1988-1990 Nissan GTP ZX-T

Images copyright Michael J. Fuller
Text copyright Michael J. Fuller

Nissan GTP ZX-T, chassis # 8805The GTP ZX-T succeeded because of prodigious power coupled with prodigious downforce.
Nissan GTP ZX-T, chassis # 8805The ZX-T's tunnels don't seem particularly special:  the tunnel walls are effectively parallal, opening up slightly at the leading edge (botom of image).
Nissan GTP ZX-T, chassis # 8805Rear fender louvers.
Nissan GTP ZX-T, chassis #8805The tunnel trailing edge height was unregulated in IMSA, so the idea was to make the exits as tall as you could get away with.  As a result, top deck heights were much higher than we're used to these days, but it was a direct reflection of the importance of the tunnels and maximizing the tunnel exit height and volume.  
Nissan GTP ZX-T, chassis #8805The turbo exhaust on the GTP ZX-T was blown into the right hand diffuser tunnel and allowed for a 93 lb. downforce increase for a 34 lb. reduction in drag.  Calculations showed a 1.7 mph speed increase on the back straight at Riverside and a .6 mph increase in cornering speed in turn 9.  Two other variants were tried that showed increased downforce (for upwards of 108 lbs.) though without the corresponding 30+ lb. drag reduction.
Nissan GTP ZX-T, chassis #8805The spring/damper is mounted ahead and inline with the upright, pulling it out of the air stream.  Considering modern car's pushrod layouts, the ZX-T's layout certainly appears old fashioned.  But the rear suspension was designed to minimize its intrusion into the tunnel area. 
Nissan GTP ZX-T, chassis #8805The cast Magnesium upright on the ZX-T actually carried over from the Lola-Nissan 810.  Coleman brakes discs are mounted here though the Electramotive would often utilize several different brands (AP, Tilton) depending on the circuit.  Note the integral brake cooling plenum cast into the upright with the brake scoop bolted to the top (blue).

ęCopyright 2012, Michael J. Fuller