EGTs, not just for breakfast anymore
 

i have been digitally logging (Power FC/Datalogit) EGTs pre-turbo for a couple of years.

quite easy to fixture and inexpensive. get the FAST acting (instantaneous) thermocouples from TEAMRIP.com, around $50 each and the solid state signal convertor at simple circuitboards.com ($35 ea).

connect to your dataloggit and start logging.

recently i realized that i had been focusing on my egt target at one bar (1550 F preturbo) but had not really considered the transition area from zero to 15 psi.

a look at my logs showed good AFRs in that area but EGTs around 1050!

so i called my go to guy, Jose Le Duc, and found that the number should be 1420!

here's the point.... my AFRs were fine. BUT my egts were, uh, not fine.

so we worked the timing and before we ran into an unrelated problem (inconsistant alcohol pressure) had the egts up to 1350.

lots better spool, torque etc.

this points out that AFRs aren't everything.

get tuning.

howard coleman

awesome advice and well explained

did u end up increasing the timing overall? is this on the stock twins or a single? and finally are you running dual EGT probes or just one? interesting observation on the EGT's during spool

So you're shooting for

0"-14psi 1420 and 15psi+ 1550

Is this correct?

yes, we increased the timing.

my setup is two garrett TO4s. total airflow is similar to a GT42 but at 25 psi.

i have an EGT probe in each of the two runners between the engine and turbo.

and yes, 1420 to one bar and 1550 after.

should be back on the dyno this week w my re-jiggered alcohol setup.

hc

How much should we add to the temperature if the bung is 6" or so downstream of the downpipe?

wouldnt you reduce the temp if it was on the downpipe? since its further from the combustion area

Yes, EGT's post-turbo are lower than pre-turbo. Lower because the turbine absorbs heat that's wasted from the combustion.

Jack

nope... the exhaust gets heated up at the turbine.

IMO too many variables... why not move the bung pre-turbo? not really that much work involved.

Howard,

How did you calibrate the sensors so that the DL will record accurately?

"How much should we add to the temperature if the bung is 6" or so downstream of the downpipe?"

i did a study re pre and post turbo egts (i actually digitally logged both at the same time) and found the relationship is quite variable depending on where you are on the map. there are numerous posts on this board stating you add 200 degrees or whatever. unless you have tested post and preturbo i believe that post turbo egts are of low value. you really want to know the pre turbo number and it DOES matter.

"How did you calibrate the sensors so that the DL will record accurately?"

since the various translator circuits generally use the AD595 i just used the look up table from AD.

hc

can info like this get stickied? this is EXTREMELY valuable.

The PLX Devices EGT units are also an alternative transducer choice. Not as cheap as the Simple Circuits units but nicely packaged. cf. http://www.plxdevices.com/products/sm/egt/.

did increased EGT's during spool correlate with actual quicker spool times, or more area under the power curve? Did you have a quantifiable improvement in performance?

yes, yes and yes.

back on the dyno this week.

If someone is running the stock twins manifold, it may not be an option.

any updates on EGT's we should target and their effect on the boost and power curve?

https://www.rx7club.com/attachment.p...6&d=1169056439

Actually... It Is an option.

what is the ideal distance from the motor for the probes? I would imagine a few inches would make a difference.

not everyone (me) has the resources to do something like that. It's much simpler if one can be placed in a certain position in the exhaust and we have a temperature to aim for from there.

LOL sorry man, but where is the heat coming from? Sounds like a violation of one of the thermodynamics laws to me. The exhaust gases heat up to their highest temperature at combustion, then they will shed heat from that point forward. The turbine heats by receiving energy from the gases, not the other way around.

The exhaust gasses will definitely become cooler as they travel downstream. As the gas moves through the exhaust components, it will shed heat primarily through convection to the exhaust side walls. The exhaust sidewalls will in turn shed heat through the three main modes of heat transfer: conduction, convection, and radiation.

So to answer some peoples' question, there is no generic "rule of thumb" offset that you can apply to thermocouples that are post turbine. Different exhaust materials, ambient temperature conditions, etc. will change this value on a case by case basis.

