Autocross brake help!

[kassed33]

just started doing some autocross. I have a 95 240sx, Sr swap with 360whp, good tires(Michelin PS2), and 300zx calipers with Hawk pads and brembo drilled slotted rotors, Non ABS. Now my problem is there not enough, i'm locking up the front brakes when hard braking, and just sliding and not being able to make some turns when coming in with some good speed. So first question is will swaping the MC to a 300zx one give me improved braking to make a difference? I know it will give me better pedal feel but i dont care so much about that i'm looking for performance. Second if i end up going with a bigger front brake kit like 6 or 8 piston can the stock MC handle that much more over the stock 2 piston? And finally any suggestions on improving my set up for the track and welcome, but keep in mind i do also drive the car on the street, not every day i have an EVO for that but i do take it out when its nice. Thanks

[nissanman04]

If you are already locking up, there is no reason to get bigger brakes. The limiting factor is the tires. Get some stickier and/or wider tires. As far as sliding when you are trying to turn, you are most likely coming into the corner too fast. Braking while turning will just compound the issue. There is only so much grip available from your tires. If you are already using all the grip to try and turn the car, there is nothing left for braking. Hence, the understeer you are experiencing.

[killernoodle]

just started doing some autocross. I have a 95 240sx, Sr swap with 360whp, good tires(Michelin PS2), and 300zx calipers with Hawk pads and brembo drilled slotted rotors, Non ABS. Now my problem is there not enough, i'm locking up the front brakes when hard braking, and just sliding and not being able to make some turns when coming in with some good speed. So first question is will swaping the MC to a 300zx one give me improved braking to make a difference? I know it will give me better pedal feel but i dont care so much about that i'm looking for performance. Second if i end up going with a bigger front brake kit like 6 or 8 piston can the stock MC handle that much more over the stock 2 piston? And finally any suggestions on improving my set up for the track and welcome, but keep in mind i do also drive the car on the street, not every day i have an EVO for that but i do take it out when its nice. Thanks

Do a little math, the effective piston area of the 300zx calipers is:

4 * (pi * ((1.59 inches / 2)^2)) = 7.94 square inches

The 240sx caliper has an effective piston area of: 2 * pi * ((2.12 inches / 2)^2) = 7.06 square inches

Therefore, if your 7/8" master cylinder (piston area of pi * (((7 / 8) / 2)^2) = 0.60 square inches) is pressed with a force of 100 pounds, the pressure applied to the brakes is 166 PSI, resulting in the following clamping forces:

300zx: 1318 pounds240sx: 1171 pounds

Combine this with the fact the rotors are larger and your pads are probably more aggressive and you have quite a bit more braking torque.

With a 7/8" master cylinder too much brake pressure is created with too little effort and the effect of this on a larger brake piston area means you have lots of pedal travel with very little feel and an easy lock up. A 1 1/16" master cylinder will only exert 112 psi if 100 lbs is exerted on the cylinder. This would make the following brake pressure:

300zx: 889 pounds240sx: 791 pounds

You need a larger master cylinder to balance your pedal feel and effort with your larger piston area.

The number of pistons a brake caliper has means nothing without knowing their size. You have to size the pistons for a certain brake bias and master cylinder size.

IMO, more than 4 pistons on a caliper is pretty much opulent overkill. I'm putting wilwood forged superlites on my 240sx, piston size is still being worked out.
Modified by killernoodle at 10:15 PM 7/27/2009

[Cone Junky]

If you're locking up the front brakes, you certainly don't need more/bigger up front.

Either look into properly setting up the bias, upgrade the rears, or downgrade the fronts.Sometimes staggering pad compounds can compensate, but better for fine tuning.

Besides, with auto-x I have always run the smallest brakes I can find. How much fade can you generate in a 60 second run?

[tunerinms]

Front suspension to hard? I dont know first hand but it could be a problem. This is gonna sound bad but in project car mag they had a s13 coupe used for drifting and when they were setting everything up they adjusted the front coil overs too hard which made the brakes lock up. But ^ all of them sound like they have experienced this or just know so listen to them before u listen to me.

[liquid_cool]

Front suspension to hard? I dont know first hand but it could be a problem. This is gonna sound bad but in project car mag they had a s13 coupe used for drifting and when they were setting everything up they adjusted the front coil overs too hard which made the brakes lock up. But ^ all of them sound like they have experienced this or just know so listen to them before u listen to me.

that was a good issue of project mag..im shure it was the issue for (project Dorifto)...yes they were locking up the brakes easy due to the lack of suspention travell...they were so stiff they had many issue's with the tranzfer of wieght to the front for effective stopping force..

with that said; you might have not thought of this...but you may have reached your limit with this platform....only you can know this if you study it in your mind....if you started out with this car and you have improved to the point that you push the car more that its capable then its probly a good time to moove on to a new platform..

good luck,what ever you do.

[kassed33]

that was a good thought i wouldnt have thought of that. But that cant be it cuz i dont have coilovers, ive got Eibach sportlines and tokico blues.

[nissanman04]

with that said; you might have not thought of this...but you may have reached your limit with this platform....only you can know this if you study it in your mind....if you started out with this car and you have improved to the point that you push the car more that its capable then its probly a good time to moove on to a new platform..

Ummm...no. He just started autocrossing, there is no way he has reached the limit with the chassis. Locking up your brakes means that driving technique needs work. So with your logic, if he went out in a ZR1 and displayed massive understeer while braking and cornering, he would have reached the limit of that platform as well. I guess then it would be time to move up to a F1 car or something.

[liquid_cool]

Ummm...no. He just started autocrossing, there is no way he has reached the limit with the chassis. Locking up your brakes means that driving technique needs work. So with your logic, if he went out in a ZR1 and displayed massive understeer while braking and cornering, he would have reached the limit of that platform as well. I guess then it would be time to move up to a F1 car or something.

no guy..i just gave him food for thought,he may have just started autocross but he is no noobie to his platform...just becouse he has just started one form of racing dosent mean he has not raced with this platform elsewhere ..so the point still stands....in this form..he may have reached his limit...he did state thou..he does not have coils..so this may be a new setting for him when he gets coils to master.....eventually..he will reach the limit of the platform....it happens to everyone sooner or later.

[nissanman04]

no guy..i just gave him food for thought,he may have just started autocross but he is no noobie to his platform...just becouse he has just started one form of racing dosent mean he has not raced with this platform elsewhere ..so the point still stands....in this form..he may have reached his limit...he did state thou..he does not have coils..so this may be a new setting for him when he gets coils to master.....eventually..he will reach the limit of the platform....it happens to everyone sooner or later.

Whatever dude, you can always improve, no matter how good you are.

[maryjane]

nice info!

like stated above just ease on the pedal, if your locking them up then theres to much force there already, no more is needed, the z32 bmc will change your pedal feel as well