how hard would it be to go from a 2.5 4banger to a 318? what parts would be necessary to do this? would it be very expensive? any help would be great. thanks.

2.5's might need brackets.

Other than that, motor mounts, tranny, flexplate, converter, driveshaft, wiring harness, brain box, radiator, clutch fan, shroud, exhaust, maybe front springs i dont remember if the 4cyl and v6 are the same. Hoses, maybe rear axle, depending if you have the smaller one if so it might break. And the list probably goes on. Thats just off the top of my head right now.

92-95 318
Bellhousing,318-340 flywheel
M1 intake, carb
Mopar electronic ignition kit or make your own from stock parts
V6-V8 block mounts
Electric fan
V8 rad

My upgrade is about 8 years old
You will also have to upgrade the rear end sooner or later

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88 2.2 5SP
95 5.2 Mag
A518
8 1/4
Electronic ignition
Custom EFI (megasquirt 2.2)

You can use any year 318, even up to 99. Depending on what you want to run accessory wise. You will have to make a decision on intake and exhaust manifolds.