new pistons,
 

I have a 69 boss 302 engine and the car to go with it. I am rebuilding the engine. The engine has been bored .030 and really needs to go .040. What kind of a replacement piston would be a good one. What was the factory piston? It now has a dome top racing style piston in it. I would appreciate all input.

Most aftermarket piston companies offer a variety of configurations in .040" over. What type of piston depends on the intended use of the engine.

If this will be a stock or mild buildup, then cast or hypereutectic pistons will be sufficient, and they will be inexpensive. If you intend to run a high rpm, high compression engine, or any power adder, you probably should spend the extra money for forged pistons.

As for piston shape, that will also depend on intended use. You will need to determine the desired compression ratio, then perform some equations to find out what you need.

You may want to contact several piston companies and talk to someone on the tech line. They can help you make a sound decision. For cast, look at TRW or Federal Mogul. For hypereutectic, contact KB Pistons. For forged, JE, Ross, and Wiseco are all excellent choices.

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Moxie Racing

The Nitrous Oxide Information Site

TRW now is Federal Mogul. There's also Probe.
Boss 302's had lots of problems with pistons craked), so it's wise to check this out.

Rev

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'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.

Original Boss 302 pistons were pop up pistons with a dome on them. I personally wouldn't want to use that much compression in a driver today but I wouldn't build a boss motor to drive anyway (too valuable versus newer 302)