[samrebel]

Also, if anyone knows the front cross-sectional area for one, also, that would be very helpful. I'm doing a top speed calculation, if you haven't already guessed.

Thanks,

Sam Milton
Jackson, MS, USA

[dave-r]

Cross-sectional area is not that useful I think? It does not give any insight into the huge drag the recessed grille and tail shape etc cause. It was not normal to measure air flow on cars back then either.

I seem to remember Sports Car Graphic saying their test car had 375lbs of drag at 100mph ( and about 340lbs of lift at the front! ) but I have no idea how they measured that.

I would put money on you not being able to push a 1970 over 180mph without modifications to the shape no matter how much power you had.

It would be interesting to know your results if you do find the drag coefficient. Keep us informed!

[samrebel]

I did this on Mathcad (engineering math program). It assumes worst case scenario drag guesses (I hope). The engine is a 535 hp Mopar 440 from an issue of Car Craft mag. Tremec gearbox, 3.55 rear end. The theoretical top speed is where the drag curve (purple dotted, going up) and the overdrive thrust curve (azure flat line) intersect at about 170 mph. It could probably be faster if I had more torque data at RPM's higher than 5500 and using a taller rear ratio. I also probably can back-calculate a Cd from that drag data you have dave-r, thanks. BTW, this was a lot better formatted when it was in Mathcad, things are out of order b/c they were side-by-side in the original worksheet. Oh well, enjoy.

Sam Milton
Jackon, Mississippi

[samrebel]

Okay, dave-r, from the drag data you gave me I back calculated a combined drag coefficient/cross-sectional area number of 15. The comparable coefficient I used was 13.5. So, its worse than what I thought the worst case scenario could be! This shows a top speed of about 165 mph, but again, it could be improved with torque data at higher engine speeds combined with a taller rear ratio. Also, I formatted the worksheet so that it would convert to Word better.

Sam

[samrebel]

I was wrong about the axle ratio and torque data. 165 is the most she'll do without more rear-wheel horsepower or aerodynamic mods. I think that 165 in a Challenger would probably scare the **** out of anybody (unless your name is Kowalski).

Sam Milton

[dave-r]

I remembered wrong (of course! ) and now I am at home and looked it up it was the other way around.

340lbs of drag and 370lbs of lift at the front end are the figures they estimate(?) at 100mph. So drag is not quite so bad as I thought.

I always figured it would be hard to push a 1970 Challenger over 165-170mph which is why I said I would put money on you not going more than 180mph no matter how much power you had. I think you would start getting bits collapsing or ripping off with the pressures if nothing else.

I can tell you everything seems OK at 145mph though.

[samrebel]

Okay, dave-r, with your corrected data, the combined drag coefficient/front area number is 13.8, which is more like what I had before. This calc brings top speed to about 170 mph, which seems about right with 535 hp. I also added a calculation which shows 640 hp is required to get to 180 mph.

Sam Milton

[dave-r]

That is VERY interesting. Thanks.

So that is 640 rear wheel HP is it?

I still think that in practice even with a 1000hp Ray Barton Hemi in there you would have trouble getting the thing to go over 180mph. I would guess the lift under the front edge of the hood could flip the car over for a start? Mind you some spoilers and a flush fine mesh grille on the front would help a HUGE amount.

I am old enough to remember the 1960s and the speeds the stock cars were getting up to was incredible. However there were quite a few occasions where doors/windshields have collapsed in with the aerodynamic pressures.

I have posted an example. Doors and hood collapsing on this Chevy (spit)at 175mph. Of course these were very likely lighter parts than stock I guess??