Finally... a 3" brake duct solution for the Evo
I always wondered this, so perhaps someone could chime in....
The "typical" ducting set up's that attach via the caliper bolts drive air to the back of the caliper and the rotor hat. This set up drives the air to the rotor...which is "better" as it relates to decreasing fluid boil and fade? Could a combination of both be the best solution i.e. run 2 separate 2" or 2.5" hoses? David Fazzino's ST-2 car has dual hoses and he doesn't have major issues with rubbing....
The "typical" ducting set up's that attach via the caliper bolts drive air to the back of the caliper and the rotor hat. This set up drives the air to the rotor...which is "better" as it relates to decreasing fluid boil and fade? Could a combination of both be the best solution i.e. run 2 separate 2" or 2.5" hoses? David Fazzino's ST-2 car has dual hoses and he doesn't have major issues with rubbing....
Joined: Apr 2005
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From: somewhere testing various tires, brakes, and suspensions.
Looking at internal cooling (veins) v. surface cooling one side (rotor face) allowing ambient to cool outward facing rotor surface.
If picking one, I prefer internal cooling since it works on both faces of the rotor.
More air cannot be bad though. I've seen other multi-cooling brake cooling setups.
If picking one, I prefer internal cooling since it works on both faces of the rotor.
More air cannot be bad though. I've seen other multi-cooling brake cooling setups.
Why would pressure be an issue? Physics wasn't my major, however, moving a given amount of air through 3" hose will require less pressure than the same volume through 2" hose. If your average speed on track is 70 mph and the duct is located in a high pressure area (bumper), that's more than enough to move air four feet from the front of the car.
Let's put this in layman's terms, for the both of us:
- Take a 1/4" diameter straw and a 1/2" diameter straw of the same length.
- Blow air through the 1/4" straw.
- Blow air through the 1/2" straw.
- Notice how you have to exhale harder to push air through the 1/2" straw?
That's what I'm talking about.
Sure, a 3" duct tube will pass air over the calipers, but how much? Will it be enough to cool the brakes effectively.
That's what I'm hoping to find out.
We can armchair this all day long, but until either of us has any concrete data (Such as tracking the same car on the same track on the same day with both size ducting and logging temps) we're pretty much spinning our wheels here.
i agree with golgo on this one, flowing the same amount of air (i.e. volume) will require more pressure the bigger the tube your using. At a certain point you wont see gains simply by making the duct a wider diameter. Im not saying the 3" is the threshold but... This is how I see it, could be wrong... Happy Tracking
Are we seriously just pulling **** out of our asses here? Seriously some of the lastpost make me want to cry. The internet is always available for blind searching if nothing else. A bigger diameter hose will ALWAYS flow more air than a smaller one. Google Bernoulli's equation. You will need to use his compressible fluid equation since we are dealing with air. If you really think that a smaller hose flows more air, then next time you go snorkeling, take a straw and try to breathe through that.
That said, to truly determine if in this application the larger hose dumping to the heat shield location is better than the usual sized hose going to the gap in the heat shield location, you would want to do temperature and airflow data collection.
That said, to truly determine if in this application the larger hose dumping to the heat shield location is better than the usual sized hose going to the gap in the heat shield location, you would want to do temperature and airflow data collection.
Are we seriously just pulling **** out of our asses here? Seriously some of the lastpost make me want to cry. Google Bernoulli's equation. You will need to use his compressible fluid equation since we are dealing with air. If you really think that a smaller hose flows more air, then next time you go snorkeling, take a straw and try to breathe through that.
Anyway, after reading a bit more about Bernoulli's principle regarding his compressible flow equation, I believe that my straw analogy still holds.
Can we get a real engineer to chime in and clear up some of my conjecture? I'm not a fan of spreading misinformation!
spdngdragon, help me out here:
- Flow rate is constant (due to the mass of air and speed of the car remaining unchanged between ducting)
- Area was originally n but is now y (where n is 2" and y is 3")
- Pressure drops in the ducting due to the increase in area (flow volume)
- Velocity remains the same since the ducting diameter is constant in both cases once past the inlet
Thus, wouldn't you need a higher flow rate (vehicle speed in this case) to offset the pressure differential of ducting with smaller area (2")?
Using the interactive flash animation on this site really helped a layman like me understand the compressible flow equation:
http://mitchellscience.com/bernoulli...iple_animation
Last edited by golgo13; Sep 24, 2011 at 09:25 AM.
Golgo- I believe you are jumping the gun by assuming that you need pressure to cool the brakes. What makes you think you pressure is necessary?
Keep in mind that all pressure is is resistance to flow
Given that fact, the larger air ducting should provide for a drop in pressure (assuming at the given speed that there is any) and increase the flow if there was pressure before. One thing to consider is velocity of the air which is important but if you are using an inlet that is comparable to the diameter of the tube (larger inlet for a larger duct) you will be feeding from a great area and should see the same velocity of airflow.
This isn't like an exhaust system on an NA car (where there is much more pressure) where the exhaust is sized to promote maximum velocity to promote an upstream suction effect that helps fully evacuate the exhaust gas from the combustion chamber
I think you should be thinking more of total mass of air first, velocity of the air second, and pressure last.
Keep in mind that all pressure is is resistance to flow
Given that fact, the larger air ducting should provide for a drop in pressure (assuming at the given speed that there is any) and increase the flow if there was pressure before. One thing to consider is velocity of the air which is important but if you are using an inlet that is comparable to the diameter of the tube (larger inlet for a larger duct) you will be feeding from a great area and should see the same velocity of airflow.
This isn't like an exhaust system on an NA car (where there is much more pressure) where the exhaust is sized to promote maximum velocity to promote an upstream suction effect that helps fully evacuate the exhaust gas from the combustion chamber
I think you should be thinking more of total mass of air first, velocity of the air second, and pressure last.
Boltz is correct, we shouldn't even be considering pressure in this case. It's as simple as this: A larger surface area will allow more air to enter at the same velocity, increasing flow. If you do want to involve pressure, it's true that a larger hose will result in a pressure drop, but all that means is that at the same volume, there is less air velocity. If you take the inverse, at the same velocity there will be more volume. In either case, you're looking at flowing more air.