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

Re: Are Brake Ducts Really Necessary? #21
TomBrooksuk Tom Brooks Leicester, Leicestershire, United Kingdom 1967 MG MGB GT	Posted: April 13, 2012 11:31AM Registered: 2 years ago Posts: 620

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

Lol Dave that are me smile, I'm sure you are right especially in the tropical UK climate smiling smiley

In terms of front valances my idea is as follows we have the Sebring style valance with 4 large cut outs and moulded brake ducts that since they are present we may as well use. My biggest concern with this valance is front end lift and nothing to do with cooling. Therefore I'm planning on making up a front air dam similar to the pics of Daves SCCA car and comparing the two during one of the test days. The air dam version will have no cut outs or ducts at all.

I will let you all know the results.

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Re: Are Brake Ducts Really Necessary? #22
Steve64B Steve Opitz Phoenix, AZ, USA 1966 MG MGB	Posted: April 13, 2012 12:07PM Registered: 6 years ago Posts: 8,487

Don... the message seems to be: Thermal management is important; it's just a question of how you achieve it.

Driving technique is critical, but if you never master "floating" then having another (more mechanical) means of thermal control... might be important.

I would think that Tony's front valance... without any holes in it would provide an aero advantage over either the stock or Sebring valance. Keeping air out from under the car reduces drag and neutralizes lift… punching holes in it would be trading away that advantage.

I thought Keith Burnett did an interesting solution to ducting heat away from his oil coolers.

http://www.britishracecar.com/KeithBurnett-MG-MGBGTV8.htm

Since the grill is a major contributor to drag at the front of the car, if you can manage the flow by evacuating it to cool the brakes… it’s a twofer… less drag and lift and cooler brakes.

Using something similar to these ducting bosses it would be easy to fabricate a pickup from a high pressure area and attach the other boss to a modified backing plate to direct the airflow to the brake disk.

http://www.compbrake.com/brake-kits/brake-ducting/brake-duct-tube-boss.html

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Re: Are Brake Ducts Really Necessary? #23
Gofanu Fletcher Millmore Titusville PA, USA	Posted: April 13, 2012 05:48PM Registered: 6 years ago Posts: 618

Air in front of the car creates high pressure, which is relieved by said air going over, under, or around the car. MGB sucks for over, because of the grille/bonnet profile. Most of it should go around, but any high pressure tends to go under, not so good. Any holes in the valence/dam let high pressure under the car, unless they are ducted to the wheel wells.
May as well cool the brakes with it as it goes past. Solid discs want distribution deflectors to cool the outside of the discs to match the inside. I assume this is what everybody means by "cans", but I might be wrong.

NACA ducts are meant to suck air off panels with smooth airflow over them; the design effectively punctures the "dead" boundary layer to get real air, without causing excess drag.
There is no point in using NACA ducts when you have way too much straight perpendicular high pressure all over the front of the car. Any reduction in the normal high pressure via diversion will reduce the amount of air driven under the car. It makes more sense to pull the high pressure in the center half of the valence than to pull it from ex parking/headlamp holes. and it's easier to duct without big restrictions and turns. Possibly the best way to get this air would be to use a wide narrow slot, with as much lip as you can do at the bottom edge of the valance into an airbox ducted to the brakes, subject to rules. That would catch the air that is running down the valance face to get under the car. Small diameter convoluted hoses are poor airflow devices; aero counts on the inside as well as the outside.

FRM

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Re: Are Brake Ducts Really Necessary? #24
dcharnet Donald Charnetski Grinnell, Iowa, USA 1963 MG MGB	Posted: April 13, 2012 11:02PM Registered: 2 years ago Posts: 950

Instructive observations, Steve and Fletcher, much food for thought, thanks. Need to ponder.

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Re: Are Brake Ducts Really Necessary? #25
Gofanu Fletcher Millmore Titusville PA, USA	Posted: April 14, 2012 03:43AM Registered: 6 years ago Posts: 618

Don-
Throw these in, from Paul van Valkenburgh's "Race car Engineering & Mechanics"

"...on sports cars with headlights, the highest pressure area is usually the undernose spoiler lip. The greatest difficulty is getting large duct hoses - the bigger the better -from the nose to the disc, with all the suspension hardware in the way. Although smooth fabricated aluminum or fiberglass ducts are the most efficient, wire reinforced flexible hose (such as 4 inch dryer ducts) passes a lot of air and yet will get out of the way if the wheel contacts it. Front spoilers prevent a lot of useful air from reaching the front discs, but as a last resort, what air does pass under the nose can be directed toward the discs by canvas shields fastened to the suspension arms."

"A reasonable estimate for high powered race cars on road courses, however, is that a 1 percent increase in downforce is more valuable than a 10 percent decrease in air drag. For example, reducing drag from 280 lb to 250 lb is less important than increasing wing forces from a total of 280 lb to 285 lb at 100 miles an hour."

