Is the 73 310hp SD455 a myth?

Asked by GuruMLXFV May 19, 2020 at 05:21 PM about the 1973 Pontiac Firebird Trans-Am

Question type: General

This is not a question, but a correction. There is a common myth the 73 SD455 was rated at 310hp. It was originally designed to, but it was NOT! Both the 73 and 74 SD455's had 290hp. Due to government regulations, no 310hp SD455 was ever sold to the public and was reduced to 290hp before the 1st one in 73 was ever sold. Fact. Rest assured, I  always thought the same thing until I did some research.

2 Answers

F_O_R answered 4 years ago

I think the 310hp engines were pre production engines that did not meet smog requirements.

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James answered 4 years ago

Beginning with the 1972 models advertised horsepower is SAE net. 1971 and older models are SAE gross. The difference is net horsepower is measured with the engine in the vehicle, accessories installed and operating, and the horsepower reading is taken at the drive wheels. Gross horsepower is measured at the flywheel with the engine not installed in a vehicle. Hope that helps! Jim

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