Author Topic: On the subject of choosing a car  (Read 5010 times)

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Offline Jeremy Blaze

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On the subject of choosing a car
« on: February 01, 2008, 04:16:49 PM »

  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!
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Offline RichFox

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Re: On the subject of choosing a car
« Reply #1 on: February 01, 2008, 04:21:59 PM »
Get a Monza. Look at what is doing very well in cat.

Offline Jeremy Blaze

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Re: On the subject of choosing a car
« Reply #2 on: February 01, 2008, 04:40:32 PM »
Whats the fun in doing what everone else is doing? :-D

  One of the things about the LSR that is interesting is the variaty of cars.

 Where can I find the info on cars and classes?  I aw the record listing, but most don't even list the car, just the driver/team info.
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Offline RichFox

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Re: On the subject of choosing a car
« Reply #3 on: February 01, 2008, 06:24:41 PM »
Maybe you can buy a program from O7. The results do not list car types. But if you don't want to do what others are doing, just do what you want. Plenty do. I wanted to do a Opel Manta. But measuring frontal area convinced me to use a Vega. Besisde It was free.

Offline Jonny Hotnuts

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Re: On the subject of choosing a car
« Reply #4 on: February 01, 2008, 07:30:03 PM »
Quote
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!


No.
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:

DON’T SELL YOURSELF SHORT. Don’t 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 you’ve 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.
« Last Edit: February 01, 2008, 07:32:45 PM by Jonny Hotnuts »
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Offline JackD

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Re: On the subject of choosing a car
« Reply #5 on: February 01, 2008, 08:08:52 PM »
The Buick parts on an otherwise Monza are faster.
The Mazda RX7 with a dead rotary motor are really cheap and easy. :wink:
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Offline Sumner

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Re: On the subject of choosing a car
« Reply #6 on: February 01, 2008, 09:02:09 PM »
Whats the fun in doing what everyone else is doing? :-D

  One of the things about the LSR that is interesting is the variety of cars.

 Where can I find the info on cars and classes?  I aw the record listing, but most don't even list the car, just the driver/team info.

You might want to read some of this:

http://purplesagetradingpost.com/sumner/bvillecar/bville%20-%20LSR%20Thoughts-Index.html

Here you can see a lot of current cars:

http://purplesagetradingpost.com/sumner/bville-cars-1/bville-cars%20index-main.html

Here are a number of links to car sites and more:

http://purplesagetradingpost.com/sumner/bvillecar/bvillelinks.htm

and lots more here if you haven't been there:

http://purplesagetradingpost.com/sumner/bvillecar/bonneville-Index.html

c ya,

Sum

Offline interested bystander

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Re: On the subject of choosing a car
« Reply #7 on: February 01, 2008, 09:20:25 PM »
If you want a low Cd- not CdA necessarily vehicle the 3rd generation Firebirds were capable of Cd's of .29-

I'd read this in Road and Track in the '80s and it's quoted in the website

3rdgen.org

Ask Dynoroom.
5 mph in pit area (clothed)

Offline Jonny Hotnuts

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Re: On the subject of choosing a car
« Reply #8 on: February 01, 2008, 09:55:43 PM »
Quote
Insert Quote
If you want a low Cd- not CdA necessarily vehicle the 3rd generation Firebirds were capable of Cd's of .29-

I'd read this in Road and Track in the '80s and it's quoted in the website

3rdgen.org

Ask Dynoroom.

With a 3" drop you could have that TransAm/Firechicken Cd go to .26!!!!

You would have to put the Knight Rider LED on the front though.
jonny_hotnuts@hotmail.com

"Sometimes it is impossible to deal with her, but most of the time she is very sweet, and if you caress her properly she will sing beautifully."
*Andres Segovia
(when Im not working on the car, I am ususally playing classical guitar)

Offline Bville701

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Re: On the subject of choosing a car
« Reply #9 on: February 02, 2008, 12:19:52 AM »
If you want a low Cd- not CdA necessarily vehicle the 3rd generation Firebirds were capable of Cd's of .29-

I'd read this in Road and Track in the '80s and it's quoted in the website

3rdgen.org

Ask Dynoroom.


This is true. Dynoroom has all the aero on those firebirds. He was with the SCCA Trans Am series during that time and has seen them go through the wind tunnel. Those cars are about as slick as you can get for the price.
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Offline panic

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Re: On the subject of choosing a car
« Reply #10 on: February 02, 2008, 11:32:00 AM »
Re: "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 ###)"

I agree with your conclusion, but not your choice of phrase.
The badly shaped wake of the rear deck is part of the Cd.
The area is only slightly larger than a sedan, and in some cases the same since the roof is no higher and no wider.

Offline Jeremy Blaze

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Re: On the subject of choosing a car
« Reply #11 on: February 02, 2008, 12:33:15 PM »
  I thought about the 3rd gen firebirds, I've always thought they were much better looking aero wise than my IROC.  In fact I wanted a firebird when I got my IROC, but was unable to find what I wanted.

  I would like to stick with a pre 81 car.

  Right now I am looking at an 81 Camaro. They look fairly good, although the front could probably use some work.

  Again, it is the same body that hot rod used recently.

 Thanks again for all the tips suggestions, and sharing of your knowledge!
Never been to the salt.  Drag racer