[965]

I have just about got everything completed on my head swap, but I ran into a problem.

My intake and exhaust manifolds want to occupy the same space, between the 3rd and 4th exhaust ports. Either the intake accumulator (center of my intake on the bottom) is too low, or the exhaust manifold sticks out too far...

My intake is my original stock YJ '88 4.2L. It does not have the lower notches, as depicted in Jaffer's write-up (monsterslayer.com/jeep). Because of this, it sits a little high, so I will have to grind my own notches into it. This would bring it even closer to my exhaust mani.

Just guessing, the exhaust mani is off of an '87 cherokee 4.0.

Not sure where I am going wrong?

 

[raymo]

It sounds like you may have to grind some of the webbing out of the intake manifold that goes between the ports. I run an exhaust manifold from a late 80's 4.0 and I had to grind the intake to fit.

 

[Tippy]

What year head did you use? I ran into simmilar problems because I used a '98 head. They changed the manifold mounting in '96.

 

[1101]

You're not "going wrong". You're just encountering the problems inherent in piecing together a system from different years and designs. If you can get it to fit by simply grinding a notch or two into the bottom of the intake manifold, and you are not risking a compromise of the water jacket or intake plenum, consider yourself lucky.

I used a '95 head, Borla header for a '95, and a Clifford aluminum intake for a 258. I don't even want to talk about the crap I had to do to get the intake on there.

 

[Guest]

The 4.0 HO head did not come out until '91. It could be the exhaust manifold is not the right one for that head. When you look for headers for the Cherokee, there are different part numbers for the 87-90 4.0 and the 91 and up 4.0 HO.

 

[965]

Tippy, I've got a '94 head.

When I said "center of my accumulator", I was referring to that manifold heater thing bolted on the bottom for emissions (adjacent to the EGR valve). It doesn't take up much room itself, but the mani expands to fit it in. Not sure if other years had this or not.

 

[Guest]

I went out and looked at mine. I see what you are talking about. The #4 exhaust pipe on mine is almost touching the manifold heater. The number 3 pipe is right there too. I don’t remember this being so close when I had the ’91 Cherokee header on. But it cracked and I put a Banks header on. I never checked it until now. It was cold and I wanted to get it running. I’m not sure how thick the manifold is in that area. How close are you? Could a combination of a little grinding coupled with a small dent in the header clear it? I used to bend small block Chevy headers to get to the bolts holding them on. I’d rather bend the header before I grind too much off of the intake.

 

[1101]

I had to grind some off the bottom of the intake plenum between #4 & #5 AND put a dent in the top of the #5 header tube. Bottom line was that the Clifford intake was just way too fat for this application - but I inherited it with the 258 short block and the temptation to put a 4bbl on it was too great.

I wrapped the header downtubes with fiberglass header wrap to keep some of the heat off the intake. It does a remarkably good job of insulating the two.

 

[Guest]

I'm glad you chimed in highfill. I thought if I stumbled on to a Clifford intake cheap, I'd buy it and put my Weber on it to see if it made a difference. I won't do that now.

 

[1101]

A few things, tkcomer:

1) My interference issues came from using the Clifford intake in conjunction with the Borla header. Your header downtubes may not stick out as far as the Borla.

2) This Clifford intake is for a 258. I don't think they make one for a 4.0 because it had fuel injection from the factory. Prolly not much of a market for intake manifolds designed for 4.0 heads and a carburetor.

3) The Clifford intake has a big square opening and plenum designed for a 4bbl. If you plan on keeping your Weber, my guess is the gains would be minimal if there at all. You might even lose some bottom end due to the large plenum design.

4) I don't know what profile your cam is, but consider that all parts should work toward the same end. I have a very mildly aggressive Crane Cam (260H) that is designed to bump the midrange and open up the top end without losing too much bottom end.

You want to make sure that your carburetor is sized properly for what you are trying to accomplish. You can calculate what CFM carburetor you want to run by doing some math with displacement, the max RPM you will turn, and the volumetric efficiency of the engine. Don't know what my (or your) VE is, but 85% (0.85) will get you in the ballpark. A quick Google for carburetor CFM calculator turned up a few. When I ran 258cid, 5000rpm, and .85VE, it put the 390 in my neighborhood.

My engine does NOT run like a 6 anymore. It doesn't have the bottom end of a V-8 or a 6 that's been really tuned for stump-pulling, but it's smooth all the way down to just below idle. Get her above 1500 and she is already pulling stronger than stock, and anywhere above 2500 she just flat out howls.

So, the answer depends much more on what your cam profile is and how much you like your Weber. Webers are friggin sweet. I had one on my stock 258 and really liked it. If your cam focuses on bottom end, you probably want to stay with a stock (smaller runner, higher velocity, less volume) intake manifold and your Weber. If you want to sing at the higher rpms now and again and your cam does too, then a big intake and small 4bbl (or BIG 2bbl!) may be for you.

Keep in mind that your exhaust plays into the picture too. The Borla tubes are pretty good sized, and I have a large pipe with no cat. Basically smaller holes (carb, intake, and exhaust) and shorter durations mean more velocity --> better low end grunt and you run out of breath sooner in the higher rpms. Larger holes mean more likelihood of flopping around in the low end, and a lot more power and room to breathe up top.

If you didn't already know some of this, I hope it helped. There's a lot more knowledge/crap where this came from. I'll be glad to share if ya wanna know!

 

[Guest]

Thanks for the info highfill. Most of my tough stuff in off-roading is in the crawl range, with short bursts of throttle to add to the terror factor. My cam is a 250-258 duration with a 462-485 lift. I want to keep my low end because I try to ease over obstacles and crawl up stair-step hillsides. When all you see is tree limbs and sky, it’s hard to stay in the throttle. I just hope OregonSahara doesn’t get mad because we hijacked his thread. Thanks

 

[965]

In reply to:

I just hope OregonSahara doesn't get mad because we hijacked his thread. Thanks

[/ QUOTE ]

Not at all. Thanks for checking your clearances. I was able to fix it like you guys suggested with a couple of small dents in my exhaust tubes. Thanks

 

[Guest]

Glad you got it fixed. You are going to love that 4.0 head change. Well worth the effort.