j9fd3s

anyone know? i expect at wot they would be pretty close, but what about the rest of the time?

Rasputin

No, the catalyst temperature is about 50°C higher at WOT and high engine speeds dur to the exothermal nature of the reactions taking place in there.

Fabrice

j9fd3s

thanks a bunch! so now i just need the max temp for the cat i wanna use and tune around that?

mike

elysium19

iTrader: (1)

Yeah- I'm trying to find this same information for the stock cat, as well. (Or for aftermarket high-flow cats as well). I want to install an EGT gauge to directly measure approximate cat temp, and keep that temperature as a threshold during tuning.

I know that higher temps will decrease cat life, but any guesses as to the normal operating temp, and what temps would melt the cat in a matter of weeks? I'll go for somewhere between the two :-)

c41250n

iTrader: (5)

so you're planning to tune your turbo kit with the cat?

c41250n

iTrader: (5)

so you're planning to tune your turbo kit with the cat?
do you have an inter-x ?

TeamRX8

iTrader: (25)

the difference will be dependent on several factors, I see a blown engine in the making ...

Razz1

How can you see with that bag over your head.

j9fd3s

no not really, the rx8's factory ecu is tuned to keep the cat under a certain temprature. somehow the factory rx8 ecu knows the cat temp too.

i just need to know approximately the max temp for the cat, and then thats one of the tuning limits....

mysql101

the car has a temp sensor for cat. the canscan can read it. and maybe the scangauge with custom codes.

w0rm

Is that sensor bung between the 1st and 2nd cat on the stock pipe, or before the 1st one? I thought it was exhaust temp, but can't remember since changing the pipes.

TeamRX8

iTrader: (25)

Supposedly the OE cat shouldn't see more than 1600 - 1650 degF continuous for very long, the CAN signal for CAT TEMP is read from the 2nd sensor between the dual cat bricks

j9fd3s

yep, if you let it go higher the cat turns liquid, got the tshirt on that one

20b + converter + leading ignition failure = smoked carpets....

rotorocks

Not happening!
With the turbo (in boost) the EGT temps easily register in the area of 1800. even when I leaned out the cruising AFRs I was seeing 1600+ temps at highway speeds when not in boost.

Tuning to keep your EGT's low, will make your car run at 150 miles per tank, and retarding your ignition will shave quite a bit of power. Not fun at all

But you are welcome to try, and post the results...

slavearm

Bah... I have melted every cat made for the RX8 now. I even got a free lunch from the Steelcat guy after he swore up and down I couldn't melt it. If you want to keep a turbo and a cat... you might want to relocate the cat further down the midpipe.

stickmantijuana

slavearm, when do you plan to visit FL?

MazdaManiac

iTrader: (3)

A bunch of things:

1) The CAT temp is computed by measuring the resistance across the rear O2 sensor's heater circuit. There is no separate sensor.
2) This computed value (via CANScan) is way to slow to be useful for anything.
3) You can't tune using EGT. EGT is used as a baseline reference after you already know the proper A/F for peak torque. I've already written extensively on the subject, so do a search.
4) Leaning out the A/Fs will increase EGT up to a point before they go down again and that point is way past 16:1.
5) Retarding timing or having unusually slow combustion will also increase EGTs to a point.

Vlad - your temps seem just a tad high (maybe 200°F), but every car is different (see point #3) and I don't know where your sensor is positioned.
Mine is right at the inlet to the turbo, which is 2" from the rear exhaust port and I see 1200° - 1300° in off-boost cruise and 1600° - 1700° under boost at the torque peak.

rotorocks

Well Mine don't work anymore. I think it has burnt
It is positioned at the beginning of the midpipe, right after the flange and before the CAT, or where the CAT was.
During the summer, I had the timing pulled and set at very conservative levels to avoid surprises in a 100F days which may be the cause of high exhaust temps.
I know, that the temps increase as mixture gets leaner. (should not have used the word "even" in the sentence that begins with "Even when I leaned out..."
I was just trying to make a point: on my car the AF is in the area of 14 - 15.7 when cruising (based on the RPM). Tuning down to 10-11:1 AF at cruise, will lower the EGT, but at the same time make the car spit fuel through the tailpipes.
You are correct, Retarding the ignition will not do any good in this case.

MazdaManiac

iTrader: (3)

Well, I run really conservative timing as well (I'd like to see your timing MAPs for the Int-X) and my probe is even closer to the engine, so my EGTs should be higher.

rotorocks

I don't know...
different gas, different ambient, different AF, different timing, different intake temps... Too many variables. It's all good as long as there are no pings
The timing is quite aggressive now that the humidity and temps are down.
I haven't taken any screen shots lately, but in general, it is around 30degrees overall, with the area of 5000 - 6500 pulled back by 5-7 degrees.
I can't remember what it is on the pressure based MAP but it is darn near dangerous. I did hear a small ping a few days ago while boost at about 10 PSI and eased off for that specific area, but it is close to scary Power is sooo addictive.

TeamRX8

iTrader: (25)

that's your problem right there, you won't solve the problem using a low cost solution

MazdaManiac

iTrader: (3)

No, that's not the problem.
Its the ton of EGT combined with residual combustion that kills the CAT in a turbo installation.
Turbo people are seeing several hundred degrees more EGT and continued combustion in the CAT, something your car won't see, Team.

MazdaManiac

iTrader: (3)

Could you take a few quick screen shots of your timing maps? That would be really useful to me.

TeamRX8

iTrader: (25)

so then you;'re conceding that the EGT exceeds 2050 degF?

MazdaManiac

iTrader: (3)

Nope. Doesn't need to.
The sustained EGT of 1700° or so is only the "softener". The fact that combustion is still occurring inside the CAT is what takes it down.

In any event, there is no CAT made that will sustain +2000°F for any useful amount of time, despite what anyone has sold you.