Golf Ball Dimples on MythBusters = Greater MPG

[strotter]

Originally Posted by kiwi303

You could try stuffing one of those inlet air turbulence generators down your collector, but I think the muffler would screw things up.

I don't mean just at transition points in the flow, I mean dimpling the entire length of the pipe. Think about it: exhaust flow is high velocity, turbulent, and in constant (pulsing) stir. Boundary friction effects are bound to be high. Our Z's (or any lowered vehicle) are clearance-challenged, so a smaller-diameter yet low back-pressure exhaust system might be welcome. Might not be hard to test...

[Pyro]

Maybe rust bubbles in the paint act as dimples that reduce drag.

so maybe it is true when some guys claim to go 150 mph in a stock and "rusted out" 280.

That explains it all!

[DatsunKing1]

It was in Popular Science a couple months ago, A company is coming out with a vinyl covering like golf ball dimples that are available to cover cars for greater MPG. Buses and Semi's are usually the first canidates.

I'll look for that magazine when I get home :P I think it's a pretty neat idea, they had a picture of a Scion with the covering on it.

[260DET]

The bellmouths in the plenum I'm getting made for the VG30DET are finished in 60 grit for the same aero reson I believe. Perhaps we should all go over our paint work with 60 grit?
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[johnc]

Perhaps we should all go over our paint work with 60 grit? . . .

What would I do with all the 36 grit I just bought?

[260DET]

Put two 36's together, end up close enough?

[jlc]

Vinyl roofs were banned from Nascar in the mid 60's because they were found to be a little faster.

[260DET]

Hmmm, wonder how a hammer finish paint on a car would go?

Car would still be easy to clean, could look good too.

[zero]

Originally Posted by Rolling Parts

Sorry, irrelevant in that I was thinking that passenger cars cannot have "pointy" rear ends for a variety of reasons. Therefore they can't be "tear dropped" so the best solution for a non-tear dropped passenger car is to control the flow (as you said) with something like VG's to fake the flow to work as if the shape was tear dropped. That's a much more elegant solution than dimpling the surfaces.

I can't find it right now but there was a aero study on passenger cars that approximated what they called a "ghost tail" instead of an elongated real tail to control turbulence.That gave the cars a "virtual " tear drop....

Its called a Kamm tail.

[Rolling Parts]

Originally Posted by zero

Its called a Kamm tail.

Ah, that's it. Thanks.
Basically an angled flat rectangle (GT-40's) rear end worked nearly ideally without incurring a large penalty in material, structural, and size that a long pointy tail would have.

Great aerodynamics, and that was done in the mid 1930s? Nice!

[Gollum]

Interesting topic, I wish I'd seen this episode.

What I'd really like to see done, is some hardcore tests comparing our giant evo style VG's and a dimply piece of metal. There's some articles floating on the net of plastering VG's all over cars like the Honda Element and Toyota Prius for well documented improvements in MPG, indicated a drag reduction, but would dimpling the car in those same areas have the same effect????

I have a hard time imagining it would. I think a factor to consider is that this is easier to apply in many areas opposed to huge vortex generators.

Anyone have a car they want to hammer-up for a possible future wind tunnel test?

Also, concerning exhaust gases, I always thought it was interesting how many super cars use that tiny extended rear section like a GT40 (which works well for a mid engine anyway) and then place the exhaust pipes right in the middle of this flat spot. Aero reasons maybe? Sure having a 30" can on the back ain't going to do squat, even with 500hp. But if you tear drop down to a certain point, maybe the gases from a 500hp twin cam V8 CAN make an aero difference?

[tyler031734]

I watched the episode and figured the dimples in the front where slowing it down with turbulence and to much separation on the flats, I belive they said it gives the air more momentum, there for giving it more ability to fight the vortex rather than sliping into it and adding to the forces

[tyler031734]

Im thinking of some VG's but i dont know if they would be best on the roof near the hatch, or if air sticks to the rear window well and i should put them on the end of the hatch. for athletic reasons I think it would look funny on the roof with such a gental rake of the rear of the car. but VG's should be used for gains in efficientcy and not pleasing to the eye

[Grim]

To the exhaust idea. Whenever I think of drag I envision it as a vacuum behind the car slowing it down, so I've always wanted to relocate my exhaust into the middle of the back of the car so that the exhaust gases fill up the vacuum a little bit and using the vacuum to pull the exhaust gasses out, therefore reducing backpressure.

[Two80z4me]

Originally Posted by olie05

I'm a roadie... been doing the txbra races for almost a year now.

dang Roadie!!! I built Dirt jumpers and fixies for extra cash through my last few years of high school lol. now I ride my santa cruz v10 in the spare 3 months of riding a year.

[softopz]

Originally Posted by jlc

Vinyl roofs were banned from Nascar in the mid 60's because they were found to be a little faster.

nice my 240z is got a vinyl top I am liking the roof more and more everyday

[johnc]

Vinyl roofs were banned from Nascar in the mid 60's because they were found to be a little faster.

Well, not really. NASCAR banned the vinyl top (actually "simulated vinyl tops") because racers were using the spray on texture to hide evidence of acid dipping. NASCAR figured this out when Petty was running a Roadrunner in 1968 and the sprayed on vinyl roof started peeling off. He got black flagged and spent two laps int he pits while the crew taped it back down. One of the NASCAR inspectors spotted the tell-tale ripples from acid dipping.

Roger Penske also got caught doing this to the TransAm Sunoco Camaro and had to buy a Camaro off a dealers lot near the race track, cut the top off, and weld it onto his TransAm car so he could race the next day.

[ShaggyZ]

Originally Posted by strotter

Could this kind of effect be applied to an exhaust system? I.E., could it be possible to reduce exhaust backpressure without increasing pipe diameter?

Sure. Straight-thru mufflers are generally perforated pipe inside, which serves the same purpose, and is why some guys have found less backpressure from a 18" Dynomax Ultraflo than a regular 18" pipe of the same diameter. I don't know if the decrease in backpressure is worth putting 10 mufflers on your car.

[dan5138]

Originally Posted by johnc

Well, not really. NASCAR banned the vinyl top (actually "simulated vinyl tops") because racers were using the spray on texture to hide evidence of acid dipping. NASCAR figured this out when Petty was running a Roadrunner in 1968 and the sprayed on vinyl roof started peeling off. He got black flagged and spent two laps int he pits while the crew taped it back down. One of the NASCAR inspectors spotted the tell-tale ripples from acid dipping.

Roger Penske also got caught doing this to the TransAm Sunoco Camaro and had to buy a Camaro off a dealers lot near the race track, cut the top off, and weld it onto his TransAm car so he could race the next day.

Acid dipping, as in eating away some of the steel to make the whole thing lighter?

[Valmont]

Originally Posted by johnc

....Roger Penske also got caught doing this to the TransAm Sunoco Camaro and had to buy a Camaro off a dealers lot near the race track, cut the top off, and weld it onto his TransAm car so he could race the next day.

That's hilarious.