I'm buying some new wheel cylinders for the rear of the Camaro. I've got the finned drums on the rear to help dissapate heat, and all new shoes and hardware.

When I slam on the brakes on the car, it doesn't stop all that well despite the front discs and Hawk brake pads...although I have no power assist. So, I'm looking for a little more braking power so I can so down from 120MPH in the quarter.

The selection of bore sizes for cylinders are 7/8" (stock), 15/16 (most 11"x2" drums), and 1" (most big cars). Is there any recommendations out there on which to use?

Are you running Power Brake Assist? What size is your master?

GM changed the rear cylinder size from 7/8 to 15/16 in 1977 to improve braking on these heavier cars.
Changing to the larger size would give you marginally better braking effect over the 7/8" stock size, all other things being the same.
You might want to investigate brake shoes with a higher C/F friction material to improve braking effort.
You can 'Google' "Praise Dyno Brake" as one supplier of better friction materials.

Also check the Power Booster if you are running one. Older diaphrams become 'stiff' and higher "foot effort" is required to get original braking effect. Changing or rebuilding your booster may really help.
Also make sure the Booster Vacuum Check Valve is in good shape and working correctly.

Lastly - do a search for past posts on HydroBoost sytems on the site. These are great systems and had the 'nuts' to drag my 1ton to a stop in no time loaded...

Rear wheel brake cylinder size requirements is tied to front brake capacity. An increase in rear wheel cylinder size can cause early rear wheel lockup which puts a car into a spin. Without power assist I would first look at master cylinder bore size to improve overall braking. Typcially 70% (or more) of stopping is on the fronts.

Bob.

Which Hawk pads do you have? When I was running manual C4/13" fronts I used Hawk HP+ which is the next step up from their HPS. Made a difference. You might try those, or if you're already using HP+, go up a step from them to a more aggressive pad. Now I have hydroboost and it stops when I look at the pedal.

I would work with master cyl bore size to get the front discs to work better.
What size master cyl do you have and what front discs do you have?

Thanks for the responses guys.

The MC bore size is 1", it's a '67 Camaro MC for manual disc (no power booster here). The discs are stock up front for '69s. The Hawk pads that I'm using are the street compound, not sure what the name is. It was recommended by several on this board.

The reason why I say it doesn't brake too well is because I can't really get any wheel to lock up. IMO, I should at least be able to lock the fronts, but maybe it's normal not to without any sort of power assist.

you should still be able to lock the wheels. what does the pedal feel lke and how much travel does it have?

The pedal has a good firmness throughout the travel; it's not squishy or rock hard. Travel is hard to say...maybe about 2"? 3" possibly? 3 sounds more accurate.

Everything is fresh by the way, about 50 miles os use.

Thanks for the extra info. I'd try a 15/16" bore, you really need to be capable of locking the front brakes. A 15/16" bore will make a difference.

Thanks David. I'll try that first, and then we'll go from there.

I agree with David, go down a size on your master.
Your pedal effort will change slightly but, your braking effort will improve.