This is LS1Tech, not NASA.

As stated above, it is merely a WIND DRAG CALCULATION. My point was not to give anybody numbers to live by, they were simply for fun and a decent comparison of what it WILL MOST LIKELY REQUIRE to run our cars at those speeds.

As for rolling friction..... NEGLIGABLE

You seem like a numbers guy though, so here ya go.

Given:
Z Rated Tires. CRF = .0062
Car Weight = 3500 (roughly)

Horsepower Requred to Overcome Rolling Friction 130 MPH:
7.882 HP Required.

Horsepower Required to Overcome Rolling Friction 200 MPH:
12.133 HP Required

For the experiment that I presented the Rolling Friction would be absorbed into the drag calculation and would be calculated as drag. Naturallly, the Drag increases as a cubic, while rolling friction increases linearly. "Absorbing" the rolling friction into the drag calculation and ignoring it vs calculating the 2 separately and giving the resultant value induces an error of roughly .860%.

So at 200 mph, I was wrong. It won't take you 494 HP to get their yet only 491.5 HP. So sue me.

<small>[ May 14, 2002, 08:06 PM: Message edited by: NoGo ]</small>

 

How's this one?

<img src="http://www.syty.org/old/imagelibrary/lsr.jpg" alt=" - " />

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">A specially prepared Sy reached a top speed of 210.069 with a flying mile average of 204.145, on Sept 14, 1990.

Normally aspirated 5.0L engine, Max rpm 8000, 549HP @ 7200 RPM, 412 lbs/ft torque @ 6000 RPM, curb weight 3585lbs.</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">http://www.syty.org/old/history.html

FYI, a regular Sy has a turbo 4.3 rated at 285 net hp and 350 lbs/ft of torque. And the body is a first gen S-10, if you want to fathom the aerodynamics of that. =)

 

You guys need to get a scanmaster..has digital speedo in there and think it goes to 255mph.
Also there used to be lots of cars even ten or more years ago or more that went like 220mph..twin turbo third gen I think some gale banks stuff I think it was..big block chevy with 1200 hp comes to mind but they had 800 hp small blocks back then two.

 

NoGo, thanks for the info., this has always been an interesting subject to me. The great thing about this kinda info is, that some crazy person won't have to do top speed runs on some deserted highway to satisfy their curiousity. There are a few things that worry me about top speed runs in an f-body:
1. My windows start pushing out around 130-140 mph - I can't imagine what the gap would be at say 190+ mph.

2. I driven the car to a calc. 165 or so mph, the car was actually pretty stable, but I don't have a front sway bar ( I don't think front sway bars have much effect on top speed runs, but it still worries me.)

3. How bad is the lift being placed on the car @ close to 200 mph?

 

NoGo: I would think tire width and reciprocating weight would have some affect as well, why does this not play into the calculations for parasitic losses?

 

Pushing around numbers for this stuff I find fairly entertaining. To answer your questions...

There are a few inherent problems with a stock F-bod that make high speed runs +165 mph a problem.

1. The rigidity of the front of the car. As most know, the front of our cars are made of some pretty flimsy stuff. At speeds approching 200 mph the equivilant force on the forward vertical surfaces of our car are equivilant to a 200 lb fat man sitting on your front grill. I'm not surprised your windows bowed out. And I would be surprised if people have cracked something at these high of speeds.

2. I don't think our hoods are rated for that kind of speed. Unless you have your hood pinned, you risk your hood latch letting go. Not good

3. Tire Rating. A lot of people forget that a Z-rated tire is only 168 mph. In excess of this you really should be running Z+ or Z++ tires. The new lambo I think comes with Z+++ tires <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />

4. As I'm sure your aware, high speed runs without a front swaybar are not recommended. Rather, turning at high speeds without a front sway bar is not recommended. The lack of a front sway bar is going to increase your body roll, with body roll comes weight transfer. Excessive weight transfer at high speeds adds to the unstability of the car. So I recommend you don't turn <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> . People interested in high speed setups should get the car low, stiff, and keep it flat.

5. I don't have an exact lift coefficient for our car, but most road vehicles have an induced lift coefficient somewhere around +.3 Using this it is fair to say that at 200 mph we generate roughly 324 lb of lift. I assume ours is biased towards the front because of our ram cooling setup (more lift up front is actually better though) So you aren't going to fly off the road, but it does add to instability.

<small>[ May 16, 2002, 12:40 PM: Message edited by: NoGo ]</small>

 

Yes, as with many other things that I neglected to take into consideration.

Tire width, and inertial (spinning) mass of the tire will be taken into consideration for the Coefficient of rolling friction, or CRF as you saw above.

Calculating CRF is enormously tedious and complicated.

Figuring the CRF of your own tires though is very simple.

Here is an experment for any racers that are interested in finding the CRF for their tires. Rolling friction can amount up to an enormous losses (20+ HP) if you are using bad tires. Here's how to see if you are <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

Find your local street; make sure it is *very* level. I have found that building concrete slabs work better, becuase they are typically made to be perfectly level.
Find a piece of flat smooth wood.
And naturally, get yourself a tire.

1. Setup your ramp. Prop the piece of wood up so that there is a slight angle from your road. Ensure that there is a smooth transition from the ramp to the road. The shorter the ramp, the more accurate this experiment will be.

2. Roll the tire down the ramp. Ensure that it doesn't bounce, rock etc... Make sure that it is a smooth straight roll.

3. Ensure that the tire rolls in a straight line off of the ramp. Measure how far the tire rolled. Write it down.

4. Do this 10 times. Omit all erratic results. Ie: The tire rolled closed to 10 ft 9 times and only 4 ft one time.... Get rid of the 4 ft.

5. Now measure the following

L: Length of Ramp Inches (from where you let the tire go to the end of the board)
H: Height tire falls Inches (pavement to point you let tire go from)
D: Average Coasting Distance of Tire Inches

6. Now calculate

A: Angle of Ramp = Arcsin(H/L) in radians

CRL: = (-tan A)/((D*(cos A)^3)+1)

7: Estimated HP Loss according to CRL

HP = ((CRL * Weight(lbs))*Speed(ft/s))*.0018182

And for the Skeptics... things I ommited:
Induced Rolling Friction Losses on Ramp
Wind Drag of the Tire <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />
Rotational Flow Fields <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />
Uncertainties... bouncing etc. I am assuming that you roll the tire strait and flat.

If I made any mistakes feel free.

<small>[ May 17, 2002, 09:23 AM: Message edited by: NoGo ]</small>

 

NoGo, I was just wondering since you seem to very knowledgeable, are you a physicist?

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by LEO:
<strong>NoGo, I was just wondering since you seem to very knowledgeable, are you a physicist?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Nope, no physicist here. Systems Design Engineer

I work as a gas turbine engineer, so alot of my time is spent pushing around physics calcs (especially air/velocity/losses stuff).

I would like to one day build a road race car (looking at the Ultima GTR platform <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> ) so there is always race car design/engineering stuff floating around on my desk.

It is fun to push the numbers around, but my plan is to test it out one day. <img border="0" alt="[devil]" title="" src="graemlins/gr_devil.gif" />

Happy Bench Racing <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />