Anybody know how to cap an EGR bung on a 94-97 Miata header?: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Dec. 8, 2009 2:57 p.m. Secret_Chimp None

I've been trying to find a non-permanent (i.e. no welding) way of capping off the EGR bung on my headers. I'm putting a 99 engine in my 97 Miata - the engine already has a block-off plate on the intake side, but that still leaves my headers to deal with.

I don't even know what size/thread pitch I need - the ever-inconsistent Miata.net said either 3/8 or 1/2 NPT, neither of which fit correctly. The Miata vendor Goodwin Racing has a specific cap that will fit, but it's $12 and they refuse to ship it any way but UPS - which means $22 for a friggin threaded cap. What can I do?
Dec. 8, 2009 3:04 p.m. Keith SuperDork

Not surprisingly, it's not an NPT thread - that's a US standard. It's M22x1.5, and you need one approximately 17mm deep.

We have 'em at Flyin' Miata for $6.95 and we'll ship it USPS if you'd like. Just call. Or pick one up locally, but make sure you get an iron one and not brass.

Another option is to get your hands on the EGR pipe to match and weld that up, then screw it into the manifold.
Dec. 8, 2009 3:06 p.m. Woody SuperDork

Keith wrote:

but make sure you get an iron one and not brass.

Why is that? Rate of expansion?
Dec. 8, 2009 3:11 p.m. unevolved Reader

Woody wrote:

Why is that? Rate of expansion?

That'd be my guess.
Dec. 8, 2009 3:13 p.m. Dr. Hess SuperDork

I'm going with dissimilar metals in a very high heat environment.
Dec. 8, 2009 3:17 p.m. Keith SuperDork

We usually put them in turbo manifolds. The melting point of brass is uncomfortably close to the temperatures seen in the manifold! Probably not a big deal for a naturally aspirated car. Then again, I've seen headers glow red.
Dec. 8, 2009 3:33 p.m. Secret_Chimp New Reader

In reply to Keith:

That's great - I searched your site but you only have the intake-side plate listed when I search for "EGR." I'll give you guys a ring.
Dec. 8, 2009 4:06 p.m. Dr. Hess SuperDork

Yeah, I could see that. Brass melts around 16-1700F. A turbo manifold might start reaching that in some circumstances, but it would really have to be built for it.

My manifold is 140 wall 304 SS. It could take it.
Dec. 9, 2009 1:07 p.m. Clay Reader

I used a steel M22x1.5 oil drain plug from Napa (P/N 704-1048). I had to trim off some threads to get a perfect fit on the length.

Ignore the heater hose connector pointed right at it. Small hiccup during my coolant reroute ;-)
Dec. 10, 2009 10:48 p.m. old_ New Reader

Clay wrote:

I used a steel M22x1.5 oil drain plug from Napa (P/N 704-1048). I had to trim off some threads to get a perfect fit on the length.

Ignore the heater hose connector pointed right at it. Small hiccup during my coolant reroute ;-)

thats a good idea.
another thing you can do is saw off the egr pipe an inch or two away from the threaded fitting. Then take the sawed off end and crimp it closed in a vice... then bend it over on itself and crimp it again. Kind of like rolling up the end of a toothpaste tube. I did this on my accord, it worked great and was free.