gunluvS14

Hey Guys,

My name is Philip and I'm sort of "new" here, but I've been reading the SC forums for few years now. I just seldom post, the only reason I joined is because my brother has a SC300 and I like the overall platform a lot. Well, I have a strong Nissan S-chassis background, and I do quite a bit of automotive related research when I was an undergrad in college. I wrote a few papers for ASME and attended quite a bit of SAE event, so you can call me a nerd I might say

Anyway, I would like to share some of the interesting information I've found about brake upgrade in particular SC300/400 (Jzz30) platform.

I bought a set of 95+ LS400 front brake for my brother as Christmas gift, before I made the purchase, I did some research on how bad of brake bias will screw up after throwing on the LS400 brake to the front and leave the stock SC300 rear on. Some folks suggested upgrade the rear to the LS400, some suggested changed the rear to Supra TT rear setup can bring the brake bias back to factory spec. So I went on and research on all the information about the SC300, SC400, 95+LS400, and Jza80 TT brake information, and the result is a big surprising.
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First thing first, I found all of these information from the Brembo website, FSM, and brakewarehouse website. If some of the dimension are off, please let me know because it might change the calculation a little bit.

Well, a lot of people upgrade their brakes to a bigger unit because they want shorter stopping distance; some just like the look of it; some claimed the new BBK reduce unsprung weight (in some case) etc.
So, does it really reduce the overall stopping distance? Yes and No, Maybe...

Myth #1: Simply throw on a bigger rotor, more pistons per brake caliper can make you stop faster!

Answer: I hope you knew the tires are what's actually stopping your vehicle, not your brakes. More brake torque doesn't necessary mean shorter stopping distance. If you over power the adhesion limit of your tires(lock up, or constant ABS pulse engagement), chances are you are not stopping any faster or with shorter distance. So you can have a monster brakes system but riding on cheap Made in China chicken tires won't help you that much.
I'm sure we all acknowledged that fact, so there's no point to go on with the tire friction crap topic; lets focus on the brakes tonight.

So let say maybe you have a fading problem with your brakes, even with good performance pads and high quality brake fluid won't solve the brake fade problem, you just need a bigger brake rotor to have higher heat resistance. Or, you maybe looking for more clamping force with a bigger brake caliper.

Myth#2: More piston(s) per caliper means more clamping force and yield higher stopping power.
Answer: A lot of folks over look the point of having multiple pistons brake caliper. More doesn't necessary means better, it is all about the total overall piston surface area. So more doesn't always mean better. More caliper pistons across the pad can definitely improve the distribution of force loading;multiple pistons caliper can take advantage of the design and use multiple pads(4-6 pads per caliper) to increase initial bite and overall feel/feedback. If there are more # of piston but the overall pistons surface area is less than stock, that's NOT an upgrade at all in term of clamping force.





After some thought from Myth #2, which bring forth tonight's topic.
#1 - LS400 4pot brakes might NOT be a upgrade for SC400 owners
#2 - LS400 4pot front mate with stock SC300 rear might not be as bad as you thought
#3 - For SC300 owners, after Supra-TT or LS400 4pot brake upgrade, adding Supra-TT rear or LS400 rear might NOT help the brake bias at all

I will demonstrate the braking power(brake torque) and brake bias (Front brake torque vs rear brake torque) by doing a simple calculation.
From fundamental physics, Work=Force x Distance, TORQUE is one type of work, so more clamping force per caliper, with bigger rotor (leverage/distance) yield MORE brake torque.
Pressure=Force/Area. If the pressure (brake line pressure) is constant, Constant*MORE area = More Force. So, the more total pistons area, the more clamping force.

Before I begin, I have to make a few assumptions: Front and Rear brake line pressure are assumed to be equal; Front and Rear brake pad drag coefficients are assumed to be the same. The caliper piston area was calculated by taking the square of the piston diameter instead of taking pi and radius into account to keep the calculation simple. As long as the front and rear brake torques were calculated with the same method, units (Pi, and radius) will cancel each other out at the end.
Also, 2 pistons slider caliper behave like a 4 piston fixed caliper, when those 2 pistons push forward, there's an equal pulling force on the otherside to create a "squeeze", therefore 1 piston slider caliper has the same clamping power as a 2 piston fix caliper with equal piston size.

