Base S550 brake upgrade ABS programming

[navseng]

TL;DR: Master cylinder piston area to caliper piston area controls pedal effort, height and feel. If we keep all else the same, though, it doesn't influence actual braking capacity or bias.
--------------------------------------------------------------------------------------------------------------------------

Let's look at these two master cylinders, 23.5mm vs 22.0mm:

That's a 14% difference on the master cylinder piston area, which means a 14% difference in braking force for a given pedal pressure. It also means a greater force change with your foot on the pedal to modulate.

• Pedal pressure for a given amount of braking would be 14% higher for the 23.5mm master than the 22mm one.
• Pedal *travel* will be longer with the smaller master. As long as nothing gets into a bad situation geometrically or with respect to travel (i.e. it doesn't bottom out or put the pedal in an over center position), it will not affect performance.
• Larger MC's (with greater effort) generally get better comments concerning modulation
• Larger MC's will have a higher and firmer pedal
• If the master is too large, then the driver might struggle to reach an appropriate peak pressure or may just have to use too much muscle to effectively drive.
• A standard automotive master (as opposed to dual masters on a race car) doesn't change F/R bias.
• The ABS controller regulates proportioning/brake bias.
• The brake booster has a big effect on pedal feel, but it doesn't sound like anyone is changing boosters.
• The staggered piston sizing of the Shelby is to reduce taper wear on the pad. Not having it on the PP brakes is just an insult. Calipers with staggered pistons are no different cost than with uniform piston sizes. It's just an effort to give the Shelby a talking point by tanking the PP.
• Pad compounds can have a much bigger effect on max pedal pressure and modulation than MC sizing.
• A big problem when testing master cylinders is getting an effective bleed. It's damned tough to beat the factory bleed, so don't crack the lines unless you have to. If you changed a master cylinder and found bias or performance differences, then it may very well be a bad bleed as opposed to a problem with the master sizing.

Has anyone ever cracked open a PP master? I took apart my stock one and it has two pistons in it , and a little floating divider. Maybe I am over thinking it, but I dont see why they couldnt have two different bore / piston sizes in the same master...

Just a thought as to why they would have a different master, I don't think pedal effort is the only reason..

 

[ChuckBilodeau]

Hello Guys, did someone ever figure out if the FP350S unit would work on a non factory race car with the OEM ecu?

thanks!

 

[TeeLew]

Hello Guys, did someone ever figure out if the FP350S unit would work on a non factory race car with the OEM ecu?

thanks!

I tried to get a GT500 CFTP unit to work in mine, but had to go back, because I had the wrong version of ForScan. If you can get it to accept the VIN, I bet it would work. FP would have to chime in.

I'm going to try the 500 ABS again at some point. I think it can be made to work.

 

[ChuckBilodeau]

I tried to get a GT500 CFTP unit to work in mine, but had to go back, because I had the wrong version of ForScan. If you can get it to accept the VIN, I bet it would work. FP would have to chime in.

I'm going to try the 500 ABS again at some point. I think it can be made to work.

Thanks, because I'm also having ABS issues from time to time... it's not 100% rock solid and predictable. After trying the BMW GT4 which has the OEM unit with custom programming... Well it's night and day with a street unit.

PS: I have the PP2 booster and master cyl.

 

[Tonymustang302]

@JAJ i just got the fp350s abs module, does it need to be programmed or install and abs bleed?

 

[ChuckBilodeau]

@JAJ i just got the fp350s abs module, does it need to be programmed or install and abs bleed?

Le me know if you manage to make it work. The plug is different and I dont have the pinout. Also I went motec and i'm not sure i'll be able to give it the can signals it needs.

 

[JAJ]

@JAJ i just got the fp350s abs module, does it need to be programmed or install and abs bleed?

Hi @Tonymustang302 - Sorry I missed this - I was traveling a bunch in October and just didn't register it.

However, that wouldn't have made a big difference - I don't know about programming the FP350S module, so I couldn't help in any case. That said, @ChuckBilodeau's question about using it with Motec is way over my head. There's no doubt that the answer is "yes, it needs programming" but the rest of it is a mystery. I do know that the OEM GT350 ABS setup gets its vehicle motion data from the wheel speed sensors, the Restraints Control Module, and the Power Steering Control Module but whether the RCM/PSCM data affects ABS or just for stability control, I don't know.

 

[ChuckBilodeau]

Hi @Tonymustang302 - Sorry I missed this - I was traveling a bunch in October and just didn't register it.

However, that wouldn't have made a big difference - I don't know about programming the FP350S module, so I couldn't help in any case. That said, @ChuckBilodeau's question about using it with Motec is way over my head. There's no doubt that the answer is "yes, it needs programming" but the rest of it is a mystery. I do know that the OEM GT350 ABS setup gets its vehicle motion data from the wheel speed sensors, the Restraints Control Module, and the Power Steering Control Module but whether the RCM/PSCM data affects ABS or just for stability control, I don't know.

If we can eventually get that FP350S module to work it could be a cheapish solution for MANY! Working on it, will let you know.