dual digital EGTs
 

as i tune my way toward a gazillian hp i have learned a few things. perhaps number one is that if you properly instrument your car you don't have to be very smart to get it right.

instrumentation may be one of the better investments. it generally is quite a bit cheaper than blowing motors and wondering what happend and, OBTW, laying out serious money to fix the beast.

thru my power fc/datalogit i monitor and log digitally both rotor's egts pre turbo(s), exhaust backpressure preturbo of course, fuel pressure and all the other stuff like knock and afrs etc.

thanks to jeff feltman's electronic diagram i built my own (o k he wired it for me)translator box between my thermocouples and the datalogit. the box takes the sensor's voltage and changes it into 0-5 volts for my datalogit to translate into temperature. a relatively simple deal and inexpensive if you have the inclination.

OR

you can go to FJOracing.com and nose around til you find their dual egt translator box. retail about 160. not a bad deal. you will then need to buy a couple of fast reacting sensors/thermocouples. i recommend and use teamrip.com. instantaneous. 45 each.

BTW, i do think that AEM has such a box. maybe 4 channel.

so there's another option for you.

howard coleman

Howard, are you running the GZ LIM? I seem to recall reading that due to the equal length runners it helps to equalize EGTs between front and rear rotors.

i am running an UIM and LIM ported by Jose Le Duc. my egt's are within 30 degrees of even under boost.

i did finally do an experiment this summer where i placed one of the probes pre turbo and one post turbo to find out what the actual diff was on my setup. i found it varied greatly with manifold pressure but was about 340 degrees at one bar and above. generally i had always heard 200 degrees.

i do run a 3 inch DP from each turbo... my exhaust back pressure is 18 psi at 15 psi boost.

howard

How far down was your post turbo probe and what was its temp? Was this without alky?

3 inches from the V band. no alky. sorry, i don't have the logs as to temp.

hc

I love it when howard coleman takes us to school. Good stuff howard, you are always improving the way I plan to use my components!

I'm running out of inputs my Haltech will log...worse case, if I could only log one EGT (pre-turbo) which would I choose? (I have seen on occassion my front runner glowing more than the rear)

unequal LIM, unequal Exh. mani...but I can trim each inj as I see fit.

My thoughts are...
If I keep an eye on the dual EGT gauge, and trim the secondaries as necessary. I should be able to obtain accurate "tune-able" data using one pre-turbo EGT...if of course, I can't find another input.

Found this reading old threads

http://www.simplecircuitboards.com/Thermocouples.html
$41 shipped.

much cheaper than any fancy name brand...
SCORE!!!

Can someone explain to me the benefits of monitoring your EGT's. I assume it is a good measure of how hot your turbos are so you prevent overheating them. What about tuning? How can you use this info for tuning your car?

we are talking about EGT's before the turbo...this is useful in tuning timing advance.

here is a snip I grabbed from a post about tuning with EGT's

A. If the AFRs are lean and the EGTs are high you probably want to add fuel to the maps at those points and re-log

B. If AFRs are rich and EGTs are high, you may be experiencing excess fuel being burned off in the manifold, try taking a little fuel out in those cells and re-log.

C. If EGTs are high and the AFRs are in the normal range, you may have a timing problem in that area and you may want to retard the ignition timing in the affected cells and relog.

D. If the AFRs are rich and the EGTs are low, you can take some fuel out in those cells and re-log.


for people using Aux inj, either Meth or H2O, this cools EGT's...which could lead to running more timing advance.

For once good advice on the internet...

But aren't most EGT's too slow to detect exact point in the map? I always assume EGT gauges were all assumption and not to useful. If I'm wrong, please correct me.

you are probably right as to "most" egts.....

i was given 2 Greddy egt gauges and compared them against my digital setup. they were off significantly and were slow to respond compared to my digital setup.

i literally advertised the two in the classifieds, commented on how inaccurate they were and sold them for shipping cost alone.

as to the slow reacting question.... i use a Power FC datalogit and can, of course, replay my events. my egts correlate instantaneously w the other data.

there is no perceptable time lag. good old electricity travels at the speed of light. that's a bit faster than an analog needle.

howard coleman

Howard, thanks for that info.. But I always thought heat transfer to thermocouplers were the problem and only few very expensive couplers will be accurate enough at such high temps.. I guess I was wrong about this.. And if you say they are accurate, I totally believe you! I'm going to pick up a set and give it a try!

