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Old 07-25-2012, 05:24 AM   #1
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Default Cracks in exhaust ports

Look what I found while putting the car back together, looks like Im gonna be a bit rushed now getting ready for the next race. Next race is labor day weekend.
Have you ever seen anything like this before?

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Old 07-25-2012, 04:08 PM   #2
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Impressive. How many hours on that motor/head? Ported?
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Old 07-25-2012, 05:58 PM   #3
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Engine had 5 race days on it prior to my purchase of the car. But the head had been on a previous engine and I don't know how many hours that engine had. This year so far, 4 race days, and testing + dyno time, approx run time this season 10 hours.

I did find out from the prevoius owner that when they were on the dyno they had the header glowing red for approx 5 minutes, im not sure what they were working on.

A little more on the engine, small nose crank, knife edged and balanced, stock damper, flex plate with 4.5 inch clutch, 10:1 comp ratio, accomplished with custom weisco pistons, the head is approx spec thickness, surfaced .004, fp 4 cams, 390 lift not unsure of duration, will have to look at the spec sheet, isky valve springs, shift at approx 7800 to 8, will pull to 8200. Rules allow port match 1 inch into runners no port or polish.

I have been told to take it apart, clean it up, glass bead, then tig the cracks, dress them, and run it.
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Old 07-25-2012, 06:09 PM   #4
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I don't think those are cracks technically. I think there is a casting line there and it is probably more like erosion at a weak point.

That should be much simpler to tig up and fix than a crack... which are a pain to stop sometimes.
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Old 07-27-2012, 07:16 PM   #5
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Those are just the casting. I suspect there is a sand core with a part line there used during the manufacturing process. most all miata heads have that feature from the start that I have seen.

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Old 07-31-2012, 09:55 PM   #6
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Doesn't really look cracked to me. More like it melted a bit. I'm sure that spot gets quite toasty under load. What EGTs do you get?
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