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

Scenarios:

At the dyno. Fans on in front of the car. By the 3rd run in about 6 minutes, power is down by 11 hp.

At the track. 280 RWHP 3.6. Cars are on my butt that normally would not be. Oil temps about 230. (Yeah, too hot....but hang on here....)
2 oil coolers, both not optimized for air flow. Yet.
(Especially concerned about track peformance)

Heat soak.

SO -

Is air cooled engine heat soak mainly or purely a function of OIL TEMPS? In other words, if I keep the oil at 200/210 or below no matter the ambient temps, will power NOT drop off much at all?

I'd like a knowledgeable discussion of oil temps vs. heat soak and all experiences with this --

TIA,

I saw heat soak when I did my Death Valley drive in my 930 last year. After eight hours of driving, everything was hot, hot, hot. My oil temps wouldn't come down much, and my power was suffering as my intake temps were about 50 degrees above ambient!

Unless everything is getting cooled with cold airflow, eventually the whole engine (everything metal) will be hot after hours of driving. Cooling the oil will keep the engine/block cool, but your intake and exhaust don't benefit from oil cooling - you'll lose power with a hot intake. Unfortunately, aside from a fresh air snorkel, you'll be breathing hot air until everything cools down.

would the "tupperware solution" be a help here? at least for the track\dyno?

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

what's your CHT temps when warmed up and after the "heat soak" ?

The 911 cooling fan can produce approx. 3,000 cfm of air. On the dyno and without the help of the moving air under the car, this air more or less stalls within the engine and cooling performance can be reduced. You really need some big fans to move enough air under the engine and through the oil coolers. On the track this is obviously not an issue. Do you feel the power drop after a while ? Are you running carbs or FI ?.

Both oil and air are cooling the engine and also interfere with each other. Both systems must work flawlessly with a high hp car to avoid trouble. It sometimes helps to run a cylinder head temperature gauge to identify trouble spots. The ambient temperature will of course always have an impact on performance and cooling.

You're losing power because of cylinder head temps. The heads are getting hot enough to cause the knock control to back off the timing to avoid detonation.

Oil temps and cylinder head temps are not very closely related. You can have high head temps and low oil temps. (broken fan belt for example, or flogging the car hard from cold) And you can have high oil temps and (relatively) low head temps (idling in traffic under no load).

Like mentioned above, the dyno doesn't give enough airflow to evacuate the hot air being pumped underneath the car. A lot of it will get recirculated back into the intake and cooling fan.

Overheating is probably the correct term. It can be caused by lots of factors. Tyson provided a likely source.

Heat soak is a term used to describe components that overheat after switching the engine OFF.

Typically, two main sources:

1) Combustion process produces too much heat for the existing cooling system.
2) Combustion process is okay, but cooling system is inadequate (air and/or oil flow)

If EGTs and CHTs are within range during engine operation, then look to improving and/or repairing the cooling system. It could be as simple as removing a rat's nest under the engine shroud, adjusting the ignition timing or as involved as changing the A/F mixture or increasing oil cooling efficiency.

my $.02,
Sherwood

I do not know the CHT & EGTs

Running Motronic FI on a 3.6.
These conditions occurred on 75-ish degree days - !

Is it then safe to say that optimized oil cooling under the above condition will reduce the quite noticeable drop in power?

~
 

The spec on the 993 fan is 1010 l/s which works out to ~2100cfm
@6100rpm

On a dyno there isn't a generally available fan or combination of fans that can pump enough air across the car to keep it cool. You need 100mph of air through the coolers and over the top and also under the rear to flush all the heat away.

On the track you want your oil tmps to be <100&degC, 80 - 90&deg C or so would be great.

For track use where temps are known to go higher than desired try to use the good high octane track gas, the DME may be retarding your timing and every little advantage helps.

2 poorly ventilated coolers are still not going to do the job of one large well ventilated front mount. On track a strong clean flow through the cooler and out is mandatory, fender mounts don't provide the flow unless gaping holes are made and sealed ducting to the cooler is used. Even for a front mount seal around the edges to ensure full flow w/ no bypass.

one more thing, you can monitor your intake manifold air temp throught the DME, you will find ~ 6&deg F drop if the air intake is situated close to the grill as opposed to the stock location or worse back where most cones pick up their air.

The power dropoff even ocurred with 110 race gas - it flat out seems as if oil cooling is the way to go to cure this problem.

Being passed by the new Maserati was weird.

230 here in Seattle? Big front cooler, bumper/tubb plumbed to feed it, remote reservoir /oil can and a tranny cooler would seem to be a plan.

Along with a diet, wider tires for a faster exit speed, an aero package to keep you on the ground and a short 5th to keep those other cars well behind you in a drag race :)

Craig,
I'll hazard a guess the 230ºF oil temps are not the cause of the power loss. If everything else is okay, your engine should be fine at 230. I'd like to see it a little lower, but I think it's something else.

How about running the car on a dyno where they can monitor A/F ratio and ignition advance?

Sherwood

I did run on the dyno a few months back and things looked AFR-wise.

I do need to go back to the shop that did the install and get the OBD2 plug working so we can give it a diagnostic.

This power droppff only occurs after several laps at elevated oil temps

Craig, what kind of rear decklid are you running?

The reason I ask is that the C2 electric spoiler doubled the volume of air when it was raised. If you're running a stock decklid, then start there by using a tail of some sort.

Even a ducktail will make a noticeable difference over a stock lid in terms of cooling. Less so with oil temps on a 3.6, since they have no engine mounted oil cooler, but definitely in regard to cylinder head temps.

Don't think for a second that race gas means you won't detonate. There are lots of guys with race motors that burned pistons or hammered rod bearings from detonation that were running race gas.

bingo.. hard info before I install my already paid for C2 spoiler.
THX

anyway I think he should install an analog CHT, or a digital that also reads the spread between high&low asap 'cause I'm really interested.. also installing a single EGT would be bonus coupons info. I think the envelope here is his CHT as soon as the oil cooling is good.
That and an LM-1 would be a home run.

I'll answer here for Craig just to move the converstaion along a bit. He is running and an original Porsche RSA wing.

If he pulls his temps down to 200 would that make any difference?

I had excellent cooling off my RSA lid but have switched to a duck. How is that going to change air flow in the engine bay?

Better or as I fear, much worse?

I'm outta my league on this thread for hard info on a track car.
" just to move the converstaion along a bit. "

maybe some street bs may be informative?
If I'm running thru summer deserts at 3.8k in 5th for hours in order to get a baseline.. the 30-40degF rise in oil temp during day running vs night running, the CHT will rise 10-15degF. There's a lot of variables going on under different circumstances.

Hopefully better oil cooling will cool the engine enough to bring his CHT in line. This thread will get interesting all over again if he still [assumed] has high CHT after oil mod. Then the LM-1 gets a real work out imo. The game is to get max EGT with good CHT imo. The fun is how to attain that.

cool info

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. :rolleyes: 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.

------------------------------------------------------------------------

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??

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.

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.

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?

"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

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!

CHT is Cylinder Head Temp. What is EGT?

Exhaust GT

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
http://forums.pelicanparts.com/uploa...1112219133.jpg

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

http://forums.pelicanparts.com/uploa...1112219239.jpg

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

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:
http://forums.pelicanparts.com/uploa...1112219864.jpg

Sides:
http://forums.pelicanparts.com/uploa...1112219898.jpg

http://forums.pelicanparts.com/uploa...1112219936.jpg

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.

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,....:)

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?

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).

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

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.

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

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.

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?

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,.....:) :)