* HEAT SOAK and 911 engines.....info needed...what is it a function of ?

[Craig 930 RS]

Ok, (yaWn) just woke up.. :

I do believe that the CHTs are elevated as a result of the too high oil temps. The 3.6 has pistion squirters which go a long way toward cooling the pistons and to a lesser extent the cylinders.

We are working on a fix for this - it should be completed next week. The right-hand Carrera cooler is boxed in and has 2 fans installed; direct 'ram' air flow is next. The nose cooler resides about 3/4" from the pan. Another case of if you want it done right next time, do it yourself....

We are moving it out on standoffs next week and boxing the sides.

"Doubled air volume with a C2 tail?" Can you define this? This can't mean 'through & over the engine' volume.

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I'll pull out the 'Craig spent time at the Boeing wind tunnel card' here -

Dane, IMO brings up a good discussion starting point -

The egine decklid area (esp on the duck tail config) is a low pressure area.
A duck tail does reside in a different location which serves to reduce the swirling lift vortices that worsen the further back one goes on a 911 (as the body curves away from the airflow). The air intake loc. on a duck would be slightly lower pressure than an RSA tail - but I strongly believe that it will NOT make a difference in cooling. But......an RSA tail has a large level surface area that does route air into the engine. Dane, remeber that the ultimate engine lid opening is about the same on my car with an RSA tail as with a duck. FWTW.

Yet, what is most important regarding air is the engine FAN and the crud that could be on the engine. It does nearly all the cooling work regarding the air cooling portion (as opposed to air into the spoiler oil cooling).

Thanks for the discussion; it does seem that the higher oil temps are the culprit. Engine power was gown by quite a bit -

I'll post results when the fix is in and the first track day is completed.

So is it safe to say that on a 70 degree day with great oil cooling that one should not feel a drop in engine power at all??

[rdane]

Couple of observations. The vents on a RSA tail are directed to scoop up the air that is available. Are you sure on the surface area of the grill? I would have thought the duck's grill was smaller than the flat surface area of a RSA tail.

The duck's grill is not directed into the air flow to take advantage of the air stream as the RSA tail is. There were several reasons I suspect that RUF used the RSA tail on Yellow bird...one being the volume of air it ran through the engine bay by the design.

Again speculation but I have a hard time getting my 3.4 up to temp let alone hitting 200 although admittedly I wasn't on the track which is a big differenece. That with the B&B plumbed some what correctly. Same thing with the the '95 3.6 which I have had at the track. After 45 minutes I did hit 200 on the 3.6 last month on a 70 degree day.

Mind you that is a smaller front cooler than the B&B (almost half in size)
on the 3.6 and not plumbed as well for air flow. Same back space problem Craig but with a better vent up front.

My take is the RSA tail should be exceptional in helping the cooling and the duck pretty poor. Best thing that you can do for the nose cooler is put in one of the TRE RSR pans or make your own to let the air out and then force the air through the cooler by sealing up the front bumper vent.

Although if it was a track car I'd vent the air up and over the hood instead of under the tubb as I did on my street car.

[Craig 930 RS]

I didn't say the surface area of the grill - the engine lid opening is what I refer to; the sheetmetal section of the actual lid. The grill does angle to 'grab' some air as I refer to above and you also mention. I maintain that if you did a back-to-back duck vs. RSA test that the cooling diffrences would be minimal.

I had temps up to 220/230 in city/around town driving! Yowza.
I now, more than ever, believe it was due to the placement and therefore the efficiency of the front cooler.
Mine sucks...........1/2" from the front pan. Sheesh.

Up and over is indeed the best idea; note that many modern race cars use this design.

[rdane]

Missed that point of grill surface area, thanks.

One of the reasons the 964 grill is so effective is it opens the lid with no reduction of air volume because the grill does not cover that air space. Engine lid opening is the same on both duck and RSA but the available volume of air that comes through them would be quite different I think just by the grills that choke them off and the angle each grill is presented to the air flow.

Maybe someone like Jack that switches back and forth from duck to a more effective tail can give some real time comparisons of cooling effects?

[911pcars]

"I do believe that the CHTs are elevated as a result of the too high oil temps."

Craig,
Most likely the other way around. Something has to cook the oil in the first place, and that happens during the combustion process. As I suggested in my other post, either the engine is producing excess heat (abnormally) or the cooling system is not creating enough cooling opportunities. It sounds like you're in the process of correcting the latter.

IMHO, 230ºF is not that hot to reduce power output. It may not be healthy for the engine in the long run, but I think it's something else.

Spark plugs. Do they indicate anything?

Sherwood

[Craig 930 RS]

Sher -

Right, and the hot oil won't allow the cylinders or the heads to cool sufficiently, correct?