Thats what i was thinking as well. The only thing i could figure is if it was actually combusting in the turbo maybe it could be hotter. But thats not really a typical system unless we're refering to a rally car with anti lag.

It is worth it in my opinion, to pay a machine shop $75 bucks to get it done.

Then you can get readings from front and rear rotor separately. The front and rear tend to have balance issues.... especially if you are running a stock LIM.

Howard, do you have any pics of your turbo manifold?

id like to see the complete turbo system!

Hey Howard, do you know what EGT's you should aim for on 100% gas fuel? Specifically Sunoco 94. I know you run a little hotter when using pump only. I've been getting 1650-1680*F peak on the rear runner pre-turbo. I just had it plugged into my greddy gauge since I still haven't received the FJO converter box to get the front and rear runners logged.

Towards the end of the dyno session every pull started getting leaner and leaner until it started giving 12.5-13 afr no matter how much fuel I added. The fuel pressure was dropping to 40 PSi. The EGT went almost to 1800*F during that last pull before I let off. There was no knock in the logs so no harm done. This was at 16 PSi already. We think its the fuel filter.

thewird

as always Howard, you provide arguably the best infomation on the board. Nice post.

Finally got my FJO converter box installed. What does it mean when your EGT's are 100 *F apart at WOT and 100-150 *F cruising and idle? I tried adding +0.10 ms lag to the rear secondary injector too see if it would compensate for possibly different flowing ports but there really wasn't a change in the EGT's.

thewird

^ what leading and trailing timing are you running? Also, it seems like every engine would have at least some variance in temperatures readings between rotors either due to what's going on inside the motor or due to sensor placement and exhaust manifold design. The question is what the acceptable range should be for a given setup.

I actually just got my FJO box hooked up and I am about to start breaking my new motor in soon (provided that I didn't screw up the motor build).

'good to see this thread back from the library shelves.

if you fixture dual egts you will typically find around 100 degrees F diff between the front and rear. i messed w lag settings but eventually settled on living w the difference. and yes, the net diff will vary a bit depending on where you are on the map.

BTW, i was on the dyno yesterday and made 506 SAE on 93 octane and meth on a motor i built w advanced port design. egts were max at 1600 at 8500. 20 psi max boost. knock averaged 20 so there is more hp to go. AFRs 11.4. IGL 13.5 w 11 split.

hc

I've been looking at this Digital EGT gauge, it's 1" x 2" x 3", high temp LED alarm and a relay (for an audible alarm?) offers on the box retransmission in 0-5v (and a number of others iirc). With their heavy duty thermocouples (fast acting- exposed element) it would be roughly $150/ logged EGT, taking up a space of 2" x 2".

What is needed to log the pineapple racing dual egt set up with the datalogit? I'd love to get that and my PLX iMFG wideband O2 hooked up to the datalogit. I plan on getting tuned by Dave at KDR once my motor is broken in and want everything important to be logged, and use my own set up for the tunning.

I dont think you can really log the pineapple setup, unless you have it go from the sensor, to the dataloggit, and then have some sort of output that sends the exact same signal to the gauge. I think splitting the signal would alter the readings... correct me if I am wrong.

So 100*F difference under WOT is perfectly normal? So when we are aiming for a target of say 1550*F under boost, do we average the two numbers or go with the highest number and work from that?

I'm getting 1730*F on the rear rotor at 8k RPM with ~11.0 AFR's @ 16 PSi with 16 leading/ 10 split (logged timing). maybe my timing is too conservative for that high of an RPM?

Going through a log I did with a a minute or so of WOT through the gears, brake, and then WOT through the gears again, it recorded 1800*F at one point at high RPM.

thewird

see what happens when you add split (retard the trailing)--it may reduce temps or it may not change them much, but I doubt it will actually make the exhaust run hotter. I've always found that within the normal range of split that people use, the split itself just seems to affect knock levels and do very little for power on unleaded gas. I never had a digital EGT setup until now, and my motor isn't broken in so I can't do any testing yet.

