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If you're above ~120 mph I think the aero point is worth considering.
Based on both tests and some behind the wheel impressions the aero balance of the GT3 is probably too forward, meaning in stock form it can use all of the rear downforce it's got.
This will probably be particularly true if your car has steel brakes, which according to Sport Auto these give the GT4 (same brakes) about 13 lbs more front downforce due to a more open escape path for air from the wheel well. So particularly for this corner case- used at very high speeds, with steel brakes- I'd personally start to think about it.
On a related note, I'd be very interested to hear from anyone who has complained about high speed balance, particularly high speed nervousness, oversteer or "snap oversteer". If that's you, are you running steel brakes or PCCB?
Hadn't thought of that. I'm running steel. Haven't felt any stability issues at high speed so far. Haven't gone to near the level I did in the Turbo yet though. And that got intense. World of difference for every 10 mph once you get above a certain point.
I would go with BBI side muffler by pass. Save over 40lbs. And no worry about aero.
I am not worry about lose 40lbs will compress the spring less because I am 220lbs and heavier than most of my friends who go to track. the weight I took off form car will offset by my weight. haha
If you're above ~120 mph I think the aero point is worth considering.
Based on both tests and some behind the wheel impressions the aero balance of the GT3 is probably too forward, meaning in stock form it can use all of the rear downforce it's got.
This will probably be particularly true if your car has steel brakes, which according to Sport Auto these give the GT4 (same brakes) about 13 lbs more front downforce due to a more open escape path for air from the wheel well. So particularly for this corner case- used at very high speeds, with steel brakes- I'd personally start to think about it.
On a related note, I'd be very interested to hear from anyone who has complained about high speed balance, particularly high speed nervousness, oversteer or "snap oversteer". If that's you, are you running steel brakes or PCCB?
Agree with everything and I have steelies....BUT removing center muffler is not causing any difference in above concerns.
Amen guys! I've trying my hardest to keep my mouth shut on topics like this. This making tiny modifications to insignificant things being a detriment to performance like deleting the rear center muffler is getting crazy. Of couse you won't notice a difference. The RSR cars don't have some giant tin can on the back of the car. They have a straight pipe.
Money,
You mean like if a bottle of automotive detailing product is misaligned on a shelf?
While the calculus of angels dancing on the head of a pin is engaging, my assessment is much easier. As a Viper and Corvette owner, I am appalled that a few tubes costs on the order of $2K. I paid less for headers on my Viper with gorgeous 5-1 merge collectors that slip fit into each primary and had a flange to the exhaust. I am also old and no longer mess with either exhaust or stereo. Liberating, quiet and in warranty! Party on you ballers!
i cannot break myself of tracking and racing, however, so please keep an eye out for me on ttrack as I circulate in stock whisper mode.
Amen guys! I've trying my hardest to keep my mouth shut on topics like this. This making tiny modifications to insignificant things being a detriment to performance like deleting the rear center muffler is getting crazy. Of couse you won't notice a difference. The RSR cars don't have some giant tin can on the back of the car. They have a straight pipe.
Modifying a car is very subjective, some of them are meaningful while the others are not. A full wind tunnel test will cost more than a new GT3, so in my opinion and for myself, it is better to stick with what Porsche Motorsport has spent on R&D for these cars. I am sure drivers at Porsche Motorsport could drive and handle the car up to 120 mph or even more when they were designing and testing the car for production.
A plane can still fly with exposed landing gear, and they can either be retracted with covers to reduce drag or retracted without the covers to induce drag. It doesn't matter, and the plane will still fly at speed. I can't speak for the stability or any other data that supported the companies to design the planes with those covers. If those covers were useless, companies wouldn't have spent the money, material, and time to design them or even carried them over to the later generations.
Back to the GT3, the cover under the engine and the muffler are designed to work together as a diffuser according to Porsche. 997 didn't have that function, so I personally believe that's an improvement over the previous 997. Maybe the diffuser design is negligible, like some say DFI is useless, some say rear-axle steering is stupid, and some say the rear wing on the car should be removed. In this case, I will open my mouth and say those features aren't necessary because I can still hear the engine noise and take pictures of my car. Some people play safe and some people play sound. I prefer the safe side. It is like whether I prefer to use a ceramic coat or a good wax, it doesn’t matter to me because I never spend time to apply any of them. FWIW 991 RSR has a race muffler and a completely different aerodynamic design including a diffuser. In another way of saying, it has a panel beneath the muffler as a diffuser. Moreover, 991 Cup and 991 GT3RS have the same diffusing function on their mufflers like our 991 GT3s.
