special tool

Wayne - read the thread, man.
Two guys with 4 channel EGT's have just said the #4 IS NOT THE HOTTEST CYLINDER!


It fails at 4 because the headgasket is too thin between the water passage and the combustion area - that's it, no rocket science here.

A.Wayne

Hello Special Tool,

I said it is the HOTTEST CYLINDER , not that it had the highest EGT!
I stand behind my explanation on the causes of why the head gaskit fails at number 4/3 cylinders and that the EGt readings and explanation stated by some are off due to improper installation of their EGT Probes. The head gaskit fails because the engine is detonating, causing the weakest link in the chain ( the headgaskit ) to go. While going to a stronger gaskit helps it does not change this That is of course, just my professional opinion .
regards

sweanders

Uhm.. Does the #4 cylinder magicly store the hotness from the exhaust or something?

Bill

A Wayne/Chris White,

My tests so far seem to incorporate what you both say yet differ.

My ETG's increase as my rpm's increase. My highest peak reading comes at constant throttle at high rpm's. At 2000 rpm to 3000 rpm constant throttle (CT) I see 1250. At 3k to 4k CT I see 1350. Above 4K CT it has climbed up to 1650.

Like A Waynes statement, I also feel 1650 is way too hot. Aluminum melts at 1250 degrees fahrenheit. Nox is created at high temps. From all of our smog tests we know Nox is an issue in our cars. I currently have smog (Nox) issues, and this is why I am taking such an interest in this issue.

After some base line runs, I changed my timing via the FQS at the DME. I have Guru chips and I believe they are very aggressive on timing. So far I have only turned the FQS 1 click (2 dergees retarded). To confirm Chris White's statement, I found it made no difference in ETG. I was a little supprised of this outcome, as like A Wayne, I belived that timing will affect EGT. My next test will be to turn the FQS 1 more click (4 degrees retard).

Being a bit scattered like I am, after the 2 degrees retard results, it occured to me that perhaps my cat was clogged. When a cat becomes clogged, the exhaust flow will back up and high temps will result. So off came the cat and in went the test pipe. To my dismay, again no change. It is after all a brand new high flow unit.

According to several dyno runs and my Zeitronix data logger, my fuel curve is spot on. But I do see my EGT's lower up to 1000 degrees after a full throttle, full enrichment cycle. That is constant throttle EGT high, stomp the gas to 10:1 afr, and drop goes the EGT. Back to CT and up goes the EGT. So like A Wayne says AFR does affect EGT.

I have somewhere in the past, read that the 944 has some stratigy they called "TOP" or "TOC". Which stands for thermically optimised p????? or combustion. Dont quite remember. At the time I just had casual curiosity for the workings of the 944, so it did not stick. I seem to recall that the statement was made without explaination, so I do not know how or what Porsche did to achieved "thermally optimised combustion". Timing, chamber design, flow, answer D "all the above".

Ahhh the mysteries of the 944 series Porsche.

dand86951

Regarding whether or not enriching fuel changes EGTs I think what Chris was saying is that relatively small changes such as going from 12 down to 11 to 1 won't show significant differences. While not on the 944 engine my experience is that small changes on afr do make a difference. Sometimes the problem is having instrumentation accurate enough and responsive enough to measure it. I can see a change in egt of 10 degrees with only a .1 gal/hr flow difference. When operating around the peak egt region the the flow has to change more to result in a temperature difference due to the egt curve being a bit flat in that region. So going from 12.5 down to 12 may not show much change, going from 12 down to 10 would.

A.Wayne

Hello Bill ,
If after advancing /retarding 2-4 degrees and you do no see a difference it is because your ECU system has very little ignition accuracy at that rpm speed.
I will assume that by advancing 2-4 degrees that the system Hysteresis is what is causing you not to see any changes ( this is assuming proper probe placement free from heat soak , sensititvity etc). This is a known phenomenon in the business and that is why on high output race engines Dizzy's are not used, no accuracy in the timing, .

Yes by increasing A/F to below 11:2 you will see a decrease in egt but this is because you have also decreased the specific output of the engine .
To correctly tune an engine you need to know both the A/f and the egt as they are both one and part of the equation.

My statement on " the hotter cylinder " has nothing to do with EGT but cylinder temp . EGT is what it state's the temp of the exhaust gases in relation to the flame front. ( there is a lot of collective ignorance here on this ) E.xhasut G.as T.emperature. An egt of 1600 with an a/f at 10.7 will hurt the turbine not the motor what is most critical to the motor is oil and water temps at this stage.

Now the trick here is , say engine output is 500 bhp and egt is 1600 deg. a/f is 12:1 if you go to 10.7 to lower the egt , guess what ? it is no longer a 500 bhp engine. ok for the hobby "sooper tooner" but does not win races against competition when you have to manage power and manage fuel consumption.

Bill at the same contant throttle ( light load) no boost engine is in Steady state by increasing the timing you will see a drop in EGT. if not maybe the 2-4 degree changes you are giving at this point is 1. the ECU is not accurately doing so, or 2. the engine actually requies more here than 2 -4 degrees.

Bill you seem to have the tools needed to play. so with a little more r/d you will have more data on what is involved to share. Happy to see this kind of technical involvement here.

Regards

A.Wayne

Ha,`ha, Ha,
Funny , with all that speed and a sense of humor to boot , Ha, ha,

special tool

If anyone wants proof, I can simultaneously run my SMT6 and Zeitronix - then watch the EGT change, or not change when I go from 14.7 to 11 or 12 or whatever anyone wants.

A.Wayne

I don't think anyone here is saying the egt will not change by doing so lutjens.
the conversation is deeperand involves more than that.

Chris White

The interesting effect with EGTs is that as you make the mixture richer you will have a greater amount of excess fuel in the exhaust (incomplete combustion) that will continue to burn in the manifold. The actual combustion chamber temp may go down but the EGT probe will see hotter temps.
My temps do not compare to a DME based system as I am running a Tec3 stand alone (With a fairly different timing curve)

My highest EGTs are at very small throttle openings at cruising speed (2k to 2.5k rpm). Just how you want it to maximize heat energy to the turbo for quicker spool up.

Don’t get concerned about the melting temp of aluminum – the combustion chamber only sees this peak temp for a short period – then a cool intake charge comes in.

BTW – the cylinder head at cylinder #4 has the coolest coolant

Chris White

special tool

I am not saying it will or will not.
And don't use a condecending tone with me - I have forgotten more than you will ever know about tuning a 951.

A.Wayne

Was that directed @ me special Tool , if so you do not know me nor my knowledge base so your statement is an empty one based on self importance. No offense was intended and non should be taken, as I'm no expert, i'm just passing thru and stopped for some technical cavorting.

A.Wayne

Chris ,
Is a 2.6L 16v turbo still a PCA GT3 car ? as i heard the rules for 06 was changing .

lart951

With 47 total post you have a way to make friends very quickly. There is no need to be a jackass when responding to a member, that response was totally uncalled.

A.Wayne

And i guess you are the welcoming committee, to the club ,calling me a jackass , looking in the mirror there buddy ! Unbelievable !

and since i only have 47 post to boot, then tell me when i can start responding to personal attacks, as special tool was the one that fired first ,i just responded as i'm not in to the disrespect business.