I didn't want to hijack 8C's thread for a peripheral issue, so here goes:

I've seen a lot of people claiming that their EGTs cruising on the highway are 1200-1300F. When you're driving along, not in boost at all, is this really true?

I find that my EGTs at steady cruise are more like 1550F. I assumed that the ECU is working hard to maximize my fuel economy, and that it is leaning out the mixture when I don't need power. Isn't that what feedback from the O2 sensor is for? The minute I crack the throttle a bit, the EGTs drop a bit, and as soon as I get boost and the RRFPR does it's thing, EGTs are right around 1300-1400.

Opinions?

Jon -

That is way to high for cruising - depending on how fast you are going.

55-65 on the interstate, I see 12-1300, 75-85 (imagine I am in Montana for the purposes of this conversation) it climbs to 1400-1425.

Did you uprate your fuel pump? Sounds like it is running lean in non-boost situations.

Hmmmm... even at a cruise I see around 1400°. Of course, my WOT temp is a lot higher, but thats another story. :)

You're probably right about your ECU trying to lean out the mixture back to stoich and causing the EGT's to raise up.

I am talking about "brisk" cruise, like 80ish.

Since there's no boost, there's stock fuel pressure, so the turbo and associated plumbing are invisible to the ECU, right?

The motor should be in closed loop mode, and thereby adjusting mixture constantly. So if the ECU reads the O2 sensor data and adjusts the mixture 'til it's happy, who am I to question the EGTs? :)

Perhaps it's just the slight additional back-pressure from the turbine that raises the temperature, even though the mixture is fine.

I thought the ECU only goes to closed loop mode at WOT. ???

I think closed loop was when it was using it's sensors to adjust, right? At WOT it is in open-loop is that is the case. It just runs off the ECU's internal fuel/ignition map.

I think that the turbo may be causing a bit more vacuum in the intake as well since there is a turbine in the way there too.

Jon,

I have the exact same results as you. My egt's are 1425-1500 at cruise depending on the cruising speed. If I give it any more throttle the EGT's drop rapidly as fuel is added. When I hit boost the EGT's really drop. I think it is just the ECU leaning out the mixture while cruising.

Keep in mind that I am dealing with 110+ degree weather though, so it may make a difference.

Also keep in mind the mounting location, and probe calibrations/brands could result in fairly significant differences when comparing it to other cars. I wouldn't be surprised to see a variation of +/- 100 or more when compraing it to "similar" setups.

Aaron
http://www.scoobymods.com

One more variable: What A/R ratio is your turbine housing? Mine is a very tight .48. My mechanic suggested that backpressure could account for 50 degrees or so.

Some interesting reading:

http://www.kemparts.com/tt07/tt07.html

This website explains in detail about open and closed loop modes and the O2 sensor.


On another note: I used to typically have 1200-1300F EGT's while cruising around. Temps would go up to anywhere in between 1350-1450F at WOT, even with nitrous. I can't say if my car was operating at optimal temps or not. This is where it was if it helps out any. Take Care!

Jon,

I had a .48 as well. It sounds like a very similar setup. ;) I say had as I am getting a slightly different setup currently capable of flowing the cfm needed at higher boost levels 12-15psi.

Aaron
http://www.scoobymods.com

60 MPH EGTs are 1350-1375.
80 MPH EGTs are 1475-1500. A/F meter indicates closed loop mode.
WOT drops the EGTs down to 1375-1400 and rise to max 1500 at 6300 rpm in 5th. :D
Idle EGTs drop to 800 after 5 or so mins.

Getting 300 to 360 miles per tank mixed driving.

~6 psi, Turbonetics T3/T04, WRX fuel pump, BEGI RRFPR, Zener @ 4.72V
I don't know the A/R ratio on the turbine though.

Why doesn't anyone taking readings in celcius? I have a greddy egt in Celcius and it's so much better with the needle going 3-12 X100 degree Celcius. Anyone remember the conversion to F so I can get in the conversation?
Joshua
Subaru Salesman

1300 = 704
1350 = 732
1400 = 760
1450 = 788
1500 = 815
1550 = 843

Jon,

I have the same EGT readings as you do. 1500 give or take on the cruise control; ~1400 at WOT, and 1400-1550 at partial throttle, depending on boost and load.

Possibilities:
1. Variations in EGT gauges and/or probes.
2. Variations in O2 sensor condition. I suppose an O2 sensor that reads on the lean side will tend to cause the ECU to run richer. (This is the fuel economy angle that Bosch uses to market replacement O2 sensors.)
3. Variations in fuel.

-WaC
Wayne

When people start comparing EGTs and wonder why their's is different, I start to think of all the variables involved with respect to sensor placement, etc. I'd like to point out one important EGT installation consideration that is rarely discussed here. Maybe it's too obvious to discuss. But, ...

It's essential that the thermocouple (that long tail attached to the EGT sensor) not be cut or shortened and that its end be brought inside the passenger compartment. Most EGT sensors we use are calibrated for 75° which means that the EGT sensor provides accurate readings if the end of the thermocouple is exposed to a temperature of 75°F. You won't find 75° in the engine compartment very often.

Just for the record, mine extends into the cabin and connects to the signal box directly with no snipping/extending.

Ditto for mine (8).
#3 Cylinder about 2" away from exhaust port.

From parts runs for a micro-garage day yesterday:
Air temp: ~80°F
Humidity: 90-100%

1. MY99 2.5RS:
N/A 2.5L
VDO EGT probe on cylinder #2, 4" from exhaust port
Cruise (75 mph) = ~1250°F
WOT = between 900°F and 1200°F (can't really tell due to slow response times).
Note: this gauge is ultra-slow, and took almost a minute to warm up to operating temps in the first place (SteveS is right!).

