View Full Version : 4.2 head work vs. 4.0 head swap
Ga Yota 4x4
09-18-2007, 05:18 AM
I've researched about swapping the 4.0 head on a 4.2 motor for increased power. Just interested in knowing if I would get the same benefit just to get the 4.2 head ported so it can breath better. Read where the 4.0 has a 45 degree flow compared to the 4.2 90 degree.
Thought that reworking the orginal head might save some pennies and have better, form, fit, and function than the 4.0. Read where some were having problems with the water jackets leaking after the swap.
Any info is appreciated!
09-18-2007, 12:42 PM
There is a lot of dinking to do a head swap onto a 258 block. You would be farther ahead time, money, and power wise to just drop in a complete 4.0 from a 91-95 cherokee. The odbI motors are very simple to wire. I only had to splice 6 wires into my harness. Fuel injection rocks! Another advantage is that you can go with all cherocar accessories and keep the serp belt.
09-18-2007, 06:34 PM
Depending on the the year of the 258 block a 4.0 head swap is not that bad.
The only major things are the plugging of the cooling passages on the drivers side of the head, I did the epoxy method and has held up well and the modifying the power steering bracket to clear the exhaust manifold. Depending if you go with a stock manifold or header depends on the amount of modification.
If you have a 87 to 89 or 90 (not sure of the change over year) the 258 block will have the same 1/2" head bolts as the 4.0 so there is no issue with getting the sleeves for the 7/16" bolts or alignment issues when installing the head.
I when TBI at the same time I swapped the head so between the 2 i had very good power gain. I can cruse at 70 on the interstate in my 8 pulling about 1000 Lbs worth of trailer.
I found one of your other posts saying which jeep you have, a 87 Jeep Wrangler 6-cyl. It should have have the larger head bolts. The 4.0 would be an option as it was available on the later YJs and the transfer case should mount up to which ever tranny was in the donor for the 4.0 eliminating issues with locating the crank position sensor.
Where in GA are you. I'm about 60 miles north of ATL.
Ga Yota 4x4
09-19-2007, 03:18 AM
4.0 Tbi would probably be the smart way to go in the long run, although I've read the 4.2 - 4.0 head combo has more torque than a stock 4.0. There's a stroker site on yahoo with some good 411.
I'm about 60 miles the other way. Do any 4-wheeling in GA?
09-19-2007, 12:24 PM
Agreed, I looked hard at the head swap b/c I was afraid to pull the engine but the water jacket, timing issues and machine work scared me off. I can find strong running 4.0s for ~$500 around me, so I went that direction. My understanding is that the stroker motors use the 4.0 block with it's larger bore and a 4.2 crank to end up with 4.6. Sorry, I can't offer much help on your original question.
rjcj pointed out the cps issue, your 87 bellhousing should have the cps mount already machined in, mine did.
09-19-2007, 06:19 PM
I mostly do camping in GA, there are a few places to go Beasely Knob, Rocky Flats are 2 that come to mind. I have not been but would like to check them out. I go up to Tellico once or twice a year for the serious off road stuff.
I'll be heading up there in about 2 1/2 weeks for the SWDF Dixie Run.
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