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4.2 Intake on a 4.0 longblock?

Swaping 258 to 4.0, 4.0 parts to 258 etc!
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crcletrack
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4.2 Intake on a 4.0 longblock?

Post by crcletrack » October 24th, 2014, 7:01 am

Hey! Im new here and I have a bit of a problem. I picked up a 1990 YJ here in North Carolina. Has 151K on its 4.2 that has a new motorcraft carb. I have a knock that Im pretty sure is coming from the bottom end. Can I take a stock 4.0 engine with the 4.0 head and use my 4.2 intake and carb setup? I'm trying to not get involved in the whole fuel injection BS. Any help is appreciated! Ray

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Re: 4.2 Intake on a 4.0 longblock?

Post by IH 392 » October 24th, 2014, 9:34 pm

No, the dowels for the intake don't line it up correctly and the exhaust will absolutely not line up with the ports.
You can get more power out of ANY engine!!!
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crcletrack
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Re: 4.2 Intake on a 4.0 longblock?

Post by crcletrack » October 25th, 2014, 7:03 am

I appreciate the response! I got a bit of energy last night and decided to pull the pan. The good news is that there are no piston skirts damaged and no metal at all. All pistons look good and the walls look good from what I can see from removing the pan.Now here is the bad news.... First off, when I dropped the pan I could see a portion of the timing chain. Now im new to the "Jeep" thing but I raced Nascar Modifieds for 20 years. I am capable of building my own frames and rebuilding a sbc in several hours during any given week. I say this because im not some backyard hack.
Back to the motor! When I dropped the pan it allows you to see a section of the timing chain. Now without exaggeration, I could move the chain left to right at least 2inches. Im fairly confident that was my motor noise. Having the pan off I grabbed each rod cap and tried to move them up/down/ side/ to/side. I have a couple of rod bearings that have several thousandths of movement. Im confident that I can pull the rod caps, and replace the old bearings with new bearings. No cutting the crank or machining. Its been my experience that the bearings are made to wear while having very little effect on the crank journals. Last night I got started by removing the fan, Radiator, Condenser and everything else that needs to go in order to have access to the
timing cover. Hopefully I can get some parts and start my build soon. I appreciate your response. Ray

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Re: 4.2 Intake on a 4.0 longblock?

Post by bbarrett » November 23rd, 2014, 6:41 am

I run the 258 intake on my high port 4.0 head, You do have to cut the dial pin holes out! But it does fit! Exhaust NO!
TEST

amceaglesx4
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Re: 4.2 Intake on a 4.0 longblock?

Post by amceaglesx4 » March 5th, 2016, 1:43 pm

Buy a throttle body intake and a 2barrel adaptor from gronk performance then you're good to go

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Re: 4.2 Intake on a 4.0 longblock?

Post by SIXPAK » March 5th, 2016, 4:55 pm

bbarrett wrote:I run the 258 intake on my high port 4.0 head, You do have to cut the dial pin holes out! But it does fit! Exhaust NO!
BINGO!

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Re: 4.2 Intake on a 4.0 longblock?

Post by Catfish » May 7th, 2016, 4:38 pm

Like was mentioned, you can do it, i did it on dads YJ,
I have to notch the bottom of the dowel holes, so the intake actually sits on top of the dowels and not through the holes.
Next thing to address if the stock washers do not reach the 258 intake.
I welded tabs to the stock washer so its basically [0 shaped like that to reach the intake and clamp it down.
Yewp you have to hold it in place still you start to snug the bolts down.
i used an adapter from MrGasket about $20 at Oreillys and put a Holley 2300 on it.
I think I stepped down in the jet size, actually I soldiered the hole up and drilled it with a small bit, .5434 or something runs very well.
Feels a lot stronger than my 258 in my YJ with a header, and Offenhauser 4 barrel and Holley Truck Avenger 470 on it.

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Re: 4.2 Intake on a 4.0 longblock?

Post by Tedo44YJ » August 9th, 2016, 12:53 pm

I see this post is from two years ago but if anyone is still looking I do this, I just did it and I have pictures in my build thread if yall are interested. Check out my post "tedos carbureted 4.6 stroker"

Jgnobles
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Re: 4.2 Intake on a 4.0 longblock?

Post by Jgnobles » October 12th, 2020, 2:42 pm

I see this post is old but i would like to see pics

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