MM3.9GT3

How much does heat soak affect the GT2? I know that turbo cars do not perform well in hot weather, and when Top Gear USA tested the GT2 RS, they estimated a loss of 70 - 80 hp, given that the surface (tarmac) temperature was 161 F. Then they took it to the streets of L. A. at night, with 60 F temperatures, and it was fine.

I have been toying with the idea of getting a 997 GT2 and adding the Manthey M600 package. But, with daytime temperatures in Dallas hovering well over 100 F in the summer, I suspect that performance would degrade quite a bit.

Thoughts?

TurboS

I've noticed the speed differential on cool days vs very hot days at Mosport, especially on the back straight. On a 15C day my terminal speed is about 260kph, on a much warmer day, 30C I'm losing about 10 - 12 kph. I was thinking of replacing the stock GT2 intercoolers with GT2 RS intercoolers, which are apparently in the Turbo S as well. Sorry for the metric, eh.

MM3.9GT3

10-12 kmph is substantial for a 15C increase in ambient temperature. I believe you are correct about the Turbo S and GT2 RS having the same intercoolers (may be Pete can verify).

Now, calling 30C a much warmer day....We call that perfect weather in Dallas. That would be 86F, and overnight low temperatures in Dallas are in the low 80's right now.

TurboS

We pulled up the schematics at the dealership, the intercoolers are identical in both vehicles. I posed the question because intercoolers that are available thru the aftermarket, say dealers in the south that start with a C, are twice the price or more. Not sure if you can justify paying double for an incremental benefit, assuming there is one.

30c + humidity and closed windows = 3 shirts needed for one track day

Even with the drop in power on very hot days, we are still showing ZR-1's our taillights cause they suffer from the same issue, and worse, or blow up. TINS.

NJ-GT

That's a significant difference, and confirms what I have been told by 2 other 997 GT2 owners.

However, this is not a 997 GT2 or 997 GT2 RS problem only, it applies to the Nissan GTR and ZR-1 as well.

Aerokitted

So the ZR1s aren't as durable as the 911s during track days? Did not know this.

How does heat soak impact the GT3s?

gt2urbo

i was at a poc event a few months ago at streets of willow. it had to be 100 plus and eally hot track temp. i was coming onto the front straight and it seems as if i lost all boost. i couldnt take the gt3 rs mk2 that had moved right for my run to pass him. i since replaced intercoolers and tune. had another track day with similar weather and it was all good felt very strong... maybe tune related. i use champion intercoolers now.

TurboS

No not as durable. Link to a track day in June at Mosport, extremely busy.
Because of the disparity in the group, a lot of faster cars that are normally lapping on their own were bunched up in groups. Great day for a comparison, and, humbling day for the pushrods.....

GT2Driver

Hi MM3.9GT3,

If you are looking for trouble free driving during full charge driving ( limited heat influence ) there is only two solutions on the market today that have acceptable characteristics and that is No 1. SECAN intercoolers from France ( very expensive $20-25.000 but the best ) or No 2. CTR intercoolers from England ( medium expensive $13-14.000 with 2-3 degrees higher IAT than SECAN ).
Toby has tested a lot of intercoolers and is today running CTR:s as myself which I will use in a 997 GT2 RSR project.

Rgds Lars

TurboS

Are you seeing more than 1.3 bar of boost with the tune?

MM3.9GT3

Other than the normal slight power loss due to less dense (hot) air, there are no issues.

Do you know which intercoolers are used by Manthey in their M600 package?

Jake951

Rule of thumb for power loss from reduced air density at higher temperatures is 1% drop in power for every 10 deg F increase in temperature. On extremely hot days (100+ deg F), I've noticed a loss of power compared to days when it's much cooler. I see it as a loss in top speed on the longer straightaways. I suspect that the engine management system may also cut back timing when the intake temperature gets high, and that reduces power further.

I think it's more complicated, however, for turbocharged cars because intercooler efficiency depends on ambient temperature. When I had a 944 Turbo running boost pressures higher than stock, the loss in performance was very noticeable on hot days, much more so than on the GT3.

TB993tt

This issue of heat on our VTG engines is THE most Important issue which will affect power output.