BENCHMARK:
SC300 Stock
Front:
275mm dia. rotor
28 mm thick
Pad width - 51mm (width of the pad radially from the brake hub center)
Pistons - 2
Piston diameter - 44.5mm

Rear:
291mm dia. rotor
16 mm thick
Pad width - 36mm
Piston(s) - 1
Piston diameter - 42.7mm

I'll convert the dimension to English units
Front Total piston area = (1.75"^2+1.75"^2)*2
Front Effective Rotor Radius is:
the Radius minus brake pad width = (10.83"/2)-2.01"
Front brake torque= 12.25*3.405 = 41.71

Rear Total Piston Area = (1.68"^2)*2
Rear Eff. Rotor Radius - (11.46"/2)-1.42"
Rear brake torque= 5.64*4.31 = 24.31

STOCK SC300 Brake Bias = 63.18% front, 36.82% rear
--------------

SC400 stock
Front:
Rotor Diameter - 11.65"
Pad width - 2.36"
Pistons - 2
#1 Piston diameter - 1.75"
#2 Piston Diameter - 1.75"

Rear:
Rotor Diameter - 12.09"
Pad width - 1.38"
Piston - 1
#1 Piston Diameter - 1.68"

Front Brake Torque=
[(1.75"^2+1.75^2)*2]*(11.65"/2-2.36")
=42.45
Rear Brake Torque=
[(1.68^2)*2]*(12.09"/2-1.38")
=26.33
STOCK SC400 brake Bias = 61.72% front, 38.28% rear.
--------------------------

SC300 with LS400 front, SC300 rear

LS400 front:
12.40" dia. rotor
#1 piston - 1.68" diameter
#2 piston - 1.68" diameter
Pad Width - 2.44"
Front Brake Torque = 42.45

LS400 front Mate with SC300 rear,
Brake Bias = 63.56% front, 36.44% rear.

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SC400 with LS400 front, SC400 rear

LS400 front:
12.40" dia. rotor
#1 piston - 1.68" diameter
#2 piston - 1.68" diameter
Pad Width - 2.44"
Front Brake Torque = 42.45

LS400 front mate with SC400 rear,
Brake Bias = 61.71% front, 38.29% rear.
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So, technically, SC300 that use LS400 front with stock SC300 won't throw off the brake bias that bad; and SC400 owners that use LS400 front isn't really an upgrade in term on brake torque. If I have a SC400, I would keep the SC400 front brake, since the LS400 front only gives 19mm gain in term of rotor size, but the thickness actually decreased from 32mm down to 28mm. On paper, the overall front brake torque of SC400 front is bigger than LS400 front. So, LS400 front brake isn't really an upgrade for SC400 guys. And for SC300 guys, with the LS400 front setup won't really throw off the brake bias that much, (63.18%front vs. 63.56% front).

Some SC300 folks had the LS400 front and then also upgrade the rear to the LS400, which will make the brake bias even worst than stock; with the LS400 front, and LS400 rear, the brake bias would become 64.07% front, and 35.93% rear.

Here are the break down:

SC300 stock = 63.18%front, 36.82% rear.
SC400 stock = 61.73%front, 38.27% rear.
LS400 front with SC300 rear = 63.56%front, 36.44%rear.
LS400 front with SC400 rear = 61.71%front, 38.29% rear.
Supra front with Supra rear = 66.08%front, 33.92% rear.
LS400 front with Supra Rear = 65.05%front, 34.95 rear.
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To sum it up, if you have an LS400 front upgrade on your SC300, either keep the rear SC300 stock; upgrade the rear to Supra-TT rear or go with SC400 rear.
If you have a SC400, you may upgrade the front to Supra-TT, don't do the LS400 since it is a "downgrade", OR, just leave the entire brake system alone, upgrade your brake pads, brake fluid, and brake line.

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I hope you enjoyed these rambling, and please excuse my bad grammar, I just got back from Wild Wing and I'm pretty trashed. Please feel free to chime in and share your thought, and once I sober up, I will be more than happy to have a full discussion with you guys.

Have a good night.



All you need is 3mm of clearance to fit the LS400 front onto the SC300, a wahser can do it all


Bling Bling

Blizzy

iTrader: (-1)

From my experience:
- The stock braking system would neither stop authoritatively nor resist fade well, especially while I was on 19s
- A test run both before and after installation of just the LS400 brakes up front was shocking in that I felt like I was hitting a brick wall with the LS400 brakes installed in comparison to stock brakes.
- After performing the TT rear swap and upgrading to EBC pads in the front, I have successfuly braked hard enough on two occassions to jolt the shifter into Neutral from Drive. I challenge anyone on stock brakes to accomplish this.

I am not doubting the science of the situation:
- I completely agree that the friction between the road and the tire is what ultimately stops the car, but if your tires are capable of handling more frictional load and your brakes are not supplying it, an upgrade in braking will yield positive results.
- I also concur that piston surface area is a significant factor for determining brake performance. Try stopping a book falling to the ground off the shelf with a single finger, and then try again with a full hand.

Nevertheless, I believe there has to be some other factors at play here as personal experience has led me to believe rather strongly that the LS400 brakes are significantly stronger. If the SC400 stock brakes were an upgrade over the LS400 brakes, why would Toyota have put the four pot brakes on the LS400 from 95-00? Between 90-94, the LS400 had the identical braking system to the SC400. I have to assume that the four pot brakes on the 95+ LS400 were significantly better than the previous two pots or else the additional cost for design and construction of the calipers would not have been incurred by Toyota to put out an inferior product to what was already in production.

