10 replies to this topic

[pfrichardson]

are posted:

http://www.scca.com/.../cars-and-rules
 

[Jim Drago]

DATE: September 3, 2015 NUMBER: RM 15-13 FROM: Club Racing Board TO: All Members SUBJECT: Spec Miata Plunge Cut Clarification In GCR section 9.1.7.1.f.3, add the following language “The throat area of the port consists of the 90 degree angle at the very bottom of the cast steel valve seat as it transitions to the aluminum casting below. It is permitted to plunge cut the throats in order to correct for core shift that is commonly found in many cylinder heads. The cut must be cylindrical and concentric to the valve guide axial centerline, within a tolerance of .005”, for the entire length of the cut. The radius tangent to the cylindrical and bottom surfaces shall not exceed 0.375”. This cut cannot extend further than the specified number below from the bottom of the ferrous valve seat. There can be no tooling or machine marks in the head below this point (including OEM machine marks). The intersection of the machined surface of the plunge cut to the port casting shall not be altered, except that the area under the short turn radius may be de-burred, with the de-burring not to exceed 1.5 mm in width. The 90 degree bend at the bottom of the valve seat and the aluminum directly below it will be measured with a gauge and must conform to the maximum diameters and depths listed below.”

[Ron Alan]

Can someone clarify? If this area is factory cast why would it have OEM tooling marks? And if in fact the original manufacturing procedure involves a human inspection with casting clean up by hand...we have to find heads that came perfect?

[Bench Racer]

Ron, in the past OEM machining (not hand machine marks) were found outside the plunge cut specifications. Dan Tiley posted pictures, hence the plunge cut specification dimension was increased. Have never hear a word referencing hand machine marks within an OEM head from the manufacture.

[Steve Scheifler]

I was looking at a '99 head today with original factory plunge cuts extending well beyond the allowed depth, then the more recent re-cuts to the correct depth. Unfortunately it can't be proved that the deeper cuts are in fact original so that head can't be used. Too bad, it was otherwise a decent casting.

Those who see a lot of these heads, roughly what percent of 99/00s are like that? What about the 01+?

[Jim Drago]

Can someone clarify? If this area is factory cast why would it have OEM tooling marks? And if in fact the original manufacturing procedure involves a human inspection with casting clean up by hand...we have to find heads that came perfect?

[Dan Tiley]

It's just one of those crappy situations where it's feasible (although unlikely) that someone with a completely stock and original Mazda engine could conceiveably be disqualified becuase of OEM production variation.  I see the same thing on all variations of Miata heads (90-05).  When we (SMAC/CRB) increased the allowance from 9 to 12mm, we still knew there were a fair amount of heads out there that were over from the factory, but increasing the number above 12 could potentially encourage builder creativity. 

 

It's glaringly obvious where the precision engine builder cuts end and the very coarse factory cuts continue on.  Typically, if its there at all, it's only on one or two of the ports in the engine, and any reasonable inspection would include 4 or more ports, especially if someone was about to be disqualified for it.   As much crap as we give our tech officials, I truly believe they would use reasonable discretion in this case if one crossed over the tech table.... and I say that having landed on both the right and wrong side of those decisions.  

[Steve Scheifler]

I might have agreed, until this latest "clarification". I presume the point was to disabuse us of any doubt on that point and it would seem difficult to use any discretion now. I would not want to show up at a Major or Runoffs with one like shown above.

[Jim Drago]

I might have agreed, until this latest "clarification". I presume the point was to disabuse us of any doubt on that point and it would seem difficult to use any discretion now. I would not want to show up at a Major or Runoffs with one like shown above.

Agreed.. It was non compliant before.. It is super duper really non compliant now

[FTodaro]

Ok so what am I missing? How can we develop a spec that is more restrictive than the variance found in the Manufacturing process? That does not make sense either. No stock head should ever fail. We are dipping back into the increasing the expense of running the class category.

[Jim Drago]

Ok so what am I missing? How can we develop a spec that is more restrictive than the variance found in the Manufacturing process? That does not make sense either. No stock head should ever fail. We are dipping back into the increasing the expense of running the class category.

I disagree Frank. The goal and what was asked for the SMAC at the time was to spec one of the best available heads from Mazda. That is what was done. The SMAC, CRB and anyone that listened knew that the rule would only encompass 95% of the heads from Mazda. Examples like the one I posted are clearly outside that spec, if we try to encompass all.. where do we stop? The "new" thing will be making "mazda" marks in the heads that help flow etc, then dull them down and put new shiny plunge cuts in to the rule. Then say, those are my marks, the rest are mazdas. It is unenforceable IMO, a line needed to be drawn, it was and it is clear.