Last edited by aznkuja328; 05-01-2015 at 06:46 AM.
Modifying a car is very subjective, some of them are meaningful while the others are not. A full wind tunnel test will cost more than a new GT3, so in my opinion and for myself, it is better to stick with what Porsche Motorsport has spent on R&D for these cars. I am sure drivers at Porsche Motorsport could drive and handle the car up to 120 mph or even more when they were designing and testing the car for production.
A plane can still fly with exposed landing gear, and they can either be retracted with covers to reduce drag or retracted without the covers to induce drag. It doesn't matter, and the plane will still fly at speed. I can't speak for the stability or any other data that supported the companies to design the planes with those covers. If those covers were useless, companies wouldn't have spent the money, material, and time to design them or even carried them over to the later generations.
Back to the GT3, the cover under the engine and the muffler are designed to work together as a diffuser according to Porsche. 997 didn't have that function, so I personally believe that's an improvement over the previous 997. Maybe the diffuser design is negligible, like some say DFI is useless, some say rear-axle steering is stupid, and some say the rear wing on the car should be removed. In this case, I will open my mouth and say those features aren't necessary because I can still hear the engine noise and take pictures of my car. Some people play safe and some people play sound. I prefer the safe side. It is like whether I prefer to use a ceramic coat or a good wax, it doesn’t matter to me because I never spend time to apply any of them. FWIW 991 RSR has a race muffler and a completely different aerodynamic design including a diffuser. In another way of saying, it has a panel beneath the muffler as a diffuser. Moreover, 991 Cup and 991 GT3RS have the same diffusing function on their mufflers like our 991 GT3s.
Oh no....it started again??? And I missed the plane, landing gear, drag, no drag, covers no covers, can still fly post this is really good stuff? Yet in the meantime my car still is not unstable in 100mph+ sweepers with bypass in place of center muffler, weird.... it's like it center muffler gone doesn't make much difference? Since earlier posts has anyone had lots of wipeouts because of bypass losing you downforce, I can't wait to hear all the stories? I'm going to buckle up for safety while my ears are peeled!
Potential negative factor with third muffler bypass systems
Originally Posted by ipse dixit
Money,
You mean like if a bottle of automotive detailing product is misaligned on a shelf?
Now THAT'S funny.
This is a classic 991 GT3 forum thread.. Very (some might say overly) cerebral, maybe a touch verbose, but all the ocd angles are carefully considered and weighed. "Calculus of angels dancing on the head of a pin".. Is a beautiful summary. Love reading this stuff.. Carry on gents.
Just for my own sanity i dug up the 991 GT3 CUP car Technical Manual and it shows 2 options for the exhaust (a) with muffler and (b) without muffler. Im guessing the non-muffler setup'would be identical as running a SW bypass ???
Just for my own sanity i dug up the 991 GT3 CUP car Technical Manual and it shows 2 options for the exhaust (a) with muffler and (b) without muffler. Im guessing the non-muffler setup'would be identical as running a SW bypass ???
Similar aerodynamically. However the Cup has a large, multi-position rear wing that can easily be adjusted to correct any aero imbalance that might arise.
PMNA, in the past 9 years of racing the 997 Cup Chassis, and while running PMNA Stock mufflers, RSR mufflers, GMG mufflers, straight pipes, etc, while at Daytona, Long Beach or Laguna Seca......PMNA Engineers never asked us or pointed out the rear aero issues we would need to consider based on what rear muffler we were running.......and this was before the cars started running rear diffusers....
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PMNA, in the past 9 years of racing the 997 Cup Chassis, and while running PMNA Stock mufflers, RSR mufflers, GMG mufflers, straight pipes, etc, while at Daytona, Long Beach or Laguna Seca......PMNA Engineers never asked us or pointed out the rear aero issues we would need to consider based on what rear muffler we were running.......and this was before the cars started running rear diffusers....
Sure, but doesn't the fact that they switched to a diffuser suggest the car is sensitive to aero in that area? As we intuitively know it is?
Presumably you were also adjusting your wing angles pretty often to tune aero...
04-30-2015, 08:01 PM
