The FV Ad Hoc Committee met on May 23
Members attending: Steve Oseth, Bruce Livermore, Phil Holcomb, Stephen Saslow, Alex Bertolucci, John Petillo, Dietmar Bauerle
Guest: Fred Clark
The meeting again centered around the meaning of "dimensionally identical". Pistons have not been manufactured by VW for MANY years now and several other companies have sold “40 HP Piston and Cylinder Sets” in the past. The ‘dimensionally identical’ statement in the GCR is vague and points to a need for more definitive specifications with regard to FV pistons.
It is the opinion of the Committee that in order to avoid a “rules creep” there is a need for a better definition than “dimensionally identical”
Over the past few months, samples of 40 hp pistons from several manufacturers (and most recently one VW branded 36 hp) were examined and although none were EXACTLY the same, one commonality among the older manufacturers was the fact that all pistons shared a 2.5mm dimension for the 1st and 2nd ring grooves. Only the Chinese AA brand piston deviated from this by having 2mm wide 1st and 2nd ring grooves. The AA piston also deviated from all the other pistons measured in the location of the top compression ring relative to the wrist pin center line. While not considered a competitive advantage at this time (because the ring groove is lower than all the other pistons measured), the difference itself gives rise to concern that this critical dimension might vary just as significantly in the other direction in future shipments.
If we accept engineering standards when it comes to +/- numbers and apply these terms to the measurements obtained, then we can establish a set of dimensions. At minimum, we are looking at specifying a maximum distance from the top of the first ring groove to the centerline of the 20mm wrist pin, the depth of the ring groove(s), and requiring a nominal 2.5mm width for the top and second ring groove. Specifying additional dimensions is still under discussion.
At the next meeting, a set of dimensions will be prepared for acceptance by the Committee to forward to the CRB. The CRB can then choose to accept the recommendation, handle it as “errors and omissions” or put it out to the membership as a rule change.
Weight: nothing has been decided regarding the question of adding to the minimum weight. Members are encouraged to voice their opinions via a letter or e-mail to SCCA
Tires: In conversations with Goodyear , it is quite possible that there will not be any more new Goodyear FV tires available in time for the Runoffs. The Committee has not been able to determine the reason(s) for this from anyone at Goodyear.
No other items were presented or discussed.
Next meeting is scheduled for June 27
May Minutes
Re: May Minutes
Why? Currently any rings and spacers can be used now. Why add $ to the cost of the engine when not required?and requiring a nominal 2.5mm width for the top and second ring groove
Re: May Minutes
I would think in the absence of a specified ring land dimension, they would be considered free. Didn't someone suggest that a few years ago? 
Seriously, the factory land is 2.5mm and it makes sense to keep that as the std.
Seriously, the factory land is 2.5mm and it makes sense to keep that as the std.The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
Re: May Minutes
Anyone is free to send in a request to the CRB to allow an alternate ring land dimension, but the original one was 2.5mm so THAT is the reason 'why' ... No other (compression ring land) dimension is currently legal.
Steve, FV80
Steve, FV80
The Racer's Wedge and now a Vortech, FV80
Re: May Minutes
Just to drive home the point. The entire point of the exercise is to develop a spec for what a piston is today. There is nothing preventing someone from sending in a letter to the CRB asking for a rule change to allow different or free ring grooves.
Stephen Saslow
FV 09 NWR
FV 09 NWR
Re: May Minutes
Just to be clear on what's under discussion, we are talking about the width of the ring grooves in the piston itself. There is always some confusion as to what is a ring groove and what is a ring land 
The stock 40 hp VW piston had (nominally) 2.5 mm wide grooves for the top 2 (compression) rings and 4mm for the oil ring. All previous aftermarket pistons (K/S, Mahle, Co-Fap, Cima, NPR, and some others as well) have had the same 2.5 mm ring grooves as far as our research can tell. The new Chinese (AA brand) pistons are the first pistons sold as "40 hp VW replacement pistons" to come with other than 2.5 mm compression rings (and the grooves to match). The current rules call for the pistons to be "dimensionally identical" to the original VW pistons (ie. 2.5 mm ring groove widths). The rings are free (what you put in those grooves).
The other issue/concern is that on the AA pistons, the location of the top compression ring is very different that all the other sample pistons we gathered to measure. In fact it was very low (a competitive disadvantage). What concerns us is that there is no reason that it be so low except that the manufacturer is not matching the original location very carefully. The concern is that on the next production run they could be too high (a possible competitive advantage). Therefore there is a perceived need to set at least a maximum height for the top of the top ring groove from the wrist pin bore. That is, we need to define at least some of what "dimensionally identical" actually means in terms of measurable dimensions of the piston.
The stock 40 hp VW piston had (nominally) 2.5 mm wide grooves for the top 2 (compression) rings and 4mm for the oil ring. All previous aftermarket pistons (K/S, Mahle, Co-Fap, Cima, NPR, and some others as well) have had the same 2.5 mm ring grooves as far as our research can tell. The new Chinese (AA brand) pistons are the first pistons sold as "40 hp VW replacement pistons" to come with other than 2.5 mm compression rings (and the grooves to match). The current rules call for the pistons to be "dimensionally identical" to the original VW pistons (ie. 2.5 mm ring groove widths). The rings are free (what you put in those grooves).
The other issue/concern is that on the AA pistons, the location of the top compression ring is very different that all the other sample pistons we gathered to measure. In fact it was very low (a competitive disadvantage). What concerns us is that there is no reason that it be so low except that the manufacturer is not matching the original location very carefully. The concern is that on the next production run they could be too high (a possible competitive advantage). Therefore there is a perceived need to set at least a maximum height for the top of the top ring groove from the wrist pin bore. That is, we need to define at least some of what "dimensionally identical" actually means in terms of measurable dimensions of the piston.
Bruce
cendiv37
cendiv37
Re: May Minutes
So, if I understand, the ad hoc committee believes that 2.5 should be the rule and that we will have to take any 2.0 piston and re-grove it? Yet, ANY rings are allowed? Yes, I understand that I or anyone can write the board and ask to allow or disallow anything. Wasn't the adhoc commitee established to sort of compile details and recommend things to keep FV viable and prices at bay? The commitee was formed to include people that had the knowledge and experience to do what is best for FV. No disrespect meant to the average racer, but most do not write the CRB, or understand all the implications of changes (or non-changes). I had hoped that the committee with experience and knowledge (and slight edge into the CRB) would help guide the class.
It sounds like for all practical purposes we may be forced to buy more KS cylinder sets at twice the cost (or add to the cost of modifying available Chinese sets). Correct?
It seems the AA sets are available and if we do use them, they will continue to produce them. If KS is the choice we can only hope they will continue to produce them when we ask. (at rediculous pricing and delays).
It sounds like for all practical purposes we may be forced to buy more KS cylinder sets at twice the cost (or add to the cost of modifying available Chinese sets). Correct?
It seems the AA sets are available and if we do use them, they will continue to produce them. If KS is the choice we can only hope they will continue to produce them when we ask. (at rediculous pricing and delays).
Re: May Minutes
I understand and agree with the concern about the location of the top ring groove, but to Jim's point, if it is legal to put a 2.0mm ring in a 2.5mm groove now, what is the problem with allowing a 2.0mm groove? If there is a concern about leaving ring thickness open, thus enticing some people to try even thinner rings, why not just establish a new minimum ring thickness rule at 2.0mm? This would allow the Chinese (and presumably all other currently available) pistons to remain legal as-is, assuming they also meet the ring groove height spec.