About the 4.9 Liter Turbocharged Engine

To explain what makes the turbocharged 4.9 Pontiac V8 so special, we should first look at it’s history as a non-turbo V8 also known in the Pontiac community as the 301.

The Pontiac 301 V8 was introduced in 1977 (a 265 cubic inch was also offered in 1980-81). It was designed to be a lightweight economy V8 during the dark times of gas shortages and strict EPA (Environmental Protection Agency) emissions regulations. With increases in CAFE (Corporate Average Fuel Economy) standards and the assumption that American car buyers would not want to give up their beloved V8’s, the auto manufacturers set out to produces small cubic inch, lightweight, V8 engines with MPG and emissions being the goals, not horsepower. Most of them were based off of their existing larger displacement engines to minimize tooling costs. Some examples are the Oldsmobile 260 and 307 V8, the Chevy 267 and 305 and Ford’s 255 cubic inch V8.

There are many differences between the 265/301 vs. the conventional Pontiac 326-400. Many of these changes were done to save weight which helped in fuel economy.

The 265/301 has the following:

Shorter block deck height
Shorter crankshaft stroke (3.0”)
Different Bore diameter (4.0” for the 301)
Externally balanced rotating assembly (weight added to the flywheel and harmonic balancer)
No center counter weights on the crankshaft (one at the "snout" and one at the flywheel flange). *Picture 1 Below
Siamese port cylinder heads (one intake port is shared by two adjacent cylinders). *Picture 2 below
Single plane intake manifold for the Siamese heads. *Picture 3 below
No oil filter adapter (oil filter pad is machined into the side of the block). *Picture 4 below
Timing cover has no timing mark. (It is a separate plastic timing indicator).
Narrower lifter valley cover due to the shorter deck height.
Narrower intake manifold.
Narrower crankshaft thrust bearing.
7/16” main cap bolts (1977-79)
Thin wall cast block (1977-79)
Center exhaust port has 3 bolts for the manifold.
Special valve lifters.
Different engine accessory brackets. (Due to the short deck height block).

Introducing the turbo…

With the strict emission regulations coming down from the EPA every year, Pontiac was having a hard time keeping performance in the lineup for the Trans Am and Firebird Formula. The Pontiac 400 V8 would not return after 1979.

The only engine Pontiac had that could pass EPA was the 301. And a decision was made to increase it’s performance with the addition of a Garret turbocharger for 1980 and 1981. In order to do this, changes needed to be made to accommodate.

The differences between the turbocharged 301 vs. non-turbo...

Thicker cast cylinder block (cast “301T” in the side of the block).
½” main cap bolts.
Special "D" shaped dished pistons with steel "strut" cast under the head. *See photo on right
Moly piston rings.
Pressure rolled fillets on the bearings journals of the crankshaft for added strength.
Special Oil pump (high pressure/volume)
Special intake manifold for turbo mounting.
Special cast passenger side exhaust manifold (for turbo piping).
Special dual stage thermostat. This is used to control coolant flow to the base of the carburetor. It heats up the carb when the engine is cold. When the thermostat opens, it blocks coolant flow to the base of the carb.
Both engines share the same cylinder heads. There are differences between cylinder heads through the years. 1977-1979 non-turbo does not have the provisions for the AIR injection pump for emissions. Both cylinder head versions are marked “01” for a 301 and “65” for a 265.

Now when it comes to comparing a 1980 4.9 Turbo to a 1981, there are some big differences. Mainly with fuel management.

Differences between 1980 and 1981 Turbocharged 4.9s.

1980 (and Export 1981):
- PEVR (Power Enrichment Vacuum Regulator) for fuel enrichment
- Special non-computer controlled carburetor for turbo
- Distributor has mechanical and vacuum advance
- Knock sensor in intake manifold (1980)
- ESC (Electronic Spark Control) module only. This does not control the timing advance. It only retards the ignition timing in the event detonation is detected.

