Are Brake Ducts Really Necessary? : MG Motorsports Forum : MG Experience Forums : The MG Experience

Are Brake Ducts Really Necessary? #1
dcharnet Donald Charnetski Grinnell, Iowa, USA 1963 MG MGB	Posted: April 12, 2012 01:16PM Registered: 2 years ago Posts: 945

I am going to buy one of Tony Jennes's new valances. My plan is to order it without any brake ducts or openings of any kind.The less air coming into or under the car the better, and if I need to later, I can add holes as necessary.

My question is whether duct holes and/or conduit are really necessary for a vintage B with decent brake pads and rotors and a vintage valence. It looks like lots of air would get underneath, and that the B has decent size rotors and pad area. I know that ducts are "standard," but some very successful hard-charging vintage B racers have never used them to no apparent ill effect.

Has anyone ever experienced fade with B brakes with or without ducts, and are ducts and/or conduit/ and/or brake hats really needed?

Edited 2 time(s). Last edit at 04/12/2012 05:01PM by dcharnet.

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Re: Are Brake Ducts Really Necessary? #2
Speedracer Hap Waldrop Greenville, SC, USA 1967 MG MGB "The Biscuit"	Posted: April 12, 2012 03:04PM Registered: 7 years ago Posts: 20,312

Well you know what I think, but here's goes anyway. smiling smiley

The SCCA Spridgets used an allowable brake upgrade, MGB caliper and Spitfire rotors, on that car, it made all the difference in the world, also I made brake cans for the Huffaker Bugeye and it made a big difference, but it had smaller brakes, than the FP Midget. My car currently has the Sebring valance and brake duct hoses just zip tied and pointing at the rotor, with Tony's valance, I plan on using hose and evetually going to brake cans. I had a couple of incidents in hard braking zones where I really had to stand on the brakes, one time to dodge a SRF, who decidied to block me once I was committed to passing him, and I had brake fade for the rest of the race, so my thoughts is I rather have them and not need them, than not have them at all. I plan on making covers for the openings in the valance, so on colder races, I could just cover them.

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Edited 2 time(s). Last edit at 04/13/2012 06:17AM by Speedracer.

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Re: Are Brake Ducts Really Necessary? #3
TomBrooksuk Tom Brooks Leicester, Leicestershire, United Kingdom 1967 MG MGB GT	Posted: April 12, 2012 04:48PM Registered: 2 years ago Posts: 595

Don, we always planned to fit ducts to the GT and still do. This to be perfectly honest is more to do with the fact that we have always used brake ducts on our race cars, infact the ducts due to go on the GT are off our last race car a porsche 944.

In reality if we didn't have the set up ready to fit I'd probably run without and see how it goes. But then again as Hap said it makes sense to have them and not need them and not the other way around.

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Re: Are Brake Ducts Really Necessary? #4
skippymga Scott Brown Northern California, USA 1957 MG MGA "The Pile" 1957 MG MGA 1500 "The Pile" 1960 MG MGA "Boomer" 1964 MG MGB "#9" 1966 MG MGB GT "Boo" → more	Posted: April 12, 2012 05:08PM Registered: 7 years ago Posts: 1,865

Hi Don - it all depends on how aggressively you drive your car. Of course car setup and what pads/shoes your running will play apart as well. We found the ducts to be very helpful at tracks like Laguna and ThunderHill where you have very high speed 4th gear downhill straights going into 2nd gear corners. Either way, it can't hurt.

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Re: Are Brake Ducts Really Necessary? #5
Speedracer Hap Waldrop Greenville, SC, USA 1967 MG MGB "The Biscuit"	Posted: April 12, 2012 05:28PM Registered: 7 years ago Posts: 20,312

Scott makes a excellent point, if I raced all the time at Roebling Road, I wouldn't need brake ducting, heck I probably would not need brakes, but at tracks like Road Atlanta with the 10A/B complex, you're going downhill at full speed into a passing zone at one of the slowest corner on the track, and you are standing on the brakes hard to get the car whoaed up for the chicane, same deal with turn 1 at VIR, so I think alot of it has to do with the tracks you are going to be racing on, and how hard you will braking into those braking zones. HP is nice, but at the end day, most passes for postion in a hard fought race are done with brakes, not HP.

Hap Waldrop
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Re: Are Brake Ducts Really Necessary? #6
blackmgb Fred McConnell Hollidaysburg, Pennsylvania, USA 1992 Mazda Miata NA "MAC"	Posted: April 12, 2012 08:37PM Registered: 6 years ago Posts: 5,193

I cant remember, but do the rules allow you to put any aero aid devices under the car between the valence and front cross member?

Something like this?

http://www.flickr.com/photos/thinkracing/6255792077/in/set-72157627795129703/

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Re: Are Brake Ducts Really Necessary? #7
dcharnet Donald Charnetski Grinnell, Iowa, USA 1963 MG MGB	Posted: April 12, 2012 11:47PM Registered: 2 years ago Posts: 945

Not sure if it is legal or not, Fred, but the thought had occurred to me. That was really the impetus for the question: there has to be some good reason to send air under the car rather than to the side.

