Exhaust Manifold Options-Renix

So, I'm getting ready to replace, repair and/or upgrade my exhaust manifold because I've identified two cracks/leaks in the original.

First of all, I'm have a nice MIG welder and I know how to use it, but I've read so much about people doing this and having it crack again in the same spot, or in a different place.

The Renix manifold seems so damn cheap (manufacture & quality wise, not price wise) and since there is no header made for a Renix model that's affordable. What are there in terms of an upgrade?

Seems that welding bungs for the EGR and O2 sensor would work fine, although seems like a PITA, but the downpipe and the way it hooks up to the exhaust is different too! So, I'm kind of stuck before I even start.

What do I have to do to get what I want done?? The HO manifolds are cheap by comparison. Open to all suggestions here!!

Bolt it to an old head, and weld the cracks, and reuse it. We had ours stick welded on the 89, and it worked fine, but the stick welding method warped the head a little so I had solve the no longer flat parallel issue to get the gasket to seal next. MIG and clamping it to a solid flat metal plate or old head should keep the faces flat and lined up.

I think the cracks are caused by a lack of flexibility in the rest of the exhaust, and or bad engine mounts, in which case it is not the header quality that is an issue. I plan to use an accordion stlye flex joint in mine next on the exhaust pipe to solve the flex problem. Lifts maybe an issue as well????

One thing you could do is get a 91-99 exhaust manifold, then combine that with a 91-?? (the one with the 4 bolt flange for the cat) downpipe, new 4 bolt flange gasket, and new donut gasket for the manifold if it doesn't come with one, and move the RENIX o2 sensor into the new HO downpipe. The sensor threads are the same AFAIK and it should all work together just fine.

EGR is an interesting concern... I have never worked on a rig that had it so I can't really say how to make that work.

The newer manifold is bent+mig welded tube (not sure what the older one is) so you should be able to weld an EGR port to it just fine if you are so inclined.

One reason they tend to crack is lack of flexibility in the exhaust system for sure, there are no flex joints in the OEM setup. Another (IMO) is how long the manifold is and how there is no real flexibility in the manifold either, along with the design of the runners bringing all the stress/flexure together at the point where the two pipes enter the collector. It always cracks there. There are some manifolds on the market that have accordion tubes in the #1/#6 tubes which I think should avoid the cracking issue somewhat.

I generally just reweld the first cracked one I find in the junkpile, stick some new studs/bolts in the flange if needed, and install it. I thought I had two spares in the shed but I cleaned up the corner of the yard recently and it turns out I have four. So whichever one looks best gets welded up and thrown on. No re-cracking yet... a friend's 95 2 door just sprung a manifold leak a few weeks ago so I know where the next one is going.

Ecomike said:

Bolt it to an old head, and weld the cracks, and reuse it.
I plan to use an accordion stlye flex joint in mine next...

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The only old head I have is on my shoulders.

I already have a flex joint ready to go on when I get this all put back together. My plan is to weld it in where it crosses in front of the bell housing.

kastein said:

There are some manifolds on the market that have accordion tubes in the #1/#6 tubes which I think should avoid the cracking issue somewhat.

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All the ones I've seen with the accordian sections 'tween #1 and #6 are HO manifolds.

Think I'm just going to go with the original plan and re-weld the old and keep my eye open for a spare at the JY.

Still open to suggestions though. Out to the shop for now to pull it apart.

I have never worked on the older Renix manifolds, but on the HO's I have seen leaks in 3 areas:

First is the collector, where cracks are common and often large. The good fix I have found is A LOT of weld. I clean them as best as I can then lay a few MIG beads all around the connector joint.

Second is the #1 and #6 tubes. As mention previously some aftermarket brands have flex joints (Walker) on the #1 and #6 tubes. I have found that the manifolds flex a lot, with the #1 and #6 tubes pulling away from the head significantly. The last manifold I repaired I bolted to an old head. I bolted only the center fasteners and the #1 and #6 were more than 1/8-inch away from the head, a lot of stress to pull those tubes in. I have also found broken studs at these positions to be fairly normal. So on this manifold I cut the #1 and #6 tubes and fully bolted the manifold and ended up with almost a 1/16-inch gap in the tubes. So I filled with weld metal with it bolted to the head. Unbolted from the old head and it seemed to remain pretty flat.

Third, I have found leaks in the tube to flange connection, specifically the #1 cylinder, leaked like crazy, filled with weld and the manifold has been leak free for a few thousand miles.

