4.2 Intake on a 4.0 longblock?

Swaping 258 to 4.0, 4.0 parts to 258 etc!
Post Reply
crcletrack
Posts: 2
Joined: October 24th, 2014, 6:42 am
Vehicle Year: 1990
Vehicle Make: jeep
Vehicle Model: yj

4.2 Intake on a 4.0 longblock?

Post by crcletrack »

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
User avatar
IH 392
I love JeepStrokers.com!!
I love JeepStrokers.com!!
Posts: 725
Joined: October 4th, 2008, 11:15 am
Location: Eugene ORYGUN
Contact:

Re: 4.2 Intake on a 4.0 longblock?

Post by IH 392 »

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!!!
ASE Master certified engine machinist, gas and diesel
crcletrack
Posts: 2
Joined: October 24th, 2014, 6:42 am
Vehicle Year: 1990
Vehicle Make: jeep
Vehicle Model: yj

Re: 4.2 Intake on a 4.0 longblock?

Post by crcletrack »

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
bbarrett
Making Progress
Making Progress
Posts: 79
Joined: July 22nd, 2009, 8:00 pm
Stroker Displacement: 331
Vehicle Year: 1987
Vehicle Make: jeep
Vehicle Model: wrangler

Re: 4.2 Intake on a 4.0 longblock?

Post by bbarrett »

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
Movin on up ^
Movin on up ^
Posts: 324
Joined: December 5th, 2015, 5:26 pm
Vehicle Year: 1981
Vehicle Make: amc
Vehicle Model: eaglesx4

Re: 4.2 Intake on a 4.0 longblock?

Post by amceaglesx4 »

Buy a throttle body intake and a 2barrel adaptor from gronk performance then you're good to go
SIXPAK
Consistent
Consistent
Posts: 217
Joined: March 8th, 2008, 5:34 am
Stroker Displacement: 280

Re: 4.2 Intake on a 4.0 longblock?

Post by SIXPAK »

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!
Catfish
Posts: 8
Joined: March 22nd, 2014, 8:44 pm
Vehicle Year: 1987
Vehicle Make: Jeep
Vehicle Model: XJ

Re: 4.2 Intake on a 4.0 longblock?

Post by Catfish »

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.
Tedo44YJ
Where's the "any" key?
Where's the "any" key?
Posts: 26
Joined: January 5th, 2016, 10:26 pm
Stroker Displacement: 4.6
Vehicle Year: 1989
Vehicle Make: Wrangler
Vehicle Model: YJ

Re: 4.2 Intake on a 4.0 longblock?

Post by Tedo44YJ »

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
Posts: 1
Joined: October 12th, 2020, 1:07 pm

Re: 4.2 Intake on a 4.0 longblock?

Post by Jgnobles »

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

Who is online

Users browsing this forum: Ahrefs [Bot] and 9 guests