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

[Craig 930 RS]

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,

[Emission]

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.

[air-cool-me]

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

[RoninLB]

Originally posted by Craig911
Is air cooled engine heat soak mainly or purely a function of OIL TEMPS?

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

[buster73]

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.

[Tyson Schmidt]

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.

[911pcars]

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

[Craig 930 RS]

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?

[Bill Verburg]

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.

[Bill Verburg]

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.

[Craig 930 RS]

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.

[rdane]

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

[911pcars]

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

[Craig 930 RS]

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

[Tyson Schmidt]

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.

[Tyson Schmidt]

Originally posted by Craig911
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.

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.

[RoninLB]

Originally posted by Tyson Schmidt
the C2 electric spoiler doubled the volume of air when it was raised.

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.

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.

[rdane]

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?

[RoninLB]

Originally posted by rdane

just to move the converstaion along a bit.

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

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.

[RoninLB]

Originally posted by Bill Verburg
, 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.

cool info