Track Day at High Plains Raceway (Good News, Bad News and O Sh!t News)

[Jon W.]

Have you checked the head for warping?

[scannon]

The closer pics are great. I'd have to agree with you. I certainly don't see the kind of marking I would expect from a blown seal ring in the gasket. I suppose it could be a quite subtle leak that we've not seen before in our experiences.

 

I don't have any other ideas. You might want to take a closer look at the cylinder liners for micro cracks. Is this engine one of the later alloy block versions?

 

The only other way to Siamese the cylinder breathing would be through cracks in the head or broken piston rings. If the piston rings were knackered, I'd expect you'd have seen a lot of oily gradoo collecting in the oil breather/catch can system. Did you happen to monitor any outflow?

 

Might be time to give Keith a bell and see if he's experienced a similar anomaly.

This engine has a cast iron block and aluminum head. Visual inspection of the cylinder walls didn't reveal any cracks no does the head show any.

 

Oil was down about a half quart, most of which was in the catch can. This is normal for this engine on a track day. No lumps or crud in it when I emptied the catch can into the recycle jug.

 

I haven't checked for a warped head yet, Rob is dropping off a good straight edge in the morning. If I don't find anything I will put in a new gasket, get it running and buy a kit to do a full leak down test. The head gasket alone is a little over $70 from the dealer with a club discount. I thought NAPA might be cheaper but they want $90+ for theirs.

 

I've been talking with Bill Cardell, owner of Flyin Miata and he has pretty much the same thoughts we are seeing here on the forum. He uses factory head gaskets on his engine builds and never has a problem with them. Neither of us have heard of a blown head gasket on a Miata but I'm sure it must have happened in the past.

[scannon]

I checked the head and block for flatness and everything is within tolerance per the factory service manual. One spot is .005" while the spec is .006". Of course, it is in the worst possible place, the divider between #2 & 3 cylinders on the head. However, there is absolutely no indication of leakage through the head gasket at this point.

 

Now I have to decide if I want to do a cleanup cut on the head or live with it. I really do not want to up the compression ratio since I am running a turbo with the stock compression ratio.

 

Any opinions?

[Hank]

Can you deck the head (flat) and run a thicker gasket?

[scannon]

Can you deck the head (flat) and run a thicker gasket?

If taking off only .005" would do it, the increase in compression ratio would probably not be a big issue.

 

I recall some thicker gaskets being available but also recall they were very troublesome.

 

I am going to put it back together with a new OEM gasket and see what happens. If that doesn't fix the problem and I cannot find anything else wrong I will just swap out the engine for the spare and use this one to build up a proper high HP motor with all the forged internals and such. Should be able to easily get 350 - 375 hp on pump gas with a built motor.

[scannon]

An update: I got the car running yesterday with a new head gasket. After warming it up I ran a compression test with a friend's gauge. This time it read 125, 95, 95, 140. My old gauge is in the garbage can.

 

The engine runs fine and hasn't overheated so far but it was only in the high 80s today and of course, nothing I can do on the street will put the heat stress on the system like a track day does.

 

It runs fine although stumbles a bit before it idles when I come off the throttle. I adjusted the idle bypass screw but couldn't get any change in idle RPM. I'll tinker with it a bit more to see if I can fix that minor problem.

 

I'm going to leave it as is for the time being and plan on doing a build up of my spare engine with forged internals and maybe some head work this winter.