258 I6

[Deepsouthj10]

Ok fellas I have pulled my 258 I6 from my 82 j10 and I am rebuilding it, I was just wondering if any of y'all have any advice? I'm also wondering what intake I should get and what carberator I should go with? Two barrel? Four barrel? Which brands?? I am looking to try to eliminate a lot of these damn vacuum lines!!

[carnuck]

Get a 4.0L head and put on EFI (you'll need to put Hydroboost on for teh brakes to clear the intake) '91 to '95 XJ is the easiest to swap.

[Deepsouthj10]

Why go that route? I would kind of like leaving it the 4.2 and leave it carbed?

[carnuck]

The head flows better so if you even go carb, it ups the power about 15HP and the 4.0L exhaust header flows better than the 4.2. The head won't change the displacement, but the extra flow increases the compression slightly too. We are using the BBD intake with 4.0L header (Renix) and Motorcraft 2100 carb in an AMC Eagle. (install is hopefully next week)

[Stuka]

You can leave it as a 4.2L and with a carb. But if you have 1/2" head bolts (Pretty sure the 4.0 wants 1/2", as opposed to 7/16), go for a 4.0 head. They are far superior. Your intake and exhaust will still work.

There is also several cams out there to choose from.

[Deepsouthj10]

From what I've been told by a local machinist is that if I go with a bigger cam I will loose my air conditioning??

[Stuka]

From what I've been told by a local machinist is that if I go with a bigger cam I will loose my air conditioning??

Er... no. If you go for some big lopy cam then you will lose vacuum, so the flappers wont work. But you dont want a big cam. You want an RV cam.

[Deepsouthj10]

He claimed that the stock cam in the 258 was already as big as you could go without loosing ac? And also what is the problem with the 4.2l head? Do they not make a good intake that is 2 or 4 barrel compatible? Should I go with a 2 or 4 barrel? It had the factory 1 barrel on it

[Stuka]

He claimed that the stock cam in the 258 was already as big as you could go without loosing ac? And also what is the problem with the 4.2l head? Do they not make a good intake that is 2 or 4 barrel compatible? Should I go with a 2 or 4 barrel? It had the factory 1 barrel on it

The ports on the head are very restrictive. The 4.0 head has much larger ports so it flows better. Intakes swap between 258's and 4.0's.

Not sure I understand what he is referring too regarding the AC. Only thing I can think of is vacuum, which would also mean losing power brakes. And A cam that big is of no use in a 258 due to them being a lower RPM engine.

[Deepsouthj10]

So I would get an intake for a 4.0?? And should I run 2 or 4 barrel carb?? Sorry so many questions, I'm new to all this stuff!

[carnuck]

4 bbl is more for racing. They are more finicky and tend to use more fuel (because your right foot gets heavier when you have more power) A 2100 Motorcraft is plenty and '81 up have separate intake and exhaust plus they are already 2 bbl.

[Stuka]

4.0 intake is for EFI, you want an 80-91 258 intake.

[Deepsouthj10]

Ok cool, so are there any good after market intakes or just the stock one I already have?

[Stuka]

There are intake for race applications, but the 80+ aluminum intake is considered to be pretty good.

[carnuck]

'81 up intake (they were conjoined intake/exhaust and tin valve cover till then) flows pretty good. Clifford makes a 4.0L carb intake and 4.2L as well. I liked the Offy dual plane I had with a 4 bbl Carter AFB (works best mounted backwards, believe it or not) Weiand had one for awhile as did Holley (not fond of the Holley one. No PS provisions. Same as some others so beware!) I built one for the 258 in my '80 IH 1210 (assembled from leftover factory parts along with several others in Canada) shortbox stepside, but I didn't get to drive it much (ex-wife sold all my cars for a case of beer each just to PMO)

[Booth755]

I just did a complete 4.0 swap from a 91 Cherokee
I bought a Clifford 4.0 intake to keep the motor carb.
sounds good but still got a few kinks to work out

[jaber]

He claimed that the stock cam in the 258 was already as big as you could go without loosing ac?

My apologies in advance, but this sounds like a lazy or inexperienced mechanic. No other reason for such an answer. I dont know of an American auto that ever came from the factory with the "best cam"...

[SJTD]

No one mentioned the water jacket holes you have to weld up on the 4.0 head to put it on the 258 block.

[carnuck]

that's only some blocks that need the welding done.

[Stuka]

The later blocks are wider and do not need the water jackets filled. Earlier 258's are narrower. And when you place the 4.0 head onto the block, it overlaps the block some, which may expose the water jackets between the cylinders.

Although some say these are not even water jackets, they are left over from casting.