whosurdaddy

I hate to start yet another thread on this. It has so long been a problem for me, I don't take changes in this department lightly.

I question some of the postings claiming that eliminating the bottom-breathing brake duct improves cooling and downforce. It makes sense to me that an underside hole is far more efficient than forward facing because a bottom facing hole sucks air pressure from the bottom of the car, and forward facing simply increases drag.

Ferrari is evidence for this. When they're at a less brake-intensive track, they reduce the size of the forward facing brake duct for better aero efficiency, whereas the new F458 uses bottom feeding engine cooling. It also uses a fender vent to evacuate air from the fender well.

We're now talking about a forward facing vent that probably increases airflow into the fender well and may increase lift (unless you have a vent). We're also talking about removing the air dam and allowing more airflow under the chassis.

So before I started cutting holes in my nose piece to route brake ducting to the front center, I though I would pose the above hoping that someone has done actual testing and is willing to share the results. If actual test results have already been published - sorry about that I haven't found them.

Thoughts?

John Shiels

Any air passing in and out of a car creates drag. Forward facing hole is getting tons of pressure if in the right place. I doubt a NACA duct under your car will take it as much air. You are trying to make the bottom of the car a low pressure area so I doubt it is ideal place to try and suck in air. As far as venting try to use a vacuum if it is not venting or even venting well.

95jersey

The ZR1 also uses flaps on the A-arms that are suppose to direct air flow into the brakes. Also, the flap in front of the front tire wheel well on the Z06/ZR1 is suppose to direct air away from the rim, which creates a negative pressure zone, so the incoming cool air can exit out of the wheel well more effectively. Supposedly without the flap in front of the wheel, the hot air just gets trapped and blown around the inside of the wheel.

I thought the OEM cooling system on the Z was pretty good and for 3 years I ran without any NACA ducts or spindal ducts of any kind and never had brake fade or boiling issues and I ran quick. I only recently put on ducts when I went to BBK, but in all honestly, I can't feel a bit of difference and the rim and wheel feel just as hot as without the ducts (I realize you need a pyrometer to actually tell) . I go through less pad, but that could be due to the BBK. I will also say I never run more than 25 minutes at a time.

Webz

Not exactly like cooling ducts in the fog lights but still shows cooling brakes from the front versus bottom of the car.

http://www.youtube.com/watch?v=AHsfo...eature=related

John Shiels

not sure how much wheels being stationary affects what they show for the wheel-wells.

95jersey

This actually shows undereath ducts, not through the front grill.

davidfarmer

the point is you don't want pressure under the nose...... You aren't "sucking" air in, the high pressure is forcing air through.

The only info I can find on 458 cooling is about a recall/fire hazard. I'd love to see the underside to see how they do it.

Webz

It definitely is not showing cooling of the brakes from the front grill.

IMHO it shows air moving thru the front grill vented out of the hood and air moving thru the front (not underneath) air damn/splitter openning venting out of the wheel wells. Going to Katechs website it shows this particular splitter/undertray is sealed entirely under the bottom so the only avenue for air to get to the brake ducts is thru the front openning in the splitter. With some deductive reasoning it would seem plausible that air could be ducted successfully to the brake ducts from the grill.

Bill Dearborn

However, it does show the efficiency of the stock ducts as the splitter just routes the air coming into the front into the stock duct. Instead of feeding off the high pressure area in front of the spoiler the duct is feeding off the high pressure area in front of the splitter. Essentially all that has happened is the intake has moved forward and there is some additional plumbing in the splitter to get the air into the stock ducts.

I think the biggest problem is when fans are installed in the ducts. At high speeds the fans reduce air flow through the ducts due to reducing the area available for air flow and the fact the fans don't turn fast enough and once car speed exceeds 35 mph they actually impede air flow. Fans will help but they can't be in the direct flow from the outside they have to Y'd into the duct so they add cooling at low speeds.

Bill

John Shiels

How did you come up with 35 mph Bill? Just asking 35 mph seems low like a potato stuck in there. NASCAR must have some fast turbine fans. Don't they run fans Bill? thanks I always thought of putting fans but didn't know the trade off point in speed / mph vs. fans.

