Aerodynamic Discussion Thread - Page 24 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 12-26-2013, 12:30 AM   #461
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Originally Posted by ThePass View Post
I would not want to have my motor intaking the hot radiator exhaust air.

"Ram air" is virtually a myth
The benefit of pressured air is greater in a FI application than a NA application.

After reading a motorcycle article test on "Ram Air" I concluded the benefits were virtually nonexistent for a NA power track car at the speeds I normally see. When I plugged the same "Ram Air" pressure data into a compressor MAP however the result was worth the effort. If I recall it was worth an extra 1 PSI at speed on my supercharged application. On a turbo application you may not see a boost increase just lower IAT's. It will depend on they way you control the waste gate.

The magic is a result of the way FI multiplies available air. The slight pressure increase on the intake side will be doubled on the output side if you are running 1 bar of boost. (SC application)

I plan to feed high pressure air from the bumper to the intake. I will be able to log the pressure difference at speed with the MAP sensor to prove the merits of the idea.
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Old 12-26-2013, 12:47 PM   #462
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A very interesting note. I had not heard of any testing for boosted applications before. That it magnifies the pressure increase is pretty cool. This is probably more handy for a supercharged setup where more boost is not so easy to come by, whereas with a turbo with a boost controller, the same net effect is easy to replicate, though the cooler air is still a benefit.

-Ryan
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Old 12-26-2013, 05:30 PM   #463
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It will be interesting to see the results on my car. I have to believe the motorcycle pressure is going to be less than that of a Miata bumper. Unlike a motorcycle which has a slippery profile the Miata bumper has lots more surface area to build up pressure. This will only compound the "ram air" effects.
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Old 12-26-2013, 05:59 PM   #464
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Quote:
Originally Posted by k24madness View Post
It will be interesting to see the results on my car. I have to believe the motorcycle pressure is going to be less than that of a Miata bumper. Unlike a motorcycle which has a slippery profile the Miata bumper has lots more surface area to build up pressure. This will only compound the "ram air" effects.
Motorcycles themselves aren't that slippery. The OEM's have done a decent job of extracting horsepower out of motorcycle engines with pressurized air boxes, but they also have sound and space restrictions and rules that we don't necessarily need to follow.

I bought a pressurized airbox for my RC51 that worked by removing the stock plastic airbox and essentially making a lower clamshell that fit over the engine. The top of the clamshell was the gas tank. The air box volume quadrupled. It worked really well, but the intake noise was much more pronounced...not that I minded.
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Old 12-26-2013, 06:59 PM   #465
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Originally Posted by k24madness View Post
It will be interesting to see the results on my car. I have to believe the motorcycle pressure is going to be less than that of a Miata bumper. Unlike a motorcycle which has a slippery profile the Miata bumper has lots more surface area to build up pressure. This will only compound the "ram air" effects.
In for results. Are you using an OEM bumper or something different?
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Old 12-31-2013, 08:55 PM   #466
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On the Ram Air note, I will add that coming from a drag racing background, specifically carbureted, we would see significant gains using cowl induction or forward facing hood scoops. Typically, the gains were attributed on N/A and nitrous motors from a reduction in IAT, or a stronger venturi signal. Without the ducted air setups or adequate underhood clearance, turbulence would lead to signal/fuel distribution problems in carb'd applications.

I'm about at the point where I may see how short an air filter I can go with, and if need be, just plop one of these on the hood with an open element.

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Old 02-05-2014, 11:21 PM   #467
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Originally Posted by 1993ka24det View Post
I put this up because of the new active diffusers (front and rear) and that is so cool