I just don't see how your timing setup is too conservative for pump gas. Mazda runs about 15 split from the factory even on nonturbo rotaries (Rx-8 for example). Remember that they need to keep exhaust temps down under load to keep the cat from burning up, and they need to raise exhaust temps during cold start to reduce emissions. It seems like you would have to have very very retarded timing to actually heat the exhaust up significantly under load. Most of the time the timing is retarded to heat the exhaust up during cold starts.

I use 94 octane (Sunoco) so I might be better off then most people that don't have that available. But the reason I think my timing is conservative for that high of an RPM is because the PFC base map which is supposed to be something close to the stock map has much higher timing at 7200+ RPM also around a 10 split, sometimes even less. Granted this is the base map and should never be really used for a car and was designed for stock ports and stock turbo's which run out of breath that high in the RPM. Also to note, my boost tapers a tad at that high of an RPM.

To give an idea of my logged timing is (leading with 10 split)... I actually just realized when I tuned it, I had 1 extra degree of timing across the board on high boost but retarded it when I went down to Deals Gap for a little extra safety with the 93 octane fuel but never advanced it afterwards. This is at 16.3-16.5 PSi and drops off to 15.5-15.8 PSi at 8,000 RPM.

<5200 = 13
5200-6400 = 14
6400-7500 = 15
7500+ = 16

My experience with split has been very different. Going from a 14 split to a 10 split gave me a 10-15 rwhp increase across the the board on a Mustang dyno with back to back runs. But for the sake of EGT testing, I will try it since I didn't have EGT logger back then. Also, I noticed increasing the leading timing (maintaining the split) had no noticeable difference in rwhp (possibly because I was already in the sweet spot but I didn't do further testing cause dyno time costs money hehe).

Here's some graphs of my EGT's....

*Red Line is rear rotor and blue is front rotor

Single Pull
http://img268.imageshack.us/img268/7504/pulli.jpg
http://img268.imageshack.us/img268/pulli.jpg/1/w875.png

Multiple Pulls through the gears (3,4,5 and then 3,4 and another 4)
http://img200.imageshack.us/img200/8613/pulls.jpg
http://img200.imageshack.us/img200/pulls.jpg/1/w875.png

thewird

What is the rest of the setup? Turbo, trim, manifold, a/r, exhaust size, cat, aux injection? I think the more restrictive the setup the higher the egts will be as the heat can't escape easily. You should hook a boost gauge up to several sections of the exhaust to see what kind of backpressure you're getting. A guy on the ausrotary site found a huge restriction in the last section of the exhaust on his car. He cut it off and put a different muffler on and dropped the back pressure a huge amount. I have a feeling this is why howard has had so much lower egt's. His turbo/exhaust setup is very free flowing.

It's a medium streetport with ported LIM and UIM with FEED bored throttle body. Turbo is an A-Spec 500R-SP with a short runner manifold. The A/R is a 0.84 with a 67 compressor wheel but that is all I know about the turbo. Exhaust is a full 3" with a blown out 3" magnaflow silencer and a Racing Beat dual-tip catback. EGT Probes are within 1" of the exhaust side flange. My methanol system is still not installed so there is no AI at this moment.

Are you suggesting I put on pressure gauges pre-turbo or post-turbo? Pre-turbo would be kinda difficult considering the size of the short runner manifold and I already have the EGT probes on there. I had considered putting one post turbo during the winter but never got around to doing it.

thewird

Hey everyone. I have a question regarding the pertinence of these readings. It seems to me that the probes are in an area that is very likely to heat soak and give higher than actual readings. It kind of seems to me that these sensors are only really good for a ball park area of actual egt readings as apposed to a reading that is accurate enough to tune off of. Especeially if it is in a situation like dyno tuning. The first couple of runs will likely look quite different than the last couple. Once everything has gotten hot from full throttle loaded runs the numbers will get a lot higher. Is this even a necessary tuning instrument for our cars? I could see it being a valid monitoring system but the validity of using it as a tuning instrument seems kind of suspect to me. It seems to me that you should be using the shape of your power curve and the location of peak torque to tune your ignition and merely monitor egts, not tune with them. Let me know what you think about this.

