I recently purchased a new 2012 Corvette Grand Sport Convertible; Z16, LS3, MYC (Automatic), 3LT, NPP, F55, etc. - I wanted to better understand the performance of my new GS compared to the other models for 2012. I searched for supporting information within the 2012 Corvette Brochure and various websites so that I could build a spreadsheet to calculate specifics for each Model; Engine HP/RPM, Transmission, Rear Axle, Tire Circumference, etc. - are these assumptions and outcomes correct??? I created a simple spreadsheet based on these assumptions. Please let me know where you see issues.
1. Engines - Horse Power and RPM Red Line
• Base Coupe/Convert/G.S. -430/436 HP, 6500 RPM Red Line
• Z06 - 505 HP, 7000 RPM Red Line
• ZR1 - 638 HP, 6500 RPM Red Line
2. Transmissions Gear Ratios
• MM6 - Manual; Base Coupe/Convertible/Z06
i. 1st 2.66; 2nd 1.78; 3rd 1.30; 4th 1.00; 5th 0.74; 6th 0.50; Rev 2.90
• MZ6 - Manual; Grand Sport
i. 1st 2.97; 2nd 2.07; 3rd 1.43; 4th 1.00; 5th 0.71; 6th 0.57; Rev 3.28
• ME2 - Manual; ZR1
i. 1st 2.26; 2nd 1.61; 3rd 1.21; 4th 1.00; 5th 0.72; 6th 0.50; Rev 3.11
• MYC - All Automatics
i. 1st 4.027; 2nd 2.364; 3rd 1.532; 4th 1.152; 5th 0.852; 5th 0.667; Rev 3.10
3. Rear Axle Gear Ratios
• All Manuals - 3.42
• G.S. Automatic - 2.73
• All Other Automatics - 2.56
4. Tire Circumference
• Base Coupe/Convert - P285/35-19; 84.364 Inch Circumference
• Grand Sport/Z06 - P325/30-19; 83.310 Inch Circumference
• ZR1 - P335/25-20; 83.550 Inch Circumference
5. 0-60 / Quarter Mile / Qtr Mile Gear
• Base Coupe - 4.2 sec / 12.6 sec @ 115mph / 3rd Gear
• Base Convertible - 4.2 sec / 12.6 sec @ 115mph / 3rd Gear
• G.S. Coupe - 3.95 sec / 12.3 sec @ 117mph / 4th Gear
• G.S. Convertible - 3.95 sec / 12.3 sec @ 117mph / 4th Gear
• Z06 - 3.7 sec / 11.7 sec @ 125mph / 3rd Gear
• ZR1 - 3.4 sec / 11.3 sec @ 131mph / 3rd Gear
6. Top Speed - 5th Gear - RPM
• Base w/Manual - 190 mph / 6019 rpm / 93% of Red Line
• Base w/Auto - 190? mph / 5187 rpm / 80% of Red Line
• G.S. w/Manual -190 mph / 5813 rpm / 89% of Red Line
• G.S. w/Auto - 190? mph / 5568 rpm / 86% of Red Line
• Z06 Manual -198 mph / 6314 rpm / 90% of Red Line
• ZR1 Manual - 205 mph / 6380 rpm / 98% of Red Line

 

Interesting!

 

I think GS has a lower top speed due to its wide body causing more air resistance. I remember seeing it listed as 182 MPH at one of the reviews on youtube, but I don't know what or if there is an official number on it.

 

In my pursuit to understand the performance of my 2012 GS and other members of the 2012 Corvette family of models I found it interesting that the Corvette Brochure clearly lists the 0-60 and Quarter Mile performance numbers for all six models, however, does not list the “Top Speed” for either convertibles (Base or GS) or the GS Coupe. I also looked closely at the drag coefficient stats from the Corvette Brochure and it calls out numbers for all four coupes but again not for either convertible. I decided to create a simple spreadsheet that would calculate the top speed in each of the six forward gears and then calculate the RPM at which each model would reach its top speed in 5th gear - disregarding drag coefficient. If my gear ratio numbers are correct for each of the four 2012 transmissions (RPO#’s = MM6, MZ6, ME2, MYC) the rest is simple math. I discover from the spreadsheet that some of the numbers seem off when looked at from a reasonableness test, for example, the Base Coupe with an MYC automatic would only be turning 5178 RPM’s when it reached 190 mph, which is 80% of its Red Line of 6500 RPM (86% of Red Line for the GS automatic). All of the four manual transmission offerings hit their top end speed at 89-98% of their Red Line RPM’s - which makes more sense. Any thoughts; why doesn’t Corvette publish top speed and drag coefficient numbers for all six of their 2012 cars? Thanks for helping me out!!!

 

The only time I've seen a car magazine test and publish a top speed for the Grand Sport was in a test they did in 2010 where they said it was 183, drag limited. They also previously tested the base coupe with LS3 and said top speed was 190, drag limited.

Considering drag coefficients are listed at .286 and .342, and considering that the frontal area is larger for the Grand Sport, it's actually surprising that it made 183 MPH, but cars with worse drag coefficients tend to hit their top speeds sooner so if there was a bit more room to run, a base coupe would probably do a couple of MPH more. But that's totally an academic discussion unless you're on a 5+ mile run.

 

IIRC from past discussions here (4-5 years ago), GM only certifies the convertible tops to 150 mph.....so I doubt you will ever see a top speed claim, from GM anyway.