Is it absolutely necessary to drill the extra holes on the deck face so they intersect and match the holes in the head gasket and head face, on a "Mopar 340 Resto Siamese block". I have read the cooling section of 'How to build big inch Mopar small blocks' and Jim suggests you should drill 2 holes between the cylinders front and rear (yielding 6 holes each side total) at 55 degrees so that they intersect to allow water flow. And then restrict the big holes front and rear at the deck face by screwing a plug in with a 0.125 hole drilled in the plug. Just wondering for a street / strip engine with 600ish HP, if this is worth it or necessary. 400 Chevs are Siamese and don't seem to have over heating issues.

Thanks
Macka

See where this thread goes but check with Ryan J at Shady Dell

400 chevys have the holes. There is no way to bleed the air from the lower "hour glass pinch" point without those holes.

I ran a 340 resto block years ago on my W2 422 build and it did not have the holes and never had a cooling issue.

I have heard that too. Just assemble it and run it maybe.

The 400s use to have a issue of cranking heads due to
them getting hot because of the lack of the steam holes..
I changed many of those heads on a company that I use to
do maintenance on their trucks.. they were the early 400s

I had the same concerns. Ryan J told me not neccessary. Been running 4 seasons now coming up on 300 passes and no issues running hot at all!. Race only no Street Time.
4.185 Bore.