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The turbo thing at altitude, at least with diesels, sometimes doesn't work.
I had an issue at the top of the Grand Canyon a few years back in a diesel that for some reason refused to make any type of boost after I shut it down (and took funny pics of me falling into the canyon) then started it up again - nothing but smoke, was at around 7700'. Total pig, was very unhappy, ran very hot. As I moved down into the valley, it improved, but the best we could make of it was there was something wrong with a pressure valve. Needless to say, when I left Arizona, thought it'd be better to go up I5, then, The Grapevine...
Yes, and a GT3 is no slouch and has 500+ HP... but has less than 340 ftlb. peak torque, and it all comes on after 5,000 RPM.
Compared to even a modestly tuned 996 Turbo, over 500 HP and 500 TQ, and a much broader, flatter torque curve that is pretty flat from 3,000 or so RPM and it's the GT3 that needs to be driven near the limit to keep up...
On high altitude mountain twisties, where having a wide power band is highly valuable, lower and mid RPM torque is huge (say coming out of a lower speed blind hairpin), advantage Turbo all day long. Not that the GT3 isn't fun, it just isn't IMHO set up quite as well for that kind of driving.
On a racetrack, near sea level where you can more easily keep the GT3 in it's power band between 5,500 and 9,000 RPM, take advantage of its lighter weight + stiffer suspension, and not lose a bunch of power to altitude, the GT3 has a notable advantage. It's what that car was designed to do....
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For NA power loss, an easy to remember number is about 25% loss a 8,000'. We start our drives at about 5,500 and will regularly hit 9,500-10,000'. Turbos will also lose power, but far less and again, it's that broad torque curve that really makes them shine in that sort of driving.
Absolutely. And we won't make as much power at altitude as sea level, even with the turbos. But again, the power loss is far less than in an NA car. Perhaps the biggest issue is heat, compressing all that air ups intake charge temps. But again, fortunately for mountain twisty driving, you are not constantly on boost like on a track, so the intercoolers don't heat soak as much. On one of my 996 Turbos, I have upgraded to the 997 GT2 intercoolers, the other I am still running stock, and I don't really notice a difference unless I take it to the track and really start hammering the boost at a much higher duty cycle.
Thank you for explaining that and for mentioning the intercooler differences. I was considering upgrading but don't track my car and really only drive it short distances.
On one of my 996 Turbos, I have upgraded to the 997 GT2 intercoolers, the other I am still running stock, and I don't really notice a difference unless I take it to the track and really start hammering the boost at a much higher duty cycle.
I want to do the GT2RS intercoolers but it seems like a waste unless you actually track the car. Do you notice the cruise IATS are lower with these ICs when off boost?
I want to do the GT2RS intercoolers but it seems like a waste unless you actually track the car. Do you notice the cruise IATS are lower with these ICs when off boost?
Although others will disagree, I highly doubt it makes much of a difference if any on a car that only sees street duty and one that is in the low to mid 500whp range.
Last night I swapped wheels on the 996s. The silver car has new Pirelli 235/40/18F and 315/35/18 R. I put them on the black car. Such a huge difference in ride and noise comfort. The black car had stock size used old and hard Dunlops. Interestingly the Pirellis slide around more in the wet than the semi-slick/worn out Dunlops.
Although others will disagree, I highly doubt it makes much of a difference if any on a car that only sees street duty and one that is in the low to mid 500whp range.
I believe that is a valid observation, yours on the other hand...
Although others will disagree, I highly doubt it makes much of a difference if any on a car that only sees street duty and one that is in the low to mid 500whp range.
Logs would tell the story but I can’t imagine you’re not going to get a noticeable amount of timing pull from high IATs in hot temps. Combine that with crappy 91 if that’s all you have in your area and you’re relying on your knock sensors to keep your motor safe, even with just a tune. Obviously depends on your driving style as well. If you’re just doing little single gear romps around town then sure, but back to back multiple gear pulls and IATs would start to climb very high.
Different platform (B5 S4), but you can see how high IATs can climb in just a single gear. 20F delta in 3rd gear and that’s with one of the best set of ICs available for those cars. Turbo to IC setup very similar to a 996. Twin turbos, twin intercoolers, into a Bipipe then into the TB.
Last night I swapped wheels on the 996s. The silver car has new Pirelli 235/40/18F and 315/35/18 R. I put them on the black car. Such a huge difference in ride and noise comfort. The black car had stock size used old and hard Dunlops. Interestingly the Pirellis slide around more in the wet than the semi-slick/worn out Dunlops.
I hate the current crop of p zeros, I share your observations about poor wet performance, they, in fact, suck in the wet.
Pss9s... However, I have buggered the front right adjustment ****, so they're going to have to come out and be sent to the folks in Cali to be rebuilt.
I hate the current crop of p zeros, I share your observations about poor wet performance, they, in fact, suck in the wet.
Ok. So it's not just me and Japanese roads.
I've always like Dunlop. Think they give the best overall performance, wet/dry, noise, price and longevity. I swapped wheels because I'm taking Blackie for a holiday drive. Torrential rains can be an issue so best mitigate as much risk as possible. Plus the wife wants to go in the RS4. But I just did the timing belt and am not confident it's done correctly. I've driven it a couple of times but.....
So figured I'd make the 996 a bit more comfortable.
Pss9s... However, I have buggered the front right adjustment ****, so they're going to have to come out and be sent to the folks in Cali to be rebuilt.
Would you mind sharing who you're going with for the rebuild and what it is going to cost? I have a set of PSS9s FVD versions that would need a rebuild sitting in my garage after moving to Ohlins.
The turbo thing at altitude, at least with diesels, sometimes doesn't work.
I had an issue at the top of the Grand Canyon a few years back in a diesel that for some reason refused to make any type of boost after I shut it down (and took funny pics of me falling into the canyon) then started it up again - nothing but smoke, was at around 7700'. Total pig, was very unhappy, ran very hot. As I moved down into the valley, it improved, but the best we could make of it was there was something wrong with a pressure valve. Needless to say, when I left Arizona, thought it'd be better to go up I5, then, The Grapevine...
Then there was something wrong with your truck. I have two turbo diesels here, a Cayenne and a Touareg. Both kick *** anywhere from 6000-11000 feet above sea level and punch well above their weight. I went from my 200 Series Land Cruiser (400hp, 400ft lbs) to my Touareg, (240hp, 406ft lbs) and it annihilated my Land Cruiser. Then I tuned the Touareg to 320hp, 500ft lbs and it's no comparison. Stock to stock, the Land Cruiser would have to down shift twice going up the passes and struggle to hold onto 75mph, the diesels hold top gear and easily do 80mph, with acceleration a tickle away.
07-16-2024, 03:36 PM
