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Putting all of this to use:
Now I'm going to use what we talked about on the last 6 pages and put it to use on two very different type cars, a Blown Gas Streamliner (F/BGS), and a Blown Gas Altered Coupe (F/BGA). I picked these as they are very different cars, but in the 2006 rule book have similar records. The F/BGS record is 246.914 and is held by Kent Riches (Airtech) and the F/BGA record is 255.767 and is held by John Rains. For the purpose of this discussion I"m going to try and see what it might take to set a new record in these classes at 260 mph. By doing this we can see how different the approach might be to reach the same speed. Both cars are using an F motor (3 liter -- 183 cu. in.) which is probably going to end up being a 4-6 cylinder in-line motor with most likely a turbo to put it in the "Blown" class, but could be a de-stroked V-8 or a V-6.
The Streamliner:
For the streamliner using a 4 or 6 cylinder in line motor should help on keeping the frontal area small. Also since we are building a streamliner let's hope we can make it very aero.
Let's start with a Cd of .15 and a frontal area of 7.5 square feet and our goal of 260 mph.
Using the aero drag formula from ( page 1 ), Drag = A X Cd X V Squared / 410, we find that the aero drag force would be 148.
Using the two formulas we have that help to figure HP needed to run "a speed" found on ( page 2 ) we get 135 HP from the first and 150 HP from the second (using a car weight of 2000 lb.) Remember this is "rear wheel HP".
Using the higher number of 150 HP we can plug that into the "thrust" formula found on ( page 3 ) and find that our thrust number is 216 and from that we know that we need 361 lbs. on the rear wheels for a .6 friction coefficient and 433 lbs. for .5 and 541 lbs. for .4. Since the car weighs 2000 there should be plenty of weight for traction without having to add any for this speed.
The Coupe:
Let's give this production car a 20 square foot frontal area and a Cd of .30. Using the formulas mentioned above I get:
Drag Force = 989
HP = 719 using both formulas and a 3000 lb. car weight.
Thrust = 1037
Weight on drive wheels = 1728 lbs. for .6 friction coefficient, 2074 lbs. for .5 and 2593 lbs. for .4
This little 3 liter is going to have to probably make over 800 HP at the crank to get the job done and most likely have to add some weight to the car to get it to hook up.
Note if I use the HP needed to run a different speed ( FOUND HERE ) and use it backwards I get that to run the current record of 256 would require about 686 HP at the rear wheels.
Head To Head:
Comparing the two cars head to head we get:
Car------------------------------------ Streamliner ---------------- Coupe
Speed Goal -------------------------- 260 mph ------------------- 260 mph
Frontal Area (sq. ft.) ----------------- 7.5 ---------------------------- 20
Cd ---------------------------------------- .15 ---------------------------- .30
Aero Drag ----------------------------- 148 --------------------------- 989
HP Needed --------------------------- 150 --------------------------- 719
Thrust ----------------------------------- 216 -------------------------- 1037
Weight on Drive wheels at .6 ---- 361 lbs ---------------------- 1728 lbs.
Weight on Drive wheels at .5 ---- 433 lbs ---------------------- 2074 lbs.
Weight on Drive wheels at .4 ---- 541 lbs ---------------------- 2593 lbs.
Are the above numbers real?? No, but they do give us some feeling for what is going on and if it was your car and you could plug in the accurate frontal area and Cd you might come up with some pretty good idea of the HP needed and the weight on the rear tires needed. You can see that even though we are trying to run the same speed with both cars the numbers to get there are very different. It would be interesting if Kent and John gave me their "real" numbers and see how this worked out then. How about it guys??
Gearing for These Two Cars:
Without knowing where peak HP is RPM wise it would not be possible to choose the gearing for these two cars, but if that was known a quick trip to the Gearing, RPM, Speed spread sheets ( HERE ) would help to determine the best gears for running 260 mph.
Conclusions:
If you take the time to use what is on these pages you might find out if what you are trying to do is realistic. You might have a favorite motor , but after seeing the HP you need to have, you might decide to look for a different one. The same thing applies to a car. Your favorite car might not have the Cd or frontal area required to realistically go after a record.
The last thing I would recommend is if you are trying to break an existing record be reasonable and conservative in your approach. Aim at first trying to break it by 3-5 mph. Then if you achieve that and your motor is still in one piece go for more. We took the approach of trying to optimize things with Hooley's Stude to first try and break the record by a few miles an hour and that worked for us. Now we can try for a larger number, but we have a record that will be in our memories for ever!!
Well that is all I'm going to post on this for a while, but later I might add to this section. I hope it has helped someone out a little.
c ya,
Sum
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