The XR4Ti has excellent aerodynamic properties as designed. The basic design of this car is a result of thousands of hours in the wind tunnels in England and Germany. Our car is a decendant of the aerodynamic research vehicle called PROBE 1. The basic shape is very similar. A professor of fluids at Texas Tech walked around my car before he had seen another and was in wonder at the good things the body engineers did.
Frontal area...........21 sq ft. Same front area as Mustang and Turbo Coupe. I agree with Trefeth that the air dams and wings are most effective visually. A wiker bill or gurney flap as the rear of a wing causes an order of magnitude change in lift. WOW.
My aero guy said if you use the big wings you will never go 200 MPH. and with numbers like that I believe. The numbers on this car are wonderful especially if you consider that it was designed in late 70's /early 80's. New design cars are much lower. Except Mustang. (Ford doesnt listen to the aero guys any longer.) Yeah the new Mustang is worse than the old. I hear from my GM friends that the new firebird is .280 stock..... Ok......
Engine cooling effects of aerodynamics
In my opinion, if you have cooling problems at highway speeds, under boost or not, you have a system problem that must be corrected before considering upgrades. The production vehicles (with charge coolers, and revised calibration would run all day at 135 MPH. (I personally know of one test for 3 hours at Arizona Proving Ground on the 5 mile oval 135 steady state, no problems. (dont try this at home boys and girls). Addition of a chin spoiler, extending the lip that is there will help by directing more air over the top of the car. The spoiler that is mounted to the crossmember under the engine is essential. It creates a pressure drop behind the radiator to increase flow as slow speeds.
I don't know if anyone has experimented with this one, but it might be possible. To enhance cooling, louvers in the hood ala Cosworth or simply punched louvers might help. Lee Clary reports improved underhood air flow with vents in the hood. He grafted vents from another car on the hood at about 2/3 of the way to the rear. He says it works so it must be just forward of the high pressure area at the base of the windshield. Anything you can do to force more air over the rad and away from the right side of the engine will help but I dont have anything more specific to offer.
The biplane spoiler is one of the few spoilers, factory or aftermarket, that has even undergone wind tunnel testing, let alone the fact that it is one of less than a dozen that actually produce downforce. Most are purely cosmetic.
I don't want to start a wasteful debate relative to aerodynamics of our marquis, but feel compelled to help everyone understand the intention and evolution of the aero aids we are equiped with. As I recall, there should be a rather lengthly discussion I wrote about 18 months ago. I no longer have copies, but breifly it discusses the differences in the bi plane, single wing, RS, and RS 500 wings. Feel free to visit and review this document.
In a nutshell, the information shared with me by the Ford aerodynamic office in Dearborn, (data from the FOG wind tunnel) indicates that there is no negative lift (down force) generated by the bi plane nor the single wing aero package. The bi plane wing is an adaption from Fords first aero research vehicle done in Germany in the mid 70's. It had the biplane wings and the look in the backlite and C pillars. The car also had active aero skirts and front spoilers...etc etc. very very advanced. The bi plane wing is designed purely for reduction of drag only. For its time the XR4 has extremly low drag numbers. .328 for production ride height bone stock car. With a frontal area of 21 sq feet (same as mustang) our cars are rather slippery. The engineers and stylists did an excellent job of working together for some good comprimises.
Part of the susceptibility to cross winds can be attributable to less than 103" wheelbase.
Short cars with a lot of power are twitchy.
As I said before, I cannot share the raw (propriority) data with you all, but as explained to me by my aero crew member my car has LIFT at 200 MPH. 211# at the front and 300# at the rear. This was extrapolated from Ford data generated from testing at 150 MPH. As my previous posts indicate, the Cosworth wings make negative lift, but at a significant trade off to drag coeffecient and a sacrifice to top speed.
Rick byrnes
