My concern with allowing sleeved blocks and different pistons and rings is that very clever engine builders seem to find ways to make their engines faster any time a rule is opened up.
Dan is mentioning it, but I doubt many understand what is being said.
It is not just about the peak HP or even peak Torque. You can broaden the power band and make more than a stock motor down low by increasing compression. I am told that there are ways to increase the "total power under the curve" without increasing the peak number.
As an example, POC (Porsche Owners Club) went to a Power to weight classify system. Within 2 years, a couple of engine builders has figured out how to build engines that destroyed a stock one without blowing the HP cap. So now, add $20-30K if you want to be competitive with them. Spec Miata has a very similar problem.

I replaced my stock 86 low compression motor with an 88 high compression and immediately noticed more mid range torque. Not more HP, but more torque down low.

I don't want to have to take complete expensive gasket sets to have to put my engine back together, as well as spend a lot of hours doing it, just because we start allowing different pistons, etc. .... and that will be needed!!

If we could find a piston/sleeve with lower compression that would be preferable.

Having it be affordable or at least equal or less than the cost of a used 88 engine would be optimal.

I have raced both cars with high and low compression engines and have won many races with both as well as set track records.

At the pointed end of spec racing a few HP does make a difference. But setup and driving are by far more important.

Unless you are winning races all the time you should be hiring a driving coach and testing setup at every track day you can.

All you need to do is pull a spark plug and put a bore scope down the hole to see what compression ratio pistons are being used. Its plainly obvious if there is no dimple. A simple inspection of other things like DME chip and AFM can tell you if they are doing any other funny business to compensate for more things done inside the engine. For all we know there might already be sleeved blocks with aftermarket 9.5 or 10.2:1 pistons competing in our class. If they meet the dyno cap, how would we know?

The easiest solution to all of this is to eliminate ambiguity. Allow a specific aftermarket piston from a specific company which can be easily inspected with a bore scope to ensure it still has the appropriate dimple like the 9.5 or 10.2 CR pistons. Also publish a generic HP/TQ curve as a template to be used to compare dyno results with.

Of the 20 or so dyno charts I have from compliance testing in the Southeast, the following narrative is consistent across all of the OEM chipped engines I have tested:

Torque Curve: Peak at ~3000, valley at ~3500, peak 3700, peak at 4400, falls off after 5000.
Horsepower Curve: linear up to a peak around ~5600-5900 then falls off

I have found one illegal chip which showed a torque/horsepower curve that didn't follow the above narrative. We swapped the DME out with a verified stock one, and the dyno chart then matched the above narrative.

I also have a dyno chart of an otherwise legal engine that has aftermarket pistons in it. The engine is otherwise brand new but the horsepower and torque curves still roughly match every other dyno chart I have, it just overall makes more power which is to be expected out of a brand new engine built by a reputable builder. We have restricted engines down before very simply and it pulls power out of the engine across the board, not just at peak.

TAKE NOTE:
Please make sure your rules changes/ clarifications are well thought out and will benefit ALL racers in terms of cost, reliability, and ease of rules enforcement. REMEMBER, WE'RE TRYING TO KEEP THE CARS EQUAL. ( I'm not yelling, just using all caps for emphasis). If/when someone pokes a hole in the rules or finds a loophole, we need to CLOSE it, not make everyone else invest to bring their own car up to speed...pun intended.

ALSO TAKE NOTE:
The spirit of the class is for all cars to be equal in weight and
horsepower and be competitive with one another. The focus will be on driver ability and not dollar
ability. This class is not intended to be an engine builder or innovator’s class.

Let's let that sink in before we go further....because all my input is based on those two paragraphs.

With regulard to selves or pistons: it would be not too hard to say go to JE and have them make an approved “spec” replacement piston to the exact weight /size/etc as the factory. Then only allow that one oem replacement. I had them make custom pistons for my turbo and it was easy

As someone who spun a rod bearing, building a replacement motor, and been looking for a set of 88 pistons, those are hard to find

This is from Bob Hahnemann he had trouble with activation


“As a spec 944 competitor I would support modification of the rules to allow Wossner pistons. These pistons are affordably priced and more reliable. OEM pistons are hard to find and typically not in good condition. The Woosner pistons provide little if any performance gain.
Best Regards
Bob Hahnemann"