991.2 GT3 lightweighting project
07-07-2018 | 04:09 PM
#1
Thread Starter
Racer
Joined: Dec 2017
Posts: 275
Likes: 94
991.2 GT3 lightweighting project
Eagerly awaiting delivery of my GT3 in October. Relatively lightweight build to start with: manual, LWB seats, PCCBs, base audio. Only weight penalties are for FAL and LED lights. So, my rough math puts the weight at ~25 lbs. over Porsche's quoted weight for the lightest possible configuration, for a total of 3,140 lbs.
My goal is to get that number under 3,000 lbs. with aftermarket options. Mostly just for fun and psychological satisfaction.
I'm already having an Akropovic full race exhaust installed at delivery (side mufflers delete, center bypass, titanium, etc.). That's good for 60 lbs.
What next?
I figure lightweight battery is a no-brainer. Liteblox would lose me another 45 lbs.
Then there are the BBS/Manthey magnesium wheels. Pricey (~$17K), but lots of benefits outside of pure weight loss. I believe they'd save an additional 25 lbs. or so? They also look amazing.
That gets me to a total weight savings of 130 lbs. (someone please correct me if I'm off somewhere).
Where to grab the next 10+ lbs.?
I was thinking maybe lightweight glass for the rear windows. Good for 6-8 lbs.?
Manthey carbon fiber wing? Don't know if any lighter than stock.
Just for the titanium exhaust, magnesium wheels, and lightweight battery, I'm out ~$30K already. Stupid? Or an awesome GT3? I'm rationalizing that a manual GT3 is currently the lightest 911 you can get from Porsche, so not so worried about eclipsing the cost of an RS. This build will be lighter than an RS and maybe be more nimble and lightfooted, though certainly less stable around a track. Or no?
My goal is to get that number under 3,000 lbs. with aftermarket options. Mostly just for fun and psychological satisfaction.
I'm already having an Akropovic full race exhaust installed at delivery (side mufflers delete, center bypass, titanium, etc.). That's good for 60 lbs.
What next?
I figure lightweight battery is a no-brainer. Liteblox would lose me another 45 lbs.
Then there are the BBS/Manthey magnesium wheels. Pricey (~$17K), but lots of benefits outside of pure weight loss. I believe they'd save an additional 25 lbs. or so? They also look amazing.
That gets me to a total weight savings of 130 lbs. (someone please correct me if I'm off somewhere).
Where to grab the next 10+ lbs.?
I was thinking maybe lightweight glass for the rear windows. Good for 6-8 lbs.?
Manthey carbon fiber wing? Don't know if any lighter than stock.
Just for the titanium exhaust, magnesium wheels, and lightweight battery, I'm out ~$30K already. Stupid? Or an awesome GT3? I'm rationalizing that a manual GT3 is currently the lightest 911 you can get from Porsche, so not so worried about eclipsing the cost of an RS. This build will be lighter than an RS and maybe be more nimble and lightfooted, though certainly less stable around a track. Or no?
Last edited by mafoofan; 07-07-2018 at 04:41 PM.
07-07-2018 | 04:32 PM
#2
SJW, a Carin' kinda guy
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Radio delete shelf ($115) and remove speakers is the easiest per pound and least expensive. You can pop out the mini headrests for a few ounces. Leave the tire slime/compressor/owners manual etc. at home too.
After the battery/exhaust/wheels you either are spending tons of money and/or sacrificing functionality and not gaing much.
Carbon fiber R hood and fenders 4kg
Lightweight Glass 4kg
CF roof 1kg
I doubt the CF wing saves much as the factory GT3 wing is already CF
Maybe 20lbs total for megabucks with no real negative impact other than to your wallet.
Robert Linton has done lightweight with his R and it is insane (in a great way). Gun drilled chromemoly axles, aluminium calipers etc.
AC delete
Remove airbags/swap steering wheel
Carpet delete
remove passenger seat
All inexpensive and save lots of weight, but you end up with a stripped out interior. Probably not your style. ;-)
After the battery/exhaust/wheels you either are spending tons of money and/or sacrificing functionality and not gaing much.
Carbon fiber R hood and fenders 4kg
Lightweight Glass 4kg
CF roof 1kg
I doubt the CF wing saves much as the factory GT3 wing is already CF
Maybe 20lbs total for megabucks with no real negative impact other than to your wallet.
Robert Linton has done lightweight with his R and it is insane (in a great way). Gun drilled chromemoly axles, aluminium calipers etc.
AC delete
Remove airbags/swap steering wheel
Carpet delete
remove passenger seat
All inexpensive and save lots of weight, but you end up with a stripped out interior. Probably not your style. ;-)
07-07-2018 | 06:44 PM
#5
Thread Starter
Racer
Joined: Dec 2017
Posts: 275
Likes: 94
Radio delete shelf ($115) and remove speakers is the easiest per pound and least expensive. You can pop out the mini headrests for a few ounces. Leave the tire slime/compressor/owners manual etc. at home too.
After the battery/exhaust/wheels you either are spending tons of money and/or sacrificing functionality and not gaing much.
Carbon fiber R hood and fenders 4kg
Lightweight Glass 4kg
CF roof 1kg
I doubt the CF wing saves much as the factory GT3 wing is already CF
Maybe 20lbs total for megabucks with no real negative impact other than to your wallet.
Robert Linton has done lightweight with his R and it is insane (in a great way). Gun drilled chromemoly axles, aluminium calipers etc.
AC delete
Remove airbags/swap steering wheel
Carpet delete
remove passenger seat
All inexpensive and save lots of weight, but you end up with a stripped out interior. Probably not your style. ;-)
After the battery/exhaust/wheels you either are spending tons of money and/or sacrificing functionality and not gaing much.
Carbon fiber R hood and fenders 4kg
Lightweight Glass 4kg
CF roof 1kg
I doubt the CF wing saves much as the factory GT3 wing is already CF
Maybe 20lbs total for megabucks with no real negative impact other than to your wallet.
Robert Linton has done lightweight with his R and it is insane (in a great way). Gun drilled chromemoly axles, aluminium calipers etc.
AC delete
Remove airbags/swap steering wheel
Carpet delete
remove passenger seat
All inexpensive and save lots of weight, but you end up with a stripped out interior. Probably not your style. ;-)
PCM/radio delete is in the future. I figure one day it will look/feel woefully obsolete.
Sounds like carbon hood is the next step.
Can't in the U.S.
07-07-2018 | 07:24 PM
#7
Three Wheelin'
Joined: Jun 2009
Posts: 1,921
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I have Dundon race headers and antigravity light weight battery on hand to be install on delivery. My Touring will have PCCB, lwbs, fal, xenon, bose, leather.
The only other thing I’m looking to add are the BBS magnesium wheels, but waiting to see if they can do light silver finish. Despite the price of the mags, I’m justifying it in my head because it’s rotating mass. But I wouldn’t spend the same amount per lbs for static weight, so fenders, hood, etc, are out of the equation. I just gotta get back in the gym. Seriously.
The only other thing I’m looking to add are the BBS magnesium wheels, but waiting to see if they can do light silver finish. Despite the price of the mags, I’m justifying it in my head because it’s rotating mass. But I wouldn’t spend the same amount per lbs for static weight, so fenders, hood, etc, are out of the equation. I just gotta get back in the gym. Seriously.
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07-07-2018 | 07:44 PM
#8
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Joined: Oct 2014
Posts: 5,403
Likes: 635
I have Dundon race headers and antigravity light weight battery on hand to be install on delivery. My Touring will have PCCB, lwbs, fal, xenon, bose, leather.
