OST-077: Nothing double natural about twincharging

[oldeskewltoy]

(05-31-2021 09:09 PM)Vaptor Wrote:  Could you point a tell a bit more about this comment: And as this will be running substantial boost, ARP studs will be used, so clearance is added so the studs can't interfere with oil flow

Thx

The oil feeds the head at #1 bolt on the exhaust side. Essentially when you use ARP studs, there is a possibility that the shank of the stud can interfere with that small hole that directs oil to the head, and cams.

When you use a stock type bolt, they have a shank-down section which can't interfere with the oiling.



The ARP stud has nothing to keep the bolt free of the oiling hole. The problem was somewhat mitigated when ARP changed the stud diameter from 10mm, down to 9.2mm, but it is still possible to cause an issue.

Formula Atlantic builders began by drilling #1 exhaust bolt hole from the bottom up, stopping just after the oil feed hole. The only problem with this method is when lowering the head the stud can "catch" on the edge created by over-drilling the bolt hole. I did this as well, until I got to OST-044, a 7AF head....



Note all the bolt holes are flush for the washer, except the one in the lower right - #1 on the exhaust side. Here was a factory modification the factory took from Atlantic and incorporated into a stock head.

I just took their lead and have run with it.





back to this head.....


2 down - getting that exhaust opened for more flow




and now to 3 down




more to come......