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Oldsmobile 403 (Olds 403) Engine - Ask Anything

L92 LS Head Swap
Josh Meyer; Sacramento, CA:
I have a question regarding an article I found online about testing the new GM L92 cylinder heads called "550 hp for Under $4,900." If I want to reproduce the numbers posted in the article, all I need are L92 heads, a Comp Cams XR281HR cam, an 850-cfm carburetor and manifold, a stock bottom end, and the same headers? I'm very interested in the bottom end of the motor. Did you do anything to it to make this power?

Jeff Smith: The story you are referring to ran in the May '07 issue where we used a stock, 6.0L short-block to make this power. The engine did make 551 hp at 6,800 rpm using the more aggressive Comp Cams XR281 you mentioned. The baseline test for the story included a GM Performance Parts Hot cam with specs of 219/228 degrees of duration at 0.050 tappet lift and 0.525-inch valve lift for both the intake and exhaust using the stock 1.7:1 rocker ratio. There was also a slight error in the story when it originally ran that a couple of readers noticed. In the story, we claimed that the engine was a base, iron-block LQ4, because that's what we thought we had. But in the photo in which we show checking valve-to-piston clearance, a reader caught flat-top pistons that are actually used on the higher-compression LQ9 engine. The LQ4 engines are rated at 9.4:1 with a dished piston, while the LQ9 engines enjoy 10.0:1 compression using a flat-top piston, which means we actually had the better LQ9. We completely missed that little clue because we were focused on making sure the valves didn't hit the pistons. The difference in compression is roughly a half point, which is worth less than 2 percent power. Even at 550 hp, that's worth 5 to 7 hp. The original baseline with the stock LQ9 cam certainly benefited from this additional compression, making 439 lb-ft of torque at 4,400 rpm and 425 hp at 5,600 rpm.

While the long-block was stock LQ9, it also enjoyed a large, single-plane, GM Performance Parts intake, a Holley 750-cfm carburetor, and a pair of Kooks 1 3/4-inch headers feeding a pair of 2 1/2-inch Flowmaster mufflers. Next, we added the GMPP Hot cam and the engine improved to 450 lb-ft of torque at 5,000 rpm and 483 hp at 6,000 rpm. That is incredibly impressive given the stock LQ9 cathedral-port heads. The test also included a set of LS6 valvesprings that came with the Hot cam kit. These initial dyno tests were outlined in the Apr. '07 issue of Car Craft. To run these LS engines with a carburetor, you will also need an MSD PN 6010 LS6 spark box that allows you to create your own spark curve to operate the factory distributorless ignition system (DIS).

The second installment in the May issue pushed the power from 483 hp at 6,000 rpm to 551 hp at 6,800 rpm with the addition of both the larger, rectangle-port L92 castings, a Comp XR281 cam (228/230 degrees of duration at 0.050 with 0.571/0.573-inch lift and a 112 degree LSA), and an 850-cfm Holley carb. While this is impressive horsepower, you are smart to ask about the short-block because at 6,800 rpm, those cast-aluminum pistons quickly become an endangered species. Higher rpm imparts more stress on cast pistons and those stock rod bolts. The question is not whether a piston will crack, but rather how much damage will occur when it does. For durability with this larger camshaft, you will need to add a set of forged pistons, aftermarket rods, and a good torque-plate-honing job. The cast crank should be fine for street use even up to 6,800 rpm.

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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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