333pg333

Anyone know about or have any ideas re changing to a Dual Master Cylinder on any P-car but specifically a 951? I don't know what it would do but I've always thought that just by changing up to 'Big Red/Blacks' would not increase pedal/pressure feel, rather give greater duration before fade due to larger surface area of the pads. There is a kit on the Kokeln site but there is no info that I could find. http://www.kokeln.com/products/951_8689/index.shtml
Thanks

Geoffrey

Speaking in general terms here, not having had experience with that particular setup, the dual master setup will allow you to run different size master cylinders so you can tune the pedal feel and pressures to the brake system you are using. They also have a balance bar so you can adjust the bias F/R.

altonj

I run one in my 911. Does just what Geoffrey says. However, once I got it set the way I liked it, I never adjust it. It is not one of the things I want to screw with a risk messing up while at a DE.

Cheers

333pg333

Thanks guys. So it's possible to alter pedal travel and make it a bit more directly reactive? That is be able to depress brake pedal less but for more gain, probably having to exert more force though.

Boxsterund914

As I understand it force is force. You can gain an advantage by changing the pedal ratio (move the pedal through a longer travel in relation to the movement of the piston in the master cylinder and it gives you an advantage). Cylinder sizing will not do this, it will just require a longer travel to move enough fluid if the master cylinder is small and a shorter travel to move enough fluid if the master cylinder is large.

Imagine that there is nothing between the slave cylinder and the master cylinder...no lines, no nothing....just as if the piston in the master and the piston in the slave were spaced apart by a certain volume of fluid at each end of the same chamber. Since this fluid cannot be compressed, if you move the piston at one end "the master" it then moves the fluid at the other end "the slave". To make it easier or harder you change the mechanical advantage of the lever (pedal) that you use to move the piston at the control (master) end.

If the master cylinder is too small then you run out of travel because there is not enough fluid to move the slave. If the master is too large then a very small movement changes the volume in the slave very quickly. But these do not have any real affect on the pressure required to move the master.

This is a gross oversimplification but the theory is correct as I understand it.

altonj

Boxsterund914 has it nailed.

Yes, when you make the MC larger you gain "advantage". You don't need to push the pedal as far to move the same amount of fluid the smaller MC moved. The downside (or upside) is that you end up with a firmer pedal. So in the case of my 911, the pedal is now much more firm (rock hard) and the pedal travel is minimal. This mod was done after trying a larger single MC on my Big brakes (bigger than big reds) Of course, the adjustability is a plus too.

Cheers

333pg333

Ok so just to clarify that we're on the same page. My intention was to decrease the travel of my pedal and increase the feeling of resistance while depressing it. So I thought that by changing up to a larger MC or maybe one of these twin kits that this would be the outcome. I think you are both saying yes? My car is still a street driven one so I probably don't need it to be rock hard but somewhere inbetween. We do mostly circuit sprints with strong braking so I wish to improve the feel and limit the existing travel. I have underbody 968 air deflectors onto the discs, s/s braided lines, and $$$ brake fluid. I am going to get some Performance Friction pads which I believe are very good. However none of this is going to change the other symptoms so a different MC setup was the next thought.

altonj

Yes, you are correct. I am not sure of the MC sizes available as a direct bolt it for your car so you may need (want) to go with a dual set up. The system itself is expensive but the each cylinder is cheap so if you want to expereiment with different sized ones in the future it won't hurt too bad.

Cheers

333pg333

Thanks for your good advice. I got onto a good site as advised by Karl from RacersEdge. http://www.tiltonengineering.com/ This looks to have everything needed for this purpose. You can even do an online form which will give you the right product for your car. Just to understand, are the 'Balance bars' in the cockpit or under the hood? We aren't allowed any brake adjustment device in the cabin. I don't have any costs yet and am not sure how much is involved but I only want to improve the modulation of my brakes as the standard ones in my car are from the 928 Gt are 4 pot Brembo's with decent sized calipers so they should be sufficient, just need a tweek.

altonj

My MC's are also tiltons, good products.

Cheers