Exh Manifold Bolt Locking Tabs
 

How many locking tabs did the factory use - all 12 positions or just the front and back on each head or ?? Working on a 1968 F'bird 400 restoration.

From a previous thread on this subject...

Perfect, thanks. I have that manual and missed that detail.

Are not the end holes a larger diameter as well ?.... My belief is larger holes for manifold expansion then locks to keep bolts tight from large holes and expansion cycles

Formulas - I secured the manifolds before seeing your note so too late to check the hole diameters for now. Next time manifolds are off the car I'll try to remember to report back...

I know the locking tabs where done away with by 75 and washers where exchanged.

This could have even had taken place back earlier as in when the low comp fully set in by 1971, but I have no definitive proof of that due to the circa of manual’s I have.

On cast iron manifolds the outer holes are larger to account for expansion and contraction (thermal cycling). I researched this when I noticed the larger outer holes on my ram air manifolds. There is a thread or two about this subject on this forum.

And the above is a darn good reason when running exh manifolds to use the factory steel gasket only and with a coat of antiseize on both its sides .