1970 was the first year for the 455 engine and last for the Ram Air IV. You'll pay a premium for a high performance 1970 GTO.
The 1972 GTO was optional on the Lemans series. The GTO can be identified by front fender vents and black recessed grilles with a GTO badge on the left side. The engines were carryovers from last year. 1972 was the last year for this body. For 1973 GTO changed completely using the new Colonnade shell.
Engines: The GTO is defined by its drive train and certain options make some more expensive and desirable than others. You could buy a 1968 with anything from a Turnpike Cruiser with two barrel carb all the way to the Ram Air II with 360 horsepower. 1969 added a Ram Air IV with 370 horsepower. The performance engines were Ram Air II, III and IV which used round port cylinder heads. In 1970 you could get a 455 engine in regular or HO trim. Pontiac improved the HO package in1971 with round port heads, Ram Air induction, hot camshaft and four bolt main bearings. The base 455 used the D port heads and was an automatic transmission only car. The hottest engines were Ram Air IV, 455HO, and Ram Air IIIs in that order. They're the most expensive and demand maintenance as they're sensitive to tuning changes. The reward is intense acceleration with mid twelve second ETS possible using slicks, headers and proper tuning. If drag racing isn't your hobby, a stout 400-four speed will satisfy you.
The Ram Air IV engine was GTO's hottest engine. The expense and maintenance issues are balanced by remarkable performance.
If you want air conditioning or use the car for travel, consider a tamer 400 or base 455. Many novices buy too much engine and regret wrestling a four speed car with manual steering because someone told them a stripped Ram Air GTO is the car to own. Match the car to your lifestyle and needs.
Those who like to drive a lot may prefer a base 400 or 455. The 455HO is a great compromise of driver comfort and power.
Desirable and Rare Options: The GTO had a large option list. We've covered the engine based ones but there are visual enhancers and comfort goodies as well. Hideaway headlamps, Hurst His'n Hers shifter, air conditioning, power windows, power brakes, FM stereos and 8 track players are desired options. Most cars had only a few of them. Many restored examples had options added to suit owners' tastes. The hideaway headlamps is a good example as probably more exist today than in 1969. By 1970, any convertible GTO was a rare beast and 1971 was the last year for that body style.
Most GTOs only had a few options and many were customized. This 1968 is typical with Grant steering wheel, gauges and rear air shocks.
Weak Spots to Look for: You should spend about sixty percent of your time examining the body and chassis of a purchase with the remainder devoted to the drive train and interior. GTOs used body on chassis construction and were fairly strong but were subjected to incredible abuse for years before they were restored. Be sure to check for these well known weak spots.
The sill between trunk lid and rear window is infamous for rust. It's made worse with a vinyl roof option with which approximately fifty percent of GTOs from 1969 and later were equipped. The trunk floor rusts badly at the back for the same reason. It's common for the rear quarter panels to rust requiring replacement panels. The hood sheet metal often bends due to its length, weight and lack of lubricated hinges. Endura noses are restorable, usually the trouble is aligning the nose with the front fender panels and hood. Reproduction floor pans, quarter skins, doors are available but obscure bits are best sourced from parts cars for correct fit.
On the chassis, the control arms arms connected to the rear axle should be checked for damage and rust. Abused cars will show twist in the arms and rounded sections where the bolts go through. A distorted rear frame cross member should have you looking at the gas tank and side rails for redrilled holes from a rear bumper replacement. Careful examination may reveal straightened metal from a prior collision. The front frame rails should be looked at from beneath at the stabilizer bar anchors and radiator frame. Check the side rails of the chassis on the inside for severe rust or signs of frame straightening in the form of tiny wrinkles or bondo. Most hardtop and coupe GTOs were open channel frames unless ordered with the rare heavy duty frame option in which case it will have a boxed chassis. This makes them easy to check for serious damage if you take the time.
Verifying Your GTO: You can find out how your car was equipped from the factory and the selling dealer by sending for a Pontiac Historic Services package (phs-online.com).The service is essential for any car lacking either an original bill of sale or a build sheet. It verifies what engine and drive train it came with along with major options, color and interior equipment. Although the '68 to '71 era GTOs are easily determined by looking for the '242' digits in the VIN tag, you can't stop there. Sales of cowl, dash and A pillar tags from scrapped cars are strong. Reproduction cowl and VIN tags exist.
In 1972 GTO became a Lemans option losing the '242' VIN code. Verifying a GTO option must be done either by contacting PHS or by a build sheet found in the car. The GTO option is listed as '334' on the build sheet or 'W62' on the dealer bill of sale. A nice feature of 1972 VIN tags is that the engine displacement is listed as the fifth digit. GTOs only came with 400s or 455s. Lemans could have any V8 engine available so don't rely on the VIN tag alone. The GTO front end was available as a $41 option on Lemans.
1972 Lemans Sports resemble GTOs with the optional front end treatment. Checking the VIN with phs-online will determine true status of any year GTO in question.
A two letter suffix code stamp under the passenger side cylinder head facing the radiator states the engine size and application. You'll find a partial VIN between the water pump inlet and outlet passages. On some blocks they'll be near the suffix code. If it doesn't match your dashboard VIN, it was replaced. Consult a guide for accurate yearly codes. The engine displacement was cast low on the block near the fuel pump starting in 1970. The engine casting number is found at the rear of the block below the passenger side cylinder head. The block casting date is found in the distributor pad area and uses a month, date, year format with A for January.
Engine casting date is near distributor well. Compare with suffix code and partial VIN at front to determine originality.
Automatic transmissions have two letter application tags on the passenger side above the oil pan rail. A partial VIN is stamped on the driver side oil pan rail verifying an original. Manual transmissions have codes stamped on the passenger side and partial VINs were added from 1968 onwards. The Muncie code is a letter-number format with either 'M' or 'N' for plant, '8' for 1968, 'C' for March and '22' for 22nd day of month. 1969 and later Muncies added a letter code 'A,B or C' to indicate wide, close range or M22 heavy duty gear sets. Rear axle codes are stamped on the passenger side tube near the top with three letter code, production date and gear set details. GTOs used 10 bolt carriers for most of the line and the 12 bolt for 455 drive trains and certain high performance 400s. This will help you pick a sweet ride from the also-rans.