Campeck

um..yeah. that!

Trucho-951

"Having probes in each cylinder is not uncommon and used mainly when adjusting engines on the dyno in full sequential mode, as this is the only true way to adjust each cylinder based on A/F and EGT. "

So, A. Wayne,
I was just thinking, for a street car without full sequential fuel injection, what would be the value added from EGT or CHT data vs. Wideband O2 AFR data?

I mean, once we set our AFR then there is not much esle we can adjust based on EGT data.

about the only thing that comes to mind is that having individual EGT's on all cylinders would aid in early detection of an injector going down. what else could EGT data be useful for on a street car?

hosrom_951

I am interested as in what the the hottest EGT one should see before being concerned.

special tool

Trucho - also for combustion balance.
Mine is mostly for product testing.

Trucho-951

just wanted to share some articles I found on the web regarding: What can EGT tell you?

EGT and detonation - perhaps why Cyl.#4 has lower EGT values?

http://www.rodmachado.com/Articles/A...EGT-Primer.htm
and
http://www.foxvalleykart.com/egt.html
also
http://www.grtavionics.com/how_it_works.htm

TurboTommy

A Wayne,
I'm addressing you on the comment you made about ignition timing not being accurate at higher RPMs on our cars. Did I understand this correctly?
I have to admit, this is the first I've heard of this and I'm puzzled and concerned.
What do you mean, exactly?
What have you experienced in order for you to make that statement?

dand86951

That is one question that may not have just one correct answer. The max safe temperature depends a lot on the metallurgy of the components involved. So what can the combustion chamber see and still survive, that depends on what kind of fuel is being used and on how good the cooling capacity is and combustion chamber design, ignition timing, afr, etc.

The exhaust valves and the exhaust port take the brunt of the heat and so for our cars Porsche saw fit to go with a ceramic lined ports to protect the aluminum and sodium filled valves to transfer the heat up to the stem and into the oil to protect the exhaust valve and ss exhaust system to make it last at these higher temps. What is the maximum temps these can safely see is a question Porsche may know but we don't.

On a typical aircraft turbo engine with sodium filled valves, no ceramic coating of the exhaust port and running 100 octane aviation fuel fixed timing of around 20-22 degrees, the engine manufacturers have set maximum TIT between 1600F to 1700F for the inlet to turbine depending on the turbocharger. Maximum egt out of the ports is not stated but I do know that a lot of articles recommend keeping those in the 1450 to 1550 max range. keep in mind this is for an air-cooled engine running steady state rpm for hours at a time, but from what I have seen the 1650 number for the TIT is a temp that the turbines can live at for at least 1800 hrs.

So will a short duration spike of EGT up to say 1700 at the exhaust port in our engines do irrepairable harm? If a lot of other factors are working correctly I doubt it. But for a long duration I think it probably would be detrimental with the stock components.

Trucho-951

About low EGT values... It is starting to make sense to me now. From the articles on EGTs and detonation that i posted above, it appears that at WOT:

1) as RPM increases, CHT's increase, and so should EGT's,
2) however, if an individual cylinder CHT increases but it's EGT begins to decrease, then this is an early sign of detonation, even if there is no audible "ping" or "knock",
3) Detonation, despite popular belief, is a gradual process, i.e. there are various levels of detonation.
In fact detonation studies have categorized them into, "light" , "medium", and "heavy" detonation. for more info on this see article: http://www.avweb.com/news/columns/182132-1.html

All the above is from literature, now for my 2 cents...

Given the low EGT on cyl. #4 info presented by Special Tool and the "run a cooler plug on #4" advice from A. Wayne, it appears to me that our 951 engines is suffers from poor cooling of cylinder #4, which leads to some level of detonaton and hence the low EGTs. If A. Wayne is correct, then perhaps the problem acutally begins with "pre-ignition"? cuased by a hot spot in the head, namely the sparkplug, hence, running a colder plug would aleviate the problem. But as has been pointed out in another thread on this forum, there is a belief that there is a "gas pocket" in the cylinder head where coolant is absent and not doing its job. So if we cant fix our cooling problem, then running a cooler plug in cyl. #4 appears to be the appropriate bandaid solution.