Plugs and all else look great. Again, it is only after extended running at 230ish that the power goes down. Steve Weiner had a coronary when he heard that I was running that high (and sometimes higher)

TOO HOT!

[Gunter]

CHT is Cylinder Head Temp. What is EGT?

[Craig 930 RS]

Exhaust GT

[Bill Verburg]

If I were going to run dual coolers I would take a clue from the current crop of waterpumpers, use 2 ducted, angled 964/993 type coolers


w/fan for street, w/o for track, fed from a large central intake and ducted out through or in front of the wheel wells, keeping the intakes near the cars center line is important



We are seeing more of these sets ups on the older air cooled GT race cars, the reports are improved cooling and down force at the front

[Craig 930 RS]

No doubt! The ideal setup. BIG coolers, easy mounting (so simple on a 996), air exits on the sides, an all-around great setup.

Thought about this exact thing while at Daytona:

Front:


Sides:

[Bill Verburg]

It can be done fairly easily on a 911 as well, I wish i took better pics of the last one I saw, but we spent more time working on the brakes.

Any big cenral intale ala Ruf, IROC etc will work, just seal the bottom and cut an exit where you want.

Much easier than the hood outlets, though not as sexy.

[Steve@Rennsport]

Hi Craig:

With all due respect to Sherwood who is a very sharp fellow, oil temps over 210 represent non-linear power losses in a 911. Its not a progressive relationship between indicated oil temps and power dropoffs,.....

You've received a LOT of good, sound information here and I'd "second" that running any 911 on a chassis dyno is a mixed bag. One simply cannot cool the engine and accurately simulate the overall behavior of the car on the road. Years ago, I did extensive testing with multiple thermocouples measuring all 6 cylinder head temps, air pressure testing in the engine compartment and some additional tests both on the road from 30 MPH to terminal speeds and then followed by multiple chassis dyno runs in the same range.

Bottom line; One only gets 1-2 good pulls on a chassis dyno before the results get skewed by excessive oil and cylinder head temps. In the case of these Motronic 5.2 engines, timing is pulled back as knock-sensor activity goes up and one can watch that in real time with a good scan tool.

Get those oil temps in the 180-200 range and you'll be a happier person,....

[Craig 930 RS]

Cool.

But can you elaborate on the higher temps vs. track loos of power; ie exactly what is going on here besides the 'puter backing off the timing?

[Steve@Rennsport]

Craig:

LOL,...I think I just told you,.... Its too hot.

Seriously tho, you need to install and connect the ECU's serial port (OBD-II) so you can interrogate the ECU and get some much needed information like knocks-per-minute, cylinder head temps and air intake temps.

One thing,.......do you run race or pump gas when on the track? The hotter these engines operate, the more they need unleaded race gas (100-104 octane).

[Craig 930 RS]

Always race gas at the track. At least a 50/50 mix.

[Steve@Rennsport]

Good to hear. One really needs good gas in these high compression motors when doing track events.

Information gleaned from the ECU will confirm it, but I'd bet that your running temperatures are creating excessive cylinder head temps that are triggering the knock-sensors to pull back the timing. Thats why its HP sags off as it gets hotter.

One more thing; Inspect the sheet metal and rubber seals that surround the engine. Even the smallest air leak permits hot exhaust to be drawn into the cooling fan from below the sheet metal and that plays havoc with engine temps. I learned that lesson a long time ago while fighting some hot running engines.

[Craig 930 RS]

Excellent as always, thanks Steve.
Should I 'expect' no noticeable power decrease during track use with proper cooling and reasonable ambient temps?

[Steve@Rennsport]

Always a pleasure,....

If you control the oil temps so they run between 180 deg and 200, you'll not see a power loss as long as you run 100 octane unleaded at the track and outside air temps are reasonable. Certainly air density (temperature) plays a role here and all of these engines, especially air-cooled ones, do MUCH better when ambient temps are in the 40 deg-70 degF range.

When air temps exceed 85 deg, you'll experience a noticable HP loss in anything,.....

As you already know, pump gasolines vary widely batch-to-batch and according to the season.

[MuffinMan]

There's some great inforrmation here! Steve, you mentioned extracting the data from an OBDII port. I have an OBDII port setup in my car, what device or method do you recommend using to view the data? I've seen a number of handheld devices on the market, and I imagine there are probably some programs for use with a laptop. What are the best options?

[Steve@Rennsport]

Hiya Rob:

I use either my Bosch Hammer or Porsche PST-2, but any generic code reader for European cars will work .

I like the PC-based scan tool made by Alex Peper; http://www.obd-2.com for its graphical interface and great price. You'll be amazed by what you will see,.....