The old quotes of 1% being lost per 10 deg rise etc are not really valid for our engines as they have so many safeguards in the programming which will subtley reduce our power output to keep the dreaded knock away and keep the engine perfect for a long lifetime.

Schmirler is the meister of this topic, through his experience in building race engines (he has probably built more Porsche race engines than anyone in the world) and he knows how to emulate race conditions on his dyno through varying IAT temperatures (using the water cooled intercooler) and he knows through experience how this will translate on the road…… But even he admitted to me that these VTG engines are “difficult”…….. he pointed to a 840hp K24/26 engine with older style 996tt management and said they are so simple in comparison but the VTG engine electronics are much more complex and interactive, they hired a Bosch engineer for 2 solid weeks to teach them how to write a program properly (ie like Porsche) for my all new GT2 VTG motor using turbo intake system and electronics.

The VTGs produce so much heat, the hot side which was designed to flow 540hp suffers from severe back pressure when made to work to turn a big 700hp compressor wheel, I guess that because the hot side has to “contain” all the exhaust energy (and cannot dump it via wastegates like conventional turbos) all the energy becomes heat stored and not dumped to atmosphere…. To run more than 680PS one needs a bypass type exhaust to relieve the back pressure….

My engine was signed off once with decent ~724PS but he tested it on the road and the IATs were too high (his IAT estimations on the engine dyno were inaccurate cos of the pesky VTGs) so it was rebuilt with some even bigger compressor VTGs which were experimental at that stage, he could use less boost but flow ~725PS worth of air at 0.1 bar lower boost to lower the IAT further….

Still the final on road programming proved quite intense, I mentioned before all the tables which start pulling boost and timing at quite low IATs, these do it very subtely but they definitely do it…..

I tested my car recently and I had the incorrect lower intercooler ducts (they were from the GT2RS to match my new bumper/fender) which didn’t cover 4cm of core so I was losing out on intercooler efficiency…… the data on the test shows the IATs getting up to ~63c at 300kph and one can see the boost being reduced exactly as the tables indicate, a 5% reduction at 63c loses me about 40hp and that is exactly what the acceleration data showed me !

So in answer to your question, in 100f heat you don’t really stand a chance, as your IATs will always be above 55c (this is Porsche factory program threshold for boost reduction) so you will always have less than the DIN (at 20c) power rating.

Yes an expensive intercooler will help, just how much I dunno, you would have to test it, my guess is a Secan/CTR could keep a factory tuned car in 35c to about 60c IAT ……. The extra problem for the GT2 (over the turbo) is it runs the stupid high boost to make the expansion manifold work, the theory is the boost is at 1.4/1.5 bar post turbo and IATs go up to 60+c (even at DIN 20c ambient) but as the air expands and enters the combustion chambers it cools from said 60+c and makes the power. It is hard to guess exactly what temp the air cools to but it must work as one can see the performance numbers and the GT2RS with the same engine (virtually) apart from its intercoolers makes 620PS…….

The Manthey 600 will be pretty similar to the GT2RS is my guess, pics of its intercoolers are below, they do not look anything special.


If you are using the Manthey in your 100f my guess is you would always be running on the edge of the 55c threshold even in street driving and on track you would be constantly in the 70s which (looking at my tables FWTW) would lose you minimum 60hp so you would be back down to stock GT2 level 540PS…… but a stock GT2 in those same conditions would probably be at 490PS !

The only way to really tell is by doing ones own testing on the road, or I guess asking Manthey, I’m not sure their PR guy (cant remember his name but I though him a bit of a ****) would have the correct answers for you but for sure one of their development engineers would have the answers since they get 30c/90f in Germany every summer. Let us know what they say, it will be interesting.


BTW, the other important item for reduced engine temps is the front radiator, this is the Porsche M/S GT3 Cup version, said to lower water temps by 8c…. every little helps

Nordschleife

its not that he's 'a bit of a ****' - he rarely meets anglophones who have done their homework, hence the 'attitude' you probably experienced.

R+C
PS but being a bit of a **** is always an option

MM3.9GT3

Toby, thanks for the comprehensive answer. This is exactly what I wanted to know.