My initial interest in starting this thread and getting advice on installing an EGT probe was to have information that would help me avoid yet another blown head gasket. I love this forum, you guys are great, I have received lots of valuable pearls of wisdom and am excited about my upcomming EGT installation, which unfortunately might have to wait for a few months..

Campeck

so your saying that #4 has a slight detonation problem that can blow the headgasket over time. it just doesnt register in the EGT because all the heat from the detonation has been rapidly given to the head...

ST. You should definatly fit some CHT sensors on your car and tell us whats up!

A.Wayne

Hello all'
There is/are different types of detonation , usually at different frequencies and there damage or result of is fully dependant on this.. Multi knock sensors =setup at different ping levels will show this . The worst is not the usual audible knock that most is familair with or that most after market knock sensors will detect. But as you have observed from other sources it will show low egt's , but you have high cylinder temps , that was what i was alluding to in the beginning of the post why most are misled into believing that no4 is GREAAAT OK ETC. But this is the key reason why you will see the kind of gaskit, piston, failures in no 4.

The more info you gather on this is the more one can discuss this without
sounding of the wall.

On my reference to ignition timing with the stock distributor, my statement was based on the fact that there is more timing Hysterisis with distributors than there is with direct spark. So high power outputs on 93octane will or could have " issues " that will not show on race gas which gives you a bigger area of protection. Hence why when more Power /cyl is needed and the octane remain the same a more accurate ignition is needed .

Also Trucho-951, if you could lower the operating temps by 25 degrees it would be the like increasing the fuel octane ( where the knock sensitivity is concerned ) we noticed this for years while dyno testing racing offshore marine engines
while experimenting with 93 octanve vs Race gas ( when you have to buy 300 gallons per weekend the 93octane price sounds good ) that just a 15 degree increase in water temps called for 3-4 degrees of retard or the knock sensors would go off.
A.wayne

A.Wayne

Trucho-951

Chip, Chip Hrrr, Hrrr , now you are on to something , when the cylinders have medium to high frequency detonation the EGT will be cool ( sometimes 2-300 deg. cooler than normal) the uninitiated would be fooled into believing that the cylinder is OK. Your Egt is just a tool , along with lambda, plugs CHT,EVT, etc, all part of a complex equation on the controlled explosion taking place inside a combuston chamber and if it really was straight forward and simple , It would not, at the highest levels of motorsport, cause so many to be humbled so many times on a sunday.

The fact that xyz works on the street for the hobby racer who only has to maintain full throttle for 5 mins a week, does not make an expert.
Hence , we learn , exchange and build on that building block of knowledge that has been passed along by many before. The importance of such is that no matter how much is learn't we will or should be , humbled by the ignorance of how much is still not known.

A.Wayne

A.Wayne

Based on the photos of the headgaskits shown on this thread i would say the Detonation is not slight , but goes along way in showing the build quality of Porsche Motorsports.
I have worked with and on may engines from all parts of this globe and i can tell you no one make engines as granite reliable as Porsche and the Krauts in particular. You would not get any Japanese or domestic power plants to handle that kind of abuse without serious damage or modifications.

A.Wayne

Chris White

A couple of thought s to throw out there – at the temps we are talking about the sodium filled valves are not really useful. The concept of the sodium valves is that he sodium will transfer heat from the head up the stem (where it is cooler). The transfer of heat is greatly enhanced by the phase change of sodium from liquid to vapor (1621 f).
If you run temps significantly over that point the sodium will remain in vapor form and have a greatly reduced cooling effect.

Some more data points – cylinder number 4 and 1 are always 20 to 50 degrees cooler – light load, heavy load – makes no difference. My theory is fairly simple – both the 1 and 4 cylinders only have hot cylinders on one side while 2 and 3 have hot cylinders on 2 side. This would increase the heat transfer capacity of 1 and 4.

The one universal truth – detonation sucks….

Chris White

Tomas L

I don't see how our distributors could effect spark timing in a significant way?!
Yes the spark may be a little delayed when it builds up enough voltage to make the jump from the rotor to the distributor cap but it still would need at least the same time before the voltage is high enough to jump the spark plug gap.

A.Wayne

Ignition as in timing accuracy , not the spark size !