While an MGB might not qualify as quite a "high powered" car, you can see why air under, aka lift = negative downforce, is evil. 5 lb net force is a vanishingly small psi under the whole car!
Consider what is going on with a stock valence as all the air from the bumper line down is being forced under a car with 3 inches ground clearance in race trim. After I read about the Cobras getting airborne at high speed, I got very aware of what my AC's felt like when going fast, and then started looking at and thinking about other cars with nice rounded front valances. Even stock MGB with plenty of ground clearance start to feel flighty at speed. I was once going about 70 in my AC Ace through a road cut when a big gust of wind in front of a thunderstorm came the other way; assuming the wind was about the same speed, my airspeed was 140, and it picked the car up about 4 feet and moved it over one lane, fortunately nothing coming!

FRM

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Re: Are Brake Ducts Really Necessary? #26
dcharnet Donald Charnetski Grinnell, Iowa, USA 1963 MG MGB	Posted: April 14, 2012 06:37AM Registered: 2 years ago Posts: 950

Now we are getting somewhere, Fletcher. And, to state the obvious, this is as much a safety issue as almost anything, in that negative downforce at high speed and of course boiled brake fluid can have serious consequences.

Safety alone would seem to dictate a more aggressive dam-shape with a small perpendicular lip at the bottom to prevent air from moving down the face and rolling under. It would be relatively easy to fabricate such a dam from a piece of aluminum or light steel with no compound curves requiring an English wheel. Based on your earlier comments, a narrow opening could be created in the center towards the bottom to let air in. The air could be captured in a box and then be directed by 3 inch hose to brake hats which distribute the air on both sides of the rotor. I presume that this would remove all or most negative downforce from whatever volume of air entered the opening. Net result, less negative downforce, safer brakes. Nothing new here relative to current SCCA practice.

What is it in the prep rules that prevents us from doing this? Why do we have to use the poorly-designed valence shape? If the standard requires prep to SCCA GCR's through '72, was the valence the only thing used back then? And even if it was the only thing used in that period of relative ignorance about aerodynamics, would what I propose not have been permitted? Would Jim Hall not have been allowed by SCCA to put this on a '63 D Prod MGB? The answer to this is probably very obvious, but I need to ask. Anyone?

Edited 1 time(s). Last edit at 04/14/2012 06:39AM by dcharnet.

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Re: Are Brake Ducts Really Necessary? #27
TomBrooksuk Tom Brooks Leicester, Leicestershire, United Kingdom 1967 MG MGB GT	Posted: April 14, 2012 07:04AM Registered: 2 years ago Posts: 620

Don, on an MGB with no other aerodynamic aids e.g. Flat floor, diffuser probably the best design for a air dam would be as you describe a more or less flat face going from under the grill to as close to the floor as possible stretching as far around the corners of the front as you can go. In a perfect world the face of the air dam would curve outwards slightly towards the bottom and end in a horizontal splitter, the outwards curve would help channel the air down and out along the sides of the car, the splitter would continue along the corners of the valance and the tips would arc upwards slightly, this would prevent the channelled air from the front of the car from being dragged into the next low pressure area which would be under the car just past the front wheels.

As you say the best place for an air intake to the brakes would be right at the very front of the valance where most of the stalled air sits and is also the area of maximal air resistance. Taking the air from here would have minimal effect on the aerodynamics and infact you could argue that since you are not really utilising the channelled air off the valance, using it for another reason e.g. Brake cooling could only be beneficial.

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Re: Are Brake Ducts Really Necessary? #28
hoffman900 Bob Adams South Jersey, USA 1978 Yamaha MC TT500 "Flat Tracker" 1990 Mazda Miata NA	Posted: April 14, 2012 07:18AM Registered: 4 years ago Posts: 417

Don,

Scroll down to 'Body and Coachwork'
http://svra.com/SVRA/SVRAHome.nsf/attachmentweb/EJEN-5ZGG5K/$file/Group+3+Regulations.pdf?OpenElement
http://svra.com/SVRA/SVRAHome.nsf/attachmentweb/EJEN-67XNGC/$file/MGB.pdf?OpenElement

Looks like an airdam of any sort will get you bumped to 'Group 8'. That's home to 300+hp 240Z's and 914-6s.

Edited 2 time(s). Last edit at 04/14/2012 07:20AM by hoffman900.

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Re: Are Brake Ducts Really Necessary? #29
Speedracer Hap Waldrop Greenville, SC, USA 1967 MG MGB "The Biscuit"	Posted: April 14, 2012 07:19AM Registered: 7 years ago Posts: 20,606

Don, yes bascily we're not allowed air dams like the modern SCCA prod class rules. On Tony's new valance that's why it was important for me to explain to him, that we could not use the lip spoiler, even though we'd would love to, it doesn't meet vintage rules. FWIW, I know for sure a air dam could improve our straight line speed, and keep air from getting under th car, but I never notice a big difference in lap time or speed with, or with w/o a air dam, I ran SCCA Spridgets before with and without air dams,and it seemed to make little to no difference.

