[bigdaddycane]

The tuners can build their product to be safe for a certain average percentage of the engines out there. But any car guy worth the grease under his finger nails can tell you no 2 engines are the same, and among mass produced engines, the can vary widely.

These are mass produced engines. All parts are built to a certain tolerance, and sometimes these tolerances stack up in an unfavorable manner. With the thousands of parts that go into the engine, the odds are quite litterally one in a million or less, but the fact is it happens.

That said, even when an unfavorable and very unusual stacking of tolerances produces an engine that may not be as robust as the average engine from a given series, it's still designed to be within the operating paramaters. When someone changes the operating paramaters on an engine in this situation, you can now take the engine out of the design paramaters in a manner its tolerances can't handle.

This is why the old-school stock car boys would "blue-print" an engine. They would literally sort through hundreds or thousands of factory parts, or buy parts measured to be at a point in the certain tolerance spread, or machine parts to a design tolerance such that the tolerances stacked up in a favorable manner. Perfectly legal way to boost your engine output in "stock" racing.

Turbo Fan,

Until just a few years ago I owned a BMW Aftermarket parts company that designed, manufactured and marketed various performance parts for many BMW models. I am clearly aware of design parameters and custom "one off" parts.

I've spent more time with machine shops and dynos than you can imagine.