I recently upgraded my 86 iroc with a big brake upgrade amd need some input on what master cylinder to run. I have been looking at wilwood but cant seem to get a actual part number for one that is a bolt on replacement.

 

It may be that you need nothing.
Check out these charts regarding MC pistons and Caliper volumes. If what you've swapped in is a close match to what you had, nothing more may be required. If the braking bias is off (after testing) then an adjustable prop valve may serve your needs.

 

I picked up a adjustable proportioing valve. I need to get a new master because i am going from a rear drum to disc.

 

What problem are you trying to solve?

I'm not sure there is any difference between a disc-disc master cylinder and disc-drum master cylinder. I think the difference is the combination valve (prop valve) used with each. Not sure changing master cylinder will do anything other than make your wallet lighter.

 

[QUOTE=QwkTrip;6250633]What problem are you trying to solve?

I'm not sure there is any difference between a disc-disc master cylinder and disc-drum master cylinder. I think the difference is the combination valve (prop valve) used with each. Not sure changing master cylinder will do anything other than make your wallet lighter.[/QUO

Only reason i am looking to change it lis because i was told by a local brake shop there was a difference and most of the online parts stores ask if it has disc or drum. Also different part numbers are listed.

 

If you examine the chart posted you will see that the piston/bores have different diameters to suit the volumes of the calipers/wheel cylinders. The 82-83 model years are listed below as an example.



It used to be that a master cylinder for drum brakes had a residual check valve built in so as to keep a slight amount of pressure on the system after the brake pedal has been released. This is an issue if discs are used.
The prop valves are also different as been been pointed out. This will affect the bias between front and rear.

 

The guy at the brake shop did mention the check valve in the master for rear drum brakes. The calioers going on the car are larger than what the factory ones are. The fronts are 2018 camaro ss 4 piston and 2015 camaro 4 piston brembos on the rear. They recommended maybe going up to a 1 1/8" bore.

 

I should clarify that its not the volume of the caliper or wheel cylinder but rather the area of caliper piston that is relevant.
Keeping the ratio of the master cylinder piston bore relative to the area of the caliper piston(s) should theoretically give you the same performance as the OEM configuration. At least that's my understanding of the science behind it.
Increasing the caliper piston area without a similar change in size for the master cylinder would result in greater clamping force on the rotor. This may come at the expense of pedal feel and /or travel so there's a balance to look for.
Without knowing the area of the new caliper pistons it would be impossible to say whether a move to a 1-1/8" MC would be a move in the right direction.