PHIL

So how exactly are you mounting the probe before the turbos?? Or do you have a single with some room between the turbo and the engine??

And from your info it seems if it was mounted after the turbo(s) that you can basically add 350 to that?? Not the most accurate way to do it, but I'm assuming that would be about the only way to do it for the twins. Or what about running the base map, or stock ECU, on a stock port and measure temps and tune for around that??

This is how Dubulup did.. But looks like a single turbo manifold.

Not sure about Stock twin manifolds though.. I have to go look at mine.

https://i7.photobucket.com/albums/y2...p/DSC08383.jpg

..

Most name brand stuff is, even when its expensive, like racepak.
But then again using a single wideband is also too slow...

Twinmani egt probe setup...

as i have previously posted, the readings are instantaneous. end of story.

FYI, the teamrip thermocouples are only about a half inch long past the threads. not at all like the ones pictured a few posts up. i drilled about an 1/8th inch hole in my manifold about 1/2 inch from the 1/2 inch thick manifold flange at the port. i welded a SS bung on and screwed the thermocouple in. it barely protrudes into the exhaust stream. i was able to place both bungs at what i thought was a similar point w regard to the exhaust flow.

as to how you'd do an OEM setup.... it would be next to impossible to infer any pre turbo egt from post turbo due to the restictive nature of the manifold.

howard coleman

Ahhh...ok now I see. I couldn't picture the manifold.

That also makes sense with the twins. This is a very useful thread. I may do this when I get the time to remove the turbos.

How about dual probes in the OEM exhaust manifold, preturbo? I see the photo afgmoto1978 supplied. Anyone with experience with this?

Howard, how do you know if your measured temps are accurate?

"how do you know if your measured temps are accurate?"

here's what the AD595 delivers:

AD595 Monolithic Thermocouple Amplifier with Cold Junction Compensation Pretrimmed for Type K Thermocouples

Product Description
The AD594/AD595 is a complete instrumentation amplifier and thermocouple cold junction compensator on a monolithic chip. It combines an ice point reference with a precalibrated amplifier to produce a high level (10 mV/°C) output directly from a thermocouple signal. Pin-strapping options allow it to be used as a linear amplifier-compensator or as a switched output setpoint controller using either fixed or remote setpoint control. It can be used to amplify its compensation voltage directly, thereby converting it to a stand-alone Celsius transducer with a low impedance voltage output.
The AD594/AD595 includes a thermocouple failure alarm that indicates if one or both thermocouple leads become open. The alarm output has a flexible format which includes TTL drive capability.

The AD594/AD595 can be powered from a single ended supply (including +5 V) and by including a negative supply, temperatures below 0°C can be measured. To minimize self-heating, an unloaded AD594/AD595 will typically operate with a total supply current 160 µA, but is also capable of delivering in excess of ±5 mA to a load.

The AD594 is precalibrated by laser wafer trimming to match the characteristic of type J (iron-constantan) thermocouples and the AD595 is laser trimmed for type K (chromel-alumel) inputs. The temperature transducer voltages and gain control resistors are available at the package pins so that the circuit can be recalibrated for the thermocouple types by the addition of two or three resistors. These terminals also allow more precise calibration for both thermocouple and thermometer applications.

The AD594/AD595 is available in two performance grades. The C and the A versions have calibration accuracies of ±1°C and ±3°C, respectively. Both are designed to be used from 0°C to +50°C, and are available in 14-pin, hermetically sealed, side-brazed ceramic DIPs as well as low cost cerdip packages.


combine two of the AD595C chips w the appropriate 0-5 volt conversion circuity, a couple of higher quality K thermocouples, AD's look up table for calibration and........ move on to other things.

howard coleman

Edit ..... wrong place

Duno how this happend but my Quote ended up in the wrong thread :\

You can get those chips as evaluation units for free from the manufacturer shoot they shipped them to me next day. Its an extremely simple circuit to create and run them. The thermocouples cost and possibility of the tips breaking off and going through the turbo has always scared me.