4.0 or 258

[Zorm]

Ok, got a 83 full size Cherokee with the 258 in her. I have the 4.0 head, exhaust and the chevy HEI dizzy all mated the a T176. The intake for the 4.0 head is the old 258 intake with a 2100 2 bbl carb.

Now, what would give me better gains,
keeping the 258 and install 4.0 fuel injection on the 4.0 head using the harness and sensors from a 91 4.0 but with a 2000 intake
OR
Swap in a complete 4.0, engine and just convert the old 91 intake to the 2000 intake
OR
swap in the 258 crank and piston arms into the 4.0 and install the 4.0 engine.


nothing is supped up in the 258.

thoughts welcome

[lafrad]

Start by getting your displacment.

4.0 head, 4.0 block, 4.0 pistons, 4.2 pistons/rods/crank. bolt up everything else you already have for the 4.2 and do some crude tuning to get it running decently, and enjoy your newfound torque and HP.

once its broken in and running well, start picking away with the new(er) 4.0L HO stuff...

[Zorm]

so LAFRAD, I can just swap in the 259 piston/rods and crank, maybe after getting new bearings for the crank and piston rods, maybe new rings, if the cylinders look good, what else? When I do that, will I need to run preim gas. I have heard that folks can have a lot of pinging when they do this swap.

[SilverXJ]

You can't use 258 pistons in a 4.0L block

[YJason]

if you have a 4.0 head already on the 258 it would be fairly easy to do a 99 up intake and go FI. The hardest most expensive part will be the electric fuel pump and regulator set up and figuring out how to do your crank position sensor.

The CPS can be done 3 different ways

1. run a 4.0 flexplate and drill the bellhousing and make a bracket for the sensor
2. run a cps relocation set up by hesco
3. run one of these (pretty slick setup) http://www.streetsideauto.com/products. ... 2godbBr6cA

IMO: Performance wise, if the carb is tuned right the power will be the same or better than FI. FI would be nice in cold weather and if driving in completely different altitudes.

[lafrad]

4.0 block
4.0 pistons
4.0 head

258 rods
258 crank

cam of choice.
the rest to fit.you can start and run with the 258 intake and carb.


You have control over the ignition timing, i bet you can get ping free by dialing back timing a couple degrees without any other work.

If you want to be able to run "optimal" timing, you will have to look into dropping the compression ratio of the build a bit: thicker head gasket and/or enlarge combustion chamber and/or dish the pistons out.

[gradon]

That dizzy is slick--might have to get my bro to buy it for the manche.

[Plechtan]

The Accel distributor will not generate a crank sig compatible with the Jeep ECU. It is designed to be used with the Accel DFI setup. It could also work with other aftermarket efi setups. The cheap way to go would be to use the stock jeep EFI distributor with a ford 6 shutter wheel and hook it to a megasquirt. Tuning will be harder than a carb. If you want a hotter spark, you can go with a MSD6 ( $200.00) and use the TFI distributor cap and rotor.

[Zorm]

Ok, I think I know what I am going to do. Get the 4.0 machined. Get the heead cleaned and 3 angle valve job. Have the engine cleaned and replaced the freeze plugs. Take the crank and piston arms out of the 258. Get the crank turned, and the piston arms pressed into the 4.0 stock pistons.
Kinda want to do as much as I can re-using the parts from bnoth engines as possable

keep the stock pistons and get them pressed onto the 258 rods. get everything together and then put on the 2000 intake and larger throttle body.

[SilverXJ]

Don't plan on reusing the stock pistons after they are pushed off the rods. They usually become damaged after they are pressed off. Also, reusing the stock high mileage pistons is a bad idea, unless you are just building something to slap together and sell.

[92tank]

i reused my pistons with 183,000 miles on them and i have over 20,000 on since "rebuild" and have not had any problems (other than elec. and acc.)

[Zorm]

ok so took the head off the 4.0 and the cylinders look good, no lip on top. Still need to get it hot tanked and replace the freeze plugs, should I have the machinne shop bore out .20 or .30 and get new pistons or just have them hone the cylinders and get new stock pistons?. What about decking the block.

I am thinking about one of the below. I also have a 2000 intake and 94 fuel injection to put on and was thinking about the larger throttle body. Thoughts welcome.


4.6L Low-buck, low CR "rockcrawler"

~ Jeep 4.2L 3.895" stroke crank
~ Jeep 4.2L 5.875" rods
~ Keith-Black Silvolite UEM-2229 +0.030" bore pistons (3.905" bore)
~ Increase piston dish volume to 30cc
8.8:1 CR
~ Crane #750501 192/204 degree camshaft
~ Ported HO 1.91"/1.50" cylinder head
~ Mill block deck 0.035"
~ Mopar Performance 0.043" head gasket
~ 0.058" quench height
~ 2.25" exhaust
~ Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines
~ 231hp @ 4400rpm, 327lbft @ 2000rpm



4.6L Low-buck, low CR "rockcrawler"

Jeep 4.2L 3.895" stroke crank
Jeep 4.2L 5.875" rods
Silvolite UEM-2229 + 0.030" bore pistons
Increase piston dish volume to 30cc
8.75:1 CR
CompCams 68-115-4 192/200 degree camshaft
Ported HO 1.91"/1.50" cylinder head
Mill block deck 0.035"
Mopar/Victor 0.043" head gasket
0.058" quench height
Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines
240hp @ 4700rpm, 315lbft @ 3000rpm



4.6L "poor man's" stroker

Jeep 4.2L 3.895" stroke crank
Jeep 4.2L 5.875" rods
Sealed Power 677CP +0.020" bore pistons
9.25:1 CR
Stock 4.0 HO camshaft
Ported HO 1.91"/1.50" cylinder head
Mopar/Victor 0.043" head gasket
0.088" quench height
Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines
248hp @ 4900rpm, 303lbft @ 3500rpm


thanks