I took the z out for drive today with a buddy of mine.  He mentioned that he saw some "puffs" of smoke between 90 and 100 mph.  I revved it up to 4500 rpm in nuetral and there is no smoke.  So Z car brain trust... any thoughts?

Was the window open?

The best way to find out how your car is running is to read the plugs

I did have the windows open.  Unfortunately, I had no Cigar or other recreational smoke so I'm left to believe it was the engine;)

 

I've looked at the plugs recently and they all look good.  It runs fine around town with no smoke, which is why I'm perplexed by the possible smoke at high speeds.

If you watch closely when driving aggressively, does it smoke when you back off on the gas, or shift?

he saw some "puffs" of smoke between 90 and 100 mph.

Could really use a lot more detail.  Where was your buddy?  In the car or behind you?  Where were the puffs?  In the car or behind you?  How much time did you spend between 90 and 100 mph?  Seconds or minutes?  What was going on with the engine, were you goosing the throttle or just cruising along at 95 mph?

 

Literally, it's not even clear that it was your car that was puffing smoke.  Maybe someone had a camp fire going and your buddy was looking out the window - "Hey look, I see some puffs of smoke".  Kind of kidding, but seriously, there aren't many clues here.

Do you or your friend have a GoPro? I watched video of my car shot from someone with a GoPro and saw how bad of an exhaust leak my car had. I also learned about exactly how bad the body roll was. See for yourself (and put it on 1080p).

https://youtu.be/k6xXvITd6Rk

longer video https://youtu.be/k6xXvITd6Rk

Thank you all for getting back to me on this.  Steve, I will have to try the GoPro.  Zed, My buddy was driving behind me and mentioned he saw "trace puffs from my exhaust pipe".  We were over 90 for several minutes at a time.   The engine was cruising not shifting.

Steve, just watched your video.  That looks like and awesome run!

So, throttles mostly open, engine working hard to push the car.  Did it miss at or stutter at all while at speed?  Does the engine use any oil?  Could just be an occasional oil ring letting some oil slip by.  Or worn valve seals, same thing.  Or a leak on to a hot manifold, vaporizing.  Do you ever smell burning oil?  It has a distinctive odor.

 

It's an interesting puzzle, but if everything else is perfect are you going to tear the engine down to fix it?  Might be one of those things you live with when you have an old engine.

Zed, I think you might have figured it out.  I went out and looked everything over and I did have some oil leak out of my oil cap.  I guess I didn't have it fully tightened down.  Since there was no stutter, but it was down a little on oil.  I will just keep an eye on it.  I certainly hope ring and valves aren't the problem since they only have 40K miles on them.  Thanks again everyone for the feed back.

Cheers,

Scot