Some modifications are bolt-on, but real performance engines require some extra custom work. The hot rod community found solutions to all the problems that plague the Olds 403. Chris Witt (an Oldsmobile Forums legend) supposedly offered a $1 million bounty for the elusive engine. Forum rumors and some Oldsmobile experts believe that General Motors briefly produced the solid main 403 in 1976 or 1979 for a few select vehicles, including the Pontiac Bonneville and the Pontiac Trans Am (with tow package). Some Olds 403 engines may have come with solid main webs. The ‘windowed’ main webs are the hollow spaces to the left and right of the crankshaft bearing. Essentially, bottom-end strength was sacrificed. Unfortunately, GM decided to hollow out the main webs which increases the likelihood of failure at high RPMs. Windowed Main WebsĪnother Olds 403 problem is its windowed main webs. From the factory, the Olds 403 was a typical 1970s smog-era motor.
Thanks to the emissions components, the stock 403 had a low compression ratio, bad cylinder heads, and poor fuel economy. Over time, old rubber lines fossilize, crack, and cause vacuum leaks. Before replacing emissions components on an Olds 403, replace all vacuum lines first. The smog pump (or ‘air pump’) can also cause problems and is known to seize up.
The EGR valve is a common failure point, though inexpensive to replace. Here we have the Oldsmobile 403 vacuum diagram illustrating the location of required emissions parts. These characteristics are typical of early smog vehicles from the 1970s.
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