James,

Actually Denver is a prime example of the extremes. I have learned a lot over my almost 40 years of living here (I grew up in Louisville, KY and went to school in Princeton, NJ and Pittsburgh, PA.)

Coming from the lowlands to Denver’s 5280’ altitude was a real experience. I can relate many significant differences but the ones that matter here are the extremes in temperature combined with the high altitude thin air. All this does is to serve the analysis of why our air-cooled 911s behave the way they do.

I have started our out-of-doors cars at as low as -30F here in Denver proper, even lower in the High Country (6-14K’.) All of our cars (911 included) have sump/block heaters. Generally speaking that is not a problem for occasional extreme low temperatures. If this were a daily situation I would make major adjustments to preserve the machinery.

The BIG issue is high temperatures during hot weather. The fact that we have thin air allowed me to see how close to destructive limits our 911s were in any hot circumstance. In ’75, when Porsche came out with the 930 Turbo 1.82:1 engine cooling fan arrangement, it was the savior of every 911 in Colorado, particularly the 2.7s and SCs. There wasn’t a car that I had contact with that didn’t get pitched on this upgrade. The ones not fitted died a heat death.

Many retained their earlier fan arrangement (5-blade or 226 mm diameter or 1.3:1 ratio) for cold weather use. The fan change was synonymous with A/C service in the spring.

Critical to making power and engine longevity is keeping the temperatures under control. That means not letting the head and cylinder temperatures exceed safe limits, even better in the lower temperatures. Porsche chose to remove the oil temperature calibrations for a reason – in my opinion it was legal and not technical. Any 911 engine that has 220+ and ++ oil temperatures is self destructing. The reason is that the head and cylinder temperatures can far exceed what I (and many others) consider safe limits.

You have to ask yourself why do valve guides wear out? Why do rings loose their sealing ability? Why do head studs pull out or break? Why don’t cams and rockers last multi-100K mi? Why do these superbly engineered engines have any failures? IMHO it is primarily too high temperature.

SO….

I would rather have my 911 engine “over-cooled” than suffer the results of over-temperature. With a little planning and effort you can have the best of both worlds.

Best,
Grady

I may be misspeaking here, but I believe you start to lose power when you engine warms past a certain point. This was one reason that they went water cooled.

I think I read that in excellence or something. I think they were talking about the 993's losing 20-30hp when they got hot.

Grady

My post was more in jest, but I see your point. I think of the old ww2 prop planes that had to be run rich and not all full power until they made a certain alt.

On my 3.6 swap I will run 2 84-89 coolers with fans. I may never need those fans but I'll be glad to have them.

thanks for the info. I always learn something from your posts.

James

Brother,

You are definitely not mis-speaking here. There is significant power loss with high temperatures (discounting altitude.) Much of the power loss is from the reduction in volumetric efficiency when the cylinder takes in higher temperature mixture. The less mass air-fuel charge, the less power. This is the primary reason that the “Rubbermaid Solution” works to increase power. The other significant determent from high temperature is the inability to use higher ignition advance and higher compression ratio without damaging the engine from detonation.

This is also one of the reasons Turbos benefit from a serious intercooler. Even an NA water cooled 911 benefits from cool air intake to make power in hot weather. There is a lot of freshman Physics and Chemistry involved here.

I’ll let some of our Pelican aviation experts chime in with the similarities. They are significant and serious business when you can fall from the sky.

Best,
Grady

Grady

Was I right about WW2 birds? Or did I get backwards?

thanks,

James

Well Grady, I happen to be an air force instructor pilot so...

Jets definitely loose power with higher temperature air both ambient or induced by something like anti-ice. I just wasn't sure that my car could really significantly heat the air from the time it hits the CIS snorkel to the time in enters the cylinder after 76 different 90 degree turns and flowing through the really hot intake runners. ;)