As I am working on other design aspects like fuel systems and brakes, I contacted Tilton Engineering to confirm the dual master cylinder sizing using the mustang II front calipers and Mazda RX7 rear calipers. Here is is my input data and their response.
Quote:
Vehicle Info
Make: Lotus Seven Clone
Model: Seven
Front Brake Information
Number of pistons within each front caliper: 1
Are pistons on one side or both sides of caliper: one
Diameter of pistons on one side of caliper (list all):
Piston 1: 2.597 in
Piston 2: mm
Piston 3: mm
Piston 4: mm
Front rotor diameter: 10 in
Rear Brake Information
Number of pistons within each rear caliper: 1
Are pistons on one side or both sides of caliper: one
Diameter of pistons on one side of caliper (list all):
Piston 1: 1.375 in
Piston 2: mm
Piston 3: mm
Piston 4: mm
Rear rotor diameter: 8.70 in
General Information
What is the motion ratio of your brake pedal (5.5:1, 6.2:1, etc)? 6.0:1
OR
If using a Tilton pedal assembly, please provide part number: -
Vehicle weight (with driver and fuel): 1340 pounds
Vehicle Weight Distribution (with driver and fuel): 49 / 51
Vehicle wheelbase: 88 in.
Front tire diameter (outer): 20.5 in
Rear tire diameter (outer): 20.5 in
What is the vehicle being used for (street, road racing, circle track, drag, etc)?: Autocross Hoosier Slicks
The response
Quote:
Hello Mark,
That caliper is way oversize for the front at 2.597" diameter. If you must
use it, you will need a bigger master cylinder in the front to reduce the
line pressure enough. You will need more than twice the line pressure in
the rear than the front and that is the reason for the big difference in
master cylinder sizes. Also included are part numbers for the 74 and
75-Series master cylinders.
1-1/8" front, 74-1125U, 75-1125U
13/16" rear, 74-812U, 75-812U
Results are not guaranteed since calculations require estimates for the
vehicle center of gravity height, tire grip, brake pad friction coefficient,
how hard this particular driver prefers to push on the pedal, and other
factors.
Regards,
Mike O'Neil
Technical Director
tel: 805.688.2353 ext. 103
fax: 805.686.1176
cell: 805.455.4475
mikeo@tiltonracing.com
I am glad I checked with Tilton, my math did not work the same using a common XL spreadsheet for brake sizing.
You can visit their website and submit your info. They responded in 24 hours.
http://www.tiltonracing.com/content.php?page=faq&view=9I will be buying Tilton master cylinders....
Mark
_________________
Building a whole car from scratch is a 1,000 little tasks, done 1 task at a time, while thinking 10 tasks ahead, then redoing it anyway.
SCCA D Mod autocross special. Scratch-Build completed 2013. Blew-up engine in 2014. Re-engineering & Rebuilding for 2016.
South Bend Region SCCA
Link to my build log:
http://www.locostusa.com/forums/viewtopic.php?f=35&t=3356
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