Hole in Exhaust Manifold
 

I hit a rock on the road and punched a 1/2" long x 3/16" wide slice into the bottom of the manifold pipe about 4" ahead of the catalytic converter. Honda service temporarily patched it with muffler repair patching compound but recommends welding it. Has anyone had a manifold welded? Is the manifold stainless steel? Any special recommendations, where to take it, etc.?

Well that blows .............. :D See what I did there?

I believe any good exhaust shop can take care of that. My stock one broke right by the flange, in front of the cat so it sounded like a tractor driving down the road :) I was about 50 miles from home, heading further the other way for a few days, so I just found the only shop I could find open (a Midas) and they just quickly welded it with no issues.

Welded exhaust manifolds (as on the S2000, not cast iron) are typically made out of 309S stainless or a similar high alloy stainless steel. They're weldable but you would have to make sure you use a compatible filler wire and patch material. If you use a lower alloyed stainless, you will likely get accelerated oxidation there. If you used a ferritic stainless patch (magnetic) you could get galvanic corrosion and possibly some fatigue issues.

Your best bet would be to pick up a used manifold and replace it. You can get one on EBay for less than $100 and they should last forever (assuming you don't puncture it again). The hard part will be removing the old one and installing the replacement without lowering the front cradle. I don't know how much room there is with the engine in place but I know that there's plenty of room if you're lowering the front cradle to do a clutch job.

At least on a LHD US model, you do not need to lower the cradle to replace the header. It is not that bad of a job.

I also vote for a used stock header.

No muffler shop is going to have the correct wire to weld stainless properly (they can weld it, and it'll last a while, but it will rust. Will it rust through? Can't say.)

Time for a Mugen header

Ha! I wish!

Many of us do :drive:

Yea there is a few diy's on replacing the header its not too bad of a job if you decide to just replace it with a used one.

Used one will be the cheapest way to go. I recently sold mine otherwise i'd offer it but @s2000Junky may have one laying around. Finding one local would avoid the shipping cost however but even after shipping a used one will be cheaper than just about any aftermarket option worth its salt.