Hap Waldrop
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Re: Are Brake Ducts Really Necessary? #30
fast-MG.com Dave Headley Cortez, 4 corners, Colorado, USA	Posted: April 14, 2012 08:51AM Registered: 4 years ago Posts: 3,326

Don, if you really want to race with a ground scraping spoiler with splitter, I'll build you a kick-ass SCCA car. Just bring your check book! devil smiley

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Re: Are Brake Ducts Really Necessary? #31
dcharnet Donald Charnetski Grinnell, Iowa, USA 1963 MG MGB	Posted: April 14, 2012 09:46AM Registered: 2 years ago Posts: 950

In reply to # 2039903 by fast-MG.com Don, if you really want to race with a ground scraping spoiler with splitter, I'll build you a kick-ass SCCA car. Just bring your check book! devil smiley

Dave, jeeze, I left my check book there with you when you completed the last round of work! Now you want my other one???

If I wanted that mega-spoiler, you'd be da man. Even the simple lug nut you just sent me has the sheen and substance of Bauhaus design.

I need to figure out what I want, first. I like your idea of no ducts, but suspect that such an approach is viable only with a pretty high level of brake-preservation management. After a year on the sidelines and being new to the car, I will be happy to keep it right side up, running, and pointed in the right direction. I am looking at the latitude available on traditional valence design and have an inquiry out to VSCDA, again--boy, will they be on the lookout for me--so I will see what they say. I will probably end up fiddling within a small parameter, dancing on the head of the pin.

Edited 1 time(s). Last edit at 04/14/2012 09:49AM by dcharnet.

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Re: Are Brake Ducts Really Necessary? #32
skippymga Scott Brown , Northern California, USA 1957 MG MGA "The Pile" ~ For Sale ! ~ 1957 MG MGA 1500 "The Pile" 1960 MG MGA "Boomer" 1964 MG MGB "#9" 1966 MG MGB GT "Boo" → more	Posted: April 14, 2012 11:20AM Registered: 7 years ago Posts: 1,891

Don - This is all you really need. Its a proper piece that will keep the car looking correct and supply you with the needed air supply.
Original British Leyland MGB vented front valance

This is the same piece I just purchased for my GT build.

http://www.ebay.com/itm/Original-British-Leyland-MGB-MGB-GT-MGC-MGC-GT-vented-front-valance-HZA592-new-/230768455863?pt=Vintage_Car_Truck_Parts_Accessories&hash=item35badf30b7&vxp=mtr#ht_985wt_1398

Edited 1 time(s). Last edit at 04/14/2012 11:21AM by skippymga.

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Re: Are Brake Ducts Really Necessary? #33
Speedracer Hap Waldrop Greenville, SC, USA 1967 MG MGB "The Biscuit"	Posted: April 14, 2012 11:36AM Registered: 7 years ago Posts: 20,606

Scott, Don is getting a Tony Jennes front fiberglass valance, same as me, it will be flush mount and contured to the front of the MGB, so it fits properly, Tony is going leave the center opening up to the customer, and we're working right now on the brake ducts, that the only hold up on finishing them, Tony not sure where to locate the brake duct holes, so he may send the prototype to me and let me locate the ducts on a couple of them and send one back to him, so he can properly locate them from then on out, and I think he may also offer then with no ducts, r opening for customizing if that is desired. It will be pretty stock appearing, but made better and better fitting,and mpore duarlbe than the steel piece. The whole idea is fibergalss front valance, thats hold it shape and contours to the to the front of the MGB, so it can be mount in manner for easy removal, so you can take it off for alignment and trailer loading purposes fairly easy. The idea was for me to debut the product at the Mitty, but we're running out of time, but it should be ready soon after the Mitty for sure.

Hap Waldrop
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Re: Are Brake Ducts Really Necessary? #34
Steve64B Steve Opitz Phoenix, AZ, USA 1966 MG MGB	Posted: April 14, 2012 11:48AM Registered: 6 years ago Posts: 8,487

There really are two topics here that have become intertwined... The aero effects of the front valance and thermal management of the brakes.

There are different front valances from the early BMC with no venting, the later vented valance in Scotts post, the AL valance that Targett sells and the valance Tony is offering.

Strictly from an aero stand point the preferred version would be the tallest valance with the fewest or smallest openings. My understanding is that the Targett valance is "deeper" than the stock valance, but "deeper" isn't quantified. Both the Targett and Tonys valances are flush mounting ( which would be preferable) and openings can be closed.

Bob Adams link to the SVRA rule indicates that the turn signal openings could be tapped to cool the brakes. From a thermal management perspective how much airflow is required? If your comparing no cooling, to optimal... Where would this be on that range?

My guess is that it's all less than 1% kinda stuff, but find 3 or 4 of them and it might make a difference.

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