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However, since the LT1 heads are part of the Gen II small-block design, they cannot be swapped onto an earlier small-block. Physically, you might be able to make it happen as the dimensions are roughly the same, but the main difference is in the cooling passages, since the Gen II used a reverse-flow cooling system that feeds coolant to the heads first, then the block, which is the inverse of most traditional V-8s. Even if these could be modified to work on a traditional small-block, it wouldn't be worth the effort, since so many excellent heads are available to bolt directly to the small-block at reasonable cost.

Axle AskingI recently bought a disc-brake Posi-traction rearend to replace the drum brake open rear in my '84 Camaro. It's a Borg Warner rear that I believe came out of an '87 Pontiac. It had a metal tag on the cover with 2.77 stamped on it. I understand rear-disc F-cars came with Moraine-type calipers. Does this rear have the same type? I know I'll need a new proportioning valve. Could I use one of those adjustable valves alone, or do I need to use it in conjunction with a stock valve? Also, the parts place has the same parts numbers for both disc and drum master cylinders. Could I use mine? Is this rearend worth it? I only paid $100 for it.Jeff MedineViolet, LA

The rearend you've acquired is what most third-gen enthusiasts refer to as the Australian axle, as that's where it was built. It's also referred to as the 9-bolt, because of the number of bolts holding the rear cover in place. It may well be a Borg-Warner design, but it's not one that was used on any other GM car here in the states. The 2.77 refers to the axle ratio, and this unit was also offered with 3.27:1, 3.45:1, and 3.70:1 gearsets. The '87 model year was the first time this axle was used, replacing the puny GM-built 7.5-inch axle used on all third-gen F-cars previously. The strength of this unit was a definite improvement over the 7.5, though that's not to say it's actually strong by musclecar standards. For a mild street car it should be fine, as long as repeated drag launches with sticky tires aren't part of your plan.

The brakes that would have come with that axle are the Delco-Moraine type, which can be identified by the cast-iron calipers-in '89, GM switched to aluminum PBR-sourced rear calipers. This change was reportedly precipitated by reliability issues with the iron calipers. The main problem is that the calipers "freeze," which seems to be linked to the parking brake mechanism.

But if your calipers check out OK, this rear axle assembly should be an improvement over your stock '84 unit, though you may be losing some axle ratio depending on what you have now. The rear brakes should bolt right up, and some sources tell us that the drum-brake proportioning actually works well with the rear discs in this particular application. As you seem to be aware, normally a disc-to-drum swap would require a proportioning change and a differently sized master cylinder. In this case, retaining the drum-brake proportioning would limit the effectiveness of the rear discs, if anything. It is possible that the master cylinder is the same for both applications in this instance. But anytime non-factory brake system changes are made, it is critical to verify that the system still works properly under all conditions. That means you need to find out if the rear brakes will under- or over-brake in heavy braking situations, including wet pavement. If the brake proportioning isn't correct, you could use an aftermarket manual-adjustable proportioning valve. To be most effective, these are usually used without the factory proportioning valve; if the manual unit is installed after the factory unit, all it can do is further limit the rear braking.

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