John Shiels

googled this 12,000 rpm set up http://www.suzukaracing.com/1%20Blower.html


note this at the site


http://forums.pelicanparts.com/porsc...apporoach.html


http://www.prosystembrakes.com/catalogpg022.htm

John Shiels

brush fan motor 165 ea

brushless 6 speed motor is 395 ea

I called them up and ask for a catalog also.

may be a nice mod.

Bill Dearborn

They do run fans. However, they aren't in the direct flow. You can calculate the air speed through the fan by using their specifications for air flow. The fans most people are using are the ones used for boat bilge blowers and they flow about 135 cubic feet of air per minute. The fan diameters are around 3 inches but the structure of the fan reduces the area of the circle to some extent. If you calculate the maximum area you get about 7 sq inches. Then assume the fan structure (motor, case, etc) take up about 25% of the area that reduces the area for air flow to about 5 sq inches. So now all you have to do is calculate how fast the air has to move through the 5 sq in area to get 250 cfm. To get 1 cubic foot of air in an area of that size you would have to have a tube with a diameter of 2.6 inches and a length of 326 inches. Multiply the 326 inch length by by 135 to get cubic inches per minute, then divide by 12 to get feet, then multiply by 60 to get feet per hour and then divide by 5280 to get miles per hour. It actually comes out to 41 mph so my guess was a little off.

Nascar may use a larger diameter but it would be hard to put a 4 inch fan in the Z06 duct. If you can get a fan with an air flow spec'd at 250 cfm then the effective speed would raise to just over 80 which means the fan would still be an impediment a large part of the time a car is running at speed on a track.

I have seen evidence that the blades will slow air flow as they are not free wheeling but turning at the speed the motor turns them.

Bill

John Shiels

what about this?
they say no to that if the fan is off. The structure of the fan expands at the motor from 3 to 5 in diameter probably to keep the same area or near it. It's also 12,000 rpm. not some boat bilge motor @ 40 bucks I would hope. One is 3x5x3 and the other is 3x5x4 for a difference hose on each end.

You can splice the motor in the nose before it gets to the plastic DRM duct going to the spindle duct.

From what I searched up I see boat bilge fans are in the range of about 2-3,000 rpm.

JDIllon

I can tell you this works great! I have done it on my car and several others. I have discussed this with many knowledgeable people before doing it and it increases down force and increases airflow to the brakes. You are welcome to give me a call and I will be happy to talk about what I have found out. All I can say is this works for me. Jim Dillon
http://forums.corvetteforum.com/c6-z...evel-pics.html

whosurdaddy

This is interesting, though like the comments on that thread, I would be concerned about water temps. Have you noticed anything in that regard?

Also, so that's a 4" OD going to the stock plastic duct to a 3" hose into the spindle? I bet you'd increase airflow to the radiator and have no loss of cooling by going 3" in the grill.

whosurdaddy

Now that is cool to watch. It doesn't apply to me thought as I'm not spending that dough on a CF splitter that I'd destroy. Plus I'd also have to put a big rear wing/spoiler on it - don't want to do that either.

Thanks!

whosurdaddy

I don't have an image, but reference to the underside engine bay cooling is made in this early review of the F458 by Autocar in the UK.

http://www.dailymotion.com/video/xcq...58-italia_auto

whosurdaddy

So did you remove the middle section and leave the flaps on the left and right side in place?

JDIllon

We have 3 C6-Z06s running with this setup, mine with a Ron Davis radiator and 2 stock radiators and all with modded engines and we run in Florida all summer and did not notice any difference in cooling. The 3" would not bring as much air to the brakes. The 4" keeps pressured air at the brakes at all times. One nice thing about this setup is that it can be brought back to stock for about $30.00. And as Randy at DRM said this is similar to the setup they run on there race cars and they have no cooling issues either. If you look at Randy's race and custom HPDE car, this where they get the air for the front brakes. JD