1969 Porsche 912 GT3 Cup

This 1969 Porsche 912 is the subject of a build thread on rennlist.com by it’s owner, forum member “Petevb”. Built by Wevo in San Carlos, California, the car that you see before you is obviously no simple 4 cylinder stock 912. That was probably unnecessary to point out, because if you are here you more than likely already know that many monster 911 street and track cars have been built from unsuspecting 901 shells. The net result of this particular blend can best be described as a “1969 912 GT3 Cup”, as it starts with the shell of a 912,  takes the motor from a 2006 GT3 Cup car, utilizes a 993 series 6 speed transmission, and then PCCB carbon brakes and wraps it all up in a package weighing just 2,180 pounds. That’s quite a bit less than the 2006 Porsche GT3 Cup car’s 2,500 pound curb weight from which it’s engine originally derived, but at the same time, this vintage car does not employ all of the aerodynamic and down force advantages that the more modern car has benefited from years of development. So, which one is better? Is that even a plausible inquiry? There is no easy answer to that question, but there just happens to be a graph included that may assist you to draw your own conclusion. We will let you chew on your own verdict while reading the rest of the story here…

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If any current car designer were asked to create a lightweight sports car using a blank sheet of paper, the vast majority would begin with a mid engine, rear wheel drive configuration. Somehow, against all laws of physics and basic knowledge of everything that we know about suspension geometry and handling, the Porsche 911 has stood the test of time as one of the ultimate vehicles with which to base a race or street car build project, despite it’s inherent design flaw. Normally, placement of an engine behind the rear axle is a recipe for disaster because it creates a very light front end, and the pendulum effect when going around a turn, with the rear end wanting to swap ends with the front. Fortunately, these car’s boxer engines benefit from a very low center of gravity which help assist transfer power to the ground, and to push their rear wheels to the pavement during acceleration. Around a track, it creates a very rewarding driving experience, once lift-throttle over steer has been mastered.

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Since this car now houses a water cooled, 3.8 liter 6 cylinder race engine in place of it’s original 4 cylinder air cooled motor, all new plumbing had to be created and routed through to the rear of the car.

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The roll cage was built with computer analysis of it’s door bars and how that, in effect, changes torsional rigidity. It’s front section was recreated from the same design borrowed from the street GT1.

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An interesting table is conjured up where “Petevb” estimates the torsional rigidity of his 912 GT3 Cup compared to past 911’s, all the way up to, and including, the current 991 series. The best estimate for his car is in the 20-25,000 N/deg range, which is much stiffer than the car was to begin with, but not quite as stiff as a modern 991, or even 997. The different past models stiffness are estimated as follows:
’88 911 7000 nm/deg (measurement by burgermeister)
964 11500 nm/deg (993 was 20% stiffer)
993 13900 nm/deg (996 was 45% stiffer)
996 20120 nm/deg (Excellence was Expected p.1381)
997 33000 nm/deg
991 40000 nm/deg (porsche used 20% torsionally stiffer as a design target, has claimed “up to 25% stiffer”)
So, it’s final figure of absolute stiffness, even at 3 to 4 times the original, lands it somewhere between a 996 and 997, although ultimately, stiffness to weight is a more important figure. Taking into consideration that this caged 912 GT3 weighs nearly 1/3 less than the newer street cars, that therefore makes it stiffer than a 997. Bam! Formula solved. Drops chalk on floor and walks away from board. Classroom cheers.

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Any way you look at it, this is one street registered Cup car project which would be a blast to drive, either on the street or track.  As with most projects, they are in a constant stage of development, and this one is not finished yet with future plans for more aero body work.

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So, what’s the final verdict? This 912 GT3, or Cup car? You Tell Us which you would prefer and why in the “Comments” section below. Don’t forget, this 912 is street legal, whereas a Cup car is not…

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Find the build thread here at:

http://forums.rennlist.com/rennforums/porsche-cup-cars/704285-69-gt3-cup.html

 

 

 

 

 

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