First let me say that I am a long-time subscriber and really enjoy your magazine. I have a vexing problem that I can’t figure out and I hope you might have some ideas.

I have an ’81 Trans Am with the WS6 option, including the factory four-wheel disc brakes. The brake system works fine. I’ve upgraded the brake hoses to braided lines and the rotors are cross-drilled. I’m running Performance Friction carbon-fiber brake pads. The car was originally equipped with a 301 four-barrel Pontiac engine and a Turbo 200 trans. It now has a ’77 Pontiac W72 400 and Turbo 350.

My problem is the left rear valve cover clears the brake booster by less than ½-inch. I’m building a 455 that will require taller valve covers due to roller rockers. I have been told that this was a one- or two-year-only brake system. I have considered the following solutions:

1) A smaller aftermarket booster/master cylinder, but I have no idea how to figure out what size I need and what size master cylinder I would need. The car is “showy,” so a chrome or polished unit would be good but not necessary.

2) A hydro-boost system. This would give me the room I need, but would clutter the engine compartment with hoses and is not very nice-looking. I used to own a Chevy Astro Van with a hydro-boost system and the brake feel was not very good, although the system worked fine.

3) Manual disc brakes. I am sure there is a formula somewhere for the length of pedal arm I would need. I am an experienced welder and fabricator.

Any other ideas or OEM booster swaps?

Michael Dinan - St. Louis, MO


Rocky Rotella responds:

Michael, thank you for your loyalty to HPP. We certainly appreciate it.

Firebird brake-booster dimensions varied with the model year, and engine and rear-brake application. As you’ve learned, ’81 is rather unique. Its brake booster, master cylinder, and proportioning valve do not directly interchange with previous years, so finding alternatives may be somewhat difficult.

A larger brake booster used with the 301 in your ’81 Firebird wasn’t an issue with the short-deck engine, but it can interfere with the driver-side valve cover on a standard-deck Pontiac engine, such as the 400 you installed. I strongly advise against reengineering or mixing-and-matching the components of any vehicle’s brake system. You need to know you can rely upon it when you need it most.

Firebird brake-booster dimensions varied with the model year, and engine and rear-brake application

There are a few different options, and it sounds as if you’re on the right track with your ideas. I don’t know that you need to go to a hydro-boost system or manual-effort brakes, however. The most complete and easiest solution is to purchase a complete kit from one of the many brake companies that offer such products. It will include a small-diameter booster, the correct master cylinder, calipers, and the associated hardware for proper operation. It doesn’t sound as if you need all that, however, since your Firebird was originally equipped with a rear-disc-brake setup, and it’s in excellent working order other than the brake-booster interference issue.

Many of the same companies that offer complete kits also offer individual components. Classic Performance Parts (www.classicperform.com) is one that sells its brake boosters individually, and in various diameters and dimensions to fit within a cramped engine compartment of a typical hot rod. I would contact its technicians to determine which, if any, of its boosters might work with your existing factory components. I suspect you’ll be able to find something smaller that will bolt into place and provide you with a similar amount of pedal effort without compromising braking performance.


Block Shock

About five years ago I completed a restoration of an ’80 Trans Am. I rebuilt a 400ci Pontiac engine, had it bored 0.030 over; installed forged pistons, ARP studs and bolts; had the stock rods re-sized; installed a Crane Blueprint cam (068 specs), stock No. 13 cylinder heads, Harland Sharp roller rockers, an Edelbrock Performer intake manifold, a Holley 750 carb, and Hooker headers. All the parts were balanced before assembly. I also used a TCI torque converter, Turbo 400 transmission, and 3.73 gears.

I love the torque, the sound of the turbo mufflers, and the tire smoke. It makes an old man (closing in on 60) feel like an 18-year-old again, back when I owned a ’70 GTO.

I just finished reading about building Pontiac blocks in the April ’13 issue. You can imagine how I felt when I realized my block is a #500557. The machine shop that bored my block said they didn’t remember a 400 Pontiac block being as light as this one. Now I know why.

I’ve driven this car about 6,000 miles since it was completed, street driving with occasional burnouts and 5,000-rpm shifts. Should I look for a different block and put my parts in it, start from scratch, or keep driving it as is? I figure the engine must make around 400 hp. Thanks for any input.

Jim Seymour - Harrisville, NY


Rocky Rotella responds:

Jim, there’s no question that the mid-to-late-’70s 500557 block casting simply isn’t as beefy as its predecessors or the 481988 casting that was revived for the T/A 6.6 in ’78. As you read in the April ’13 issue, its cylinder walls and main saddles (or bulkheads) were thinned considerably to reduce casting weight. It was just one of many attempts Pontiac engineers made in that era to shed overall vehicle mass and improve fuel economy.

The lack of material and the rigidity issues it creates makes the 500557 susceptible to failure when combined with a long-stroke crankshaft, high-speed engine operation (above 5,200 rpm or so), and/or a combination producing more than about 400 hp. Many have successfully used the 500557 up to that level and even slightly more over the years. I personally don’t recommend exceeding the 400hp mark simply because I feel the block is incapable of reliably enduring the operational characteristics associated with it.

Assuming your particular 500557 block was in excellent reusable condition and was rebuilt properly, I don’t suspect you’ll have any issue at your current performance level or with the way you’re driving it. I certainly don’t suggest boring it any further, and wouldn’t recommend any additional modifications to dramatically increase performance. If that’s your goal, then I highly suggest beginning a new build using a better foundation. But it sounds as if you and your machinist paid close attention to the details, and that should yield reliable engine operation for years come. So continue enjoying your Pontiac just as you have. I don’t believe you have anything to worry about.