I like the sound of that process!!!! If I run into a bad one again I will try that!!!

cm12385 said:

I have never worked on the older Renix manifolds, but on the HO's I have seen leaks in 3 areas:

First is the collector, where cracks are common and often large. The good fix I have found is A LOT of weld. I clean them as best as I can then lay a few MIG beads all around the connector joint.

Second is the #1 and #6 tubes. As mention previously some aftermarket brands have flex joints (Walker) on the #1 and #6 tubes. I have found that the manifolds flex a lot, with the #1 and #6 tubes pulling away from the head significantly. The last manifold I repaired I bolted to an old head. I bolted only the center fasteners and the #1 and #6 were more than 1/8-inch away from the head, a lot of stress to pull those tubes in. I have also found broken studs at these positions to be fairly normal. So on this manifold I cut the #1 and #6 tubes and fully bolted the manifold and ended up with almost a 1/16-inch gap in the tubes. So I filled with weld metal with it bolted to the head. Unbolted from the old head and it seemed to remain pretty flat.

Third, I have found leaks in the tube to flange connection, specifically the #1 cylinder, leaked like crazy, filled with weld and the manifold has been leak free for a few thousand miles.

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The problem with the Renix is you need the bungs for the EGR tube and the O2 sensor.

So, you have a welder--DIY.

Buy the APN header, part numbers 15343 or 101212.

Purchase 2 correct size weld-in bungs. Jegs or Summit Racing if you live in the boonies, any muffler shop worth its salt will have them for about $4 each.

Use the correct size hole saw, cut holes in the correct places, weld in the bungs.

NOW--and this is the most important part--add a short piece of SS flex tubing in the exhaust between the downpipe and the CAT, where the pipe runs across the vehicle from left to right. This flex pipe allows the engine to torque around without breaking the manifold. You want the SS flex tube that is woven, not the old-fashioned flex pipe stuff.

Good luck.

Like said before, I haven't been able to find a Renix manifold with the flexies at #1 and #6.

So, I got it out and looked it over carefully. Crack at #6 at the weld goes about 20-25% around that I can see. Also a crack at the weld on #5 about 1/2" around but wider. I'm happy to see that the internals of the cylinders & valves, so far as I can see, look sqeaky clean. Especially for 25 yr old engine. Looks like it'll be easy to clean up the manifold and lay the weld right in the crotch of the pipe. No cracks at #1 or at the big tube. I'm also going cut the pipe at the bell housing and cut a section out for the flex joint. Coming right along.

I'll look at it in the morning with a magnifying glass...since my old eyes don't see so well, and I'm tired.

If you're familiar with Renix manifolds they have a chintzy stamped metal collar that provides the air box with warm air when it's cold. It's kind of a passive heat thing controlled by a little vacuum servo on a stock air box.
Looks like I can remove it since I don't have a stock airbox anymore.

Also, anyone wrap their manifold to reduce under hood temps?? Seems like a decent idea...any cons??

Old Man I Think We Have Talked About That Before, And Thats What I Plan On Doing To My Ho Edelbrock I Have Laying Around, Just Havent Gotten Around To it

ParadiseXJ said:

Like said before, I haven't been able to find a Renix manifold with the flexies at #1 and #6.

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Those "flexies" are a non-fix to a real problem.

The problem with the XJ is the amount of BODY FLEX along with an extremely RIGID exhaust system.

However, if you want the flexie manifold just do what I posted above--hole saw, weld-in bungs.

The APN header is a more robust unit--IMHO.

The FIX is adding the SS flex pipe that puts FLEX between the exhaust system hangers and the engine/manifold.

Trust me, I was with the goobermint and I am here to help you. :looney:

joe_peters said:

Trust me, I was with the goobermint and I am here to help you. :looney:

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Riiight!!

I'm sitting here watching THIS movie...Hmm.

http://www.imdb.com/title/tt0822854/

I bought the 8" long woven SS flex joint. Cut the pipe, welded in one end off the truck, tomorrow I'll fit it up to the pipe and weld it in...underneath. I also replaced the mounts today.

Old thread I know, but how well does an HO manifold work on the Renix head in terms of the ports lining up?

And does anyone know what the threads are for the egr tube and O2 sensor so I can get new bungs?

I need a new manifold and renix ones are all the same and it seems like the HO style is a better design