Jim,
This is an easy measurement installed in the engine. There are two measurement surfaces from the head reference point shown in the factor manual to the deck of the block. Just add in 1.1 mm for the head gasket thickess and you have the installed height from teh block to the reference surface.

These measuments were take using the numbers in the change propoals at Nationals both this year and last year. It is a simple measurment to take. I takes about 5 mintues with set of calipers and can be done on a hot engine. A hot engine will give you a little taller head due to thermal expansion. This will aid the competitor.

If you check your own head and are too close you have two options. First is to get another head and be happy you found it early and never got whistled. Second could be to install the 1.4mm headgasket. That is sort of a freebie to save an older head. I will make sure the actual rules allow using that 1.4mm headgasket and the extra height it creates will benefit the competitor.

Just remember through if you have head shaved to the max you could be over 10.5:1 There is variation in compression measurements and if you biuld to 10.49:1 you have risk that simple carbon build up on the top of the piston can bump that over 10.5:1 and earn you a DQ by whistler or be an acutal cc measurement of both head and piston top.

Now lets say you get an installed measurment done and it too short. If it is by 0.001 or 0.002 you are very close to measument error of calipers even in good hands. If you are off by more it will probably be a DQ. If you wish you can dispute that by removing your head and getting the bare head measurment. Both will be listed in the rules and that measurement is a bit more straight forward. However at that point the head is off the car and believe you me alot more parts will be inspected along the way.

Lets also remember the original intent behind shaving the head. It was not to max out compression, but to allow a driver to save good head by machining it true and flat. These are all old parts and tossing sight beat up head because you need to shave off 0.005 to make it flat again is dumb. If you are using 9.5:1 pistons there is alot you can remove before you even get close to 10.5:1.

Also.. the single biggest factor in engine compression is pistons and head thickness. There are others, but those are the big ones. Pistons can be visually identified through the spark plug. Heads can be measured. The two togther cover most of the way you can increase compression. After this is is all small stuff. However due to that small stuff keeping the 10.5:1 is smart.

AS a reminder here is are the actual numbers that will be used.

2011-6.) Publish rules in maximum head shave
Proposal: Head may be shaved to a minimum thickness of 0.891in(22.62mm) for 9.5:1 pistons and 0.927(23.54mm) for 10.2:1 pistons as measure on an uninstalled head in factory specified location – Factory manual page 15-16a dimension A. Installed heads measurements are as follows .934in(23.72mm) for 9.5:1 and .970in(24.64mm) to the surface of the block. Engines must comply with both minimum head thickness and compression ratio limit of 10.5:1. Tampering with the measurement surfaces in a way that distorts the actually head thickness measurement will be subject to penalties. For reference stock head thickness is 24.0mm +/- 0.1 (.945 in +/- .004) and stock head gasket is 1.1 mm (.043in).Justification: Publishing the limit on head thickness will make it easier to validate compliance of compression ratio when tools such as a whistler or more direct volumetric methods are not feasible. Cars will need to meet both the limit on head thickness AND the 10.5:1 limit.

cbuzzetti wrote:


The whistler has is flaws as well any measurment. Just like running over the scales at 2600lbs you are legal, but who knows next set of scales that could be 2597 and a DQ. That is why nobody runs at 2600lbs even. Too much risk and not enough reward. Put it another way. Do you want to shave to .927 and hope compression is always right at 10.5:1? Do want to gamble that your inspector can measure to .927 +/- 0.000?

Publishing this limit does two things. 1) It makes it easier to ensure you are not running way over on compression and it makes it clear what to build to and what you will be inspected to. This takes the guess work out of compression when you have the head shaved. My advice is to give yourself 0.005 room to allow for variations in compression measurments and inspections. Better than holding your breath during an inspection.

Joe, thanks for your reply to Charlie's post but you did not respond to his point that his head at Nationals was legal by compression but not by your measurement.

To me, that means your proposed measurement is not correct. Since we still need to meet the 10.5 compression limit, it seems to me that the any measurement that would be used to DQ someone, based on measurement alone, needs to be thin enough that there is NO question that the head is illegal regardless of which head gasket is used, what the deck height might be and how the valves are installed. To declare an otherwise legal head, illegal is a big deal to me and should be avoided, at all costs. It is much better to error on the side of too much compression than too little in making a head illegal. I guess that is our societies rationale that it is better to let several guilty people go free than to imprison one innocent person and, as hard as that is to accept sometimes, I agree with it.

While I agree with you about trying to get to 10.5 and taking a risk, the rule was put into place, as you point out, to allow late heads to remain legal. I know that I do not shave my head for compression. I shave it for flatness only but over the course of years, we will have problems with heads becoming too thin from rebuilding and not based on trying to achieve max compression.

You comment that publishing this limit does two things and then summarize the two reasons by saying that it takes the "guess work" out of compression. I am sorry to disagree. If the head measurement rule was the only rule, fine but you propose to still maintain the compression rule making us comply with two rules on the same issue rather than just one compression rule and I don't see how that makes any sense. Use one or the other but not both because now we will have to deal with both issues on a rebuild rather than just one.

Publish the thickness information in the rules as "guidelines" and cause for further inspections, possibly but don't make them DQ items.

Again, you make help make my point by talking about the skill level of the inspector having an impact on the measurement being taken. That is a separate, scary issue to a DQ item.

I have another thought but will talk to you in person at the track this weekend, if you are able to make it out.

Jim Foxx

No matter in the long run - but do all keep in mind the head can be left entirely alone and the block decked instead or in concert with. Same result.

OK, so what I am reading on this is that rather than mill the head to increase compression, one can deck the block during a rebuild to increase compression and not make the block any thinner with exactly the same result. Is that correct?

More expensive to do but gets around the head measurement as a DQ item and we are back with the real compliance issue being the compression.

Why force someone to do the expensive route if all we are trying to do is make sure we control actual compression. We have the rule now and the tools to police it. We don't need this new rule. We have a protest procedure and NASA has the ability to do it's own inspections so what we need is enforcement of our current rule if someone feels that there is a problem.

Enforce the compression limit and keep our rules simple!

Jim

I am told that this rule is no longer "Proposed" but, rather, it will be the rule. In my opinion, there has not been enough thought about it. If it makes a legal head illegal, it is a bad rule.

Charlie, your legal head will now be illegal.

Joe, you say that "Publishing this limit does two things. 1) It makes it easier to ensure you are not running way over on compression and it makes it clear what to build to and what you will be inspected to."

It does no such thing. A head can still be over on compression while meeting this rule so you plan to ALSO enforce the compression rule. A head can also be under compression limits but be illegal now. The only thing it does do is add another way to be DQ'ed based on a measurement that Joe agrees is difficult to measure to the 1,000th and can be off by more depending on who does the measuring. It actually adds cost and complexity to something that has NOT been a problem and is not a problem.

In addition, the proposed rule does not seem to take into account the gasket thickness issue. Is there a reason for that? Does that mean that we can not use the thicker gasket to stay legal?

I had a simple proposal to allow a competitor to choose to remove the head for accurate testing of the compression, if the head thickness was an issue at inspection, with the compression being the final determiner of legal or not. Of course, someone could just accept the DQ and not pull the head if they so choose. Was there no consideration given to providing a more accurate way to determine the legality of a head?

It seems to me that after the exhausting debate over all of the contentious issues this year, this rule was put out as some sort of well meaning "compromise" to those that were not successful with their other rule making desires and many of us are just tired of the fight even though this rule has lots of problems and will create more cost and trouble in the future. I believe that it is a mistake to make rules like that and urge NASA to reconsider this rule.

Jim Foxx