Forgive me for some slight cross-pollination.

The quick backstory is that I have owned a 2011 RX-8 for about 2 years now. It currently has 28K miles on it. I just bought a 2004 MazdaSPEED Miata last week. It should arrive next week or the week after. If I think it has potential on the track, the 8 will be for sale.

The 8 has been a great car. I absolutely love how it handles on the track and how smooth the power delivery is. But it has always been weak in the power department. I have always felt the need to deploy oars and row on the straights on track days. Right around 20K miles, I noticed it missing a bit, so I replaced the coils, plugs, and wires with a BHR kit. Then, I had the cat inspected at the dealership. With a clean bill of health, it seemed to be back to its prior performance level--it perked back up a bit. Mine has always outperformed the other RX-8s at the track, but those guys know they are down on compression or have other problems, and are quick to admit it. They point to mine as how a healthy 8 should run. OK. Fine. Makes me feel good.

This is where it gets strange. I took it to another track day yesterday. It was a completely different car. I'm not saying it suddenly had the power of the gods or anything, but it was much faster. Shift points were different all over the track. I was up-shifting to 4th much sooner and more often, because the car was actually reaching 95mph and 8.5K rpm sooner. My lap times clearly reflected the difference. I normally turn in laps at 1:35:2 very consistently on this track. Yesterday, I was consistently turning in 1:32:9 on average. That difference is absolutely huge. And, it wasn't me or the conditions or anything environmental. Same tires, gas, oil, everything. Similar weather to the last time out too. IT WAS THE CAR.

The obvious question is, what happened? Vacuum leak that mended itself? Clogged cat that broke up and blew out? Stuck butterfly in the throttle body that became unstuck? Stuck VFAD valve that unstuck itself? Dragging a brake pad all this time? Pressure plate that was never fully clamping for some impossible reason? It knows it has competition on the way and wants to prove itself?

I'm going with that last one.

 

Accidental shot of NOS?

 

Well, I did sneeze a couple of times (which is weird in a full-face helmet).

 

Maybe you are just getting to know the track better and therefore are putting up better times with it?

 

Don't underestimate the importance of the air temperature in the efficient running of the engine. I had a time trial event where I ran two practices sessions, one qualifying session and one timed session. I ran 1 1:50 which I had done previously in the year during the coolness of spring. However, this summer TT resulted in sessions that were consistently 3 seconds slower and the only variable was that the temperature increased from in the low 70's to high 80's and low 90's.

This was probably exacerbated by the fact that I was at a mile high altitude which further reduced the air charge. RX8's really need a lot of oxygen when running wide open throttle.

 

As much as I would like to take credit for it, I don't think it was me. I tend to improve about 0.2 seconds per track day on average. 2.3 seconds on average is huge. Weather conditions were similar to the prior track day (65 degrees and clear), and I am only 500 feet above sea level, so I am pretty oxygen rich here at all times. To put things into further perspective, I was running on my street brakes, as my track brakes are shot. So shave another half second off my average lap time.

 

In that case I'd guess it was a clogged cat that blew out.

 

I'm really going to kick myself if I find out I could have installed a BHR midpipe 2 years ago and had a much more powerful car. If that were the case, the MSM would very likely not be on its way.

 

Just for fun, here are 2 videos taken at the same track at the same time of day with similar weather conditions about 1 month apart. The main differences are that I have an instructor in the car and my track brakes on in the first video. I am solo and running on OEM brakes in the second video. The presence of the instructor makes no difference, as I drive ***** to the wall either way when I am not in traffic.

First lap is a warm-up lap. Last lap is a cool-down lap. So, ignore both of those.



[The turbo'd spec Miata referenced in another thread makes a guest appearance in both videos.]

In any case, the difference is obvious to me when watching laps 2-6 in both vids. On the front straight in the first video, I shift to 4th right before entering the long sweeper and barely have to brake at all since I am barely able to manage 80mph there. On the back straight, I almost never shift to 4th, because I don't need to before hitting the Ricochet turn--again hitting about 80mph max. In the second video, I always need to shift to 4th right at the starting line on the front straight, because I am miraculously running 95mph there, and I need to brake hard going into the turn. On the back straight, I shift to 4th nearly every time at the halfway point to the Richochet turn, because I am going 95mph there too. (You can occasionally hear the beep, which is right at 100mph in 3rd). The car sounds fine in both videos. I don't hear any evidence of anything wrong with it and never have before. It is just simply faster now.

 

getting the other person out of the car is the difference..

really.


beers

 

Nope. I had an instructor in the car all morning in video 2, and he was a 250 pounder. Sure, the car was faster without him, but it was still a lot faster even with him. In video 1, the instructor was 110 lbs soaking wet.

 

We are finally supposed to have some decent weather this weekend. So, I'm planning to put the car up in the air to see what I can find. Of course, it will be hard to tell anything since it is now back to putting down normal power, but I'll check everything anyway. Obviously, I'll start by focusing on the cat, since it is the simplest and most likely explanation. The fact that it was just inspected by the dealer and given a clean bill of health makes it even more likely IMHO.

 

This is something like trying to prove a negative. The car is faster through no intervention on my part. The only thing that changed was going from track brakes back to OEM. That raises the possibility that I might have somehow been dragging a brake pad before, but I saw no evidence of that when I swapped the brakes. And, I swap the brakes frequently, so I would have noticed.

Anywho, I pulled the cat tonight and thoroughly inspected it. With a small, ultra bright flashlight shoved up the rear end, I rolled the cat around and looked through the honeycomb at every angle. I found absolutely no evidence of clogging or anything else. It is a good cat.



Then I pulled the plugs. Each one has some carbon buildup on it, but the electrodes are clean, and I saw no trouble signs.

Still a mystery.

The MSM turns out to be no competition for the 8 for now, but they look cool parked next to each other.

For all its little frustrations, the RX-8 is such an awesome car, I can't see myself letting it go just yet. The 8 rides for another track season.

 

I just realized I have data from one of the track days on which my car was painfully slow. Anyone see anything wrong here? There is a CSV file in the shared folder at the link below. It is clean and virus free.

https://onedrive.live.com/redir?resi...t=folder%2ccsv

 

Did you have the BHR kit in for all track sessions? Also you could have blown some carbon off the internal parts.

 

Yes. The only thing that changed was brakes. My track brakes were worn out, so I put my OEM brakes back on. In theory, that should have made me slower.

The three working theories that make sense are:

1. The cat clogged at the back and blew out. I would not be able to see that with the inspection methodology I used. I simply made sure I could see through all the honeycomb from the front using a backlight. This makes more sense after driving the car to work Monday, as I noticed the very slight sound of marbles in a can coming from the muffler. I'll pull it this weekend and see if I can shake anything out of it. I also noticed a stronger than normal exhaust odor. This is the most likely explanation.

2. I was dragging at least one brake pad. I tend to doubt this, because I change my brakes frequently and always check for that. I am very meticulous about the condition of my brakes and inspect everything every time I change them, so I would be very surprised if this was the problem. Possible but not probable.

3. The engine was carboned up pretty badly, and I finally blew it out. I bought the car with 10K miles, and the previous owner drove it like a grandpa. He actually told me he tried to keep the tach at 2K as much as possible to get better gas mileage, which seems to be what the manual recommends (didn't know people actually read those). He also drove it mostly in the city on short trips (it didn't even have a toll tag, which is unheard of here). Maybe I should decarb the engine for good measure. Still, as 'spirited' as the last 18K miles have been, that should have taken care of itself to a good degree long ago.

Or maybe I should stop trying to prove a negative and just enjoy my newly faster car! :D

 

Just because I hate it when someone posts a thread with a problem and never comes back and posts the resolution, I'll update this thread with where things stand now.

I removed my muffler and poured a few little chunks of catalyst out of it. I took those along with the car to the Mazda dealer for a cat test, which it failed. The dealer offered to replace the cat under warranty, but I declined. There seems to be just enough catalyst in there to fool the downstream O2 sensor into thinking it is working, and I seem to have a few extra ponies now. I'm going to drive it like this until I decide to get a BHR midpipe, and have the cat replaced then. I'll swap the new cat back in a few hundred miles before inspection time. I really want the BHR, but really do not want the CEL that comes with it.

 

Since it's ceramic, the remaining part will probably shatter in fairly short order.

 

I thought of that, but decided to see how long it lasts. I have years left on the cat warranty, so there is no hurry.

 

Anyone else wish to give their thoughts on the wisdom of waiting to replace the cat when the dealer is willing to do it under warranty now. I don't want to sound like a naysayer here but Mazda dealers can be so wishy-washy on approving repairs under warranty, there is no guarantee that down the road something you may have done to the exhaust system could give them the opportunity to deny your cat replacement under warranty. If I was in your exact situation I would take that cat replacement now under warranty and not risk an expensive surprise down the road. Anyone else feel this is a valid argument here, or am I wrong on this advice. I have seen some stranger outcomes in 42 years of rotary car ownership.

 

I appreciate the concern, but I'm not really worried about warranty problems in the future in this area. The service manager has turned into a pretty good friend, and cat warranties are federally mandated.

I would really like to get the BHR, but I really don't want the CEL that probably comes with it. And, I need new track tires before season, which starts next month. My car money will be tied up there soon.

 

Gave in and ordered that BHR midpipe today. Next track day is March 7. Can't wait.