Pro Gear B GT....


Not 200 mph...just 177.858 mph

Cool though..

 

The air density altitude at Bonneville on a hot day probably exceeds 6000 feet. The air is thinner, but the hp is way down. I don't know all the tables. Carl's 394 hp at sea level corrected might be in the low to mid 300's over 5000 feet.

I was told from going over the years that my 79 body would only need low to mid 500 hp to exceed 200 mph. I do know that during Open road race testing for me to maintian 174 mph @6500 rpm I was able to back out of the throttle and cruise at that speed in sections for 20-30 miles at a time. I was in a class that I could not exceed 175 mph

I don't remember what each car was actually running. Things are not ideal on the salt. Traction is a limiting factor. Some of the powerful cars detune the motors and run faster. I would see my tach climb at over 150 mph when i floored it. You really have to ease into the gas to keep from spinning your tires.

 

When the '84 'Vette came out, Car and Driver spec'ed the drag co-efficient of the '84 @ .29. They went on to explain that it was a huge improvement over the '82 'Vette, which was @ .41. The '82 Impala was better @ .38!

 

That's wrong. The 84 did not have a 0.29 drag coefficient. The C6 does, and that's about as low as any sports car has gotten. The C4 was more aroung 0.34. And my aero book lists an 82 vette at 0.36-0.38.

In any case, you don't need all this data to say that gears won't help (by themselves). Also, drag coefficients can change quite a bit just by modifying ride height, rake, and other simple things that are probably allowed.

 

You're right, CRS kicking in again. I found some documents on google: 2005-06=.28, 1984=.34, 1980=.443, 1979=.503.

 

I've been digging for information on the different C-3's running for land speed records. All I have been able to find is how the rake the car and add chin spoilers and even bottom plates to clean up the under air and the addition of oval exhaust pipes. Most of the cars use a measuring device to determine front and rear body lift and or compression. They use these numbers and change the tire diameter and spring height to adjust needed rake.

The nose down attitude is very desirable for speed and stability

The air density altitude can very during the day from:

Air density, which can range from 5400 ft to 7600 ft elevation (on the same day!) has proven maddening.

 

The nose down attitude is only desirable for stability. That is why I said trim the car as flat as possible while maintaining enough front down force to keep it safe. Let me measure a few things on my car and I'll get back to you with an example.

 

If a car's front end is lower than the rear end, then the widening gap between the underside and the road creates a vacuum, or low pressure area, and therefore "suction" that equates to down force. The lower front of the car effectively restricts the air flow under the car.

 

Ok, if a Corvette is lowered 1" in the front and raised 1" in the rear that accounts for an approximate 3% increase in frontal area. Because the frontal area and drag coefficient are multiplied factors in the drag equation whatever percentage value change they see will change the total drag by the same percentage. So a 3% increase in Cd or frontal area will increase drag (and HP required) by 3%. Additionally, a nose low attitude may also increase the Cd.

This is not to say that you shouldn't experiment with the rake of the car. Just understand that it will increase drag. Many times the additional down force the rake creates will allow you to put more power to the ground or it changes the overall airflow over the car in a beneficial way and thus it overcomes the additional drag that was created. Lower drag doesn't always mean faster if you are talking lift (down force) induced drag but there will be a trade off point where you don't need anymore down force. From then on you will only be slowing the car down by adding more drag. Also, there are better ways of generating down force that don't include increasing the frontal area.

 

Hey George,
Got your message last night - I'll post results here.

first of all - in terms of HP - Best we can tell it's 458 at the crank - take out 10% for parasitic drag loss - we are looking at 412 hp. the carb we are running was built specifically for this engine - for this application - when you hit 130 mph - it feels like afterburners kicking in.

The meet started tuesday - but we couldn't get out there till wednesday pm - so we lost a day. since we were moving into a higher speed class - the car spend over 2 hours in tech inspection - until we were approved to run up over 200 mph.

then we had to get scott licensed to drive over 200 - which entails a series of increasing speed runs. we got in 4 runs - he's approved up until 175 mph - then the rain came and shut down the whole meet! Didn't matter to us - we needed to look at why we couldn't get it up to 175 anyway.

So now we will head back out for the World Finals - Oct 11 - 14th.
we have made significant changes - tires will be 4 " wide - 28" or 26" diameters will be our 2 choices. After doing the math and getting info from you guys that we need shift points based on HP - not torque - we will be shifting at about 6000 - if that doesn't work - we wil try shifting at about 4500 - as the torque drops significantly after that!

we will be running the 3:08 rear end - unless someone can convince us to go to the 3:73 and the gear ratios are 1:1 for 4th - and a 0.68 OD (thats killing us right now!)

just for the hell of it - we will go to the new Larry Miller track and run track days Oct 7th and 8th - might as well have a bunch of fun before the snow flies again!

Carl Johansson

 

Carl - i'll be watching the Oct 11th weather and keep my work calendar clear for that week.

burners - I understand what your saying about about lifting the rear of the car adding to the total Sq footage. Most of these cars in the above pictures don't really lift the rear. They drop the front and it give the car the forward rake. You see everything imaginable tried out there.

 

Ok, new data. I had to whip up an engine on my dyno to get the torque and horse power curves. I came up with 459 HP at 6000 RPM and 459 Lbs/Ft at 4000 RPM at the crank. Is this close to your motor Carl?

Anyway, I ran this engine in the "Virtual 'Vette" with a 3.08 rear gear and 28" tires using the .400 coefficient of drag. The simulation says it will do 175 MPH but your going to have to twist it a little tighter at 6350 engine RPM. If you try to use all 5 gears it will slow to 172 MPH at 4700 engine RPM.

Just to see what would happen I changed out the 3.08's for a set of 2.73's and "SHAZAAM", picked up 2 MPH at 177 MPH/5700 RPM using 4 gears.

I also tried changing the CD number to .44. This is the best published number I have been able to locate for the '80 to '82 Corvette. The VV ran 172 MPH/5530 RPM using 4 gears.

I have a question for you Carl. Are these numbers at all close to what you are seeing with your car?

BigBlockk

Later.....

 

he is going to run 4" wide tires.......that drops Cd like a rock. Your calculations will be way off.

By the way......anyone know what the frontal areas are for the various gens? I know the C6 Z06 is 22.3 sq ft but I have never seen numbers for the other gens. It seems that the C3 and C4 would have smaller frontal area than the C6.

 

32valves, I just made a few crude measurements today and got 21.4 sq ft.

 

More horsepower/torque to break 200+. The car in the Avatar ran 218mph at Daytona but at that time was putting out 760hp and running near sea level. All of the mods and aerodynamics are important but power increases are critical and everything reaps diminishing rewards for every mile per hour gained. A front valance/air dam may help but trades off frontal area.

FYI; We are currently putting together/working on another rebuild project, the 87 Oldmobile Aerotech Quad 4 Short Tail which holds the 7th fastest piston driven speed record at 257.123mph on the Firestone test track in Fort Stockton Texas. This car was max aerodynamics and 1000hp. A small pic is in the "My Corvette Photos" section under the Avatar.

Good luck on your upcoming runs, send me an email if you would like to talk directly