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Oldsmobile 403 (Olds 403) Engine - Ask Anything

The Forgotten Olds 403
Tim Campbell; Morristown, TN: Many people have the Olds 403 engine in their car and would like to upgrade. When you do the research on the Olds 403, you get a very broad range of opinions on the web ranging from "the blocks are no good" to "these engines can be made to produce some decent power." How about some help? Most of us would like to keep the Olds 403. With what you guys at Car Craft have done before with other oddball engines, we know you could build good horsepower and great torque. We are not talking about a race engine, but a true driver that is reliable-something you can beat on. We would love to hear that our engines have potential and that building them is worth it.

Jeff Smith: We called our Olds guy, Dick Miller at Dick Miller Racing (DMR), to get his input. He mentioned that even an average street Oldsmobile 403 would benefit from the typical improvements involving heads, intake, headers, and cam timing without having to go too deeply into the engine. We'll also assume that you would prefer to retain the stock torque converter and rear gear, which means being conservative with the cam timing. The stock Oldsmobile 403 enjoys the benefit of a giant 4.351-inch bore diameter with a relatively short 3.385-inch stroke. Miller says when Olds opened up the bore on these '70s-vintage engines, it intruded into the main webbing area requiring larger areas around the main webbing that weakens the crankcase. This isn't an issue with a mild street engine, but he recommends his five-cap halo-style main cap girdle for any Oldsmobile 403 motor that will see more than 6,000 rpm. The production Oldsmobile 403 also suffers from the typical late-'70s handicap of lame 8:1 compression by way of large, 83cc chambers.

One popular budget approach is to use 350 Olds heads to pump up the compression. Olds heads are identified by a large number cast into them. The 350 heads with a 5A casting offer a 68cc combustion chamber, the 6 head measures 70 cc, and the 7 head comes in at 69 cc. Miller says these 350 heads are the best, but there are still caveats. The universal problem with reviving old cast-iron heads is that by the time you've invested in new guides, a valve job, new stainless steel valves, filling the heat riser passage, and filling the depression between the center exhaust ports to prevent header leaks, you've got more money into a set of stock iron heads than the price of a pair of brand-new aluminum Edelbrock heads. DMR sells a set of Edelbrock aluminum Olds heads for $1,675, but keep in mind that these heads also require aftermarket aluminum roller rockers that will also pump up the price roughly another $250. The iron heads might be cheaper once they're rebuilt, but the flow probably won't be as good. Moreover, Edelbrock has revised the Olds head with improved flow, the combustion chamber is larger at 77 cc, but that will still gain some compression over the stock 83cc heads.

Assuming you will stick with a stock converter and gearing, Miller suggests a relatively mild hydraulic flat-tappet cam along the lines of a 219/233-degrees-at-0.050-tappet-lift cam with 0.476/0.508-inch lift and a lobe-separation angle of 110 degrees. This cam sells for $209 (PN 210-4) and will make some serious torque when combined with the Edelbrock Performer RPM intake you mentioned (PN 7111) and a set of 13/4-inch headers. All these parts taken as a whole represent a sizable investment, but you can do this a step at a time, spreading the cost out over a year or so, and still drive the car between mods.

More Info
Dick Miller Racing

Hernando, MS
662/233-2301
DickMillerRacing.com

Edelbrock
Torrance, CA
310/781-2222
Edelbrock.com

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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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