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Oldsmobile 403 (Olds 403) Engine - Ask Anything

Performance Gas Cap
Vince Terrana; Bradenton, FL:
A couple of years ago I was looking for a motor for my daily driver. A friend had a 350 Chevy ready to be assembled but never did. I bought the basket case and put it together. When first built it had a Magnum 280 cam, a Performer dual-plane, headers, a Holley 650 vacuum-secondary carb, an HEI with an ignition box, stock heads, and a 2,000-rpm stall convertor. I installed the motor in an '83 G-Body Olds wagon. I was not impressed with the performance and realized it had too much cam. First, I put in a set of Rhoads lifters but still was not happy, so I changed to a Comp 268. Still not much change; this car could not spin the tires. The Holley carb was new, but I changed to a Quadrajet. That felt a little better but not much. I played with timing, different plugs, whatever I could think of with no change. I vented the tank by modifying the gas cap by removing the restrictors and drilling a hole in it. I also left the vent line uncapped. I'm running a stock mechanical fuel pump with no return. Recently, after a gas stop, I left my gas cap behind and that created the biggest performance increase ever-it's a different car now. My question is-what happened?

Jeff Smith: Sometimes the simplest solutions are the best. From your description, it sounds like a simple case of insufficient venting. This is not an unusual situation. It is much like trying to pour liquid out of a closed container with no vent. I have one of those 5-gallon plastic fuel cans on which the vent hole has not been opened because when fuel is stored in the can, I don't want it to vent. This is the one I use to store fuel, but every once in a while I try to use it to pour gas into one of the cars. With one of those 1-inch hoses on the end of the jug, it takes forever to pour fuel into the car because there's no vent. Use a jug with a vent and the fuel shoots into the tank in seconds.

Your gas tank works the same way. Combine a high-output engine that has greater fuel requirements with a too-small vent and the result is that insufficient fuel will reach the carburetor. Mechanical fuel pumps don't really "pull" fuel toward the carburetor. These pumps operate by creating a low pressure area in the fuel line and tank. Higher atmospheric pressure pushes on the fuel in the tank, moving the fuel toward the engine. The greater the pressure difference between the fuel pump and the atmospheric pressure in the tank, the more fuel moves. With a restricted vent, atmospheric pressure drops inside the tank and to no one's surprise, the fuel moves more slowly. So figure out the best way to increase the vent size on your tank and you will be good to go!

Ask Anything-We've got solutions!
CarCraft@CarCraft.com
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Car Craft Mag
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65 comments
Charles Nott
Charles Nott

I have a stock 1/2 worn out 70 455 w-30 in my jet boat. It still hauls. wish I could upgrade with a edelbrock top end and rebuild the bottom

Bill McBath
Bill McBath

I had this in my Nova for one last race before I retired, what a ride it was... Thanks to all my fan's ans supporters through the years.... The Raceway Hugger ---- signing off...

Thumper Stahr
Thumper Stahr

To me, Olds is second only to Pontiac. I love these engines.

Nathaniel Green
Nathaniel Green

Yup!!! Ev er since my lon.g gone 87 307 beat a mustang gt more i.nterested in burning out than racing. That 403 deserves to go into an oldsmobile. I suggest you guys dig up a late 70's cutty or something for it.

Herb Edgell
Herb Edgell

joe mondello is your olds power guru.

Jeffrey Roseling
Jeffrey Roseling

I got a 78 olds delta with a 403 runs good with 250,000 mile on it and never rebuilt

Larry Fogle
Larry Fogle

It pisses me off when they put a Chevy in anything that is not a shevy keep the Olds and make her run.

Christopher Shipes
Christopher Shipes

My Dad has a 403 olds in his 79 Pontiac Trans-Am. We still have to redo it. Haven't had the time or money to get it right.

Chris Welch
Chris Welch

Definetly, i had an 81' Olds Cutlass with an Olds 455 in it. That was a fast car, I wish I had it back.

Travis Kerns
Travis Kerns

Build a 455 race motor. Up to 500ci. All motor. Naturally aspirated.

Michael D Taylor
Michael D Taylor

403,307...... run for ever...R.E. Olds would have liked them.

Greg Reinarts
Greg Reinarts

With the added strength of H-beam rods these engines can now be run hard and make lots of torque, and you can find them in self service wrecking yards at bargain prices.

Shawn Dumas
Shawn Dumas

Damn! My first car had that engine they have power yes!

Scott Myers
Scott Myers

Yeah I need one for son's 79, its .030 over, ported heads, forged pistons, Compcam, and a 175 shot of nitrous..

Chip Wilson
Chip Wilson

I've used the Olds engine in a Camaro swap before, fits under the hood better than a Chevy engine and is a lot torquier. Also used the Olds engine in several Chevy pickups.

Marty Decker
Marty Decker

Had a 330 with a power glide in a 66 cutlass ran that thing forever. Pigtailed a pushrod one time was running 100 MPH in 1st gear installed a new one and she was running like new again.

Chad Bauer
Chad Bauer

I had one with a mild build in a 77 buick lowrider. It had no problem roasting those little wheels.

Frank Mahon
Frank Mahon

Big Olds freak. Just put a stout 66 330 in my 87 Cutlass Salon...have a 71 455 on the stand for teardown.

James Motor
James Motor

I'm a olds freak!!! Blaaaa!!! Yeah I had a 403 that was bad as hell !!! Dounuts for dayyyys!

Damon Stickney
Damon Stickney

I have a 403 .030 over in my 85 el camino and a 425 .030 in my 1976 cutlass and they both scoot down the road quite nicely Thank you

Doug Burks
Doug Burks

Love Oldsmobile I've had several olds torque monsters just like Buick were most everyone will bash and say Chevy is better I've had both they are all good but I like not being in the majority

Lee Atkinson
Lee Atkinson

GREAT motor for the street, super-easy to make into a 13-second daily driver. Not much harder to get into the 12's.

Zach Knouse
Zach Knouse

What's the deal with the gold edelbrock valve covers?

Greg LeBlanc
Greg LeBlanc

Olds 455 in my 1975 olds omega, bast to drive!!

John Royal
John Royal

I am just finishing up one for a customer

Aaron Lancaster
Aaron Lancaster

Lol not a 403. I have one in my Trans Am, I wouldnt give a plugged nickel for. It's going in the trash as soon as my big block chevy is done

Dennis L. Young
Dennis L. Young

I had a 77 Olds 98 Regency with a 403 it was to heavy to get off the line fast , but it was a cruiser on the open highway.

Jeffrey Ralph
Jeffrey Ralph

Hey I got a 383 stroker small block chevy in Chevelle what's a good set of headers???

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