2015 Spec Miata Cylinder Head Rules

Class Petition

An appeal to SCCA and NASA



Compromise Spec Miata racers proposal to the SCCA/NASA Spec Miata Head Rules


SCCA/NASA Spec Miata Rules Committee.

A Call To Action By The Spec Miata Community

Due to a protest and disqualification of several racers and pro motors at the runoffs, SCCA and NASA have met and have proposed reversing the current plunge cut head rule, in favor of returning to the rules in place in 2009. The Stock Head Rule. This means that any competitor who had built a head to the current rule over the last 5 years will no longer be compliant.

The goals of the class have been to promote participation, close competition, and low cost across multiple platforms. The SCCA/NASA proposed rule change does not address these goals. We submit this alternative proposal to address those goals and the concerns of the class.

The current proposal is to add a weight penalty to the current competitor’s non-compliant heads, such that it will encourage them to convert to a stock head, over the next year or two. There are not sufficient heads to meet the immediate demand. The conversions to a stock head will entail hundreds of heads and hence hundreds of thousands of dollars of cost to Spec Miata competitors.  The proposed weight penalty will likely promote conversion making hundreds of cars noncompetitive while they wait for available heads.

The signers of the class petition wish to express their desire to propose a compromise that will allow the vast majority of the existing heads to remain complaint. Our proposal incorporates the existing rule with a slight modification and will address Testing and Measuring.


Permit the current plunge cut rule to stand and allow deburring to .250”.

See diagram below.







Testing and measuring.   We have confirmed with technical members of the club that measuring tools can be produced and/or measurements can be taken to confirm compliance to the rule. This rule will allow for specific guidance as to what is permitted and what is a violation.

Petitioners fully support the appointment and training of a technical position (a technical Czar) within the SCCA/NASA who will be trained and have the expertise to consistently evaluate compliance.




The compromise proposal will resolve several issues that will be created by reverting to the 2009 rules. For example:

1.      It will prevent the entire class from being punished for something they did not do.

2.      It  will allow the vast majority of existing heads to continue to be legal

3.      It will avoid a huge cost to the entire class.

4.      It will create a definable rule that will be able to be checked in tech.

5.      It will eliminate a pile of non-complaint heads currently in circulation.

6.      It will not enrich the motor builders.

7.      It will NOT move the rules significantly from where we have been for 5 years.

8.      It will allow home builders to now compete with the pro builders.

9.      It will prevent head rules with no specs, thus encouraging exploitation of the stock heads for additional power.


This is the most productive and orderly way to resolve our problem. A permitted deburr of .250” is in no way a major expansion of the rules.



The following signers urge the organizations to reconsider the extreme nature of the proposed SCCA/NASA rule changes and consider implementing our proposed changes that will result in no cost to racers while concurrently providing greater technical compliance and performance parity.