1981 (US spec):
- CCC (Computer Command Control) with ECM (Engine Control Module)
- ESC module is different than 1980 and communicates with the ECM.
- Added sensors for CCC:
  - MAP (Manifold Absolute Pressure)
  - TPS (Throttle Position Sensor)
  - O2 (Oxygen Sensor)
  - BARO (Barometric Pressure Sensor)
  - CTS (Coolant Temp Sensor)
- Distributor has no mechanical or vacuum advance. All timing is controlled by the ECM and ESC.
- Knock sensor located in the block next to the distributor.
- Carburetor is computer controlled and has an electronic MCS (Mixture Control Solenoid).
- No PEVR.
- The AIR injection system, for emissions, has a tube going to down to the catalytic converter.

Myths, theories and random BS about the 301….

Q: Can conventional Pontiac heads be used on the 301 block?

A: Yes…kind of. The 301 uses the same head bolt pattern as a regular Pontiac head. The issues you run into are:

1.) the shorter deck height requires a custom made, narrow intake manifold. You cannot use the 301 intake due to the siamese ports.

2.) A custom head gasket is best. Although some people have used conventional 400 style head gaskets but, the top corner oil drain holes become very close to a water jacket port in the 301 block. Conventional heads have been successfully used on a 301 block in a non-turbo application using Butler Performance head gaskets and a custom made intake manifold. The gasket sealing surface at the water jacket hole is very small, but it seemed to work. To learn more about the differences in the cylinder heads and cooling passages, see our YouTube video.

Q: Can I use a 326-400, 3.75” stroke crank in a 301 block?

A: Again yes…kind of. The 301 does use the same 3" diameter main bearings as the 326-400 but the issue is with the narrow thrust bearing of the 301. It has been done successfully on a non-turbo application using a custom made spacer on the block to use the 326-400 thrust bearing and main bearing cap. Also, the bearing locking tab is in a different position on the 301 vs. 400 so another bearing “notch” needs to be added to the block.

Q: Was the Turbo 4.9 offered as a 4 speed?

A: No. In fact all 1980 Trans Ams were factory built with automatics. No manual transmission was available. In 1981 the 4-speed returned, but with the 305 Chevy V8. A non-turbo, 4-speed, 301 was available in 1979 in the Firebird, Trans Am, Grand Prix, LeMans and Grand Am. This is a special flywheel due to the external balance of the 301. Using this flywheel, or one of our billet steel flywheels, along with all the other 4-speed parts, one can convert a Turbo 4.9 to a manual transmission.

Q: Do Turbo 4.9’s have special heads or camshaft?
A: No. The turbo engine uses the same heads and valves as the non-turbo 301. It also uses the same camshaft as the low-performance, non-turbo 301. In 1981, the 301 Turbo head added rotators to the exhaust valves.

Q: With such a short stroke and a short deck height, the 301 should really be able to turn some high RPMs?

A: Not really. The heads are the main problem. They are restrictive and the engine just doesn’t make power past 4500 RPM.

Q: What octane fuel should I use in my Turbo 4.9?

A: With any "forced induction" car (turbocharged or supercharged), you should use the highest octane fuel available. Lower octane fuel will lead to detonation which can cause engine damage.

My theory as to why the Turbocharged 4.9 gets a bad reputation from the muscle car enthusiasts…..

The early 80’s were a dark time for performance. GM had a corporate policy that all their engines were to be able to run on 87 octane, no lead fuel. Low octane fuel is not good for a turbocharged engine. It is more prone to detonation and the knock sensor would see this, retard the timing and kill performance.

Everyone was used to the tire shredding torque of the big cubic inch V8’s of years prior. In fact 4 short years earlier, you could still get the Trans Am with a 455 cubic inch V8 and a 4 speed transmission. Now, with the standard 3.08 rear axle ratio, hefty curb weight and the delay until boost came on (aka turbo lag) the Trans Am was not the stop light terror everyone was used to.

But, it was refined into a great touring car. With the WS6 suspension package you got larger sway bars, 4 wheel disc brakes, quick ratio steering and 8” wide wheels (7.5” wide in 1981) and the Trans Am became a great cornering machine. The Trans Am still had a presence about it too. The Camaro looked like it could kick your butt, but the Trans Am looked like it was coming over to do it.

My experience with the many TTA's we have worked on, is that it is a fun car to drive. Yes, punching the gas pedal from a dead stop is not going to instantly set you back in the seat and send the tires up in smoke, but when rolling at 30+ MPH and hitting the gas, it will get up and go.