Reply to "Ground Effects"

Thanks for the tips, Bob. I'll be meeting Dick Koch in a few weeks. He and some other Pantera enthusiasts are going to come by my house Tuesday night, April 26 and we'll caravan out to Vegas for the track event the following day, so I'll have the pleasure of being able to see his setup and maybe he'll field a few questions from me. Jack DeRyke wrote a post in this forum a couple of years ago about his 351-C mods and they sound a lot like your engine. It's an upgrade planned in a year or two, for me. So it's just at the study phase, sort of like this ground effects topic.

Back to the ground effects topic. I got PI Motorsports 2004-05 Catalog today, and it's 160 pages. Notably, page 158 has the graphs of the wind tunnel tests done on the original Pantera and the original GT-40. Page 159 has photographs of the monocoque body/frame. Those are the intesting pieces of information I'm going to comment on in a second. Right now, I have to say that Jerry and Dave and Linda have done a lot of work compiling this catalog. There's exploded diagrams of everything. That's valuable to me for when I need to tackle a project, I can see ahead of time how it was assembled at the engineering designer's drawing board. It's truly inspirational to see all this Pantera stuff, and to me, quite humbling. These guys are extreme Pantera enthusiasts, and I'm a babe in the woods on the information-Pantera aspect of life.

First, the wind tunnel results, page 158. At 160 mph, the 'stock body' Pantera produces about 290 pounds of lift in the front and 120 pounds of lift in the rear. The GT-40 produced 260 pounds of lift in front and -40 pounds of lift in the rear. So, the GT-40 produced 40 pounds of downforce in the rear, or generated 40 pounds of ground effects. At 160 mph (260 kph), the Pantera produces 554 pounds (252 Kg) of drag and the GT-40 produced 477 pounds (217 Kg) of drag.

Drag is visualized by the seeing a box pushing against 160 mph of air, vs. a ball of the same size pushing against 160 mph of air. It has nothing to do with lift of lift's inverse: downforce. Drag is resistance to movement and the Pantera consumes 238 hp just to compensate for the aerodynamic drag. The GT-40 requires 217 hp to balance the air resistance of 160 mph wind. So, the efficiency of the two body styles are similar in terms of drag. F-1 cars have pointy noses, and similar features, creating less drag, and so require less hp to go 160 mph. What all this means is drag is something takes hp to overcome. More protrusions, like scoops, create more drag, so will accelerate less quickly from 160 mph to 200 mph with the same hp. I don't see any cost effective way to reduce drag. It's what it is already with the existing body style.

Lift is a bad thing, downforce a good thing. There's 1,365 pounds of weight on the front wheels of the Pantera standing still. Subtract 290 pounds for lift at 160 mph, and the tire contact patch gets smaller because the 'weight' on the front wheels is only 1,075 pounds. At 120 mph, lift is 160 pounds on the front. Simple extrapolations tells us at 200 mph, 290-160=130, so 130+290=420 pounds of lift at 200 mph. So, the tire contact patch (control of vehicle) is lessened as the apparent weight of the Pantera is 1,365 pounds on the front minus 420 is 945 pounds on the front tires.

I won't bore you with so many details.

Summarizing, I did a similar extrapolation to 200 mph for drag using the graphs, and it would take 376 hp to compensate for aerodynamic drag at 200 mph. Same extrapolation for the lift at the rear: At 200 mph, 160 pounds of lift occurs at the rear wheels of the Pantera.

Conclusions:
The drag problem is not easily improved, but can be made worse, and it is a compromise issue. For example, if there's a large front spoiler which is 1/4" off the pavement in front, it will create more drag, but will reduce the front and rear lift. This is because the air speed (wind) creates lift, reduce the ability of the air to get under the Pantera, and it will improve the 'downforce' or at least reduce 'lift'. True downforce will be generated by near absence of wind, or air speed, under the Pantera, just like the Saleen S-7.

Another conclusion:
The front of the Pantera is where the most effort needs to be focused, because that's where the greatest lift is happening. The front is also where the drag is happening. True, there's some drag happening at the rear of the Pantera, where the exhaust fumes get sucked back and plated onto the rear bumpers and bodywork, but it's the front that needs the most attention.

Final conclusion:
Like the Saleen S-7 seems like it would be severly compromised going over a speed bump, it is more focused on going very fast on a very smooth track. And the opposite also, I can clear speed bumps fine, but my Pantera doesn't seems like it would be stable at 200 mph, as is. It would need to be lowered to reduce the amount of windage underneath and it would need an underbody tray that sort of copycat's the S-7's underbody tray.

Last, and the final final conclusion (for now):
The main difference visually comparing the Pantera and GT-40 is how the air is channeled through the radiator. The stock Pantera has the air exhausting out the back of the radiator and underneath the car. The GT-40 has the radiator exhaust air exiting out th top, over the hood of the car. This may account for their differences in drag: 252-231=21Kg x2.2=46 pounds less drag in the GT-40 at 160 mph and front lift: 35 popunds less in the GT-40. The pictures of the monocoque frame/body seem to be suggesting to me that there's probably only one economical way to make these lift/drag problems better. Lower the Pantera and install a full body under-tray, meaning the radiator would have to exhaust out the hood vents.

The truth is: If I want to friggin' go 200 mph, I should just go rent one of these supercars, and pay up that way, it'll cost much less that way. Maybe there's just no way to have it all, a car to go around town in without scraping every bump in the road and take 200 mph at the track. I think I'll just hang out with you guys and let the Lamborghini and Ferrari guys talk about 200 mph without actually doing it, them or me. I give up on this for now, but would like any feedback, so I'll hand over the microphone to the next speaker here....

See you guys in Vegas...