Chevy 350 vs. Oldsmobile 350: How are they different? – Jalopnik

Oh, General Motors, you’ve almost gone out of your way to confuse people with your engine size. We’ve already talked about how the Chevy 350 and Pontiac 350 are completely different engines, but there’s also the Oldsmobile 350. Oh, and the Buick 350, which was actually a 349, but what’s a cubic inch between friends?

Now let’s focus on the Oldsmobile 350 and Chevrolet’s first-generation small-block 350. We’ll start with the most essential distinction between Chevrolet and Oldsmobile V8s: Chevrolet never converted its 350 to run on diesel (although Chevy did use the Olds diesel in some pickups). Any discussion of Oldsmobile 350s ultimately comes down to the diesel, but before you get too deep into it, know that the Olds diesel V8 isn’t that bad. Well, depending on the year of construction and maintenance by the owner, at least.

Here’s some brief Chevy V8 history. In 1955, the small-block 265 Chevy V8 debuted to loud cheers as Chevrolet took back the sales crown from Ford. The “mighty mouse” engine grew to many sizes, from 283 cubic inches to 327, 350 and more, all the way up to 400. It remained in production with various refinements until it was replaced by the LS engines in 1997. The 350 Chevy small block had a 4-inch bore and 3.48-inch stroke, and was eventually blessed with aluminum heads.

The Oldsmobile 350 started life as a 330, which replaced the borrowed aluminum block Buick 215 V8 in 1964. Like Chevy’s V8, the Olds V8 used an iron block, although the nickel content was higher than Chevy’s for greater strength. It was stamped out to 350 cubes in 1968 and 403 in 1977. 350 versions used a 4.057-inch bore and 3.385-inch stroke, and unlike Chevy’s V8, they always had factory iron heads.

To be fair, Chevy hasn’t always made small blocks with power in mind, either. Plenty came with puny two-bolt main caps instead of sturdy four-bolt caps, which are preferred for bottom strength. There are exceptions, such as four-bolt 400 blocks that are weaker than two-bolt versions, but we’re talking generalities here. Still, hot-rodders build two-bolt mouse engines to reach 500 horsepower, so they aren’t as compromised as the Olds 350s of the late ’70s.

It’s a shame because Olds 350s started off strong. The L74 in the wonderfully named Oldsmobile Rallye 350 reached a friendly nod of 310 hp, and the 1968-1970 W-31 reached 325 hp at 5,400 rpm. As tough as it was, even the W-31 was overshadowed by the 1970 Chevy 350 LT-1 with its 370 horsepower at 6,000 rpm.

Oddly enough, small- and large-displacement Oldsmobile V8s are virtually identical, except for deck height. Whether you got a 455-powered 442 in 1970 or a 307-powered Custom Cruiser in 1989, the bore center distance was 4.625 inches. However, Chevy V8 engines are supposed to be contrarian; The small block drill centers are 4.4 inches apart, while the big block drill centers are 4.84 inches apart.

After numerous head gasket failures, injection failures, camshaft leaks and main bearing cap loosening, Oldsmobile attempted to address these problems. The new DX engine, which first debuted in 1981, featured improved gaskets, strengthened and extended head bolts, properly installed main cap bolts and a hydraulic roller lifter setup. It even had a water-in-fuel sensor since the engine debuted without a water separator. But the reputational damage had already been done and GM dumped the Olds diesel V8 into a shallow grave in 1985, just when the going was good. The gas-powered 307-cube version limped along until 1990 and still had a carburetor, because improving that engine would have been like giving antibiotics to the corpse.

Chevrolet’s small-block also suffered indignities. It was sidelined in favor of a Lotus-designed, Mercury Marine-built DOHC V8 for the C4 Corvette ZR-1 (which royally annoyed Chevy engineers). The 400 engine received inadequate cooling and terrible heads that were prone to cracking, and in 1975 versions of the 350 in Corvettes had a shockingly paltry 165 horsepower. But Oldsmobile’s 350 was much dirtier on a fundamental level.