Is there really a need to vent brakes? Dave Headley never used any ducts on his B's, and his SCCA air dams kept much more air from the rotor than our valences. The BMW 2002 I raced years ago had tiny rotors and pad area which were quickly overpowered by that heavier sedan, and the brakes went away very quickly unless you were ducting air properly. More than once I sailed into the weeds with boiling fluid. The formula cars I have raced needed nothing. Where is the B on that spectrum?

This is a game of small increments of advantage, but of course you well know that.

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Re: Are Brake Ducts Really Necessary? #8
BritishV8 Curtis Jacobson Longmont CO, USA	Posted: April 13, 2012 12:04AM Registered: 6 years ago Posts: 1,658

Of ten MGB vintage racecars featured on http://www.britishracecar.com/, only exactly one has brake ducts installed.

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Re: Are Brake Ducts Really Necessary? #9
TomBrooksuk Tom Brooks Leicester, Leicestershire, United Kingdom 1967 MG MGB GT	Posted: April 13, 2012 12:20AM Registered: 2 years ago Posts: 595

In reality its going to depend on a combination of personal preference/driving style/car setup/race circuit.

In terms of aerodynamics alone its clearly better to have a plain deep front air dam as per Dave's old SCCA car, however if one of those is not allowed in your rules and you have to use the narrower almost standard depth front valance the difference in having holes for brake ducts or not is probably not going to make any difference IMO.

So i suppose in essence I'm saying that if you run a plain nose to floor air dam i would be tempted to try without holes for the ducts to maximize the aerodynamic benefits of the air dam. However if you are running a narrower front valance i would be inclined to include holes for ducts as you are not loosing anything aerodynamically and the ducts are there if you ever need them.

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Re: Are Brake Ducts Really Necessary? #10
Gofanu Fletcher Millmore Titusville PA, USA	Posted: April 13, 2012 02:22AM Registered: 6 years ago Posts: 610

"This is a game of small increments of advantage"

You could make the argument that if the brakes don't get hot, you're not driving hard enough. Probably is most average vintage/amateur drivers. If you are in fact using the brakes to the limit of the tires, and they don't get hot, then they are too big, too heavy, thereby costing you unsprung weight and rotational inertia = slowness. Brakes that get too hot without air ducts but are OK with seem best, ducts being sprung and lightweight and cheap. And if you can gain aero by taking high pressure air off the front and duct it out the side rather than under, all the better, and maybe calling for the biggest duct you can get away with, even if the brakes don't get hot (like because you have to use stock bits). Air dams only are good for keeping air from going under the car and causing lift, and fighting the airflow out of the engine compartment, so rerouting flow to the sides shouldn't hurt anything. Downside being that then you might go faster and need bigger brakes!

Nascar seem to have this where they have the brakes figured out to the point that if all goes as planned, they are fine with ducts at speed but need fans to keep the brakes from frying when they slow down.

FRM

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Re: Are Brake Ducts Really Necessary? #11
dcharnet Donald Charnetski Grinnell, Iowa, USA 1963 MG MGB	Posted: April 13, 2012 06:27AM Registered: 2 years ago Posts: 945

In reply to # 2038758 by BritishV8 Of ten MGB vintage racecars featured on http://www.britishracecar.com/, only exactly one has brake ducts installed.

I had noted that, Curtis. The inquiry narrows: Is a valence duct without conduit to the rotor the worst of both worlds, incrementally speaking, in that it lets some disruptive air underneath but doesn't really benefit the rotor? Mere nose candy, as it were?

Tom's question is interesting too. These valences let so much air under that a few more holes won't hurt and might help.

And having ingested my share of boiled-fluid runoff-area weed (but I SWEAR, Skye, I never had the nose candy and am NOT promoting its use on this forum), I could argue that in the presence of ambiguity on the question the safer side of the line to be on is to feed air to the rotor with conduit.

An extension of that logic is to build a catch-can on the rotor. The conduit attaches to the can to better direct cooling air on the rotor. That's what we did on the BMW 2002.

Another option is to use the parking ligh holes above the valence and duct air to the rotor with hose using that opening.

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Re: Are Brake Ducts Really Necessary? #12
Speedracer Hap Waldrop Greenville, SC, USA 1967 MG MGB "The Biscuit"	Posted: April 13, 2012 06:37AM Registered: 7 years ago Posts: 20,312

In reply to # 2038758 by BritishV8 Of ten MGB vintage racecars featured on http://www.britishracecar.com/, only exactly one has brake ducts installed.

Actually the #9 Huffaker car has the same set up as Don's car, but we couldn't take advantage of it with SVRA rules, the headlight ducts had to be taped up. Even the Sebring valance w/o hose gets some cool air back towards the brakes. In my talks with Tony Jennes, I told him, his product needed to have brake duct connections like the Sebring valance to be competitive with that product, and advised him to add this to his design, if people don't want then, they simply not use them, but some might choose to buy the other product if his prodcut did not have this feature. Racing is monkey see, monkey do, if the fast guy in a MGB vintage race car tommorow has brake ducts, all the rest will soon follow.

