass. Wish me luck. I've waited all my life to build my own car and this will probably be the one and only.The 3.9 will fit, if a 318 or 273 fits, it will fit. 3.8 V6 has been a very strong and durable engine, some rocker arm problems in the first couple years, not a problem for more than 20 years. With the 3.8, you need to use the flywheel and transmission out of a Jeep, last couple years they have had this 3.8 as RWD, which is a problem with the other V6 engines, but there is the Dakota 2.5 that is a 5speed ( I will be using one of these in a 63 TR4 Triumph in the future), and pretty sure the 3.5 will fit, charger sedan, Magnum, 300 and Challenger all have available transmissions for RWD in that department.In all these applications, I would recommend getting the full wiring harness and fuel system so as to match the whole package before modifying any, but in all cases, more power than what you have right now, and equal or better mileage, too. No idea on the 3.5 flywheel bolt pattern, someone else will have to answer whether or not there was or is a manual transmission offered with the engine, I haven't seen one, but there may be something out there, possibly Keisler.
Hi Calvan. Did you investigate the possibility of retaining the stock MPI, and how much of the Jeep's underhood 'junk' that would need to be brought with it? I also have a 1998 XJ 318, destined for a 49 Plymouth coupe. I am thinking it will be cheaper, parts-wise, to do this. As opposed to buying a manifold and aftermarket TBI or carb. (And ignition, and, and, and?). If I do settle on the aftermarket TBI, do you have any advice? What did you use for a manifold, fuel system, ingnition? Was the FAST solution as easy as it is sold as? Are you happy with the performance?I decided to go with a 318 Magnum from a 1998 Grand Cherokee. I'm giving it F-A-S-T injection and a Keisler 5speed. I'm also changing to a Magnumforce K-member with power r&P, coil-overs and 4 wheel discs on an 8 3/4 with 2.93 gears. Like I said, I don't want fast, just a good cruiser for the canyons. Right now the poor thing is stripped down and we're just ready to trial fit the tranny. By the time we're done the only original pieces will be the sheetmetal and glass. Wish me luck. I've waited all my life to build my own car and this will probably be the one and only.