Oakleyguy

Hi all,

Long time lurker and now a newer face around, but wanted to quickly introduce myself. Long time car enthusiast, having had various affairs with BMW, Nissan, VW (Karmann Ghia), and Subaru.

My most recent car was a 2015 M4 6MT that I loved but sold off to finish securing a property. Luckily that chapter is coming to a close and I'm back on the market for a new car. The past six months have lead me to the 911 after backing out of a deal on a GT4 from a buddy since the wifey didn't like getting in and out of the buckets.

I've driven the new C2 991.2 and a GTS 991.1 and both were fantastic in their own ways. I'm planning on driving the two back to back next week to get a better feel of power delivery.

That said, I've been curious what kind of HP penalties I'm looking at being in Denver.

Has anyone in Denver had their 991.2 dyno'ed yet? Any 991.1 owners with dyno information in Denver as well?

ace37

Dyno numbers are often very misleading as corrections will typically adjust for the altitude.

If any are available, look at drag racing times and you'll get a better idea. Try the loss of trap speed of a TT vs. a Carrera at your strip vs. something at sea level to get a good idea.

I live in Salt Lake City at 4400 ft, so not quite as high as you but close. NA is down about 15%. Turbo cars are down anywhere from 3-7% depending on the headroom in the design. I suspect stock 911s will be close to that 3% but a tuned car will lose the headroom and show higher loss.

I expect in Denver a 991.2 S will match a 991.1 GT3 for thrust and beat it in torque.

Oakleyguy

Very good point regarding the quarter mile times! Agree with the corrections on dyno charts, it's quite easy to manipulate the data.

ace37

Oh I wasn't even thinking about manipulation which is also a problem - rather, I think the SAE correction which helps with manipulation intentionally corrects results down to a standard density altitude. Usually that's great, but it complicates things for people like you and I. And uncorrected numbers can be misleading for obvious reasons.

But I do hope you find some data and will be interested if this thread grows as most of it applies here as well. Mediocre data is far better than none at all!

pfbz

I think you'll find even a 991.2 base will easily outperform a 991.1 S or even GTS at 5,000'+ altitudes. Probably at sea level as well. 991.2 S versions, the difference is even bigger.

Stevinson in Denver will sometimes do extended test drives. Go take a 991 base over Berthoud Pass, prepare to be very impressed.

In general, one usually figures about 3% loss per 1,000' with a normally aspirated engine. At 6,000', thats 18% reduction. Turbocharged engines will still have altitude power losses (mostly because the software doesn't attempt to fully compensate), but they will be much lower.

So just on paper, the 991.1 GTS's 430HP is down to ~353HP. The 991.2 base's 365HP stays pretty close to the rated power, plus has a huge torque curve advantage.

Oakleyguy

That's great to know! I've been working with a gentlemen at Prestige, but I haven't requested an extended drive. Good info in this thread!

pfbz

Stevinson gave me the keys for a 991.2 C4 cab on a Saturday afternoon and wanted the car back Monday morning.