La Ferrari - YouTube
ooooh I like that active diffuser design. Great idea changing the angle of attack based on the spoiler's. I wonder how much that shifts the balance of the car rearword on braking. More than just the active spoiler "airbrake" alone. Could be done fairly easily with connecting rods between the two...
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Old 02-06-2014, 12:32 AM   #468
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Originally Posted by Supe View Post
On the Ram Air note, I will add that coming from a drag racing background, specifically carbureted, we would see significant gains using cowl induction or forward facing hood scoops. Typically, the gains were attributed on N/A and nitrous motors from a reduction in IAT
I agree with this. I was doing some dyno tuning last year and my IATs kept creeping higher and higher. My intake is 3 pieces of silicon hose clamped together (2 90 degree elbows, then a long section that points back toward the firewall) so I loosened a hose clamp and rotated the intake to point straight up. I think IATs dropped by 60 or 80 degrees, down to ambient. I picked up 2 or 3 peak hp, but midrange gains were huge- I think 8lb*ft at one point. I've had a NACA duct pointing straight at the air filter ever since. Minimal drag increase but constant supply of ambient temp air for the filter.
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Old 02-06-2014, 01:02 PM   #469
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Originally Posted by ecc3189 View Post
ooooh I like that active diffuser design. Great idea changing the angle of attack based on the spoiler's. I wonder how much that shifts the balance of the car rearword on braking. More than just the active spoiler "airbrake" alone. Could be done fairly easily with connecting rods between the two...
What thread is that quote from? I didn't see it in this one. Edit: The video quote from 1993ka24det.

I'm really excited to be seeing more and more active aero in production cars. I was worried we'd never really see that since active aero R&D is of no use to factory race teams since (I think) there are no racing series that allow it.

So basically the flaps in the under tray of LaFerrari are used to control air pressure under the car to compliment air pressure over the car? I saw that when the rear spoiler was raised, so was the rear diffuser flap (and vice versa). Are these two things connected in a way where increasing the diffuser AOA helps the spoiler create more downforce at higher AOAs? The only other explanation I could think of is that they are independant of each other and that each element moves to create either less drag or more downforce depending on the circumstances. The only thing that confuses me with that theory is that I was under the impression that a diffuser gives downforce with (relatively) no additional drag. So why is it adjustable?
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Old 02-06-2014, 10:14 PM   #470
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it is the opposite. the spoiler/wing "drives" the diffuser. Because if this, you can increase the angle of the diffuser.
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Old 02-07-2014, 02:01 AM   #471
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So as the AOA of the spoiler increases, pressure behind the car decreases (accidentally wrote increases) which lets the diffuser run a higher AOA without getting separation of the laminar flow?

Also, how are the font flaps designed to change with conditions? It looked to me like they are really just there to relieve pressure built up by the splitter into the under tray. This would give less downforce up front and possibly add more to the rear by flowing more air through the diffuser. Maybe it just makes the car more slippery on the straights. Thoughts?

Last edited by mx5autoxer; 02-07-2014 at 12:01 PM.
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Old 02-07-2014, 08:23 AM   #472
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So as the AOA of the spoiler increases, pressure behind the car increases which lets the diffuser run a higher AOA without getting separation of the laminar flow?

Also, how are the font flaps designed to change with conditions? It looked to me like they are really just there to relieve pressure built up by the splitter into the under tray. This would give less downforce up front and possibly add more to the rear by flowing more air through the diffuser. Maybe it just makes the car more slippery on the straights. Thoughts?
when the AOA of the spoiler increases it would drop the pressure behind the car, thereby allowing the diffuser to be at a steeper angle without the air detaching. Since you get downforce from the air accelerating into the diffuser the added low pressure from the spoiler changing AOA would add more downforce.

Since I'm planning to do an air brake down the road, an adjustable diffuser would be fun to add if I can do the math right to make sure it actually works...

P.S. for the front flaps, based on the quick view we get as the video slides past it looks like there is an opening above the flap and a channel after so my guess is that when the diffuser and spoiler incease their respective angles they require more air to be effective so the flaps in front drop added air under the car. Things you can do when you have ferrari's budget, engineers, CFD, and windtunnels o.O

Last edited by ecc3189; 02-07-2014 at 08:29 AM. Reason: answered second question
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Old 02-07-2014, 09:08 AM   #473
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Quote:
Originally Posted by Supe View Post
On the Ram Air note, I will add that coming from a drag racing background, specifically carbureted, we would see significant gains using cowl induction or forward facing hood scoops. Typically, the gains were attributed on N/A and nitrous motors from a reduction in IAT, or a stronger venturi signal. Without the ducted air setups or adequate underhood clearance, turbulence would lead to signal/fuel distribution problems in carb'd applications.

I'm about at the point where I may see how short an air filter I can go with, and if need be, just plop one of these on the hood with an open element.
Supe, you have a center, forward facing intake and you want to make sure you get cool air while also ducting the radiator to the hood right?

