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Oldsmobile 403 (Olds 403) Engine - Ask Anything

There is a larger question, however, that should be addressed. In the original story, the swap to the rectangle-port heads and big cam sacrificed mucho torque below 4,800 rpm. Add to this that the engine's power band (the rpm between peak torque and peak horsepower) has now migrated to between 5,400 and 6,800 rpm. That means the engine's power curve doesn't start until 5,400 rpm. To take full advantage of all that power, you also must shift the engine at 7,000 rpm or higher. The reason the L92 heads are so attractive is that you can purchase a pair of brand-new heads and the necessary offset intake rocker arms for around $1,100. The heads we tested were from Scoggin-Dickey Parts Center, priced at $899.90 a pair while the rocker arms and valvetrain parts are another $225. While these parts make excellent peak horsepower, the combination sacrifices midrange torque to get there.

An alternative idea is to port the original cathedral heads to improve the airflow while maintaining the higher port velocity of the smaller cross-section port area. A milder cam will put the peak horsepower rpm at 6,000 (rather than almost 7,000), and the peak torque will also drop down to a more useful 4,500 rpm. Why would we want to do this? To better illustrate the idea, I plugged the 551hp power curve into the Quarter Pro dragstrip simulation program using a 3,600-pound street car with a 3.55:1 rear gear and a 2,800-rpm converter. The program estimated the run at an 11.52-at-114.9-mph pass shifting at 7,000 rpm. Next, I increased the torque by 22 lb-ft between 3,000 and 5,000 rpm and reduced the peak horsepower by 30 hp to 520 at 6,000 rpm. While most enthusiasts might think that losing 30 hp would guarantee a slower run, the Quarter program generated a quicker and faster 11.42-at-115.3 mph. This occurred because the added torque in the middle helped accelerate the car more efficiently with the car's street-oriented 3.55:1 gear and mild stall speed. Conversely, if you had a drag-race-only car with a much deeper rear gear and perhaps a four- or five-speed, close-ratio manual trans, then that big head/big cam package would take advantage of the higher power band and run quicker.

The bottom line here is that you could spend roughly the same amount of money to have a stock set of cathedral heads CNC ported and match them to a milder camshaft and you would have an engine that makes great power and is very tractable on the street. This milder package won't make heroic horsepower numbers, but if your goal is quicker acceleration rather than just bragging rights at the next bench racing session, then the more conservative approach just might be the way to go. As an example, West Coast Racing Cylinder Heads offers a Stage 2 CNC porting operation for the stock LQ4/LQ9 317 cathedral-port heads that will flow virtually the same numbers at the midlift up through 0.500-inch lift as the L92 heads while delivering far superior port velocity. Plus, WCRCH will port your supplied castings for $1,375, which is only a few bucks more than the price of the new L92 heads and valvetrain. The WCRCH heads come with new 2.02/1.57-inch stainless valves and Patriot springs. The cathedral heads will tend to run better with a shorter cam similar to a Comp XR269HR (216/220 at 0.050 with 0.525/0.532-inch lift and a 114 degree lobe-separation angle). This will make a bunch of torque in the usable rpm range for a street engine compared with the larger 281 cam. The thundering herd is infatuated with L92/LS3 heads right now because those big-port heads offer sewer pipe flow numbers. But for a mild street engine, I believe the more conservative cathedral-port heads are a smarter choice.

More Info
Scoggin-Dickey Parts Center

Lubbock, TX
800/456-0211
SDparts.com

West Coast Racing Cylinder Heads
Reseda, CA
818/705-5454
ProHeads.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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