Max EGT? Options

[technicalninja]

The title is the question.

I know what to look for with water-cooled stuff.

I have no experience with air-cooled stuff yet...

What say you?

Is there a normal range?

A never exceed number?

Anyone ever use 4 thermocouples?

Was there any noticeable difference (#3 is of concern to me)?


Thoughts, tips, any data would be greatly appreciated!

[Mikey914]

In aircraft it’s around 1450.
Technique is to lean out for max EGT, and go about 75 less.

[technicalninja]

Is that an air-cooled aircraft?

Seems hot to me, getting close to max water-cooled EGTs.

Maybe cooling power/type has no difference regarding EGT?

Next question is "are aircraft cooling systems superior to a T4?"

I'm betting they are.

That is a fixed throttle engine.

I'm understanding that your numbers are actually cruise numbers that are maintained indefinitely...

Hotter than I would have expected.

[GregAmy]

What's your goal with installing EGTs?

I'm a pilot (as many on board here are) and the point of EGT in an air-cooled airplane (almost all of them are) is to properly set the mixture, as easily as possible. In your typical General Aviation airplane, the pilot controls the mixture.

You don't have that problem in the 914, so why bother with EGTs? If you're looking for tuning, you're better off using established guidelines like AFR and CHT, of which we have a lot of experience, on the dyno.

And you're incorrect that it's "fixed throttle" and/or just "cruise numbers"; it's managed by the pilot in all phases of flight, regardless of whether it's fixed-pitch or constant-speed prop. Generally speaking, I would agressively lean on the ground while taxiing to keep the plugs clean (of lead deposits, mostly), then go full rich on departure to minimize the EGTs and CHTs. As I pitched down for cruise climb I'd slowly reduce the mixture until I got a light roughness then give it a wrist-twist rich (vernier mixture). Once I got at cruising altitude and RPM started to rise (fixed-pitch prop) I'd richen then lean to a slight roughness, note the EGT, and give it about 75-100 degrees richer. On descent under lighter load I'd pull the mixture back leaner to keep the plugs clean (and reduce fuel consumption).

Very few GA airplanes came with EGTs, they were commonly add-ons. So we learned to fly by the seat of the pants. But this overall technique (along with massives on the bottom spark plugs and fine wires on top) resulted in clean plugs and cylinders that lasted for a thousand hours or so (a feat within itself).

But you're doing none of that. Your mixture is fixed by either the "computer" or the jets. You cannot control the mixture in the cockpit so that knowlege of EGT is not particular useful.

If you're still curious, my recommendation is to get some dyno time and tune the engine based on the well-estabilshed knowns of CHT and AFR through the various phases, and observe what EGTs that results in. Then you'll have the info you're looking for. - GA

[gereed75]

I also come from an aviation background. What Greg said

EGT is a different way to “monitor” mixture. Pretty much what was available prior to having O2/AFR equipment readily available.

If you monitor AFR via O2 sensor then I would say also reading EGT is maybe superfluous but nice to know.

I agree with Greg, max is somewhere around 1450 F., depending on a number of variables. Max power is produced somewhere around 100 - 75 rich of peak, corresponding to AFR around 12.5 -13. Best economy (and lowest CHT) is 25 - 50 lean of peak, AFR around 14.

Your car’s computer is trying to operate the engine in these ranges depending on throttle position RPM, load, MAP , engine temp, IAT etc etc. the computer adapts fuel flow and timing to produce what it thinks the situation calls for.

One other note, the EGT that the probe sees is highly dependent on where it is placed in the header. The temp inside the “flame cone” (my term) varies considerably by location within a band of an inch or so.

On another note, I know of no modern engine control system that monitors EGT as a control parameter except maybe in turbo applications. Then it is call Turbine outlet temp.

[VaccaRabite]

I don't know that max EGT matter much, so long as you re not melting your headers. If the tune is too rich or lean its going to show in head temps. Getting your CHTs right though matters a lot. More then oil temps IMO. And there is good research that has been done on head temps for tuning a TIV.

Zach

[gereed75]

Rich helps keep CHT low. Lean can also produce low CHT if lean means a mixture that produces a EGT below the peak EGT for that engine condition.

High CHT comes from running near peak EGt and is an indication of high internal combustion pressure (ICP)

[technicalninja]

CHT is first in my air-cooled book. I have never used one on a water-cooled build
AFR is second.
EGT is way down the list of important logging data for me.
It's still important enough that I prefer to log it.

I know of no other way to set individual injector pulse widths...

Most of the available aftermarket ECUs have the ability to individually tune each injector.

Has anyone adjusted individual injector pulse widths WITHOUT EGT couplers in each exhaust port?

How did you decide which way to go?


As to the fixed throttle comment.
What I meant was the throttle position is set by the throttle and an aircraft/boat/stationary power supply is run with only minor adjustments to it.
The power requirements are static as the aircraft/boat requires the power at all times.
Just imagine trying to run a 914 at a constant 75% of throttle.
One of my mentors, Corky Bell, built a big block Chevrolet that could produce 1450 hp in the early 90s. That's not shit in an 8 second drag car, pretty much anyone can do that now and many could back then. Corky's engine was for an offshore endurance racing boat and that engine could hold 1450 indefinitely for hours...
1450 for 8 seconds is easy; 8 hours is HARD!

