- When it debuted in 1965, the 425 Oldsmobile engine came in several models producing several power outputs. The engine was released with either a two-barrel carburetor or a four-barrel carburetor. The two-barrel types had a bore and stroke of 4.126 by 3.975 inches. Its compression ratio ranged from 9-to-1 to 10.25-to-1. It was able to produce a torque of 430 to 450 lb.-feet at 2,400 rpm. Its maximum power output was rated at 300 to 310 horsepower at 4,400 rpm. The two-barrel variants were released from 1965 until 1967.
- The four-barrel models were also released from 1965 to 1967 and produced a more powerful output when compared to its two-barrel carburetor variant. It had the same bore and stroke as the two-barrel variant, but its compression ratio ranged from 10.25-to-1 to 10.5-to-1. Two four-barrel variants were released; one that was able to produce a torque of 470 lb.-feet at 2,800 rpm and one with 470 lb.-feet of torque at 3,200 rpm. Maximum power output ranged from 360 to 370 horsepower at 4,800 rpm.
- The four-barrel Toronado version of the 425 was the most powerful 425 engine released on the market. It was produced for only two years; 1966 and 1967. This engine was able to produce a torque of 475 lb.-feet at 3,200 rpm and its maximum power output was rated at 385 horsepower at 4,800 rpm. Like the other models its bore and stroke was 4.126 by 3.975 inches, but its compression ratio was 10.5-to-1.
- The standard 425 two-barrel engine was labeled as the "Super Rocket" and came equipped with the top-of-the-line 88 and 98 Oldsmobile models from 1965 to 1967. The four-barrel versions were labeled as the "Starfire," as it was only equipped on Starfire models from 1965 to 1967. The four-barrel Toronado variant was labeled as the "Toronado Rocket," and was also known as the "Ultra High Compression" 425 engine.
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