Keith Tanner said:3" doesn't package well on a Miata. I've gone from 2.5" to 3" on my car and it helped a lot, but there are lots of clearance problems and full lock is not possible.
I've got a couple of interesting variations to play with - coming off the printer today - then they're heading to the track for testing on Scott's car.
Have you considered providing for some type of screen to prevent rubber build up in the bell or duct?
No, that would be a lot of rubber! I'll leave that as an exercise to the installer.
In reply to Marcus_NineLivesRacing :
3" really doesn't work well, esp with the 10"/245 combo we're running... we only have one bend (approx 90*) where it follows the sway bar.
We haven't had issues with cooling, but if we were able to keep the rotors even 100* cooler at max it'll help our pads keep their cooler temp bite even towards the end of a race.
The printers were busy this weekend.
I scaled down the bellmouth by 75% to cut the area approximately in half, then used a diffuser design to bring that back up to 2.5". This should accelerate the air and provide better cooling per the article shared earlier. The longest version delays the diffuser until the airflow has reached maximum velocity in the bellmouth, the shorter version starts the divergent section immediately. There's also a 75% normal bellmouth that's not really useful but I can use it for some experiments.
The big one wouldn't fit the printer so I made it in two pieces. This is a press fit, but not as tight as I'd like so it will need to be secured for Racecar! use.
Fun fact: I don't have any 2.5" SCAT hose handy. My own car uses 3" ducting, and it's due for replacement due to abrasion. So all the testing on these may be up to our apexanimal friend.
Somewhat on topic, are fenders best vented (for brake cooling) on the top or behind the wheel? Is there any reason other than brakes to do one or the other? I've read inside the fender is a high pressure area but I dont think my street driven NB is fast enough to have significant issues there, but brake cooling is always good, especially with my "spirited" driving style
I believe that venting the side can have beneficial effects down the side of the car, but if you're looking primarily at the effect of pulling air through the wheel well I'd think you'd be looking for the spot with the greatest pressure differential. I'm not sure what that looks like on the inner surfaces with that wheel whipping the air around. There's certainly low pressure on top.
I'd love to know more.
Would the yarn test to find a low pressure area outside the car help?
I did some testing on the above wheel vents:
I will be doing some testing on the rear of the front quarter panel vents at some point... the car is needing more attention than i was hoping at this stage in the season, but we plan on getting to it
Thank you, that's awesome. I wouldnt have guessed forward was better because my brain wants to look at inside the fender like a parasail at the beach, the air inside "stacking up" against the back side of the inner fender, making a vent behind the wheel useful
it's going to be friggin hot this weekend, at Mid-Ohio. Might end up being a good test environment?
I'll refrain from quoting Roosevelt E. Roosevelt.
re: over fender vent vs. rear fender exit
I dunno if anyone's done much of a comparison in the benefit between the two.
Frequently rules tend to dictate if you can have an over-vent or a rear-vent... and there are tradeoffs to be made about drag and downforce in that decision.
One challenge with the miata is its relative lack of space between the back edge of the wheel opening and the door to affect a rearvent. This is also complicated by how much the foot well occupies that area behind the fender. So, there's not as much room (as compared to loosecannon's MGB) to 'ramp' the higher pressure that collects in the wheel out along the body. So, the flow leaving that area has to turn sharply around two corners, while also be 'swirled' up by the rotation of the wheel/tire.
ymmv
In reply to sleepyhead the buffalo :
they may also be relieving high pressure air from different sources. I'd guess in general an over-vent is relieving high pressure above a spinning tire (lift on the body above the tire) and a rear vent is relieving high engine bay pressure (to improve airflow through the coolers).
I'm not sure how much either high pressure source is affected by the brake cooling air. I thought in general the brake cooling air went in the rotor on the engine side in the center and out of the rotor at the edges, and then I assumed it went out of the face of the wheel - hence why some spoked wheels offer better brake cooling and wheels that are almost solid often have vents. But I guess that could be a false assumption and that brake cooling air could exit the rotor and return to the engine bay area or under the car.
My thinking is that lowering the overall pressure inside the wheel well will improve the flow through the brake cooling apparatus. Since the rotor does exhaust the cooling air around the perimeter, it would seem that a turbine-style wheel would be the most effective way to get rid of the hot air. But without the wheel actively pulling the air outboard, I'll bet most of it goes inboard into the wheel well.
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