JesLet

iTrader: (19)

Is that polished? Nice LS caliper man

gunluvS14

I wouldn't exactly say SC400 is an "upgrade" over LS400 brakes, but on paper, apple to apple, same pad, same condition, SC400 front 2pot brakes put down more brake torque than LS400.

To answer your question why Toyota/Lexus switch to 4pot unit after 1995, in my opinion, a science and manufacturing point of view, the best benefit is WEIGHT SAVING. The 2pot unit is cast iron, 4pot unit is cast aluminum.
You would shave off a good amount of dead unsprung weight.
2nd - aluminum stock is always cheaper than steel in the industry. At the foundry, casting aluminum is so much cheaper than steel, because Steel melting point is almost 3 times higher than the melting point of Aluminum. It takes so much more energy just to cast steel. Recycling aluminum is way easier than steel also.
3rd - in term of manufacturing, machine tool life last so much longer and machine time is much shorter to machine aluminum. In the big picture, the company can save money on aluminum stock, casting process, and machine process.
4th - Marketing. When Toyota/Lexus try to compete against BMW, Infiniti, Audi etc. in the same class. They better have the hardware line up and attract the general consumers. A lot of folks think more is better, bigger is better.

My 2 cents

ConSynX

iTrader: (1)

...cooling

and torque arm for estimation purposes would be minus half the pad width.

i also don't have access to my material's program right now, but i was under the assumption that aluminum would be more expensive.
not in general, but when comparing the types.
any cast iron ferrous compound versus a high quality aluminum capable of handling the temperatures and loads seen. I could be wrong though.
definately agree on the machinability of it though.

LCSC

iTrader: (4)

I think anyone would agree that your tires need traction to stop a car. that being said it does not take much torque to break the tires loose when stopping around town. But with 19's at really anything over 70 mph in my 95 sc300 with new pads, it was not good and at over 100 it was just not there. The first time I tried to stop at 120 in my car I would say it was scary because my brakes were just not there (my old sc400 did OK but not good). Now that I have TT front brakes I have no trouble stopping at any speed. It is a hough improvement over stock. Around town there is little change because any brakes can get the job done at slow speeds. TT brakes work great at the track too.

2 cents

StiCk3

iTrader: (5)

sorry if im hacking a bit, but this writeup reminded me of a similar article in Sport Compact Car a few months back. they did some brake testing on project RSX and used all the same calculations as well as some real world tests. Here is the article:

http://www.sportcompactcarweb.com/te...ech/index.html

ConSynX

iTrader: (1)

^^^
same as i thought as i have that magazine due to my little sister needing subscriptions and that being the only car mag

aliga

iTrader: (147)

if its not an upgrade, why did you/brother upgrade??

gunluvS14

ahhhhhh, if you read the thread, I said the LS400 front isn't an upgrade for SC400 in pure math. My brother has a SC300, it gives him a slight increase of front brake torque and shave off a few pound of unsprung weight.

Beside, me and my brother are tight, I like to buy him stuff whenever I want to

TheMole

iTrader: (13)

Can you breakdown how you calculated the front brake torque for the ls400 brakes like how you showed for the stock sc3/400? Just curious as you only listed 2 piston measurements of the 4 pistons on the ls400. Looks like good stuff here.

greyBLITZ

iTrader: (2)

Which years for the SC400 and LS400 are we talking about? I believe both have received larger brake upgrades over the years as well.

I think my '94 SC4 has much smaller brakes than my dads '99 LS400, much more than 19mm difference.

gunluvS14

Yes sure, in fact I will post a pretty handy spreadsheet that I made later on, I just need to find a host. Its a sweet spreadsheet, just pretty much input the known input and result dump right out.

To answer your question why I multiplied the 95+ LS400 caliper pistons number by TWO instead of 4 is just how the equation works.
Remember, for 2pot slider caliper, it provides the same amount of force on the other side of the disc, not just from the pistons side. (Newton's 3rd law). So if the 2pot slider caliper has the same pistons area coverage as a fixed 4pot caliper, they will have the same amount of clamping force

So if I included all 4 pistons area in the calculation, it will come out as a 8 pistons caliper.

Let me find a place to host that file, its a pretty niffy spreadsheet

SCoupe

I am far from an expert... but isn't there a more than offsetting increase in rotating mass resulting from the larger, heavier LS rotor? (note your pix). Rotating mass has substantially more impact than unsprung weight correct....


lol, proper recognition for writing while under the infuence. I couldn't come close to this with a fresh cup of coffee and a full nights sleep.

gunluvS14

Well, you are right,
New setup - 23lbs rotor + 9lbs caliper = 32lbs per corner


Old setup - 16lbs rotor + 17lbs caliper = 33lbs per corner


So I think we still come out on top

About posting under influenced, my apology. Doing calculation and engineering is a 2nd nature to me. I do that for living.