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Unread 10-18-2004, 06:37 PM   #1
MillerHalrey76
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4.0 head swap

what kind of gains am i lookin to get off my cj 4.2 with the 4.0 head swap? how much total am i lookin at paying? is it worth it or no is what im trying to figure out. thanks for the help guys

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Unread 10-18-2004, 09:01 PM   #2
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Quote:
Originally Posted by MillerHalrey76
what kind of gains am i lookin to get off my cj 4.2 with the 4.0 head swap? how much total am i lookin at paying? is it worth it or no is what im trying to figure out. thanks for the help guys
I was wondering if doing the 4.0 head swap and keeping it carburated is going to net some gain as well...
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Unread 10-19-2004, 03:51 AM   #3
Greezy Gringo
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This has been discused about a billion times. Do a search for it.
Or read this write up:
http://monsterslayer.com/jeep/40Head/40Head.htm

I just put a new motor, with warranty, in my 80 CJ7. Im going to do the head swap once the warranty runs out. Everything Ive read says you get like ~40 HP and lotsa torque from the upgrade. Ive been watching a head on eBay that was designed for the swap. http://cgi.ebay.com/ebaymotors/ws/eB...category=33617

Keep in mind that you'll need new intake manifold...
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Unread 10-19-2004, 01:16 PM   #4
gosupes
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Quote:
I was wondering if doing the 4.0 head swap and keeping it carburated is going to net some gain as well...
Yes it does, a large gain. FI is still the better way, but a carb is a low buck, low tech way to get started.

Quote:
Keep in mind that you'll need new intake manifold...
I have heard that the old intake can be used with some grinding. A new exhaust manifold is a must. The eBay head is a bit expensive but if you have more money than time, still a good option. Look for the 7120 head, better flowing than the others.

Overall this is a good cost to power ratio mod.
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Unread 10-19-2004, 03:06 PM   #5
djfuzzy
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http://www.cjoffroad.com has a whole forum dedicated to this swap. Tons of info there that I haven't seen other places. From what I have read, it is completely worth it.
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Unread 10-19-2004, 04:46 PM   #6
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Quote:
Originally Posted by gosupes
Look for the 7120 head, better flowing than the others.

Overall this is a good cost to power ratio mod.
What is a 7120 head off of???? How can you tell the difference???
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Unread 10-20-2004, 07:47 AM   #7
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I'm not 100% sure of all of the casting numbers, but I would not do the swap with a pre-HO head, that's the big difference. Someone check me, but I think it was like 92 or 94 when the HOs came on line.
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Unread 10-21-2004, 12:13 AM   #8
Greezy Gringo
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92-94 sounds right to me.

I'll be doing this upgrade around this time next year (when the warranty expires on my new motor.) I was looking at upgrading the cam too. Anyone with cam experience? It's a DD when the weather is nice. Soo like a good low-mid range torque boost?
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Unread 10-21-2004, 06:25 AM   #9
gosupes
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Quote:
Originally Posted by Greezy Gringo
Anyone with cam experience? It's a DD when the weather is nice. Soo like a good low-mid range torque boost?
I run a 260* cam which has a low torque curve, not a DD but it has been seeing a lot of miles lately. A 264* would be good also.



Quote:
What is a 7120 head off of???? How can you tell the difference???
Yeah, the 7120 is the casting from the 92-94HO engines, they flow better than other HO engines. But any HO head is still better than the stock head.
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1986 CJ7, 4.2 w/4.0 head, TFI-HEI hybrid ignition, Clifford manifold w/Holley 390 w/cold air intake, OBA, 4.5" lift, Woody CV shaft and Tattons in front, 4.10 gears - lunchbox in front, Truetrac in the back, twin-sticked, blower upgrade for running topless, trying to keep it simple.

It's just a Jeep, and if you don't wheel it once in a while, it's not even that.
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