--Hank

EGT's only tell part of the story, the same way AFR's only tell you part of the story. Power curves would be another bit of the story but I don't think its as helpful as EGT's and AFR's. And Dudemaaanownsanrx7 has a very good point about backpressure which I had completely forgotten about since the winter. It's easy to tune a car to be safe with just AFR's and make decent power with generally accepted timing but if you really want to fine tune your machine I think you need to look at all the tuning devices together and make it work.

thewird

If you're in a sauna and I put a blowtorch to your arm do you think it will really matter what temp the room is around you? The combustion temperatures are much higher then any amount that heat soaking could account for. So when you make changes to fuel and timing it will show up in egt's. Yes egt is a valid way to tune, whether it's required for tuning is a debatable topic. If egt's are too high you can melt turbo parts and reduce the life of the engine. If they are too low exhaust velocity is lower and reduces spool and probably overall flow. So using egt's can be helpful. Some people tune only using them, others tune using only afr's and some tune using both.

Also by using dual egt probes you can find problems from one chamber to the next. For instance if you're getting misfire but only on one rotor, or one rotor is running leaner then the other for some reason.

As far as the back pressure I would probably start right at the beginning of the downpipe right after the turbo. If there isn't a lot of back pressure then the system from that point back is fine, if it's high then work your way down the system until you find the bottle neck(s). The .84 housing is smallish and could be a source of restriction that's keeping egt's higher, the only way to check the back pressure here is a fitting somewhere before the turbo. The turbo will always be a source of restriction not sure how much before the turbo is considered high though. It's probably been posted somewhere though.

Oh yah, I forgot to mention a theory I had about the EGT difference. My turbo hotside is jammed right up against the LIM with a blanket. I think that may effect EGT's too because the air would be less dense going to the front rotor. Does anyone have a take on that?

Here's the best pic I have of what I mean, you can kinda see it...
http://thewirdsdomain.com/rx7/parts/vmount14s.jpg

thewird

I've heard the LIM has a flow imbalance that causes the rear rotor to run leaner. This could account for the difference if your isn't flow matched or the fuel on the rear hasn't been adjusted. I subtract a little lag with the pfc for the rear secondary injector to try to make up for this and give it a small amount more fuel. I don't monitor egt's though so i can't comment on any temp differences between rotors or if this helps equalize them.

My LIM and UIM were both ported by hand and port matched to the engine ports so its not stock but the flow imbalance might still be there since no flow testing was done. I did add +0.10 lag on the rear secondary injector but no noticeable difference was seen in the EGT imbalance. I was afraid to add more so there wouldn't be a big power difference between rotors.

thewird

I'll be interested to see what the EGT spread is between front and rear rotor on my s5 (T2) LIM, which doesn't have the flow imbalance of the s6.

I would like to know who these tuners are using only egt's so I can avoid them like the plague lol. Exhaust temps are great to use as an additional tuning tool but never as a sole source of information.

If you can get about the same psi for boost and backpressure your doing great. If at say 15 psi your seeing 23 psi backpressure, it's time for a bigger turbine housing.

I don't think its quite as common on a rotary engine due to how knock sensitive our motors are but I've read about it on piston engines before. Usually its done in conjunction with a dyno so you know your heading in the right direction.

Another tuning metric is looking at spark plugs. It's more of a drag thing where only WOT matters and you can shut the engine off immediately after a run and pull the plugs.

But this thread is about EGT's so I think we should keep it at that :icon_tup:

thewird

Of course reading plugs is important. I come from piston land and I can tell you, dyno or no dyno, no good tuner will tune with just an egt without knowing afr's first.

Ok so I've been working on my base tune. At about 2/3 throttle I'm hitting 1650 degrees rear rotor and about 1500 front rotor. This is with a series 5 LIM (no flow imbalance). Boost is about 13.5 psi, leading advance 15 degrees with 15 split, 8.5:1 rotors.

So how hot is "too hot" on straight 93 pump fuel?