"Optimum" EGT's?
 

Guys,
This topic has probably been covered before, but I couldn't find it under the "search" button. Anyways, I just wanted to know the optimum EGT to look for under HEAVY load and also cruise...obviously when cruising on the freeway, the EGT's are higher, but what is considered TOO HIGH? Any feedback from knowledgeable tuners is GREATLY appreciated!


***Also, I have the DUAL EGT guage, but wanted to know how much deviation from each rotor is acceptable?

I dont know whats allowd for deviation between rotors, however have some insite into optimum temp's

The way it was explained to me was there is no magic number you can shoot for with egt's. Engine type, modifications, egt location etc can drasticly change what etg you are going to look for.

I was informed the the only way you can truely find your peak egt is on a dyno where you can adjust ignition while holding an rpm and watch tq in real time. My understanding is your egt will start to climb very quickly when you have to much advance, power will start to fall off etc, back off 2-3 deg, and your done. I was told to do this a few times and make sure you are ending up with the same egt, if you are, then you have it. (I belive that your fuel tables have to already be done to be doing this)

I suppose the same method could be used with a good knock sensor and some datalogging software, however I am realizing how hard it is to actualy 'road tune' effectivly, and how innacurrate it can be, so i suggest a dyno

-Jacob

Here are some opinions/readings form members of this board:

900 C 1652 F absolute safe max 1600 F is optimum; 200-300 F lower on the dyno

EGT readings of members and location of probe
1390 4"
1292 6"
1500-1600 mani
1652 mani
1200
1450 6"
1300 4"
1292
1652 mani
1472 cruise 1292

I recently dynoed my car (stock twins) while data logging EGTs. The only changes made were timing for 5 runs. From this single experience, I assume you could find an optimum EGT for a specific EGT for a particular rpm/torque but I would guess that that EGT would only be optimum for that rpm and torque.
If you are attempting to isolate peak EGT, it appears to happen (for my car) near the end of the run or closer to peak horsepower, not peak torque. Perhaps you could perform a base run to obtain a peak EGT, then on a following run hold steady at a particular rpm as CrackHeadMel suggests then calculate a proportional peak EGT from that measurement.

[QUOTE=88fc3sw/HX83]...obviously when cruising on the freeway, the EGT's are higher/QUOTE]

Wrong, are lower there. Jacob is correct, the only way to tell true EGTs is to keep the engine at a constant load at a fixed rpm. for a period of time.

Some dynos can do this and step up the rpm. Thus in one dyno run the engine can be held constant for a fixed period of time in fixed rpm steps. This would give the best information from your log.

[QUOTE=cewrx7r1]
Tell me how it's wrong? Isn't a LEANER A/F ratio gonna make the EGT's HIGHER?

Have you ever tested this? I have. Leaner is not hotter unless associated with high engine loads. One match burns the same as 1000 matches, but the 1000 would measure a hotter temperature. At cruise most of the heat is absorbed and radiated thus the temperature is lower, under power more of the heat goes out the exhaust thus higher temps. Power = more heat and higher temps.

Then why is my EGT's HIGHER when driving on the Freeway?...<---TESTED!

Chuck,
Keep in mind, my motor is not "Fully Tuned" and I'm still in the "break-in" period. I have yet to bring my rpms above 4500 rpm. When I said that my EGT's are higher on the freeway, I was comparing them to the EGT of the motor idling and not at WOT...:)

FYI: My probes are placed about 2" from the exhaust port.

There seems to be a lot of misinformation being brought forth in here...

Load has really nothing to do with EGT's, only except the fact if we're leaning to the point of misfire - leaning under heavy load at this same point will kill your engine due to detonation.

Now, I'm assuming we're not all trying to brag about max peak EGT's and risking our engines!!!

The highest I've seen an EGT go was 4k - 4.5k RPM freeway cruising, which implies very light load.
The EGT's was going OVER 1100C!!!
That's slightly OVER 2,000F!!!
Now, I was trying to lean the AFR for better gas mileage (Haltech), and I was surprised the 13BT actually didn't misfire under those conditions...
Now, this was too hot for my tastes, so I richen it up and drop the EGT's to 950C.

EGT, under light load conditions, escalate in relation to RPM.
If trying to run lean, it'll tend to run hotter and hotter as RPM's climb.

It really has nothing to do with load.
At WOT, EGT's tend to stabilize and not really rise...well, this is how I tune Haltechs at least.
Try running 14.7:1 AFR's all the way to redline - it gets HOT really FAST!


-Ted

Thanks TED, that's some useful information to know about!...So what EGT in degrees F should I NOT reach?

Will location of the sensor/probe have an impact on the readings you are getting from the EGT gauge? If so where is the best place to tap and place the probe?

This is the same question Ive had. About to install a divided manifold and I have no clue where to tap the EGT, i.e., which runner and how far from the engine.

You are correct, Jim. I've seen the same thing myself.

B

I put mine 12" down the dp from the turbo for my wb, im going to put my egt right next to it

I put my egt probe on the downpipe about 5-6" from the turbo hot side. Untuned I'm seeing about 1200f at about 3K rpms.

This response is to provide some data and not an interpretation of that data. One must realize that this data is from one dyno run (WOT) on a particular twin turbo car. I do have 4 additional runs that were logged. Perhaps others with logged EGTs would provide their data to help understand EGTs more fully.

