GCR piston question

[Art Smith]

poking through the 2008 GCR section on pistons
(part of the process of buying a new set) I've come across
what looks like a "broken link" at the bottom of 9.1.1.B.3.f:
Localized machining of the grudgeon pin bosses to achieve
balance and weight by simple machining; all external surfaces,
dimensions, and profiles shall remain standard with the excep-
tion of the top surface of the piston crown which may have
simple machining to achieve balance, and as required in Section
9.1.1.B.3.c.

9.1.1.B.3.c says:
The flywheel shall be a standard component or the approved alter-
nate Elite-001. The minimum weight is 14.4 lbs. with ring gear.
The flywheel may be machined to achieve minimum weight. Spot
machining to achieve balance is permitted. A 1600 GT starter ring may be
fitted. The use of any single plate clutch is permitted provide no
modification is made to the flywheel other than changing points
of attachment of the clutch to the flywheel. Carbon fiber clutches
are not permitted. (see attachment for context)

does anyone know where 9.1.1.B.3.f is supposed to point?? if 9.1.1.B.3.f
is supposed to point to 9.1.1.B.3.d it's material and more than
an academic question. 9.1.1.B.3.d says:
3. Pistons shall not protrude above cylinder block surface at
TDC.
a motivated soul therefore might see 9.1.1.B.3.f as a compliant means
to reduce recipricating weight through the use of a short deck height block;
only the weight of the piston, rings, pin, and connecting rod (small end
bush and pins included) assembly appears to be controlled by the GCR.
recipricating weight is horsepower; rotating weight is only acceleration!!

Art
artesmith@earthlink.net

[Dave Gomberg]

Art:

Thanks for catching this. This error has been present for several years. It finally occurred to me to look at the S2000 specifications (since they should be the same with respect to the engine specifications). Indeed, this should reference 9.1.1.B.3.d. (I'll get a correction in the works ASAP.)

As for your short deck height block question/idea, I think you may be contemplating a forbidden journey. 9.1.1.B.3.ee reads:

ee. Only modifications or additions specifically covered by these regulations are permitted. All engine components not covered by these regulations shall remain completely standard and unmodified.

That would include the block. There are no provisions that I can find that allow modifying the deck height.

Even if there were (and I'm not intimately familiar with these piston assemblies), I wonder how much there is to be gained (even if there were no other breach of the rules)? That is, I'd guess that these assemblies come in pretty close to the minimum weight. And, since approved connecting rods are required, you wouldn't be able to reduce the deck height by much before you would be running a race between thinning the piston top to the point of risking burning them or going under the minimum assembly weight. Now, if my assumption about the assemblies being near minimum weight is incorrect and/or there is a lot of meat at the top of those pistons, you might be on to something. An awful lot of "ifs" here.

Dave

[Rick Kirchner]

Dave - doesn't an engine builder skim the top of the block whenever it's re-sleeved? That was done on my engine at least once - and even without that skim, my J&E's protruded above the block A BUNCH (sorry, I didn't keep the measurements - but you couldn't have put the gasket on and then set the head down) and had to have the (very substantial) tops trimmed to get back to flush - I'm thinking it was over .020 the first time.

IIRC, that skim also changes the size of the offset key since the head is a tad lower and the belt would have it rotated a bit more....

There's no definition of standard deck height anywhere to my recollection, nor the originally manufactured tolerance, so if one were to attempt to apply the "no other modifications apply" rule there's no published standard to start from.

It does seem to me however, that eventually the combination of min rod/piston weight, and removal of the piston top to achieve "flushness" will eventually render a block useless. If you have the pistons trimmed to min wt, re-sleeve the block ona subsequent re-build then the pistons will be throw-aways at that point as well.

[Art Smith]

Dave-

thanks for the reply AND for volunteering to get the correction made!! checking the S2000 section was a great idea that didn't occur to me.................

like most 2-liter blocks being used today both of mine have been around for a while and no telling how many times they've been decked. head gaskets really appreciate two flat surfaces!! the one being worked on this time is getting sleeves so the machine shop will have to take at least 0.005" to 0.010" to get everything flat again........ while thin, cast iron sleeves as a repair process are explicitly allowed and by association the decking required in their installation process. in a more practical sense, I'd be thunder struck if there's any 2-liter blocks being raced today that haven't been decked at least once................. decking blocks to get everything flat and drilling & tapping holes for fasteners to secure freeze plugs are probably both wide spread practices that need explicitly approved status in the GCR. neither of my blocks have been drilled & tapped, aluminum freeze plugs don't need retension fasteners because of the difference in coefficients of thermal expansion.

based on the NASCAR experience your concerns about piston crown thickness are well founded; when the new JE's get here I'll have to measure them to see how much material is there............... without having done any work yet it's my sense balancing the books for total assembly weight is a very doable task within the GCR's current bounds for compliance. minimum piston weight survival is a horse of a completely different color.....................

best wishes for the new year

Art
artesmith@earthlink.net

[Dave Gomberg]

Rick:

As a practical matter, you are probably right about there not being a reference deck height. (Trying to apply paragraph ee in this situation is the kind of thing that gets "strict constructionists" into corners from which there is no exit.)

From what you describe, the JE piston thickness at the top allows for a fair amount of "adjustment". But, as you note, there is a point beyond which this is academic because of the minimum assembly weight. And, while there may be a small performance advantage at the margins, I can't imagine it would be much.

Dave