Research Topic: How to Identify a 1968-1970 Big Block Chevy II or Nova

1. The Heater core:

The 1st clue and probably the most obvious is the heater box and how the core tubes exit from the middle of the heater core cover.

Here is a comparison of a small block (top) to a big block (bottom)

There is seal that is used on the pipes of the small block heater core (right). Since the big block core is reversed a plug is used to cover the opening (left).

And then there is this special code on that bracket used where the tubes exit. Code is "AS".

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2. The Fan Blade:

Now another obvious clue should be the special 5 blade fan which looks like this and an original will have a marking of a "W" or "M" on one of the fan blades. This fan was installed on a early 1970 Model year L34. See note below.

Note: There were 4 different part numbers for 5 blade fans used between 1968 and the 1970 model years. 1968 used a clutch fan with 5 blades. 1969 and 1970 used a non clutch fan with 5 blades. The L34 fan was different than the L78 for part of the 1969 and 1970 model years.

The Nova Research Project is seeking clear pictures of the 1968 - 1970 Big block fans and the 1968 big block fan clutch.

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3. Radiator and Support:

The radiator support has a larger opening to it and it looks like this when out of the car.

It looks like this when mounted.

An then there is the fan shroud. As you can see in this picture, the shroud does not hold the radiator to the radiator support. The radiator bolts directly to the support with 4 bolts.

Now the big block cars use a rubber flap to cover the gap between the radiator and support.

The flap is held down by two types of things. I only have a picture of the one kind. This one is a black round plastic plug and it has a line that runs across the center of it. Here's what it should look like. These round plugs were also used in some of the early 70 cars to hold the TCS relay to the wiring gutter. The Metal clip was used in the 1968 and 1969 model year. It was also used in the beginning of the 1970 model year. The switch happened before December 1969.

Now the radiator should be a Harrison radiator and these are the codes that were on my 70 with a manual transmission. The passenger side has "OFO" on it which looks like this:

The driver's side has a code of "IL" on it which looks like this:

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4. Motor Mounts:

Now the big block uses specific motor mounts which offset the engine to the passenger side. The mounts look like this.

Here are a selection of Motor mounts. The closest one is a V8 Small block. The next two are Big Block mounts.

Top 3912598 RH & 3912597 LH Big Block replacement engine mounts.
Middle 3980942 RH & 3980941 LH Big Block engine mounts.
Bottom 3980938 RH & 3955183 LH Small Block engine mounts.

Here is the L34 Big Block set installed.

5. Valve Covers:

Here's the valve covers:

When it is put all together, it should look like this and notice the offset of the motor to the passenger side.

See 400 Cu. In. Engine Released For more information on the 1970 396 big Block

Pictures courtesy of Ron Bentz and Allen Cardo

Research Topic: How to Identify a 1968-1970 Big Block Chevy II or Nova

1. The Heater core:

The 1st clue and probably the most obvious is the heater box and how the core tubes exit from the middle of the heater core cover.

Here is a comparison of a small block (top) to a big block (bottom)  

There is seal that is used on the pipes of the small block heater core (right). Since the big block core is reversed a plug is used to cover the opening (left).

And then there is this special code on that bracket used where the tubes exit. Code is "AS".

---

2. The Fan Blade:

Now another obvious clue should be the special 5 blade fan which looks like this and an original will have a marking of a "W" or "M" on one of the fan blades. This fan was installed on a early 1970 Model year L34. See note below.

Note: There were 4 different part numbers for 5 blade fans used between 1968 and the 1970 model years. 1968 used a clutch fan with 5 blades. 1969 and 1970 used a non clutch fan with 5 blades. The L34 fan was different than the L78 for part of the 1969 and 1970 model years.

The Nova Research Project is seeking clear pictures of the 1968 - 1970 Big block fans and the 1968 big block fan clutch.

---

3. Radiator and Support:

The radiator support has a larger opening to it and it looks like this when out of the car.

It looks like this when mounted.

An then there is the fan shroud. As you can see in this picture, the shroud does not hold the radiator to the radiator support. The radiator bolts directly to the support with 4 bolts.

Now the big block cars use a rubber flap to cover the gap between the radiator and support.

The flap is held down by two types of things. I only have a picture of the one kind. This one is a black round plastic plug and it has a line that runs across the center of it. Here's what it should look like. These round plugs were also used in some of the early 70 cars to hold the TCS relay to the wiring gutter. The Metal clip was used in the 1968 and 1969 model year. It was also used in the beginning of the 1970 model year. The switch happened before December 1969.

Now the radiator should be a Harrison radiator and these are the codes that were on my 70 with a manual transmission. The passenger side has "OFO" on it which looks like this:

The driver's side has a code of "IL" on it which looks like this:

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4. Motor Mounts:

Now the big block uses specific motor mounts which offset the engine to the passenger side. The mounts look like this.

Here are a selection of Motor mounts. The closest one is a V8 Small block. The next two are Big Block mounts.

Top 3912598 RH & 3912597 LH 1968 Big Block engine mounts.
Not shown 3950114 RH & 3950113 LH 1969 and Early 1970 Big Block engine mounts.
Middle 3980942 RH & 3980941 LH Late 1970 Big Block engine mounts.
Bottom 3980938 RH & 3955183 LH Small Block engine mounts.

Here is the L34 Big Block set installed.

5. Valve Covers:

Here's the valve covers:

When it is put all together, it should look like this and notice the offset of the motor to the passenger side.

See 400 Cu. In. Engine Released For more information on the 1970 396 big Block

 

Pictures courtesy of Ron Bentz and Allen Cardo