How to Install a Magnaflow Exhaust Manifold

How to Install a Magnaflow Exhaust Manifold

I bought a 1998 Civic for $760. The beater-to-project CRX’s abhorrent rust finally cracked its subframe, so it’s in a mechanically induced coma, and I needed something else to drive. When you buy a car for $760, unless it’s from your grandmother, and she’s not Cindy McCain, you’re going to have some issues to fix. The most obvious on this Civic was a cracked exhaust manifold, so I fixed it. With a little help from Magnaflow.

How to Install a Magnaflow Exhaust Manifold

A broken exhaust manifold isn’t just an aesthetic problem. On a ’98 Civic with a d16y7 engine, the upstream oxygen sensor is right there, sticking out of it like a middle finger to automotive simplicity. Air can slip into the manifold through any break, confusing the sensor and therefore confusing the car’s ECU. It might decide to dump extra fuel to cool the valves, which would ruin efficiency. The valves might burn up anyway.

How to Install a Magnaflow Exhaust Manifold

When my “high temperature” epoxy burned up and flaked off a day after it was applied, I decided on a more permanent fix: this Magnaflow exhaust manifold and catalytic converter. Honda decided to put their catalytic converter (yes, I’m just going to call it a “cat” from here on, so don’t accuse me of animal cruelty) right there on the manifold, just below the collector. It’s a single piece. This prevents just about every pathetic thief in the world from sawzalling out your cat in the middle of the night, but it also means that when you replace one, you have to replace both. Cracked manifolds are a common problem on these cars, and cats aren’t the cheapest. They’re so stealworthy because they’re packed with precious metals like platinum or palladium.

How to Install a Magnaflow Exhaust Manifold

Thankfully, Magnaflow’s lightweight, high-flow, stainless steel, durable, awesome, dateable, welded manifold and cat unit didn’t cost too much more than an ugly OE equivalent made from pot metal. Another weak, cast iron manifold was not going to be an option.

How to Install a Magnaflow Exhaust Manifold

The part arrived on Tuesday, and I installed it after work. I was almost done before it got dark. Here’s how that went:

How to Install a Magnaflow Exhaust Manifold

Good presentation, Magnaflow. This is not a shiny, chromed header. You can’t polish it to a mirror sheen. But the welds are neat and tidy, and the flanges are thick. I have zero doubt this thing will last me a long, long time.

How to Install a Magnaflow Exhaust Manifold

The first thing I did to my brand new, semi-shiny manifold was hack it up. This unit includes a pair of brackets to mount the stock heat shield, but since I’m eventually going to paint the manifold and show it off like I’m stuck in an early Fast and Furious movie, I won’t be running a heat shield, and I cut them off using my angle grinder and a Dremel. I got tired and bored, so I left the cutoff stubs ugly and on there. I’ll finish them when I take off the manifold for painting. (I later found that the lack of brackets made installation easier.)

While I did this, I had the car’s hood up so it could cool. Joining hot metal to cold metal is never the best idea, and also you could burn yourself, which could get expensive. I also disconnected the battery with a 10mm wrench, in order to reset the ECU, in case the confused O2 sensors actually had tripped a code.

Next, I unplugged and removed the oxygen sensors. The downstream sensor is located just below the cat section, and is easy to get to from under the car. O2 sensors are notoriously difficult to remove, and I’ve found that the best method is to prep the sensor with penetrating oil, then use an oxygen sensor socket at the end of a long breaker bar to turn it out. This special socket is deep enough for the sensor body, and slotted to make room for the wire. My upper sensor bung was part of the cracked area of the manifold, so that sensor spun out easily, but the lower one fought me more. Even if you’re replacing both O2 sensors with brand new ones, removing the downstream sensor will make the whole unit easier to remove.

How to Install a Magnaflow Exhaust Manifold

Now, as I’m sure you’ve noticed, my engine is filthy. The previous owner didn’t know the difference between a valve cover gasket and a velvet scrunchie, so there’s a fine coating of…protectant all over everything south of that shiny Honda hat. I found this protectant extremely helpful in loosening the 12mm upper manifold nuts. Any hardware that gets very hot and is also exposed is extremely susceptible to rusting and seizing, so if your Honda engine lacks a gigantic oil mess (fat chance), be sure to prep the hardware ahead of time with penetrating oil (after the engine has cooled). I prefer PB Blaster. This goes for the upper and lower fittings.

