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Old 01-12-2012, 10:47 PM
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Default 4.0l head swap on 258

What is the advantages of doing this swap if not for just better flow (intake and exaust)? Is it the same or less of an advantage to just port and polish the 258 head? What is the differance in a port and polished 258 head and an HO 4.0l head? Good upgrade or not a good investment of money and time?
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Old 01-12-2012, 10:54 PM
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It fixes the leaky plastic valve cover and improves air intake flow slightly, but the efi does a lot of the power boost as does the better cam timing.
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Old 01-16-2012, 06:45 AM
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Originally Posted by Uncl-N8 View Post
What is the advantages of doing this swap if not for just better flow (intake and exaust)? Is it the same or less of an advantage to just port and polish the 258 head? What is the differance in a port and polished 258 head and an HO 4.0l head? Good upgrade or not a good investment of money and time?
Porting and polishing will gain you nothing on either head.

It's a jeep....real jeeps rarely go above 3k on the RPM's....and that is only if your getting on the fwy on your way to your fav rock crawling spot.....

Porting, polishing, headers, Cams...etc.....those are not for jeeps....they only help when you get above the 3K rpm range....

You will gain some improvement with the 4.0 head....and like carnuck said, the real gains are from the FI.

If your thinking of doing a 4.0 head swap but using a carb....not worth the effort.
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Old 01-16-2012, 09:07 PM
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Default Cold hard truth.

Just like you said three grand will be about the tops for this ol beast, I totaly agree. My plans are to do a GM TBI fuel set up. Its in my budget and I have all the parts. Other than the HEI or TFI ignition upgrades, what are some other alterations I could do to make this 258 closer to the top of its class. Im not looking to get +300hp or even +200hp just more than your run of the mill 258, and I know the 258 is not known for its hp but rather its torque, but you get the idea. Just trying to get more educated about my engine, and there seems to be good direction and experiance round here. Thanks for all the assistance.
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Old 01-26-2012, 07:17 PM
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Quote:
Originally Posted by Uncl-N8 View Post
What is the advantages of doing this swap if not for just better flow (intake and exaust)? Is it the same or less of an advantage to just port and polish the 258 head? What is the differance in a port and polished 258 head and an HO 4.0l head? Good upgrade or not a good investment of money and time?
The 4.0 head has a much higher intake port location compared to the inline ports of the 258. "Supposedly" the 4.0 head is good for 25-40 more hp. I'd say closer to the 25 level if you ran the junk 4.0 EFI and no header. And the 40 to 50 hp range with a good header like the Pacesetter 72C1129 and a Holley 600 vac secondary 4 barrel. Slap a 2 inch carb spacer under the carb. Throw in a nice Comp Cam and mill the head a touch. You'll be in business then. I have one that pushes 286 rear wheel hp and 316 ft. lbs of torque. Again that's rear wheel HP pushing 39.5 inch x 18 wide Boggers with a real deal Detroit Locker.

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Old 01-26-2012, 09:54 PM
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Default 258? or 4.0 (242)

Is that a 258 or the 4.0l? What else has been done? Some pretty impressive numbers.
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Old 01-27-2012, 08:26 AM
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Quote:
Originally Posted by Uncl-N8 View Post
My plans are to do a GM TBI fuel set up. Its in my budget and I have all the parts.
We finished the TBI install on my brothers 258 ('84 CJ7) over the summer and he is in LOVE with his Jeep again. OTOH, after 25+ years with the POS Carter, anything is an improvement!

If you make it to that point (and don't scrap the idea in favor of a drop-in 4.0L) and have any questions, LMK... I'm not an expert, but this was my 2nd install from scratch, so I getting there


Timex gets a pacemaker (258 TBI)
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Old 01-27-2012, 08:45 AM
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Quote:
Originally Posted by Uncl-N8 View Post
Is that a 258 or the 4.0l? What else has been done? Some pretty impressive numbers.
Here's my list.

1. 4.2 block with the 4.0 head. Did a little port clean up. Basically I raised the roof far as the gasket would allow. Slightly increasing the intake port height. Left the floor alone. Gasket matched the sides of all ports. Did the same on the exhaust. Little bowl work with smoothing of rough edges in all ports. Little milling action on the deck surface.

2. I had some .040 over forged pistons made that we 9.2 to 1 compression with the 258 head. With the 4.0 head it's around 10 to 1.

3. Cam and lifters are Comp Cams. 68-239-4 - Xtreme 4x4? Hydraulic Flat Tappet Camshafts NOT FOR FUEL INJECTION

4. Pacesetter header as mentioned above into 2.5 inch pipe with a Magnaflow muffler. Nice deep tone and not that typical 6 cylinder jeep rasp. Sounds really close to a v-8.

5. 1850 Holley 600cfm with the black secondary diaphram spring. Mine runs fine off road. Never chugs or pours black smoke. No need for EFI and it's power limitations. A friend of mine bought the Holley Truck Evenger carb that's built for off road conditions. No troubles either with his. We've both done severe angles and been in lots of rough stuff. And not the typical rock crawler slow creeping mess either.

6. Offenhauser 4 barrel manifold gasket matched again. Super Sucker 2 inch carb spacer.

7. Accel 300+ ingition system and coil. MSD 8.5mm 50 ohm wires.

tinycj7
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Old 01-27-2012, 08:58 AM
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Anybody ever heard of a DIY port injection with MAF sensor? If I were going to go to the trouble, that's the way I'd be inclined to go.
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