7.5 lb class for GT

[Lynn A McCarty]

Originally Posted by Fishlips

Dan,

You can not factor a car for aero drag since it increases as the square of the speed. This means a 10 mph head wind will have twice the effect on a on a dirty car as it would on one of the new jelly bean shaped cars. On a calm day your factoring would be fine, but at tracks like Las Vegas, Sonoma, Tucson, Fontana, Fallon... Well you see what I mean, everywhere we race, it wouldn't work equally. At Vegas I have had to dial the Monte Carlo up 2.5 tenths for the head wind. How much have you had to add in your Camaro? See what I mean.

Maybe I should build a new Monte Carlo and take advantage of the new designs, Ah hell no. If I build anything it is going to be slippery!

I agree with your thought process here Fish, but it isnt true. Most people have a very false impression of the affects of aerodynamics of a drag car. I used software and wind tunnel coefficients to compare my 90 TA which has a .35 drag coefficient from wind tunnel testing to my 69 Firebird that has a .45. We calculated them both on a 9.90 run at 135mph. There was only a .04 difference. While that number is significant, it is not nearly what most people think. Like many issues it gets exaggerated way out of proportion.

The differences are many things not just aerodynamics. My brother's car built by MPR is closer to a Pro Stock car than it is to my old Gen 3 Firebird. He has less rotating weight, more room for straight headers, more carb spacer, more hood. I guarantee he can support traction on a 12.2 radial way better than me. His rotating weight on suspension is way lighter to reduce parasitic losses.

My Gen 3 firebird is much better than old firebirds, but there are many items that are not. The old Firebirds can fit way more spacer. We show definite HP loses on the dyno without spacer. A 69 Bird has ram air of which our motors all were rated with, but in a GT car we dont get it. The 101 wheel base of a Gen 3 Firebird is much harder to control than with the new Grand Am or the old 69 bird. I did back to back testing for my 1980 Sunbird, and we lost an average of 40HP from a 4 inch spacer verses setting the carb flat on the intake. It was so bad we must scrap the Victor intake for the Sunbird. A short runner intake with a spacer is now done and ready for testing, but we definitely are losing power due to losses in cross sectional area.

My best 60 foot is 1.29 at 2500 feet corrected. It is very hard to maintain that without the monstrous wheel stand effecting ET. The Grand Am with MPR's design and the 69 Alf Weibe Firebird will be much better in that department (especially with 70 lb cranks, 800 gm rods, and counter balances that arent pendulum cut ).

I have a program with several drag coefficients published by the Big 3 automakers. If anyone wants an estimate I will try to calculate it for you. However, if you analyze the numbers, a .35 verses a .45 drag coefficient represents a 28.6 increase. This calculates to .04 seconds and about 1 mph. We could easily calculate wind resistance correction within a reasonable margin for a GTAH class. Then, if someone wants to run 48 Packard refinement could be made. I would argue the Ram Air, carb spacer, wheel base advantage of a 69 Firebird equalizes or out does losses in aerodynamics if the suspension is the same level of technology.

Lynn
lmc3470@aol.com
317-839-8378