How to Install a Magnaflow Exhaust Manifold

After loosening the top nuts, I removed the 14mm lower nuts. And by “removed,” I mean “broke off.” They had rusted and seized in place. This was fine, since Magnaflow includes 3 shiny new stainless nuts (15mm) with the manifold. However, there are 4 nuts required. Three bolt the exhaust in place, and the other holds the manifold to a support bracket, which bolts to the engine. This keeps the weight of the exhaust from straining the upper manifold fasteners. You’ll need to save this nut if you can. Or just have a 15mm nut with an equivalent thread pitch ready to go. I removed the 14mm support bracket bolt from the engine.

How to Install a Magnaflow Exhaust Manifold

Next, I removed a strap that holds an AC line in place, just next to the condenser. This strap got in my way while I tried to wrestle the manifold free. This is a 10mm bolt.

How to Install a Magnaflow Exhaust Manifold

I backed the manifold off of its upper studs, then manhandled it vertically out of the engine bay. Then I chucked it across the yard in vengeance. I also removed the stock upper manifold gasket and compared it with the replacement gasket Magnaflow included in the box. The stock unit was a bi-layer metal job, and I’m sure it worked just fine. Magnaflow’s gasket is a thick, composite steak of a thing, and I’m sure it will be awesome.

I cleaned the gasket contact patches as well as I could. I didn’t go nuts because I was paranoid about knocking anything into the open exhaust ports on the engine.

How to Install a Magnaflow Exhaust Manifold

Next I slipped on the new upper gasket, and forgot about the lower gasket. If I would have remembered it, I would have put it in place. The lower gasket is a simple, ring crush gasket, and there’s no groove cut in either the exhaust flange or the manifold flange to help it seat. The exhaust flange sits at an angle, so the gasket could slide off center. I put a little anti-seize on the bottom of the gasket to stick it, centered, to the exhaust flange, and it worked. Did I ruin the seal doing this? I hope not. Tell me if I did, internet.

The Magnaflow cat is much smaller and slimmer than the stock unit, so it dropped easily into place. It took some wiggling to get the lower studs seated through their holes on the exhaust flange. I had to get a little rough, and I was worried about messing up the stud threads, but these are hardened, high temperature fasteners, so a little force won’t fowl them.

How to Install a Magnaflow Exhaust Manifold

The lower studs now seated, I hung the upper flange on its own studs, then applied some anti-seize to all the threads, upper and lower. It only takes a little per stud. I hand snugged all nuts in place (you’ll need to reuse your stock upper nuts), then torqued them down. Upper nuts should be torqued to 23 lb-ft, and lower nuts to 25. When tightening the upper nuts, start from the innermost nut and work your way out in a spiral pattern. This will help insure that the gasket gets the best seal.

How to Install a Magnaflow Exhaust Manifold

All nuts torqued down, I went to replace the lower support bracket and found that it wouldn’t quite fit between the manifold and the engine. The bracket already has a funny bend, so I put it in a vise and bent it a little further. A hammer would probably work in a pinch. I put it back in place, and it fit just fine.

How to Install a Magnaflow Exhaust Manifold

Finally, I screwed the O2 sensors back in after putting plenty of anti-seize on the threads. They should be torqued to 33 lb-ft. Yes, I probably should have replaced them with new ones, considering the dubious health of my old cat, but I’m cheap, and I’ll do it soon. Thus the anti-seize.

I replaced that annoying AC hose strap, plugged in and bracketed the O2 sensors (make sure the wires are not coming into contact with the manifold or cat), and reconnected the battery.

Expect a smell. Even if you clean it well beforehand, the new manifold will still carry some residue that will need to burn off. This is not a big deal. It will dissipate after a couple of days, and it’s a nice reminder that you’ve fixed something, and that you’re awesome.

Also after a couple of days, the exhaust will begin to change color with the heat. Mine has purpled quite nicely, and I’m enjoying the look. If you don’t like it, well, maybe I don’t like your stupid jeans, so there.

Pro Tip: Don’t forget to recycle your old cat. Not just to save the planet. Those precious metals are still in there, and your local cat recycler (Google it) will pay you a nice dividend. Some are worth $200, and that’s a big chunk off the price of the new part.

Good luck, and don’t hesitate to call us if you have any questions.

 


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