The only other thing I’m looking to add are the BBS magnesium wheels, but waiting to see if they can do light silver finish. Despite the price of the mags, I’m justifying it in my head because it’s rotating mass. But I wouldn’t spend the same amount per lbs for static weight, so fenders, hood, etc, are out of the equation. I just gotta get back in the gym. Seriously.
The only other thing I’m looking to add are the BBS magnesium wheels, but waiting to see if they can do light silver finish. Despite the price of the mags, I’m justifying it in my head because it’s rotating mass. But I wouldn’t spend the same amount per lbs for static weight, so fenders, hood, etc, are out of the equation. I just gotta get back in the gym. Seriously.
07-07-2018 | 07:55 PM
#9
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Joined: Sep 2015
Posts: 987
Likes: 85
From: Little Rock, Arkansas
07-07-2018 | 10:01 PM
#13
Three Wheelin'
Joined: Jun 2009
Posts: 1,921
Likes: 308
For example, I’ve had Dymags wheels cars in the past. If I remember correctly, unsprun weight savings have a ratio of around 6:1 vs sprung weight when on wheels. So a combined 34 lbs weight saving on wheels (about 8lbs savings per front wheels and 9lbs savings per rear wheels, oem vs mags) would translate to the equivalent or around 204 lbs sprung weight savings, not 51-68 lbs. I’ve driven cars with magnesium/carbon wheels in the past, and the difference vs stock wheels is significant, not imaginary. Well above a 2:1 weight ratio.
07-07-2018 | 10:34 PM
#14
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Joined: Sep 2015
Posts: 987
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From: Little Rock, Arkansas
Source?
For example, I’ve had Dymags wheels cars in the past. If I remember correctly, unsprun weight savings have a ratio of around 6:1 vs sprung weight when on wheels. So a combined 34 lbs weight saving on wheels (about 8lbs savings per front wheels and 9lbs savings per rear wheels, oem vs mags) would translate to the equivalent or around 204 lbs sprung weight savings, not 51-68 lbs. I’ve driven cars with magnesium/carbon wheels in the past, and the difference vs stock wheels is significant, not imaginary. Well above a 2:1 weight ratio.
07-07-2018 | 11:16 PM
#15
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Joined: Oct 2014
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Kinetic Energy of a translating component: KE = 1/2 * m * v^2
... m = mass
... v = velocity
Kinetic Energy of a translating + rotating component: KE = (translational KE) + (rotational KE) = (1/2 * m * v^2) + (1/2 * I * w^2)
... m = mass
... v = velocity
... I = rotational moment of inertia
... w = angular velocity
For simplicity, let's look at a tire whose translational velocity v and angular velocity w are related by the tire radius:
... v = w * r
... r = radius of the tire
Assuming all the mass of the tire is concentrated in a ring at that outer radius, it's moment of inertia is:
... I = m * r^2
Substituting these into the translating + rotating component equation (to calculate the KE of the tire) results in:
... KE = (1/2 * m * v^2) + (1/2 * m * r^2 * v/r * v/r) = (1/2 m* v^2) + (1/2 * m * v^2)
... KE = 2 * (1/2 * m * v^2)
... KE = 2 * (KE of a purely translating mass)
So the kinetic energy of a tire that rotates proportional to the vehicle velocity is simply twice that of an identical spare tire that is just sitting in the trunk.
If you repeat this analysis for something like a wheel and assume the mass is more evenly distributed across the surface of the disc (rather than at the outer ring), then the inertia is instead I = 1/2 * m * r^2, so you'll get roughly:
... KE = 1.5 * (KE of a purely translating mass)
You'll actually get less than that if you accurately calculate the wheel radius (which is shorter than the tire radius).
Long story short:
... weight reduction in the tires is roughly equivalent to 2x normal chassis weight reduction
... weight reduction in the wheels is roughly equivalent to 1.5x normal chassis weight reduction
... weight reduction in the rotors is even less than 1.5x (because the radius of the rotor is even smaller than the wheel)
This is all just for comparing equivalent masses for straight line accelerations...
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