AP Racing Catalogue Issue 4

44 visit www.apracing.com for installation drawings & up to date product range details BRAKE DISCS - Operating Advice & Part Numbering DISC OPERATING ADVICE This section on operating advice has been produced as a guide only, as many formula or racing series may have different requirements. DISC TEMPERATURES In order to achieve optimum racing brake performance and prolong disc life it is essential that the brakes operate at the correct temperature. In general discs should run at similar temperatures front and rear and from side to side, dissimilar temperatures will lead to varying brake balance. Temperature balance can be checked as soon as the car stops in the pit lane using a Pyrometer such as AP Racing Pyrometer kit CP2640-24 (see below). However a pyrometer reading is not a good indicator of disc operating temperature which decays rapidly with time when the brakes are not being applied. Under racing conditions disc bulk temperatures should normally be maintained in the range 400°C to 600°C for best performance. Disc face peak temperatures may be higher but should not exceed the maximum recommended for the pad material being used. An effective method of checking maximum disc operating temperature is by using temperature paints applied to the disc. A suitable paint kit can be obtained under AP Racing Part No.CP2649-1, this kit contains three paints, Green (430°C), Orange (560°C) and Red (610°C) plus thinners and brushes. When assessing brake temperatures it is important to complete several successive laps (5 or preferably 10) at race speeds and vehicle weight to allow temperatures to stabilise at a representative level. Typically when running within the correct temperature range the Green paint (430°C) will turn throughout, the Orange paint (560°C) 50% to 100% throughout and the Red paint (610°C) turned up to 5mm from each brake face. If the Red paint (610°C) turns throughout, the discs are running too hot. Circumferential disc face ridges are also an indication of running too hot. Circuits and drivers vary enormously in the amount of work they demand from the brakes and therefore the brake system has to be tuned for each circuit by adjustment of the cooling airflow. The temptation to over cool the disc should be resisted. The aim is to keep the temperature as stable as possible within the working temperature range . High maximum to low minimum tempera- ture cycles are the enemy of disc life and cause performance variations. DISC BEDDING All cast iron brake discs need to be bedded-in to ensure heat stabilisation and improve resistance to cracking. Cracks or even disc failure can occur during the first few heavy stops if careful bedding is not carried out. APRacing recommend the following procedures or visit www.apracing.com for the latest advice. RACE CAR INSTALLATIONS: 1) If ducts are fitted they should be ¾ blanked off. 2) Use previously bed- ded pads. 3) For a minimum of 15Km use brakes gently at first from initially low speeds - Progressively raise speed to normal racing speed but still using gentle applications. 4) For the final 2 or 3 applications brakes can be used quite heavily. 5) If AP Racing thermal paints are used then only the Green paint (430°C) should have fully turned to white and maybe also just the Orange paint (560°C) on the outside edges of the discs during the bedding procedure. 6) Allow to cool. 7) AP Racing offer a pre-bedding service at nominal extra charge. This ensures that discs are bedded consist- ently assuring better performance & life. Contact AP Racing for details. ROAD CAR INSTALLATIONS: 1) For the first 10 miles, light braking from 50/60 mph down to 30 mph if possible in blocks of 5. Do not attempt any high-speed stops down to zero at this point, as only the faces will heat up with the mass remaining cool along with the mounting area. 2) For the next 100 miles increase the braking pressures similar to stopping in traffic, again avoiding if possible full stops from above 70mph. By now the area around the mounting bolts should be a light blue temper colour. This is a good indication that the correct heat soak has been achieved. 3) For the next 100 miles gradual- ly increase the braking effort after this full power stops can be used. The disc should now be an even dark to light blue temper colour, depending on the pad type and the braking effort being used during the process. This process must be completed before any race circuit use. Track Day Use: For the latest Track Day Bedding Instructions visit our website. DISC COOLING A good source of cooling air should be supplied preferably through the up- right to the disc throat. A typical venting cross section of 100cm² (16in²) is usually sufficient. The pick up should preferably be in an area of clean high pressure air flow and the ducting should be arranged to avoid sharp bends or changes in section which may choke the air flow. Careful design of the Mounting Bell is important in achieving effective disc cooling and avoiding problems. Typically 80% of the airflow should be directed up the disc vents and 10% up each face of the disc. This ratio can vary consider- ably in practice but it is important that both disc faces are cooled equally by adjusting the air gaps. Unequal face temperatures can lead to disc distortion and a long pedal. Lightening holes in the bells should be avoided as available cooling air can be lost without cooling the disc. SAFETY AND CARE OF DISCS Cast iron brake discs should not normally be operated at bulk temperatures in excess of 610°C and above rotational speeds of 3000 revolutions per minute. Discs must be regularly and frequently inspected for excessive heat crazing and cracking. After heavy and prolonged use some surface crazing will often be evident, if this turns into distinct surface cracks which are radiating towards the inside or outside diameter the disc should be changed. Discs with cracks emanating from mounting holes / slots, inside diameter, scallops, or outside diameter should be changed immediately. IF IN DOUBT REPLACE. TEMPERATURE MEASUREMENT ◘ DIGITAL READ-OUT PYROMETER CP2640-24 Digital pyrometer for brake, disc and tyre temperatures. Highaccuracydisplay reads in centigrade. The unit comes complete with probes for both brake discs and tyres in a heavy duty carry case. ◘ THERMAL PAINT KITS CP2649-1 kit comprises of three paints for monitoring peak Brake Disc temperatures. The three paints are:- - Green changes colour to White at 430°C. - Orange changes colour to Buff at 560°C. - Red changes colour to White at 610°C. The kit also comprises, one bottle of thinners and three brushes. ◘ BRAKE CALIPER TEMPERATURE STRIPS CP2650-11 Temperature indicator strips for monitoring caliper temperatures. - Temperature range 149°C to 260°C - Each packet contains 10 strips. ◘ TEMPERATURE RECORDING PAD CP2640-25 Allows the user to record temperature data for Brake Discs and Brake Calipers. PART NUMBERING When ordering discs please use the correct part number wherever possible. An example part number is explained below:- All AP Racing brake discs are individually marked with the following information: PART NUMBERING EXPLANATION Basic Disc (casting) Type Stroke Number Bedding (if applicable) CP3581 - 1042 CG8 B1 Disc Face Suffix (see below) ◘ HANDING: - Even Stroke Numbers are Right Hand. - Odd Stroke Numbers are Left Hand. ◘ FACE TYPES: P - Plain / D - Drilled Face / G - Straight Grooves G3 = When G appears with a digit, this denotes the number of grooves per face on the disc. e.g. G4/G6/CG8/CR12 etc. / CG - Curved Grooves / GD - Grooved & Drilled / CR - Curved Grooved backward facing running out to O/D. / PG - Par- tial Groove. / RD - Radius Drilled / SD = Similar to RD but with smaller holes. J Hook Designs = RA - 2 groove across face, grooves run-out. / - GA as RA, but grooves do not run-out. / - RC as RA but with 3 hooks across face - GC as RC, but grooves do not run-out. / - B1 = A “B” and a Number added to the end of the part number i.e.CP3581-1042DB? means the disc has been pre-bedded with a particular pad material.