For ease of viewing open the file in Excel.

Thanks for confirming this B...for a minute I thought I was CRAZY! Does anyone know how hot is TOO hot for "us" rotor heads?

i ran SCCA GT3 for 6 seasons, a tube frame rx3. the car was originally Roger Mandeville's 3 time Nat Champ IMSA car. Roger built my motors for 3 seasons and Daryl Drummond built my motors for 3 seasons. the motors were full bridgeport 12As running a Weber downdraft. usable power was from 7000 to 10,000. normally aspirated, 259 hp limited by the 38 mm choke ( think restrictor plate.)

the only tuning i ever did in 6 seasons was to run the car in top gear to redline and look at the EGT gauge. we then changed the main gas jet if necessary to attain 1750 degrees. if it was cold we leaned the jets and if it was hot we added more fuel.

the 1750 was derived on the dyno. i had virtually no motor problems in 72 National races and 5 Runoff weeks running 1750.

of course we are in a slightly different world making 400-600 hp and w a turbo.

i will shortly ( 2 weeks) be refiring my motor for 05 and now have 2 egts each located one inch from the exhaust port. i will be logging temps as well as exhaust manifold pressure and fuel pressure and do plan to be on the dyno in early april.

i will report in... BTW books, thanks for posting the interesting log. this could develop into an excellent thread w additional contributions as tuning using egts is not only the way to make max torque thoughout the rev range but keep the motor together .

howard coleman

Howard,
Thank you for your input! 1750 seems really high...my dual EGT only goes to 1600...lol. Anyways, maybe we should make this thread a "sticky"!

I am currious what are you guy's seeing at iddle I seet between 400 and 500 deg C, and then when I step on it even when I start to boost .5 bar I only see tepms as high as 600 Deg c. is my timming advanced too much?
AFR at idle is 13.9
AFR at WOT @ .5 bar is 11.4
also on the highway I see 600 deg c again and that is at 14.7 afr.
Anybody with some insight as to why my EGT's are soo low?
also the EGT Probe is placed 4 inches in the DP from the Turbo Outlet.

I've noticed the low EGT's on the highway with my TII as well.
AFR in the 14's, timing around 32-34* BTDC, EGT around 650-700C (1200-1300F).
Probe is about 6" down the DP.
Tuned by Steve Kan.

using the aforeposted egt #s...

approx after manifold temp av 1300 f
approx manifold egt 1575 f

general chatter is temps cooler when egt is after the turbo by 200+ degrees so the above numbers would seem to be in the ballpark.


jreynish idle temp appears in line: 450 c is 842 and i hear lots of people idle around 900 f.
600 at cruise and under boost: 1112 f plus 250 to get to the port temp 1362... probably a bit cool by 200

obviously there's ignition and fuel. since his afr is o k i would really look at total timing advance carefully.

if you are firing early your egts will be low due to the increased time for the explosive force and temp to cool before heading out the exhaust.

firing too late creates the opposite effect: too much of the force rushes out the port instead of driving the rotor. result more exhaust temp. an early opening exhaust port also can be a cause of higher egts for the same reason.

howard coleman

thanks Howard,
I would however like to know what your timming advance is for highway cruising, your proble location, and the resultant EGT's. Even though My AFR's are 14.7 I still am only seing 25mgp... So I am thinking my timing could use a little bit of an adjustment.

It's hard to say.
As a general rule try not to go over 900C, which is about 1600F.
You better NOT be getting that kinda EGT's with the sensor after the turbo in the downpipe!

I recommend anyone who is serious in playing around with EGT gauges to get it "calibrated on a dyno".
Minute changes in fuel and / or ignition timing will show up as a change in power.
Get too much fuel - power will drop, but EGT's will drop.
Get too little fuel - power will drop, but EGT's will rise!
Get too much ignition timing (advance) - power will drop, but EGT's will rise!
Get too little ignition timing (retard) - power will drop, but EGT's will drop.
Extreme ignition retard will actually cause fuel to burn out the exhaust, which WILL cause EGT's to RISE - this one stumps a lot of people.

I've seen significant deviations between identical EGT gauge brands on different engines.
I dunno if it's the EGT gauge / sensor or the different engine set-up's, but it could be off by as much as 40C - 60C!
That much variance can kill an engine if you're shooting for an EGT "number", so I really don't give out recommendations on what target EGT to shoot for - ala like wide-band tuning.
Seriously, I don't want to be responsible for anyone hurting their engines!
There is so many variables that affect EGT, and the list is HUGE.
One of the more interesting variables is the turbo (turbine) itself.
I got to messing with a Garrett GT35, which uses a very "open" turbine wheel, and EGT's were VERY high due to more heat passing through the turbine section.

Most of the aftermarket (Japan) EGT gauges like to "redline" at 900C - this is a pretty good guide for MAX EGT's, especially on stock ECU's.
It would be nice if all of us could install EGT gauges on stock RX-7's and watch them for a few weeks.
You get a very good idea of what the EGT gauge should be displaying at any certain situation.


-Ted

WOT = redline?
What kinda ignition timing advance are you running at those points?
If you're getting 600C @ 4k - 7k, the EGT's are too low.
Since AFR's are ok, I think you're ignition timing is too retarded.
I would run about 25 to 30 degrees of total ignition advance at 7psi.


-Ted