1.18 on street tires? Actual street tires? I don't think so. That would be significantly higher than a Viper ACR or GT3 RS on Michelin Pilot Sport Cup tires, which are just a step below full blown top of the heap DOT r-comps like Hoosiers.

The trouble with "g numbers" is that they can very easily lie. For example, in a major magazine a BMW M3 was tested @ Laguna Seca and pulled 1.6 g at the bottom of the Corkscrew but on a skidpad the car pulls less than 1g. Banking is just one reasons numbers can change. Also for all the numbers I see bandied about, I never see proof of them. This is one reason I post videos on youtube... our camera has an accelerometer to show the actual forces. I'll readily admit that I am on Hoosier A6's for competition and they make the grip much higher. But Griggs does the same thing. Steeda uses Nitto R-comps. But they don't really come out and state as much too often (if ever).

Here's a link to a video taken eariler this year. It was @ South Georgia Motorsport Park. The lot is asphalt, and flat. Lateral G numbers are on the right side of the screen. You can see if I'm fighting the car (I'm not). The car is a Shelby GT that's mostly stock, but with Koni's added and some better swaybar links, and brackets and a different alignment. Note the numbers, well higher that what most claim--and it's video proof (untampered with, you can see that at the start I'm pulling no g either way). http://www.youtube.com/watch?v=FfOjGDXw1h8 And the car is much better riding just via the Koni's in place of the FR3 dampers. Hell my daily driver GT is more comfortable and surefooted on Koni's vs. stock shocks.....

My advice, build up to what you want. You didn't say what Porsche you had, what mods, what tires, or anything. A Porsche is lighter, better balanced and lower too. You can't make a Mustang a Porsche. This is where someone says "in Grand-AM" a Mustang can run with a Porsche. Well, while technically true it's rarely mentioned the Mustangs are tube-framed race cars with all the trick bits, where a Porsche is a 997 that is taken off the production line and lightly upgraded with the things need to compete (cage, fire suppression, etc).

The tires I'm on in that video are technically street legal. But they are not meant for street use. However, there are tires that are streetable and not a whole lot less sticky. The numbers will go down depending on what tires you are on, but it wasn't long ago I did a Camaro that on true street tires cut off 3.5 seconds over a 1:30 lap before and after just with a spring, bar and shock change alone. And fwiw, the baseline was set on Michelin Pilot's, the after time on my suspension was set on full tread Nitto 555's (not R's, not RII's) which all else being equal are slower heads up. And then we slapped some Nitto NT-01's on and dropped another 3.4 for a total of 6.9 seconds faster without reinventing the wheel.

 

Sam the 2010 Roush's advertising 1G on the skid pad 1.18G doesn't seems like to much of a stretch on street tires, the Porsche I was in was showroom stock 09 Turbo. My uncle had just bought it and we thought it might be fun to race a few of the other cars against it, I wasn't as impressed with the M6 but that Turbo Wow. Never driven anything that seemed so tame and comfy on the street but could tear apart the track like that.

 

Well I just wrote a long *** reply and got this:

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The ACR viper is my day job's shop car and an employee privilege. We've taken it on the track maybe 8 times a year. It's the one that has a set of stripes on it that look like they were aligned on by blind moneys using bristle tipped ladders and supersoakers full of PPG paint solvent to make it even less straight. We call the shop car Merideth .

Anyway at speed without downforce it gets 1.2g on a track. Which is less than the 1.18g. The ACR normally gets 1.08g. On a track you get more grip compared to an autocross circuit which would be a clean parking lot that's not driven on fast normally. The track is grippy because it's peppered with melted rubber like the dig area in a drag strip. Every car performs slightly better on the track, which is why I mentioned that. I wouldn't post deceptive g numbers without mentioning their circumstances like being uphill or on a bank or skidding. I get about 1.5g-1.6g max. The best part about my setup is that it isn't bone jaring harsh though. My car was setup and tested with help from the Muscle Milk Trans Am racing team and their equipment actually has a vertical accelerometer which was used to compare the ride harshness to an Infinity FX45 SUV my friend brought, back to back the saleen and it performed about the same when physically measured on the same rout which shows it's comfort.

 

By chance are you the team that went to Nuremberg with the ACR The tires on the ACR are barely street legal but still wow. What is the set up on your Mustang?