Rocket Boost by
Ron is a friend of Texas Trans Am Service and Restoration. He was fortunate enough to buy his 1979 Chestnut Brown Trans Am in near mint condition from a Museum/Classic Car Showroom in Illinois, so we can't take credit for much of his results. We heard of his success at the track with careful modifications to the Oldsmobile engine.
He was kind enough to share his recipe with us, and let us shoot some video at Texas Raceway in Kennedale. Like it or not Trans Am lovers, a vast majority of Trans Ams from 1977 to 1979 were equipped with the corporate 403 Oldsmobile engine.
Unlike the Oldsmobile 400, 425 and 455, the 403 was a small block. Unfortunately most 77-79 Trans Am guys will avoid the 403 like the plague. In actuality the Olds 403 can be one super motor. From the factory the 403 was rated at 185hp and 320 ft/lbs of torque.
The bore /stroke ratio of this motor is awesome. The basic geometry is similar to the Ford and Chevrolet 302 CI small block. Most guys will admit to the high- winding capability of both those engines.
This is where the 403 gets a bad rap. The windowed mains of the 403 prevent the engine from winding past 5000-5500 rpm without risk of damage.
Fear not Rocket Power fans, help is on the way. With a minimal investment you can be putting out 300 to 350 hp and tire-frying torque. The 403 responds well to more compression and cam, and like all late 2nd generation Trans Am's a true dual exhaust. Always check your local emission law before making modifications. The 403 4A Olds head is a 83 cc smog head. The result is a compression ratio of around 8.0:1. Try to find a set of 1968 to 1972 Olds 350 heads.
A set of early Olds 350 heads have a 64 cc chamber and will raise compression to around 9.5:1-10:1. Make the effort to clean-up the ports and pockets on your heads. You will see a vast improvement in horsepower. Edelbrock aluminum heads are an option, but that's an extra $1,500.00 and their ‘77 cc chamber will give you 8.5:1 compression.
You will want to add a cam and intake to match the heads. The Edelbrock Performer intake is pretty much an aluminum copy of the factory intake, just a lot lighter. If you bolt on a Performer intake with no other changes you will notice little improvement.
The Performer intake is thick enough that it can be port matched to your early Olds heads. If you opt for the Performer RPM intake manifold, overall height will increase causing shaker hood scoop clearance problems... the choice is yours. Any factory style 650 to 750 cfm Q-jet carburetor will fit the Performer manifolds. The factory camshaft should be pulled and a flat tappet cam between 206 and 220 duration @ 0.050 inch lift can be used. You can install a larger cam 214/224 if you change rear end gears to 3:42 or 3:73 and advance the cam 4 degrees. Advancing the cam will lower the 214/224 @ 0.050 inch lift torque range 300 to 500 rpm. This will make your factory torque converter with a 1500 to 1800 rpm stall, usable. You can also consider a stall converter with 2200- 2500 rpm stall and a cam. By all means degree your cam! I run a 214/224 @ .472/.496 lift with 110/320 lbs valve springs and 3:42 gear on an air-conditioned, daily driver Trans Am.
Upgrade your HEI to include an 50,000 volt coil, performance advance kit and adjustable vacuum advance. You will need to drop a range or two from the factory 403 spark plug. I run 68 Olds 350 plugs. You may consider dumping the cast iron exhaust manifolds and installing headers. Because I show my car I still run OEM exhaust manifolds ... the choice is yours. Doing the above mentioned will help you address the main performance weakness of the 403 - the cam and compression. I must stress, the details (degree the cam, port match the intake and heads, performance HEI with curve kit) will maximize your performance gains.
Do these simple and low budget modifications and your 2nd generation Trans Am will be running mid 13's at the strip on pump gas.
My 403 parts list:
403 ci Olds stock bottom end
1968 #5 Olds 350 heads, drilled for 1/2 inch head bolts, milled
.015, 3 angle valve job with full port and polish.
110/320 valve springs and stainless steel OEM size valves.
Edelbrock #3711 intake port matched to the heads.
Jet stage 1 Q-jet Carb
Pertronix performance HEI kit.
SSI 214/224@ 472/496 lift cam and performance lifters.
Dynagear double roller timing chain.
2 1/2 inch dual exhaust with Dynomax Ultra-flo mufflers.
Richmond 3:42 ring and pinion with kit
BandM Shift kit
I did all work except the head milling and valve job. Total parts cost: $1,661.99.
Return to NFTAC Tech Tips Page