it or not Trans Am lovers, a vast majority of T/A's 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 T/A guys will avoid the 403 like the
plague. In actuality
the Olds 403 can be one kick @$$
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 T/A'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
$1500.00 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 T/A.
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 T/A will be running mid 13's at the strip on pump gas.