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Oldsmobile V8 Engine: Olds 403: 500hp, 403ci - Horsepower!

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JMS Racing Engines / El Monte, CA - Oldsmobile 403

While working on our Blue Collar 454 build appearing in this issue, we spent a lot of time at JMS Racing Engines in El Monte, California. That’s not a bad thing; any day away from our corporate cube farm is a good thing. Plus, it gave us the opportunity to check out the other builds it has going on. Case in point is this Oldsmobile 403. It’s a 6.6L Oldsmobile 403 block/455 head hybrid destined for the engine compartment of a Smokey and the Bandit Pontiac Trans Am.

1. Olds 403 - Accessory Drive

Check out the March accessory drive. The owner preferred to maintain air conditioning and power steering. Here at Car Craft, we tend to skip over the billet parts, spending that money on other stuff, but we have to admit this front dress looks great next to all the polished parts. By now, it should be obvious this shiny gem will be going into a show car. The owner plans to take it to the Specialty Equipment Market Association (SEMA) show in Las Vegas, and nationwide to Pontiac and GM car shows. Thankfully, he won’t relegate the car to trailer-queen status. He wanted to make power with this combination, and JMS is expecting just north of 500 hp when the Oldsmobile 403 engine is strapped it to its DTS engine dyno. That will get him to Texarkana and back, for sure.

2. Olds 403 - Long-Block

From the late ’70s through the ’80s, GM mixed and matched engines and platforms regardless of the badge on the grille, so it’s no surprise to find an Oldsmobile V8 engine in the compartment of a Pontiac Trans Am. This Oldsmobile 403 block was bored 0.030-over and fitted with custom Ross pistons. The crankshaft is stock, and JMS polished and shot-peened the connecting rods. The heads are Edelbrock Performer RPMs with 77cc chambers and 188cc intake runners. Final compression ratio is 10.0:1, and the whole thing is screwed together with ARP fasteners.

3. Olds 403 - Cam and Valvetrain

At the heart are a custom-ground Comp hydraulic flat-tappet cam and a matching set of Gold Series aluminum roller rocker arms and pushrods.

4. Olds 403 - Polish

It’s impossible to ignore the polish job on the aluminum parts. After all the fitting, welding, and grinding was done, JMS sent these parts out to their secret mad-scientist polisher. Even the Q-Jet carb will have its day against the buffer wheel.

Oldsmobile V8 Engine Intake

To get this Oldsmobile v8 engine combination to fit under the stock Shaker hood, JMS elected to reassemble this Oldsmobile v8 engine with the stock Quadrajet carburetor and an Edelbrock Performer Olds 350 intake manifold. This manifold does not match the intake ports in the 455 heads, though, so JMS had to weld the top of each intake port on the manifold, building them up with filler material until they completely covered the intake ports in the heads. Then they ground the openings to match the heads and milled the mounting flanges before sending the manifold out to be polished.

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I just thought that I would add an alternative to the intake that they added material to the top of the port, Edelbrock offers the Performer RPM #7111 just for the small block w/ 455 cylinder head combo. The port still needs to be opened up however the welding labor and any problems arising in the aluminum from the heat-affected zone after welding don't become an issue. I know that this manifold will not fit under the stock shaker scoop on the Trans Am but maybe with a small modification to the shaker and milling the carb flange it would work since it is two inches taller than stock. Just something possibly to consider. It is always nice to see another well thought out build on an Olds!

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