Go Back   986 Forum - for Porsche Boxster & Cayman Owners > Porsche Boxster & Cayman Forums > Boxster General Discussions

Reply
 
LinkBack Thread Tools Display Modes
Old 07-11-2007, 11:11 AM   #1
Registered User
 
Join Date: Sep 2004
Location: Atlanta
Posts: 1,820
Road and Track: 250mph Carrera GT?!?!?

are these guys really this stupid? the cover of the magazine (July) pays hommage to the 250mph Mirage GT (Gemballa Carrera GT) inside. i read the article. gemballa adds 40HP to the car for a total of 652HP (in addition to ruining the body as usual).

they expect us to believe that 40HP take the car from 205 to 250?!?!? an F1 car with zero wing will hit 250 with about 1/2 the frontal area of a CGT. the Veyron takes 1001HP to hit 253. me thinks the R&T boys should lay off the bong rips.

__________________
insite
'99 Boxster
3.4L Conversion

http://i156.photobucket.com/albums/t...1/KMTGPR-1.jpg
insite is offline   Reply With Quote
Old 07-11-2007, 11:15 AM   #2
Pat
Registered User
 
Join Date: Jun 2007
Location: Littleton, CO
Posts: 456
Quote:
Originally Posted by insite
are these guys really this stupid? the cover of the magazine (July) pays hommage to the 250mph Mirage GT (Gemballa Carrera GT) inside. i read the article. gemballa adds 40HP to the car for a total of 652HP (in addition to ruining the body as usual).

they expect us to believe that 40HP take the car from 205 to 250?!?!? an F1 car with zero wing will hit 250 with about 1/2 the frontal area of a CGT. the Veyron takes 1001HP to hit 253. me thinks the R&T boys should lay off the bong rips.
Well, what other changes are made? A car with 652 hp is certainly capable of hitting 250 mph. A lot more goes into it than just power. What about the torque? What is the Cd of the Mirage GT? Did they change the gearing?
Sure, ceteris paribus, another 40 hp won't increase the top end by 45 hp.
Oh, and the Cd for an F1 car is about .8, not .3 like the CGT.
Pat is offline   Reply With Quote
Old 07-11-2007, 11:59 AM   #3
Registered User
 
Join Date: Sep 2004
Location: Atlanta
Posts: 1,820
Quote:
Originally Posted by Pat
Well, what other changes are made? A car with 652 hp is certainly capable of hitting 250 mph. A lot more goes into it than just power. What about the torque? What is the Cd of the Mirage GT? Did they change the gearing?
Sure, ceteris paribus, another 40 hp won't increase the top end by 45 hp.
Oh, and the Cd for an F1 car is about .8, not .3 like the CGT.
not much goes into it but power. top speed is a factor of drag area (Cd x frontal area), rolling resistance, and horsepower. that's it. torque, gearing, and weight have nothing to do with max (drag limited) terminal velocity. and you're correct that an F1 car with wing has a high Cd due to downforce considerations. in my post, i was refering to a test Honda did where they removed the wings (not physically, but to zero angle) and tested top speed on a runway.

648HP isn't nearly enough to propel a car the size of the Carrera GT to 250MPH (even if they achieved an obscenely low Cd).
__________________
insite
'99 Boxster
3.4L Conversion

http://i156.photobucket.com/albums/t...1/KMTGPR-1.jpg
insite is offline   Reply With Quote
Old 07-11-2007, 01:17 PM   #4
Pat
Registered User
 
Join Date: Jun 2007
Location: Littleton, CO
Posts: 456
You said, "...gearing, and weight have nothing to do with max (drag limited) terminal velocity."

Do we know for sure the CGT is limited by drag? Maybe it runs out of gears, so all it would need is a taller gear.
I have NO idea if this is the case, but thusfar there is no info in this post negating that possibility. Maybe a taller gear combined with higher revs than allowed by the factory?
Like I said, I have NO idea, but am just throwing out possibilities. I'm just surprised a reputable publication would make a claim if it weren't true. Just trying to come up with some kind of explaination.
Pat is offline   Reply With Quote
Old 07-11-2007, 02:22 PM   #5
Registered User
 
Join Date: Jun 2007
Location: Ohio
Posts: 307
Guys its just marketing headlines on the cover to get you talking about it and buy the magazines! I love marketing.
__________________
Lamborghini Murcielago (current)
Supercharged Viper SRT-10 800 HP Special Edition #49 of #50 (current)
Ferrari 360 Spider
Lamborghini Diablo VT Roadster
911 Cab
Boxster S (current)
08 Hummer H2 (current)
BMW Z3 (current)

Limos in Ohio and PA - First Class Limo Columbus Limos

http://pteam.net/avatar3.jpg
my car collection *Porschephiles agree, Desnorkify your Porsche!*
pteam is offline   Reply With Quote
Old 07-11-2007, 02:46 PM   #6
Registered User
 
Join Date: Sep 2004
Location: Atlanta
Posts: 1,820
Quote:
Originally Posted by Pat
Do we know for sure the CGT is limited by drag? Maybe it runs out of gears, so all it would need is a taller gear.
it's drag limited to 205 (manufacturer's data)

Quote:
Originally Posted by Pat
Like I said, I have NO idea, but am just throwing out possibilities. I'm just surprised a reputable publication would make a claim if it weren't true. Just trying to come up with some kind of explaination.
i'm with you here. it shocked me that they would print that, and on the cover, no less. the DID state that the 250mph claim was a Gemballa number. my bet is that they confused 350 kph and 250 mph. the extra 40 bhp coupled with some extra power from the ram-air effect of the roof scoop could MAYBE get it to 350 kph (217 mph).

just for grins, i decided to run some calculations. the CGT has a frontal area of 20.88 sq feet and a Cd of .396 (yes, .396). it's drag limited to 205. a drag area of 8.268 sq ft would require 486 WHP. a car of the CGT's mass would require roughly 21.6 WHP to overcome rolling resistance. that totals 508 HP at the wheels required to hit 205. from this, we deduce that the CGT's drivetrain losses are 16% (since it actually makes 605 HP at the flywheel).

now that we know a bit about the car, lets see what happens when we toy with things. what if we want the car to go 250MPH with no changes to the aero? that would require 1,082HP (1,051 for drag and 31 for rolling resistance). that's an increase of 477HP (79%) to increase top speed by 50 mph (24%).

what if we do away with the venturi tunnels, wing and splitter? maybe the Cd drops to .28 (on par with a 997). if we hold HP constant at 605, the reduction in drag takes top speed to 230mph. this makes sense if we consider the McLaren F1, whose top speed was in the neighborhood of 230 with just over 600HP.

now let's assume that they don't go all the way to .28. let's assume that they leave the venturis in place, the wing in place, etc. somehow, they manage to reduce the Cd to .36. now let's assume a 40HP bump in power from engine mods and an additional 15HP at terminal velocity from the ram-air effect. that's a 55HP bump. that puts us at 217mph, which is 350kph.

the interesting thing about all of this is that the faster you go, the more power it takes to increase your terminal velocity by just one mph. this was a long winded physics exercise. sorry for the bantering....this stuff is just interesting to me.
__________________
insite
'99 Boxster
3.4L Conversion

http://i156.photobucket.com/albums/t...1/KMTGPR-1.jpg
insite is offline   Reply With Quote
Old 07-11-2007, 04:12 PM   #7
Pat
Registered User
 
Join Date: Jun 2007
Location: Littleton, CO
Posts: 456
Man, I love engineers!


Pat is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -8. The time now is 06:20 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page