Bengt Sweden

Hi John,
I have the probes 2.5cm from the head.
Cruising/Idle is at 650-700C according to the Zeitronix.
WOT at 6500 is showing 1000C
I lowered AFR to 11.8 and get 950C but it doesn't seem right.

No shortage of power though!

Bengt

hosrom_951

650C-700C (1,202.00F-1,292.00F) is good.

You should check out the timing, 1000C (1,832.00F) is way too much. A good 300F lower (148.89 celsius) is what you have to aim for.

I'd say you have to advance the timing up more, but you don't want to? you already don't have any knock till 6,000rpms or so. Even then, it reads at the lowest sensitivity. But do bear in mind, these knock sensors just "listen" for knock, so at higher rpms, there is more "noise" from the valves, injectors and also knock. Doesn't have to be knock (although you always have knock, very very low, but it is still present).

Bengt Sweden

Hi Hos,
thanks for trying to help, but really you should re-read my posts to see on what level of understanding I am starting at, and whether you can actually contribute to improving it.

How do you know?

I stated that in my very first post. What I need is someone with experience from using the KnockSense to tell me if they have experienced a noise filtering problems or not.

I am trying to "check out the timing", that's what this is all about.

Normally you would go for max 900C. In the case of insulated exhaust ports it may be higher. I would appreciate if someone who has measured EGT on a tuned 951 (2,5 or 3.0) could share their experience.

Thanks anyway.
Bengt

hosrom_951

Bengt: I hang out almost daily at the local Porsche tuner for months now, i see how the EGT's, Timing and AFR's are all related. Also, it has been a couple of months since we (the local tuner and myself) have seen and "tuned" the timing, AFR and playing with difference turbochargers in relation to back-pressure problems.

How i know that 650C-700C (1,202.00F-1,292.00F) is good, because as a rule of thumb, 1500F is what you should be seeing on WOT. On crusing it is less (more or less than what you currently experience). The tuned 911's here never had over 1600F in EGT's with the "proper" timing and AFR.

Regarding the knocksense, i do not have experience in that directly. But again, it is basically reading the voltage from the knock sensor (obviously) and displays the "amount" of knock (again, through the FVD tuner).

900C max (1,652.00F) is more/less still high, and no, i never measured the EGT's on tuned 951's. But giving out the "basics" of what the tuned 650+hp 911 turbos go through here. We have yet to "enter" the 951 timing, but that is where my car comes in.

Sorry for trying to help.

Chris White

Aim for 1600f but be ready to live with 1700f. I have had thermocouples mounted for the last several years and a properly turned 2.6 cannot get much under than at high output on street gas. The problem is timing. On street gas 20 -22 BTDC is about as aggressive as you can go. Using that along with a rich mixture means that combustion has not completed by the time the exhaust valve opens. Running race gas (or a mix) will allow more timing advance and less EGT temp and a little more power.

Can’t help you with the knock sense other that to say that the 8v heads are pretty noisy!

Chris White

Bengt Sweden

Thanks Chris,
so 890C-940C would do.
I was down to 950C just with additional fuel so a few degrees more than the current 18 degrees timing and I'm home.

I'll do some tests with lower boost to check if I still get knock indications. Otherwise I'm open for other knock detection suggestions.

Bengt

Duke

BTW how much boost do you run?

Bengt Sweden

1.1 bar.
I used to run 1.3 bar with the 2.5, without knock sense, without EGT and without worries...

Duke

I imagine the car runs pretty well
Make sure you post your results with a tad more aggressive ignition!

tammons

The melting point of aluminum is really low. From what I understand your car is running way too lean. One little detonation blurp and you are going to melt down.

I asked a tuner one day about EGT tuning, and he mentioned you want to tune it just under where the engine melts down for the most power. Of course he was kidding, sort of, and then he said to be safe on a street car he would tune it at 1350 F. I set my car up at 1350 under normal boost, 1300 at high boost and higher rpms and 1450 at cruise and no boost and it ran great and i got decent gas milage. Mind you that was a turbo 928 though.

special tool

He is not lean - he has stated his afr.

He is having high EGT because he is trying to reach a good compromise between the base timing of the 2.5 and his 3.0.

Chris white has already mentioned realistic 951 EGT goals.

dand86951

Bengt, just to add a bit of information as a cross check on what acceptable EGT's could be, you can look at some turbocharged aircraft . On several that have opposed six cylinder engines where the turbine inlet temp is measured just in front of the turbo, which is usually some distance away from the ports due to mounting issues, the max temps are in the range of 1650F to 1750F. Most of the engines use sodium filled valves which is similar to our cars. The difference is most aircraft operate in a steady state and for cruise the recommendations are all over the map, but generally in the 1400F to 1500F range.

Timing on these engines is usually kept at a static 20 to 22 BTDC.

From actual data the individual port temperatures are usually lower than the turbine inlet temps in aircraft. From that and considering we do have insulated exhaust pipes your turbine inlet temps could be over 1900F and I am not sure how good that will be for the turbine metallurgy.

Do you have a thermocouple before the turbine by chance?

Bengt Sweden

Yes I probably lowered ignition too much, going from 22 to 18 degrees.
If the knock sense is giving false alarm, it is just to raise a bit and it will be ok.
Yes, I believe in targeting the values mentioned by, Chris.
High EGT will not melt aluminium but burn valves and reduce turbo life.
Even if alu melts at 800C and valves at 1600C it is the valves that get's hit first, since this is more about heat transfer than absolute temperatures (even if they are linked). The EGTis an indication though.

Bengt Sweden

Hi Dan,
thank you for the input.
If you have 1750 at a distance from the port you probably have quite high temps at the ports!
The timing values may be an indication but it is really different to transfer from one engine to another since timing depends so much on combustion chamber shape.

My understanding is that very few turbines can take 1900F for an extended period. The high heat will deform the wheel and reduce efficiency. In gas turbines for aircraft I have heard that you have to shorten the blades due to creep after long time service.

Bengt

dand86951

Bengt, what I tried to convey is that the exhaust gas temps just out of the exhaust port are lower than those just in front of the turbine wheel inlet. This is from actual direct observation. So with a turbine inlet of say 1650F the temp at the exhaust port would be in the range of say 1580F or so. You are measuring your EGT just out of the exhaust port so I wanted to let you know that in all probability your turbine temps could be in the 1900F range which as you said is not so good for the turbine wheel or the housing.

I agree that timing is sensitive to combustion chamber shape etc, however the aircraft engines are probably not far off since they are simple two valve designs as are our engines. It is a known fact aircraft engines could use and benefit from more advance during cruise, 75%, power settings, but since they don't have electronic engine controls the timing values have to be a compromise and so they are generally set in a turbo engine to ensure no knock during full throttle, full boost operation.