2. MY98 2.5RS:
2.2L with VF22 @7 psi
~9:1 CR, EJ25 injectors, fuel pressure 75 psi (est'd)
Autometer Competition Probe on up-pipe entry (after y-pipe)
Cruise (75 mph) = ~1450°F;
WOT = ~1400°F at 5000 rpm and under; 1650+ at 6000 rpm and above.

3. MY97 OBS:
2.2L with T3/4 @5 psi
9.7:1 CR, EJ25 injectors, fuel pressure 75 psi
Autometer Competition Probe on cylinder #1/3, 4" from exhaust port
Cruise (75 mph) = ~1510°F;
WOT = ~1400°F all RPMs

All gauges and pyrometers are in the cabins, unmodified probe leads.

I still don't see how you RS-T guys can run 7+ psi on stock injectors. :confused:

-WaC
Wayne

I see about 1400F when cruising over 70MPH. I would suggest that seeing close to 1600F while cruising is a Bad Thing, but I don't know for sure. If you have modified the lead wires for some reason (i.e. to lengthen them), then maybe you will see false higher readings since the resistance could be higher. Other than snipping the ends, my leads run directly into the "black box" supplied by Autometer. Note that I am running a type K thermocouple rated at 200F/s with 4' leads.

And Wayne, I've recently been messing with my boost settings and I am currently running 9psi on stock injectors. I don't have a fuel pressure gauge hooked up, so I don't know what I'm running when the RRFPR kicks in. I'm going to do something about fuel delivery, just haven't decided what. Whatever happened to the idea of using the Nissan injectors?

Steve
http://www.forcefed4.com

Oh yeah, one more comment:

2. MY98 2.5RS:
2.2L with VF22 @7 psi


BLASPHEMY! :lol:

Steve, I think your car is the Chosen One. Aside from the head gasket problem, it seems to defy tuning logic. Or you may have gotten extremely lucky and the injectors are going static just when the engine needs the extra fuel.

Both 2.2L motors are using unmodified 10' Competition Probe leads as supplied by Autometer. I now have a Westach 4' probe set. I will be able to check it against the Competition Probe.

SR20DET injectors (370 cc/min) should arrive sometime this or next week. We'll try them out on the 9:1 CR motor. I'll also install Legacy Turbo injectors (360 cc/min) in the 9.7:1 CR motor. Not sure when all this will happen, though.

-WaC
Wayne

Is the VDO gage ot thermocouple slow? Can I swap the VDO thermocouple for a quicker one?
If the whole VDO unit is bad (I highly doubt this), I just blew $132.....and IM gonna be pissed.

Just replace the sender. With the Westach sender, my VDO EGT gauge responds as quickly as a $300 GReddy gauge.

Where do I get the westach thermocouple from?

Bert Arano at Union7 has them in stock. union7@erols.com or 610-701-0717

Hey SteveS, the stock RS with the VDO gauge was me, and I also wanted to say, YOUR RIGHT!. I'll stop saying the gauge is so great, I just stress the probe sucks..

I never really knew what it should do, and Wayne showed me his setup in his car. So, my gauge is really slow. I did have the car up to WOT a few times for a long period of time prior to meeting with WAC (Stock '99 RS with Amsoil Filter and Rallispec 2.25" Cat Back), and the gauge never reads over 1450.

Paul G.

Thanks Jon, just ordered one...

I finally got around to installing the Westach Type K probe. It is installed in the driver side exhaust header. The Autometer Competition Probe is installed in the passenger side header. Both probes are connected to a Westach #254-19EP 2-position switch. The switch allows me to quickly select either probe and use the same Autometer pyrometer and gauge. Both the Westach 4' probe and Autometer 10' probe wires are uncut. The 2-position switch adds another 1.5' of leads to each probe. (Westach says that as long as the thermocouple leads are un-cut, calibration will be retained even if the switch leads are modified.)

I took some measurements at various engine loads:
Autometer Westach
1100°F 1160°F
1200°F 1240°F
1250°F 1280°F
1300°F 1340°F
1350°F 1410°F
1400°F 1460°F
1450°F 1470°F
1500°F 1520°F
This is not a true A-B test, since I didn't bother swapping the probes from each exhaust header, and I don't have a lab-quality instrument to calibrate each probe. However, when I first moved the Autometer probe, I noticed that the passenger side does run about 50°F cooler near the high end. So there could be a combination of calibration errors between the two probes as well as real EGT differences between the two exhaust headers.

This is the more important finding: the Westach probe is quite a bit slower than the Autometer probe. The best measure of response time I could think of was to force the injectors off and on under load, e.g. climb a long hill on the freeway and cycle the throttle between zero and WOT, and do the same going downhill. The Autometer's response time is about 200°F in 1 second, or 200°F/sec. The Westach's response time is about 200°F in 4 seconds, or 50°F/sec! This measure of response time seems to hold up throughout the normal EGT range of 700°F to 1500°F. (during testing, I just had to wait at least 4 seconds before recording the numbers.)

Why the difference? The Autometer uses an exposed junction, while the Westach uses a grounded (shielded) junction. The extra material in the shield adds mass to the thermocouple junction, and therefore slows the response time. For what it's worth, I recalled that the VDO EGT gauge had a response time on the order of about 200°F in 30 seconds or perhaps even longer!

Is the Westach probe fast enough for engine tuning? I'd say yes, for steady-state loads (make sure the EGT gauge holds steady for at least 2-3 seconds before taking the reading). But I'd be weary if you are tuning for drag-style engine revs and think that 1400°F is the true EGT while the needle is still climbing - it's probably a few hundred degrees hotter than you think!

Hope this helps,

-WaC
Wayne