gs4power

Regarding the spare, a relatively cheap and simple solution is a wheel spacer , for those who have the stock 17" spare.

Manaray

Miguel - Great point about brake upgrade vs. SuperCharger...

I agree with you, I think my GS430 is fast enough and I would much rather have a brake upgrade first...then again, I don't really have a choice, I don't think ANYONE has a SuperCharger for the GS430 yet...

$2600-$2700 For Brembos...hmmm, why did I think they were in the low $2K? Is that Steve's price?

Y2KGS4

Miguel,

I won't totally disagree with you; fade resistance and endurance are not the best. However, the stock brakes on almost every car are far better at deceleration than the engine is at acceleration. Look at any 0-100-0 test and you will notice a trend for the majority: Acceleration to 100 mph takes about 70% of the total 0-100-0 time. Deceleration only takes 30% of the total. In simplest terms, the brakes are 2.3 times stronger than the engine.

For a real world test, start your car. Put your foot on the brake. Now floor the accelerator. Didn't go anywhere did you?

For a backup test, at 55mph start applying brake and accelerator until both are fully depressed. You stopped quick didn't you?



Mitch

gs4power

Hi Mitch.

Interesting discussion. Due to some thermodynamical restrictions, braking power will always outperform the acceleration power of a car's engine: everything from a Mc Laren F1 to an ice cream truck will fall into these laws.

In theory, you can convert all kinetic energy into heat, BUT NOT THE OTHER WAY AROUND! That means, brakes can be 100% efficient in transforming the kinetic energy of a moving car into heat. On the contrary, only about 30% of the thermal energy from the motor's combustion cycle can be transformed into work. And after that, you must add all the drivetrain and aerodinamic losses. Thus, even the most mediocre brakes from a Yugo will "outperform" a V12 engine!. Comparing braking to acceleration is not a fair comparison, brakes will always win!

BUT all this is true ASSUMING THERE'S NO TEMPERATURE LIMIT FOR THE BRAKES! In other words, this applies for BRAKES THAT ARE NOT FADING! Once their temperature raises to a certain level you could get longer 100-0 MPH than 0-100 MPH distances!! Limiting factors are: materials failure, fluid boiling and frictional properties.

Bottom line, braking performance depends on the heat rejection capacity of the brake system: Huge discs will always reject heat better and have more consistent performance.

Y2KGS4

Miguel,

All sounds about right. Brakes won't be 100% efficient due to the limitations of friction coefficient between tires and road, but close enough for government work.

Bigger rotors don't have that much more advantage over smaller ones when it comes to dumping heat. Comparing a 12" to a 14" rotor, there just isn't that much more thermal mass in the 14 incher. Then you get vented rotors and they help some. We already went into cross drilling before; that's done only for weight as it actually hurts cooling capability.

That's why any serious track vehicle has some sort of brake cooling aid whether it be vents or scoops or tubes or whatever. Adding in convective cooling is much more effective than conduction and radiation alone.

Then you get into material selection like carbon fiber and the price sky rockets.

Bottom line: We can joust on the engineering all day. I'm a mechanical engineer and understand most of the theory. Big brakes are really nice. They do help you out especially if you plan to torture your brakes. They are not on my wish list above the supercharger. Even with 100 more HP from the sueprcharger, my stock brakes are more than a match for the engine.

gs4power

Hey Mitch, nice to know I have a colleage in the club! I’m also a mechanical engineer. BTW, I’ll be flying over to UC Berkeley for a doctoral degree, starting this Fall!

Hey, don’t take it as a joust, I really enjoy sharing engineering thoughts!!

Cross drilling isn’t done only for weight reduction. It has important advantages at high operating temperatures. The extreme pressure and temperature conditions on the pad – rotor interface will promote chemical reactions on the pad compound, and some of the byproducts are gaseous. Drilled brakes allow proper out-gasing of these products, thus preventing trapped gases to form a layer on the interface. This layer can act as a gaseous lubricant, reducing friction and brake performance.

About the thermal mass: It’s more important the rate at which the brake can reject heat to its surroundings (initially by conduction, ultimately by convection) than its thermal mass. Heavier brakes are definitely not better rejecting heat than lighter ones. (the brembos are considerably lighter than stock) We both agree that the heat is rejected mostly by convection, so surface area and convective enhancing features like the drilling, curved vain vents, etc are more important than mass. Cross drilling will enhance convection, improving cooling capability.

Hey, I hope Muhammad will release his supercharger soon!

Y2KGS4

Miguel,

Your concerns with outgassing from hot pads are a bit dated. The old organic compounds did emit fade inducing gases during extreme use conditions (racing), but modern pads for the most part do not. And again, cross drilling has historically been done for savings in unsprung weight, not cooling or degassing. Slotting is probably the better choice to dump gases if that's really a concern. We haven't even broached the stress riser problems caused by cross drilling. Or the decrease in thermal mass. Or the decrease in swept area.

But even after having said all that, I would still love to have these brakes because they look so nice. And I'm looking forward to seeing pictures of them on your car. Or maybe in person; I have some "need to visit" relatives about 40 minutes from there in Blackhawk. I'll be there in late September for sure.

And yes, come on supercharger!

Mitch

gs4power

Hi Mitch,

Good argument on the pads! Even though newer pads do emit gases to some extent, you’re right: the conditions need to be pretty severe.

For those concerned with the stress concentration, I had some discussion with Brembo some time ago about the reliability of their discs. Fortunately they take some effective measures AND stand behind their name:

-The discs aren’t drilled, the holes are actually cast-in and chamfered. They are also heat treated, blanchard ground and stress relieved. This method reduces the possibility of crack nucleation.

-High strenght cast iron is used (cast iron tends to be fragile, but they make it more ductile by means of alloying and heat treatment).

-The modular construction of the discs allow them to expand and contract freely over the hat, so thermal stress is greatly reduced. Even with the cross drilling, stresses will be much lower than on single piece discs.

I’ll post the pics fore sure!! Sorry, I’m not taking the car for school

Y2KGS4

Miguel,

Good info on the Brembo manufacturing methods. No wonder they are so expensive. But, if my company built something like that it would cost 10x more.

Cast iron is very popular in the realm of high performance sport bikes; excellent frictional properties.

Hey, I have no idea what you're specializing in with the PhD, but automobile braking would be a good in-depth project. You could probably sneak it into just about any curriculum: heat transfer, vibrations, dynamics, FEA, materials science, etc, etc. It's been a long time since I was in school, but I always tried to make things more car related.

Mitch

gs4power

Hi again Mitch,

Yeah, brake design is a very broad (an interesting) area, many disciplines are involved, maybe I can do research on that. Most likely I’ll be majoring in Controls, focusing my research on vehicles/transportation . Controls is a strong area at Berkeley, involved in good part with the auto industry. For instance, the PATH project (Partners for Advanced Transit and Highways) is centered there. There’s also the VDL (Vehicle dynamics lab), currently working on advanced supensions and cruise control systems.

Although not intended for transportation, take a look at the smallest rotary engine in the world , (about the size of a dime) created at the Combustion Lab, very interesing stuff. Check it out at

http://www.berkeley.edu/news/media/r.../02_engin.html

or also at

www.me.berkeley.edu They’re now working in an even smaller one, to be used in electronic applications.