71 lemans

[smoking joe]

the original 400 engine block is toast and I purchased a1978 engine , the motor mounts from the 1971 won't bolt to the 1978 block , I purchased 1978 mounts and they won.t fit the frame mount and would move the engine back against the fire wall , what mounts do I need to make this conversion ?

 

[melsg5]

You are 100% sure that original engine is a 71 and the new one a 78. Starting in late 70 blocks were cast with 5 holes. They used 2 in line and one above in the middle. Starting in 77 the blocks had 3 holes using the same arrangement. Look at the Ames Performance catalog for more details.

 

[cammerjeff]

Pontiac blocks from 67 to 69 were set up for either fitting a Firebird (3 motor mount holes), or any other body style (2 Motor Mount Holes), 70 to early 76 were set up to install in any body style (5 motor mount holes), then in the middle of the 1976 model year they eliminated the 2 Motor mount holes previously used by the non Firebird body styles and adapted the other cars to use the current model year Firebird style motor mounts. And they stopped drilling and tapping the 2 motor mount holes they used.

So you need this Kit

https://butlerperformance.com/i-24453652-pontiac-engine-mount-adapter-kit-for-76-up-engine-in-a-69-earlier-chassis-70-lemans-set-bpi-mm5.html?ref=category:1393557

it is easy to install, and you use the original 1971 Motor mounts with it.