Landracing Forum
Tech Information => Aerodynamics => Topic started by: BobDcuda on July 19, 2013, 08:11:20 PM
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Looking for some input on how much nose-down rake is desirable for a door slammer ('66 Barracuda F/CPRO). Or - how much is too much? Some comments I've read here have said no more than 2 degrees, but then I see photos of most of the Avanti's that have raced the Salt. Most, if not all of them, look like anywhere from 4 degrees and up.
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Too much rake effectively increases frontal area.
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Using a specific number from another body type would likely not be right for your application.
I'm pickin you still have the torsion bar front end so just adjust the hight & see what works for you.
What do you have in your slant? I built a lot of them back in the 70's & just bought another 65 Barracuda.
Sid.
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I would put the nose as low as I could to eliminate as much air going under as possible... if you have tall tires to make the speed you need, then you will have a lot of rake...
While there may be some science to do it right... and a little time in the wind tunnel, that is how it happens for most folks. Air caught under the car causes drag.
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Thanks for your comments guys. Stainless, that's just what I'm up to now, getting the nose down as low as it can go. Just hoping when it gets there I'm not looking at 4 or 5 degrees - assuming that's likely too much. If so, don't think I have enough tire clearance to use lowering blocks. Should get this all settled by Sunday. Yes, still got the torsion bars.
Sid, I've got the 170 ci slant bored out to a whopping 174 ci. Got the usual cam, carb, headers, valves, etc., and some extensive head work. Combustion chambers were welded in to get 30cc chambers, milling and porting, 13:1 compression. Engine dyno made 252 hp @ 6,800. Final bit is to get the nose down and aligned. I hope to go fast, but do want the wheels to stay on the ground. :-D
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Wheel on the ground is always a plus but it looks like a pretty soft record.
I used to get the best results with "the leaning tower of power" engines by cutting the deck down to bring the chamber to the piston. These days a long rod would be more desirable.
If I get a chance I'll look you up at SW.
Sid.
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Super speedway testing showed 1 to 1 1/2 degrees was best for Mopar "B" body cars.
I can see no reason "E" body cars would be different.
Doug Odom in big ditch
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Super speedway testing showed 1 to 1 1/2 degrees was best for Mopar "B" body cars.
I can see no reason "E" body cars would be different.
Doug Odom in big ditch
Doug beat me to it. Look at Blowfish and the other similar cars. Yours is just a mini version of that bodystyle!
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Thanks again for the tips. Sid, do stop by if you can.
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E body is a totally different animal, bigger, wider & not a fastback but I don't see you getting into too much trouble with what you have. If you have a sway bar for it, put it on. You have a big plus with the torsion bar front end, you could find some speed there.
Looks like a lot of fun from here. :cheers:
Sid.
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A "E" body Mopar is a "B" body front clip with an "A" body rear clip.
At one time I had the full size blue prints for both because that was what the Chrysler Kit Car was.
Doug Odom in Big Ditch
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This is kind of on topic with Bob's original post but what about a Mini Trucks like the Rampages that SteveM and I are working on.
Should there be any rake on them? My thought would be that there should be, especially at higher speeds, to add downforce in the rear.
Sway bars be recommended?
Gregg
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So how high off the ground (at the lowest point, like the air dam) do you set your front ride height to? My car is a Gas Coupe FYI...
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FS, not sure if your question is for me or Gregg. I'm in Production class, so no air dam allowed. I'm lowered down 'til I've got only about 1" clearance for my bellhousing. My exhaust also hangs down too low, however I don't figure I have enough time to correct that before loading the trailer for Speed Week.
Gregg, you might try your question over on your Build Diary; may be more folks perusing there than here.
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From my rough understanding of aerodynamics, With the large sloping rear deck on the cuda, while being very slick, does it not have the inherent desire to be airborne? More rake= more frontal down force= more rear lift and the chance of the butt end becoming the front end.
Keeping air out from under the car is great, and if the bottom is slick enough, may even counter some of the lift generated by the rear window via a crude rear diffuser shape of rake and floorpan.
So that being said, i would guesstimate less than 3* of rake and get the butt down too.
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I don't think Bobs sexy bitch with a "wopping 174 inches":-D will have enough legs to get him into trouble. I've had a 65 in the 150 range a few times & it behaved better than my 70 R/T Coronet & my Challengers.
Sid.
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A thought on the amount of rake for you Cuda. The reason that rake helps is that it assist the air flow over the rear section of the car. If the angle of the rear window, in your case, is more than some place in the 7-10 degree area then there is a good chance that the air going over the top will become unattached which makes big drag. So if you stick you anglemeter on the back window and measure the angle and if you can get enough rake to get the angle in the 7-10 degree area you should be helping your aero.
Rex
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Rex, thanks a bunch for sharing that with me. New information for me, but it does make sense. I'm away from my car for a few days right now, but I'll definitely take a look at that when I get back to it. :-)
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I saw the car in impound and it looked like you were hot lapping it pretty good. What was the outcome at the end of the week? Car looks great, nice work!
:cheers:
Dan
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Dan, we had a couple runs better than our record but less than our backup run earlier that morning. Went to Impound on the second one, but when there figured out our problem was the rev-limiter (MSD 6AL) kicking in 1,000 rpm early. Out of Impound and back for a shot at a better qualifier. Lost cylinder #1, still sorting through the issues why. That was our fourth run of the day. Came home with a record but had hoped for more - plans are underway for next year!
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We always hope for more Bob. You did good & looked like you were having fun to me.
Sid.