justjim

I have a 2007 RX8 with 75,000 miles I track about 3-4 times a year for the last 2 years at Sebring, Florida. I have routinely been able to hit lap times of 2:45 and my best lap was a 2:42 when I first got the car with about 30,000 miles on it. I had an HPDE this past weekend, temps were 95+ and humidity was very high. I was sweating like a pig. The car ran flawlessly and my coolant temps measured on the Cobb AP were hovering around 220-225F. The engine is stock except for the Cobb AP.

I didn't time myself in the morning but the best I could manage in the afternoon was a 2:47 and several of my laps were 2:50 which is about 3-5 seconds off my usual times. So here is my question. Is my RX8 engine getting tired or is it just the heat? The car runs fine and without the stopwatch I would not know anything is amiss. I'm just wondering if
1. My compression is off, I've never had it tested.
2. The catalytic converter is clogging, ( I use premix with outboard oil).
3. The heat is the problem and I just haven't timed myself on these really hot days before.

dannobre

iTrader: (3)

By 75K miles you are loosing shocks for sure......that will make a difference in how the car feels when you push it

What are you using for tires and brakes...that will be an issue as well...

Motor...sure it can..maybe get a compression test to answer your question And the heat won't help

justjim

I'm using Nitto NT01s 255-40-17 on 9" wheels. I'm using Cobalt XR1/XR5 pads. Handling in the corners and braking doesn't seem to be the issue, I'm hanging or gaining on faster cars in the corners. My top speed at the end of the straights seems to be down from the 118mph to about 112mph so my thoughts turned to the engine. It was very hot and humid but then I thought maybe my cat is clogging. What are the symptoms of a clogged cat? It could also be that I'm getting old I'm afraid to get a compression test for fear of what it might tell me.

DarkBrew

Could be temperature. Have you taken your car to a dyno?

I'm struggling through a debug of power loss at high RPM. Didn't really know about it till dyno day. No other symptoms.
Check the usual suspects
Coils, plugs, plug wires, air filter, dirty MAF, dirty throttle body.
You can drop the cat and inspect it. I suspected mine but it was fine.
If your engine starts well and idles well then your compression isn't likely to be the problem

All I've found so far is a loss of MAF flow 6K to WOT... won't break 200g/s. (AP is an awesome tool )
The only mechanical issue I've found is a small leak in the SSV vacuum actuator. Once the unit is replaced I'll be able to confirm a fix. (or not)

Props to Jon316G for helping with the debug and to WCS for swinging wrenches with me.

olddragger

iTrader: (3)

if you ? the engine--take a vacum reading and look at the maf flow via your cobb. If you vacum is below 16 ot you maf flow reading is down then the engine may be tired.
OD

dannobre

iTrader: (3)

If your CAT was failing...you would know it on the track...it would get hot enough to melt the pavement under the car

Like others have said....check it out..and maybe get a compression test...cheap insurance..it will give you time to get your oil change receipts gathered up and be ready if you need a new motor

DarkBrew

Apologies to justjim,
OD, Under what conditions do you take the vacuum reading?

olddragger

iTrader: (3)

engine fully warmed and idle at no load. then at 2K--- same--no load.
OD

justjim

What is a good MAF reading at idle and at 2000 rpm under no load, I got up to about 216 g/s near redline in 2nd on the way home, and where does one connect the vacuum gage?

DarkBrew

216g/s is very good on a redline pull.