I'm from an aircraft background as well.
Dad was flying Voodoos when I was born.
He went on to flying with United.
9/11 destroyed his life. Luckily, he turned 60 almost 1 year before and was doomed to the FE position on 3 person cockpits. The last aircraft he was "Captain in Command" of was the United flight 175 that hit the tower.
That was HIS airplane 1 year before...
He was born 9/15/40 and was retired out of that airplane on his 60th birthday 360 days before the attack.

Had I not been born with a genetically weak right eye I would have taken the same route.
I was flying gliders (real ones) by the time I was 15.

I am a turbo guy; Corky is thought by some as the "father of modern turbocharging", and I got an early education from a grand master of his field. I helped him edit "Maximum Boost" which is a killer basic overall book regarding turbos.
The manuscript was far cooler than the book. So many of Corky's idiosyncrasies were edited out. I liked them!

Someone mentioned Turbine outlet temps.
With a turbo I want TIP/TIT and TOP/TOT (turbine inlet and outlet pressure and temperature). I also want both pressure and temperature from multiple sources on the intake side. Turbo inlet/outlet, intercooler inlet/outlet.

The absolutely most important ratio is the TIP to boost ratio. If you get boost higher than TIP, then the power production goes through the roof as you no longer have back flow/pressure during overlap.

This is EXACTLY why Porsche employs variable aspect ratio turbos on all the S variants today!

Corky was screwing around with VATN (Variable Aspect Turbine Nozzles) turbos in the 80s.
Aerodyne was the first...
We had to put snubbers on them to slow the boost rise down. These could hit boost as low as 1500 rpm and hold big boost all the way to redline.

Boost is NOT an indicator of how much power you can make!
Boost is an indicator of the resistance to flow that an engine has.
Put that same turbo on an engine that has been massaged and you will see more power at the same boost level as before and you can achieve the original power figure at lower boost which helps thermodynamically.

TIP/Boost is what shows the efficiency of the system and almost no-one mentions it...

All these measurements are for the tuning phase. Once I'm done provisioning a system the "science project" gets removed and a much simpler monitoring configuration is installed.
One boost and IAT at throttle inlet.
TIP/TIT at turbine inlet.
WBO2 24" down the down tube.
CHT on an air-cooled. I don't plan on trying to boost a T4.
Looks like too much heartache for my tastes.

I was just trying to adjust my EGT expectations in regard to air cooled engines.
This is a tuning thing, not a log forever and actively monitor from the cockpit thing.
The CHT is critical thing, both in logging and active monitoring.

Thanks for all of the replies guys!

Rick

[stownsen914]

Decades ago, we didn't have reasonably priced wide band O2 sensors, so people did use EGTs to tune racecars. I still have one on my 914/6 racecar, mostly as a vestige as this point. As suggested, AFR is probably a better method as O2 sensors are more responsive than the thermocouples that EGTs use.

If you prefer an EGT, and assuming you put the thermocouple about 1.5-2" from the exhaust port as recommended, I was told by a couple Porsche racers that normally aspirated, aircooled Porsche motors like about 1200 degrees F.

[technicalninja]

Bingo! That's more like what I was expecting.

Any others have direct experience?

[ChrisFoley]

When I was racing, I was ok with my EGTs going up to about 1375F at full throttle, end of straightaway. Anything higher and I wanted to go up a jet size. 1350F was preferred.

[ChrisFoley]

1200F is super rich and probably giving up a lot of power.

[gereed75]

No direct experience with Porsche but I agree that EGT would be the best method if you are trying to balance combustion in each cylinder. Maybe you could get close just by thermo imaging each exhaust runner without the need to actually mount thermocouples in each runner.

Also agree that 1.5 - 2” below cylinder is about right. More important is to make them all the same

There really is no right number for temp, it will always be moving and depends on thermo couple location and engine state. Maybe you could see delta between cylinders and tune accordingly.

Balancing is done in aircraft by changing out injection nozzles restrictors. They can be had in .5 gph increments. Even then you are not looking at absolute temperature values, you are looking at which cylinder peaks first as you lean at a set power setting. First to peak is the leanest cylinder.

Back in the day, It was common practice to tune go cart race engines on the fly using EGT and a driver adjustable mixture knob.

Chris, were you running 4 sensors and if so could you see any delta?

[technicalninja]

When I was racing, I was ok with my EGTs going up to about 1375F at full throttle, end of straightaway. Anything higher and I wanted to go up a jet size. 1350F was preferred.

1200F is super rich and probably giving up a lot of power.

@ChrisFoley
Thank you SOOO much!

That's the data I was looking for...

(IMG:style_emoticons/default/beerchug.gif)

The stuff you sell is more "bespoke" than any other vendor I'm aware of.
The engineering and logic look flawless IMO.