Why not try a design like the ford GT or viper with a bifurcated radiator duct and have an intake box and filter on the nose and the radiator duct split around the intake tube going into the throttle body:


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Old 02-07-2014, 12:14 PM   #474
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Quote:
Originally Posted by ecc3189 View Post
when the AOA of the spoiler increases it would drop the pressure behind the car...
I meant to write "lower pressure". I shouldn't try to contemplate the intricacies of CFD at 2 in the morning.

Quote:
Originally Posted by ecc3189 View Post
P.S. for the front flaps, based on the quick view we get as the video slides past it looks like there is an opening above the flap and a channel after so my guess is that when the diffuser and spoiler incease their respective angles they require more air to be effective so the flaps in front drop added air under the car. Things you can do when you have ferrari's budget, engineers, CFD, and windtunnels o.O
Ah. That makes sense. I was talking to the CFD guy for the Virginia Tech Formula SAE team at an autocross last year and he was saying that the front "intake" of the under tray has to be adjusted whenever you play with the AOA on the rear. They actually had to add scoops to force more air in to run their steep diffuser.
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Old 02-07-2014, 09:37 PM   #475
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Originally Posted by ecc3189 View Post
Supe, you have a center, forward facing intake and you want to make sure you get cool air while also ducting the radiator to the hood right?

Why not try a design like the ford GT or viper with a bifurcated radiator duct and have an intake box and filter on the nose and the radiator duct split around the intake tube going into the throttle body:


I was fabricating a split radiator duct out of fiberglass to do just this. Unfortunately, it just took up too much real estate on things I often need to get to at a track day and was creating coolant routing headaches. Also, the limited hood clearance and strut tower brace were making a forward facing inlet not possible. If I make the move to forced induction, it all would have to be redone, so I went down the path of a one and done deal.

Thankfully, I think I have enough clearance having dropped the brake booster and gone to dual masters inside the car to make an offset cowl induction setup that should work without sucking in hot air.
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Old 04-07-2014, 01:58 PM   #476
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Searching for quite a while on the internetz and not finding a straight answer..

We know there's a magic ratio of about 1:3 for duct opening size to heat exchanger surface area, but that's for a straightforward single duct for a single exchanger.

Now, if you're supplying multiple heat exchangers with a given duct (such as with a radiator and intercooler like most of us have) then do you add the surface areas of both together, which would then require a bumper opening in some cases almost double the size of the opening for a radiator-only duct?

If the heat exchangers are stacked together, perhaps there is some average between the two that is ideal, but especially for a setup which has gone through the trouble to seperate the surface of the radiator from the surface of the intercooler so they both get their own air, it seems to me that the duct opening needs to grow much larger than the roughly 96 square inches opening size that we usually see agreed upon for miatas (1/3 of 12"x24" radiator surface)

-Ryan
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Old 04-07-2014, 02:06 PM   #477
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If the heat exchangers are are stacked like in a normal setup I would, duct the back of the intercooler directly to the radiator, which means some section of the radiator the same size as the intercooler core is going to get hotter air than the rest of it. But if you didnt do that flow through the intercooler would be non-existent since the pressure on both sides of the core would be more or less equal. Unless you can make the intercooler exit not directly into the radiator, like under it or something. So then the main duct to the radiator only needs to be the size of the radiator - the intercooler blocking the flow /3.

Every time I think about ducting I think about just running an EP style nose because it would make connecting the ducting to the bumper about a billion times easier.
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Old 04-07-2014, 02:17 PM   #478
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My radiator is no longer 'sharing' air with the intercooler, hence the reason I'm contemplating this more now
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Old 04-07-2014, 02:26 PM   #479
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I think Leafy has it right, you wouldn't add the two areas. You would have to run calculations on the heat gain of the air going through the IC and the area of the radiator that it affects. Then do some funny math where you took the free area of the radiator with ambient air plus the area covered by the intercooler with the heated air and figure out what the new total inlet area you would need.

Or just seal the ducting from the bumper inlet to the radiator and the air will flow through both. KISS as they would say
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Old 04-07-2014, 02:30 PM   #480
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Right with the v-mount you have the total area of the radiator + the intercooler. So the hole needs to be as big as 1/3 of those two added together.
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