I figure I would start a new thread as the roof rail got a bit off topic.
Trying to decide on a car to build, and was wondering do the long roofs of a wagon over any advantage ofer a coupe?
Thanks again in advance!
A longer body tends to have a slightly lower Cd but the difference between a wagon and sedan would be nominal. Plus you would have a HUGE area behind the car that would generate an aerodynamic wake (huge drag ###) and this would greatly offset any advantage because it was longer.
The question you should ask is "what should I look for?". Rich has a point in some respects, that taking a look at what has been successful in the past can be a very good way of considering a project of your own. But I also like to see someone take a different approach and see where you are coming from.
There are 2 primary aero factors to consider:
1. A = (frontal area)
2. Cd = coefficient of drag
When you multiply the Cd X A you will get your "aero number". This number can be used to determine what HP is needed to make any given speed.
I have not seen the specs on the Monza that Rich mentioned but I can see from this profile that the gently sloping rear window and nice lines of this car would in fact make a good choice for LSR. By looking at the car I would think that the Monzas Cd should be in the .38 (the front needs work, .38 is decent) range and no clue what the frontal is but looks very good.
There are many other cars out there that are as good or better, you just have to look. Many of the new generation of cars conscious about fuel are using vast amount of research $ on making the cars more fuel efficient. I see many new cars that greatly eclipse their older counterparts regarding lines. A late model car may also be good hunting grounds for a LSR project.
There are many sources for your CdA numbers.
Here is a good place to start:http://www.mayfco.com/tbls.htm
(The last table listed for the individual cars is the aero #; use that number with the curve chart to see how much HP is needed. Remember that the bottom of the curve (red) starts at a CdA of 4 and every higher line is +2 (next is a CdA of 6 and so on).
For instance I can see that a 93 Corvette CR1 with a CdA of 5 will need about 300 RWHP (at Bonneville) to make 200 mph while in contrast the 93 S-10 extra with a CdA of 11 will need 600 RWHP to make 200. Even if the S-10 is free the cost in motor to equal the same speed of a car with better aeros will not offset the difference of whatever a good body choice VS. 400 more HP (and it gets worse the faster you go).
And one very important thing to consider:
DONíT SELL YOURSELF SHORT. Donít convince yourself that if you make 150 you will be happy, after you make 150 are you going to quit? I will be willing to bet that once youíve made 150 you will want 200 and then more. Choose a car that has the ability to grow with you and not end up being a burden.