Lots of your stuff looks "should have done it this way from the get-go, Porsche!"

I recently described the pressure relief valve in another thread as "Must have at ANY price!" and the fact that it was only $90 made it "freaking easy to swallow."

Your exhaust systems are ART in my book...

I'm going to be a customer of yours soon!
My wish list:
Fire wall bushing
Bad assed pressure relief valve.
Fuel lines
Throttle kit for IDFs
Trailing arm brackets
Side shift linkage
Bunch of reinforcement crap
Clutch pulley bracket

OH CRAP! you've solved another problem for me with your oil cooler kit #3. New stuff!
I have questions about that...
PM will be sent

And, If I build up a big T4 one of your exhaust systems will be a requirement!

Wouldn't surprise me to be in 10K with Tangerine Racing...

Thanks again

Rick

[gereed75]

Cool comparison - 1350-1375 is where I run my Lycoming for best power. That is about 75-100F below peak. FYI, at sea level I flow about 18 gph to make 180 hp.

That holds amazing similar to my 200 hp outboard. Ain’t physics/thermodynamics/combustion efficiency a cool thing!

[technicalninja]

No direct experience with Porsche but I agree that EGT would be the best method if you are trying to balance combustion in each cylinder. Maybe you could get close just by thermo imaging each exhaust runner without the need to actually mount thermocouples in each runner.

Also agree that 1.5 - 2” below cylinder is about right. More important is to make them all the same

There really is no right number for temp, it will always be moving and depends on thermo couple location and engine state. Maybe you could see delta between cylinders and tune accordingly.

Balancing is done in aircraft by changing out injection nozzles restrictors. They can be had in .5 gph increments. Even then you are not looking at absolute temperature values, you are looking at which cylinder peaks first as you lean at a set power setting. First to peak is the leanest cylinder.

Back in the day, It was common practice to tune go cart race engines on the fly using EGT and a driver adjustable mixture knob.

Chris, were you running 4 sensors and if so could you see any delta?

Another juicy post!
Thanks!

I can change "nozzles" on the fly, in increments so much smaller than .5GPH via a keyboard per injector. I can also alter injection "timing" on some units.

I can do the same with ignition timing on individual cylinders.

I'm hunting the "delta". I thought that was the only way to truly tune individual cylinders.

I'd love to have 4 WBs and 4 thermocouples for truly accurate tuning.
I think you need BOTH AFR and EGT to see the whole picture.

All this crap is for initial tuning only guys.

I want to design/build a plenum-based intake for the T4 and will need "the biggest picture" during POC (proof of concept) phase. POC also stands for "Piece of Crap". They can be one and the same for some projects...

Another question that popped up for me is:
Has anyone installed CHT thermocouples on all 4 plugs and what was the delta between them all?

I BELIEVE that cylinder # 3 runs hotter and is the most critical in the engine but...
I've never tested this myself!

I believe because EVERYONE else does.

What's the difference?
Is it 5 degrees or 40?
5 doesn't bug me.
40 does!
40 would make me want to try different things electronically to reduce the delta.

Injector pulse length, injector timing and ignition timing are the only easily applied adjustments IMO.

[ChrisFoley]

Chris, were you running 4 sensors and if so could you see any delta?

I had visual data only for all 4 cylinders, on a single digital readout, scanned in sequence at one second intervals. If one went out of range the readout stayed on that cylinder.
There was some variation but in general it was fairly uniform.
At times I reamed a jet orifice to make the spread smaller.

[ChrisFoley]

Aerospace Logic changed the standard 5 second scan interval to one second for me, same with my CHT.

[technicalninja]

Just dying to know.

Delta across the CHT sensors?

Did you see any evidence of any cylinder being significantly different than the others?

Did the car have the racoon sized tube from the front during these tests?

I'm guessing that was the biggest improvement to the cooling system you did.

Ever ingest anything?

[wndsrfr]

For my 2316 I put in 4 TC's because I could and to monitor for a cylinder going lean for whatever reason. This engine is fuel & spark controlled with SDS so I created the map by dyno tuning so wanted to be watchful for not going lean. Wideband O2 is there of course. Here's the install, you can pick out the TC's on the headers if you squint....

Here's the readout at idle.....

What I watched for was to not exceed 1250 at sustained WOT to avoid detonation risk but will commonly see 1350 at light throttle sustained around 3500rpm. Remember I'm on SDS and at light throttle I'm on closed loop so AFR's are around 14:1.
So then the SDS is set to go off of closed loop with throttle position over about halfway open and revert to the coded in fueling map to keep AFR's quite rich at WOT. I'll attach a couple of Youtube clips where I did a brake dyno run on the highway by getting up to 3'rd (or 4th) gear about 4000 rpm and flooring it while holding the brake pedal to keep it at thata rpm & watch the AFR's.
Sooo...that's my story on 4 EGT's...Oh yeah, turn up the volume!!

https://www.youtube.com/watch?v=A4jyPRQaVNw


https://www.youtube.com/watch?v=lNUNWDupcWk