To start with you really need to find out if the vehicle still has its original engine. You need to see if the engine serial or production code ties up with the vehicles VIN (vehicle identification number). The VIN can usually be found on a small plate on top of the dash on the driver’s side of the vehicle. This is best viewed from outside the vehicle, through the windscreen, best to do this with the vehicle stationary! As you can see from this 1999 C5 Corvette, fig 1, and the 1974 Challenger, fig 2, the VIN plate hasn’t moved much in 25 years, as indicated by the white arrows.

Fig 4. 10th Digit decoding in 17 digit VIN’s

Having briefly covered the two extremes of engine identification, let’s try to cover that all too familiar grey and muddy area. This is when you have an engine and you think you know what it is but your not 100% convinced. All you really need are a few pointers to guide you in the right direction, just to confirm your beliefs. There are many tell tale signs that can help you with your identification. For instance have you ever been to a car show with a friend, and been impressed by the way they instantly know, “that’s a small Chev” or “what a great Pontiac lump.” Your friend obviously knows the small peculiarities of each engine. In the immortal words of Sherlock Holmes, “These are the things you may have looked at, but not observed.” Things such as valve cover size and bolt fixings or the number of bolts that mount the water pump. It is these simple but important features that sometimes allow almost immediate identification of an engine type.

As an initial example lets take a look at some GM engines that were fitted in various models during the 1970’s. Possibly the most confused engines from this period are the 400 CID Pontiac and the 403 CID Oldsmobile engine. These were both fitted into Trans Ams from 1977 to 1979. Unfortunately Pontiac show both engines as 6.6litre. So if you have one of these beasts, how do you tell them apart without decoding VIN's or collecting engine cast numbers. The water pump is a good place to start, the 400 CID Pontiac engine, from this period, has an 11 bolt mounted water pump whilst the Oldsmobile water pump has 8 bolts. The valve covers also vary in as much as the Pontiac has 4 bolts retaining each cover whereas the Oldsmobile can have up to 10 bolts per cover. There are some other minor differences, but this should be enough information to tell the two apart. Other engines fitted to the Firebird and Trans Am of this time were the 305 CID and the 350 CID small block Chevrolet engines. These are easily identified by the 4 bolt retained valve covers and the water pump which is mounted on two legs, one either side of the timing cover, using four bolts, two per leg. During the early 1970’s Chevrolet were fitting some of their ‘big block’ engines to various vehicles. These can be identified by the 4-bolt water pump, also mounted on two legs. The valve covers are retained by 7 bolts and are 7 inches wide. Pontiac was also fitting 350 CID and 301 CID engines. The 301 CID engine may be identified by its laterally mounted oil filter; i.e. it screws to the side of the block lying down, as opposed to being vertically mounted. Also fitted into these ‘F-body’ cars, as well as several Cadillacs of the time, was the 350 CID Oldsmobile engine. Oldsmobile were also producing a diesel version of their 350 CID engine, which was fitted into Cadillac and numerous other GM models during the mid to late 70’s. Obviously identified by type of fuel it uses! If you have a Cadillac with a petrol engine and are not sure what you have, as a general guide if the distributor is at the front of the engine it should be a Cadillac powered car. Cadillac’s with rear mounted distributors are usually Oldsmobile powered. Towards the end of the 1970’s Buick were getting in on the engine sharing bandwagon, and their 350 CID engine, easily identified by its front mounted distributor, was finding its way into various Oldsmobile and Pontiacs. These were interesting times indeed for General Motors, the vast array of engine sizes they had to hand allowed them to offer an equally large amount of option packages for their vehicles.

Briefly moving away from GM and heading over to Ford, and the two engines here that are most often confused. In one corner there is the 351 Windsor engine named after the Canadian City where it was first produced. The city being Windsor not ‘351’. In the other corner is the 351 Cleveland engine. Strangely enough named after the city in Ohio where it was first produced. Many people often confuse these motors. The quickest and easiest method of identification is valve cover bolt count. The Cleveland engine has 8 bolts retaining each cover whilst the Windsor only has 6 bolts per cover. If after this you are still unsure pull out your measuring stick, the Cleveland covers should measure 6 inches overall width and the Windsor 5¼ inches. The Cleveland engine went on to become the 351M or modified engine and has the same valve cover bolt count and size as the Cleveland. Unfortunately, the 289 CID and 302 CID engine configurations are very similar to the 351 Windsor engine, and consequently determining actual displacement of the engine has to be done through cast or stamped numbers on the block or an internal investigation........ wasn’t that a hit for Dire Straits. 

With the interest in early 70’s muscle cars being better than ever at the moment, a lot of Mopar vehicles are popping out of the wood work. Mopar, obviously covering vehicles from the Chrysler, Dodge and Plymouth stables. The most sort after engine from Mopar being the 426 CID ‘hemi.” Easily identified, as is any hemi, by the row of spark plugs down the centre of the valve covers, with the front mount distributor putting it in the big block family of engines from Mopar. The small block Mopar engines may be identified by their rear mount distributor and 7 bolt water pump. The remaining big block Mopar engines have a front mount distributor and small circular 4 bolt mounted water pump.

In summary, the first course of action should be to find out if the engine belongs to the vehicle. VIN decoding is then required to identify engine size and year. For exact identification of any engine without having the VIN or stripping it down and measuring stroke length and bore size, you will have to refer to the engine blocks cast numbers or stamped serial or production codes. For rough identification there are numerous little peculiarities that engines have to use as a guide. These will generally tell you whether an engine is Ford, GM or Mopar; it is rare you will never tell exact engine size just by looking. Remember to make use of your local American car club or American spares supplier, ultimately these are the people who will be able to help you in your quest.