Ferrari has, as virtually every other manufacturer, installed a proportioning valve on the rear braking circuit. The purpose of this is to provide a specific balance between the front and rear brakes. A 50/50 balance is not provided or wanted. According to the factory shop manual it states "Braking regulator ratio...Front - ...Rear 0.46". The stock regulator consists of a plunger, seal, and a calibrated spring assembly. The higher the brake pedal force exerted, the greater the amount of rear braking action. Notice illustration as out of the shop manual below.
This is a fine system for going to the grocery store or opera. But for those of us that really like to drive, this proportioning valve does it's job TOO WELL. It is too forgiving. The design anticipates the worst possible drivers behind the wheel. You know, Johnny Racer, who never went to driver's school and never had any track time.
To the rest of us who drive aggressively, (never above 55 mph on public roads of course), we need to stop as fast as we go. Installing an adjustable rear proportioning valve is the answer. Tilton Engineering makes a great one for $89.00. It's part number is 90-103. It's available at racer's supply stores or call me and I'll ship you one. The valve mounts instead of the stock one in the lower front right of the motor compartment. A steel support bracket welded to the frame is necessary to keep the unit and lines free of vibration. After bolting in, it's hook up line in, line out, and bleed the brake system, removing the air. Because the unit is adjustable, you can increase front to rear ratio or decrease, based upon your driving habits. Typically, less in the back and more in the front is used for track and aggressive driving. Keep in mind, the more front (less rear) also means less predictability in the right situations. In the wet, where the front tires need more adhesion during hard braking, more rear is acceptable.
After a simple installation, try the various positions on the valve starting with maximum pressure on the rear. Accelerate in a safe area, and stand on the brakes WITHOUT LOCKING THEM UP. Does it stop in a straight line? If so, go to the next setting and repeat the braking. Continue on in the same procedure. When the car's control and predictability begin to fade, back up the setting one notch. At this point, the rears should lock up JUST before the fronts. You will be amazed at the responsiveness and additional braking achieved. The following is data on the Tilton unit. Compare it to the stock illustration below.
As a final note, proper installation and responsible driving can not be overstressed. Drive fast, drive safe!
About the author: Located in San Diego, Gary Bobileff has been a Ferrari addict since 1970, servicing and restoring them exclusively. If you have any technical questions, feel free to call him at 619 622-1600.
For a complete look at Sempre Ferrari, you may want to check out the rest of the articles from Volume 1, Issue 2 - July 1994