Hap Waldrop
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Re: Are Brake Ducts Really Necessary? #13
Rick Starkweather Raleigh, NC, USA	Posted: April 13, 2012 08:01AM Registered: 8 years ago Posts: 697

FWIW, I lost out on a second place at Carolina Motorsports Park several years ago because I did not do a good job of taking care of my brakes -- and the car (an FP Midget) had both front and rear brake ducts. I know of other Production car racers who have suffered similar fates at VIR, etc. because they did not have ducts.

My MGB has the "plain deep front air dam" like Dave's SCCA car, and will have a single center duct for the oil cooler, which is mounted below the front valence rather than on top in front of the radiator. Then I'm going to duct air from the headlight holes to the front brakes. Here's a picture of the old air dam.

Rick

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Re: Are Brake Ducts Really Necessary? #14
skippymga Scott Brown Northern California, USA 1957 MG MGA "The Pile" 1957 MG MGA 1500 "The Pile" 1960 MG MGA "Boomer" 1964 MG MGB "#9" 1966 MG MGB GT "Boo" → more	Posted: April 13, 2012 08:41AM Registered: 7 years ago Posts: 1,865

Don -
It took us years (yea I know, too long) to sort our brakes out on out 2 MGAs. Reason, not many MGAs running at our lap times so we couldn't pull info from anybody. We tried all the best brands of pads and shoes and even had our rotors frozen. Your at a great advantage here with the wisdom on this forum and you should have great brakes first time out. How do you know if you need duct? After lap 5, your pedal begins to get softer and longer, by lap 7 you find your self pumping the pedal between corners, by the last lap your pumping 3 times to get any pedal at all, (and that happens to be your fastest lap of the session) thumbs up

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Re: Are Brake Ducts Really Necessary? #15
dcharnet Donald Charnetski Grinnell, Iowa, USA 1963 MG MGB	Posted: April 13, 2012 08:58AM Registered: 2 years ago Posts: 945

Rick, will this be a vintage car?

My original thought about Tony's nice duct was that his 3 inch diameter duct holes were too small, and that if there was to be a duct at all, I would be better off getting it with no holes, buying NACA ducts, cutting my own holes, and putting them in myself.

Hap's though was that 3 inches was enough if there was a brake hat to precisely direct the flow.

There is no doubt that a pair of NACA's would collect and flow more air.

Now I am not sure what to think.

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Re: Are Brake Ducts Really Necessary? #16
fast-MG.com Dave Headley Cortez, 4 corners, Colorado, USA	Posted: April 13, 2012 09:27AM Registered: 4 years ago Posts: 3,221

Unless Butch McK. has added ducts since he got the car from me, he is racing W/O and he mostly runs VIR. Hawk blue pads, semi metallic rear shoes and 600F brake fluid.

IMO, the ducts are a bunch of "clap-trap" not useful for an MGB.

I learned to save my brakes when I raced in show room stock.

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Re: Are Brake Ducts Really Necessary? #17
dcharnet Donald Charnetski Grinnell, Iowa, USA 1963 MG MGB	Posted: April 13, 2012 09:54AM Registered: 2 years ago Posts: 945

In reply to # 2038994 by fast-MG.com Unless Butch McK. has added ducts since he got the car from me, he is racing W/O and he mostly runs VIR. Hawk blue pads, semi metallic rear shoes and 600F brake fluid.

IMO, the ducts are a bunch of "clap-trap" not useful for an MGB.

I learned to save my brakes when I raced in show room stock.

Dave, please describe your techniques for saving brakes. I know for sure that it isn't "just drive slower."

Don

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Re: Are Brake Ducts Really Necessary? #18
fast-MG.com Dave Headley Cortez, 4 corners, Colorado, USA	Posted: April 13, 2012 10:08AM Registered: 4 years ago Posts: 3,221

Trail braking and float the car into the corner. The only time you need to really jump on the brakes is when attempting an "outbraking" pass manuever. The harder the brake application the more heat is driven into the pads. Heat does not dissipate well from the pads, better from the rotor.

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Re: Are Brake Ducts Really Necessary? #19
dcharnet Donald Charnetski Grinnell, Iowa, USA 1963 MG MGB	Posted: April 13, 2012 10:20AM Registered: 2 years ago Posts: 945

In reply to # 2039044 by fast-MG.com Trail braking and float the car into the corner. The only time you need to really jump on the brakes is when attempting an "outbraking" pass manuever. The harder the brake application the more heat is driven into the pads. Heat does not dissipate well from the pads, better from the rotor.

Thanks. Expand on "float" please. Is this "ease?"

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Re: Are Brake Ducts Really Necessary? #20
fast-MG.com Dave Headley Cortez, 4 corners, Colorado, USA	Posted: April 13, 2012 10:50AM Registered: 4 years ago Posts: 3,221

I don't know if I can adequately describe that in only a few words.

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