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Aerodynamics of the Gremlin |
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WesternRed 
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Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5596 |
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 Topic: Aerodynamics of the GremlinPosted: May/15/2023 at 11:36pm |
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Just have a few random thoughts about aerodynamic things.
According to history, Wally Booth ran both the Gremlin and Hornet hatch with the exact same driveline and the Hornet was 3 mph faster, ending the career of the Gremlin in Have to assume the difference was mostly due to aerodynamics, now the front half of the Gremlin and Hornet is pretty much the same, so presumably the difference in rear body shape is the issue. What can be done to improve the aerodynamic performance of the basic Gremlin body and how much difference could it make? I notice a few people running roof extensions off the back of the car and Kevin has some fancy little winglets on the back of his Gremlin. I’ll just pop this here for future reference Drag reduction by application of aerodynamic devices in a race car | Advances in Aerodynamics | Full Text (springeropen.com) Edited by WesternRed - May/16/2023 at 3:17am |
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I've finally given up drinking for good...........now I only drink for evil.
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mixed up
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Posted: May/16/2023 at 12:49am |
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just the back shape of the gremlin would cause drag stick shifter a forum member has some kind of v shaped things on the side of his gremlin by the back of the car anything that would eliminate air of the back like a wing would help take drag of the back
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PROSTOCKTOM
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Posted: May/16/2023 at 2:03am |
It was in Pro Stock 1973, not Super Stock. When Maskin & Kanners debuted the Hornet X in Gainesville (Gator Nationals) 1973 it was running 4-5 MPH faster with the same drivetrain that they were using in their prior Gremlin. M&K "Hornets average speed was in excess of 3-1/2 MPH faster and .012 to .013 second quicker." than Wally's Gremlin. Wally had dynoed both his and M&K's engines and they were both within 5HP per Wally Booth. Also note that a Gremlin is 98" wheelbase and a Hornet is 108" Tom |
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Molnar Technologies Full Service Dealer - Crankshafts & Connecting Rods
1969 AMC Rambler Rouge Race Car 1974 AMC Hornet Hatchback, Wally Booth Outlaw Nostalgic Pro Stock Race Car Project |
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WesternRed
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Posted: May/16/2023 at 3:27am |
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Fixed the link in my first post, some interesting data there for those who are interested. Tom, I used to think that Wally actually swapped out the engine at the track, but makes more sense that they would compare performance between cars with the same engine output. From some online reading, the difference in ET was 0.15 seconds and 3.5 mph, quite a significant improvement. Not sure if the wheelbase difference would make much of a difference in ET and MPH, but would probably help with stability. Any other differences? A production Hornet is probably heavier than the Gremlin, but pro stock would presumably have some weight requirement that had to be met. |
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WesternRed
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Posted: May/16/2023 at 6:09pm |
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Ok, not sure how accurate this number is but apparently the Gremlin has an Aerodynamic Drag Coefficient of 0.49, which is pretty woeful by today's standards.
Cand find any numbers for the Hornet so far but apparently the Pacer was much more efficient at 0.32 (or 0.43 depending on source), would be good to have some verifiable data.
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PROSTOCKTOM
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Posted: May/16/2023 at 8:16pm |
Pro Stock back then ran on a pounds per cubic in formula that had lots of variables, but the weight they ran under per my 1974 NHRA rule book would have been 6.65 pounds per cubic inch for car with 105" wheelbase or less and 6.45 pounds per cubic inch for cars with 105" wheelbase or longer. Since they ran engines in the 340"-345" range your looking at a Gremlin weight of 2261 to 2294# min. The Hornet would have weighed 2193 to 2225# min. So when the Milan testing was done M&K's Hornet could have weighed 70 pounds less than Wally's Gremlin. When I talked to Wally Booth at The AMC Homecoming 2017 he told me the most powerful engine he ever had made 585HP Tom Edited by PROSTOCKTOM - May/16/2023 at 8:19pm |
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Jeff Lee
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Posted: May/16/2023 at 8:54pm |
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My last Stock Eliminator 390 dyno’ed @ 555 HP. But it had the R4b and 780 Holley which were legal at the time. Come a long way!
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PAGAENT
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Posted: May/16/2023 at 9:15pm |
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Actual measurements taken at El Mirage dry lake gave a value of .46 for my Pinto, in 1993 a Ford Probe was rated at .29-.32 depending on model. I would be surprised if a Pacer was anywhere near that. In addition to the CD you also have to account for the frontal area which the Pacer has an excess of. Juggling the cars attitude could effect your CD and would be easy to try at the track with front or rear spacers.
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Hurst390
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Posted: May/17/2023 at 8:40am |
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Its on record here that Wallys best engine was 820hp
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CamJam
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Posted: May/17/2023 at 11:02am |
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I'm guessing .43 would be more accurate for the Pacer. My Opel GT, which was considered pretty aerodynamic at the time, is .41. The C3 Corvette was .44.
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WesternRed wrote: