67 Impala SS front air dam - Impala Tech
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post #1 of 12 (permalink) Old 02-15-2013, 12:44 AM Thread Starter
 
 
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67 Impala SS front air dam

Hey guys, I got a 67 Impala SS that I like to drive at high speed, (empty roads at 2 am), it tops out at 143 mph at about 5400 rpm. Built 350, 700R4, 3.73 gears, 13.7 quarter mile. I think maybe some aerodynamic help is needed to reach redline in 4th gear. Anybody have any ideas about air dam or bellypan design? Or do you know of any companys that supply aero parts for my old car?
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post #2 of 12 (permalink) Old 02-15-2013, 10:08 AM
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No one that I know makes those parts. You can probably adapt a more modern chin spoiler (used to keep air from going under the car). As to belly pans they where never available commercially and all where hand formed out of aluminum for attacking the salt flats.

My concern is for your safety in terms of brakes (or lack of them) and tire speed rating. The only deaths in drag racing in the last twenty or so years has been due to tire failure at speeds above 300 mph (drag slicks are rated to only 300 mph and racers are again pushing 330 mph even in a reduced thousand feet of track).

Your car's mass is a fixed amount so you can not throw weight overboard before you come to stop. Therefore you must have brakes capable of stopping your car. If you are driving a pre 1970 car the engineers designed your brake system to drag your car to a stop safely from only 45 mph. This is because when the car was on the drawing board (the 1965-'70 series was designed in late 1961 to 1962 drawn on paper using slide rules) there were no Interstate Highways and most roads had a 45 mph top speed.

The amount of energy that has to be dissipated as heat is equal to ½mv² with the m equal to the car's weight and the velocity being the speed of the car squared. You need to run that calculation twice. Once with the 45 mph that car was designed to stop with and your 143 top end charge. You will note that the energy increases exponentially thanks to the squared velocity term.

To have adequate brakes you should consider mounting the four seventeen inch rotors off of the C5 and C6 Corvette (that has a 170 mph top speed) and bolt on a second set of calipers. Brakes that large require twenty inch wheels that some like and use even without a brake upgrade.

Most American car bodies (this was discovered by NASCAR investigators after a number of crashes) reach rotation speed (the velocity at which a craft becomes airborne in aviation terms) at about 125-130 mph. Most aircraft have dedicated control surfaces and wings to convert the rotation speed into controlled flight. Most American cars are lacking these basic features and crash after lifting up.

I think you should look to the salt flats and read their safety rule book before you continue.

Big Dave
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post #3 of 12 (permalink) Old 02-15-2013, 11:41 AM
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Have you ever thought about a Deer walking out in front of you while your traveling at 143 mph at 2 AM ?
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post #4 of 12 (permalink) Old 02-15-2013, 01:24 PM Thread Starter
 
 
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Thanks for your concern about my safety. I do have C5 brakes front and rear with Hawk race pads, Z rated tires and other suspension upgrades. I never thought of an aerodynamic lift problem and car doesnt feel floaty at speed. I will mount and aim my gopro camera at the suspension on the next speed run to check for lift.
I have a chin spoiler off a 90s chevy truck and a sheet of aluminum, just thought I would check with Impala guys before I started on this phase of my project.
No deer in my area, I do have to watch for drunks and CHP.

Thanks for your input
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post #5 of 12 (permalink) Old 02-15-2013, 04:54 PM
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I don't think you need aero, I think you are going to need HP. What are the specs on the 350?

Two doors, four doors, wagons, and ragtops.
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post #6 of 12 (permalink) Old 02-15-2013, 06:11 PM
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Sounds like a fun car to me.
I'm with Jay here. Certainly Aero help is needed on the 70 Impala front end and you'll benefit from it, but, at that MPH and RPM and tranny/gear ratio, I think you're very near the motors limit to overcome the aero.
On that note, have you done the math to calculate your theoretical top-end?
Also, just for my own curiousity, how do you validate the MPH? GPS? A '70 is pushing a lot of air out of the way at 143mph!

I'm not aware of any aftermarket spoilers or belly pans and such, I think you'll have to make and adapt on your own. Totally do-able.

