OST-077: Nothing double natural about twincharging

[oldeskewltoy]

So in October of 2020 my client contacts me about building him a head for a twincharge build.

He'll will be running a supercharger from a Mazda Millenia, and the turbo he is planning on is TD06sl2-20g




The head arrives, and gets dismantled, and sent out to be cleaned.




once back, it gets measured.... it has been machined before... 0.12mm, or about .005"




The head gets deburred....




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




More to come.....

[banpei]

A twin charge! That's interesting and I'm looking forward to see this progress!

[oldeskewltoy]

(05-25-2021 11:41 AM)banpei Wrote:  A twin charge! That's interesting and I'm looking forward to see this progress!

1down




As this is a boosted build that will be running up to 40 psi, every effort is being made to minimize detonation, including "softening" the spark plug opening.




Also the exhaust ports are opened up a fair bit




more to come....

[Vaptor]

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

[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......

[oldeskewltoy]

With the port work complete, it is off to get its valve job.


As this head will be running substantial boost levels, minimum specs (.5mm valve margin) just will not cut it, and the original exhaust valves while still within those minimums are just too thin............. I find 8 replacements with more margin.




More to come......

[oldeskewltoy]

As this is being twincharged (for those unknowing - twincharge is using both a supercharger and turbocharger in the same engine)...... Coming up with a cam for this beast was no easy task. After consulting with the engineers @ Cat camshafts, a "new" camshaft design was built.

258 overall, 224@1mm(.040") with 9.25mm of cam lift.




This cam should tick all the boxes, but to run this aggressive of a cam a shim over system just will not work, so this head will be running 1SZ shimless buckets.


To do this I have a set of 8 "sizing" buckets (8 of the thinnest) that I'll use to determine actual clearances, and then order the appropriate bucket to set the clearances.




More to come....