7.5 lb class for GT

[Fishlips]

Dan,

The front wheel drive conversions like Grossi's won't fit into a 7.5 lb class because it would be more than the allowed 250 lbs above or below their factory shipping weight.

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!

[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

[Dick Butler]

Aerodynamics is in the picture but I agree with Lynn, probably less than people think.. All cars have some problem with head wind. Having raced at TOPEKA with an 89 camaro SS/AA and Beretta GT/GA and Sunbird GT/FA we ALL lost et and mph into the wind. I will not guess what it was but in the range of .1 to .15. I am checking with the kids for their memory.
With a rapid factoring system like the comp C.I.C. major differences might be corrected very early in the year if more class heads up racing were done.

[Bryan Broaddus]

Lynn,

You left out part of the equation. Frontal Area.
The combination of frontal area and coefficient of drag are combined to yield total drag.

[Just Observing]

Originally Posted by Bryan Broaddus

Lynn,

You left out part of the equation. Frontal Area.
The combination of frontal area and coefficient of drag are combined to yield total drag.

x2. I couldn't agree more.

[Racin Mason]

Fishlips
7.5 lbs x 322 hp = 2415 +170 for driver = 2585. Shipping weight on a Cavalier is 2617 and Sunfire is 2771. By my math they will fit in 7.5 lb class unless the 2500 lb minimum applies to car only without driver. I don't have a rulebook handy and I don't have the FWD Comp, oops I mean GT rules memorized.
Regardless, a quick phone call to Glendora by the right folks would probably allow those cars in anyway. It's not like they haven't ignored the rulebook in the past.

I'm wondering how much appeal this new class might have? I can count the number of big blocks in division 7 on one hand and the number of big block GT/AA cars on one finger. We are a dying breed my friend.

Also, in terms of new cars being built, there are at least several dozen new Cobalts running around and Chevrolet has only been making them for 2.5 years now. McClanahan's Camaro is at least 3 years old and the other car mentioned has never been run. I think this is Dick's point in that the new cars are GT cars, not old school muscle.

[Douglas Broaddus]

Rulebook says minimum weight in GT with driver is 2670 pounds. The little teenie tiny small block cars won't measure up.

Doug

[Fishlips]

Lynn,

Here is the equation for total drag.

Total Drag:

D=CDA p/2 V2

Where
CD= Coefficient of Drag

A= Frontal Area

p= density of ambient air

V2= vehicle speed squared

This is a big difference when you compare a Cobalt or somthing little to the Older Super Stockers with a big wide front and tall roof line.

I believe your calculations used cars with similar frontal areas.

[Lynn A McCarty]

Originally Posted by Fishlips

Lynn,

Here is the equation for total drag.

Total Drag:

D=CDA p/2 V2

Where
CD= Coefficient of Drag

A= Frontal Area

p= density of ambient air

V2= vehicle speed squared

This is a big difference when you compare a Cobalt or somthing little to the Older Super Stockers with a big wide front and tall roof line.

I believe your calculations used cars with similar frontal areas.

My software includes drag coefficient, frontal square area, ride height, it was all included. (cant get a number unless you enter all the numbers) You pick the vehicle from the data base for the frontal square area or you can do it yourself. Then you measure the height of the car off the ground. Yes we all know these are approximations,, and aerodynamics is a factor of many, but these big ET losses simply arent reality. (One guy told me 5 tenths)

On the other hand, how much is Ram Air, hood clearance, and wheel base worth? You gotta consider everything not cherry pick. If you want to try one I will run the software for you. I dont have all the body styles, but I have a pretty good list of the common ones.

Just think about it, you can scrub 5mph off at the end and it simply doesnt affect ET that much.

Lynn

[JCQuinn]

Originally Posted by Lynn A McCarty

My software includes drag coefficient, frontal square area, ride height, it was all included. (cant get a number unless you enter all the numbers) You pick the vehicle from the data base for the frontal square area or you can do it yourself. Then you measure the height of the car off the ground. Yes we all know these are approximations,, and aerodynamics is a factor of many, but these big ET losses simply arent reality. (One guy told me 5 tenths)

On the other hand, how much is Ram Air, hood clearance, and wheel base worth? You gotta consider everything not cherry pick. If you want to try one I will run the software for you. I dont have all the body styles, but I have a pretty good list of the common ones.

Just think about it, you can scrub 5mph off at the end and it simply doesnt affect ET that much.

Lynn

Lynn is this something you do commercially or just for your own edification? If you don't mind I am curious how an 85 Mustang would stack up against the Colbalts.