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
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post #7 of 12 (permalink) Old 02-17-2013, 04:03 AM Thread Starter
 
 
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The engine is a 4 bolt main 350 round seal block, 10:1 compression ratio with the Edelbrock performer rpm top end kit, includes heads, roller cam, manifold and carb. Don't know the HP or torque.
I checked my top speed with a GPS. Verified that with tire diameter, gear ratio, rpm minus 500 (for torque converter slip) calculation; also recorded speed/rpm readings at the digital speed radar signs and used Y=MX+b.... (rpm-500) x 0.0295 -2 = MPH.
All agree within a couple mph with the GPS.
I just need another ten or so mph and I'm over budget (according to my wife) on this project, so I'm hoping several hours of labor and a few materials will achieve my goal of the top end of a 6 cylinder BMW.
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post #8 of 12 (permalink) Old 02-17-2013, 09:09 AM
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Only let the wife know about half the money you spend. That will cut the resistance in half.

A couple of five foot by ten foot sheets of aluminum can be fabricated up with hand tools to form a belly pan. Anything you can do keep air out from under the car improves speed and enhances safety so lowering the car further would also help. I do not think it would be easy but a nose cone fabricated out of aluminum sheet metal; as well as blocking off the radiator opening with clear acrylic plastic fastened behind the grill would also improve aerodynamics (the chin spoiler will deflect enough air up into the radiator opening to cool the car).

Big Dave
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post #9 of 12 (permalink) Old 02-17-2013, 01:03 PM
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Quote:
4 bolt main 350 round seal block, 10:1 compression ratio with the Edelbrock performer rpm top end kit, includes heads, roller cam, manifold and carb
About 325hp (gross), 350ft-lbs torque will be my guess. You are HP limited, not aero.

Two doors, four doors, wagons, and ragtops.
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post #10 of 12 (permalink) Old 02-17-2013, 02:15 PM
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Well air resistance increases with speed at an exponential rate until you reach compressibility. By the same token the rolling friction from tires and bearings in the car requires only seven horsepower to maintain forty five miles an hour on a hard packed level surface. Anything faster than forty five and air resistance is the biggest contributing factor to resistance.

The nose of the Dodge Charger used to race the high bank oval track of Daytona resulted in a coefficient of drag of only 0.28 which allowed a 429 cid Hemi producing about twice what you are making to reach a top speed of 200.447 mph at Talladega on the 24th of March 1970. This was a ten percent increase in speed over the same car without the aero treatment (because of this improvement NASCAR promptly banned it in 1970; just like they had baned Ford's 483 cube FE block motor in 1963, limiting displacement to seven liters (430 cubes), and in 1965 the over head cam variant of their 427 FORD engine was also banned and further stipulating that Detroit only build single cam in block motors in the future)

Quote:
The first-generation Viper, with its aerodynamic shape, had a cd of over .5; the 1994 Plymouth Duster had a cd of .42. ; the mid-1990s Eagle Talon had a cd of .36. Even the sleek Eagle Vision had a drag of .31, considerably higher than the 0.28 of the 1969 Charger Daytona.

Original is at The Plymouth Superbird and Dodge Charger Daytona, supercars http://www.allpar.com/model/superbir...#ixzz2LBMlKcGj
You won't see too many Jeep CJ's racing at Bonneville due to there less than optimum aerodynamics, but a lot of people put the same Ford built Jeep motor in an old Mustang gas drop tank and stuck on Ford Model A suspension to attack the salt. So the motor's horse power isn't as important as the aerodynamics if you seek high speed.

By the same token it took not one but two jet engines out of a B-58 supersonic Hustler bomber to break Craig Breedloves old world speed record from 1965 of 600.601 miles an hour; made with only one big jet engine due to that exponential increase in horsepower required to increase the speed.

As with all forms of racing "How fast can you afford to go?"

Big Dave
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post #11 of 12 (permalink) Old 03-07-2013, 04:23 AM Thread Starter
 
 
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Picked up another 4 mph and got there a little quicker. I changed out the old Blackjack headers and muffler shop exhaust system for Hooker super comp headers and Pypes 2.5 inch mandrel bent exhaust system. The Hookers didn't fit (of course), the #2 cylinder pipe interfered with the right tie rod even though my engine has been moved back two inches. Measured the #2 pipe length then cut most of it out and made a new piece from a couple of 180 mandrel bends.
Just 8 more mph to 155
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post #12 of 12 (permalink) Old 03-07-2013, 04:41 PM
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I had heard that the Thunderbird back in 1988 was more aerodynamic backwards.
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