Is this GCR spec a typo??

[bob darcey]

Page 303 of the 2016 GCR includes the following specs for the Kent motor CP pistons:

Bowl depth: .470" minimum
Centerline of wrist pin to crown: 1.702" +/- .002"
Overall height: 2.80"

Since the CP pistons are ~.505" bowl depth, I assume the .470" minimum is an allowance to add unswept volume for over-decked blocks. Is that the intent? If so, that would reduce the overall height by .035", so the overall height should read 2.80" +0/-.035". Then the pin height spec should read 1.737" +.002/-.035; in that context, it can't be 1.702" +/-.002".

Can someone shed some light ?

[racingflyboy]

Funny, I was just thinking about contacting SCCA about that very subject. You must have been talking to Pete!

[bob darcey]

Exactly. Pete's in a state of shock.

[Dave Harmison]

If you did cut that much off the piston, would it be legal weight?

[Roland V. Johnson]

These numbers are correct. The engine builders requested them so they could save many over decked engine blocks. Remember that there is still a minimum 42cc requirement for the combustion area in the cylinder / piston and the valve heads may not protrude more than .040 out of the head. You are allowed to increase the valve pocket .050 also to get the compression ratio correct. You still must not exceed the 9.3 compression ratio. So decking the pistons is no advantage. If you start off with new pistons that haven't been lightened you shouldn't have a problem. If you need to take that much off the pistons you were never going to have a legal engine anyway. You were going to have way too much compression.

[bob darcey]

Thanks Roland. It's all about saving overdecked blocks, and it makes OK sense except the overall height and pin height spec. A pin height spec of "1.702 +/- .002" makes a bone-stock piston illegal, and whatever you mill off the piston has to be subtracted from 2.80" for the overall height.

[Roland V. Johnson]

I finally see what you are complaining about. My bad. When I measure 4 NOS AE pistons I get 1.735 from the top of the crown to the centerline of the pin. That is what the standard size is (I don't know why I still have these new with rings.) Wanna buy them? That measurement should be the max as it used to be. The SCCA must have taken that out. The other measurement should be the min. We should all just get Honda's. I haven't seen any published specs so we would all be legal.

[problemchild]

We should all just get Honda's. I haven't seen any published specs so we would all be legal.

This total falsehood gets eaten up by other uninformed people and is a complete disservice to our FF community. It is completely valid for you to dislike one of the engine options, but making up stuff is just discounting your own credibility. Perhaps you should be criticizing the people that created the poorly worded rule revision being discussed.

[Roland V. Johnson]

I'm sorry, the last time I asked for a complete set of Fit specs including cam profile I could not find it. Where are they posted?

[problemchild]

Roland,
Focus, man. I'm taking time from adjusting the valves on my Ivey kent engine which I plan to install in my Reynard tomorrow. I am not interested in another high school pissing match about Honda vs Ford engines. The SCCA GCR has rules for Hondas that are fine for me. I do have concerns about the SCCA GCR rules for kent engines, which other people are questioning. Lets talk to the people who wrote the specific rule being discussed, decide if the rule needs correcting, or if it is fine as written.
Cheers!

[Art Smith]

was the rule change under discussion posted in Fastrack; I don't remember seeing it......? without regard to if it's a poorly written rule in need of updating, by what authority was the rule changed in the GCR??

Art
artesmith@earthlink.net

[bob darcey]

Art: The .470" bowl depth has been in the rules for a long time--as far back as 2010, but I couldn't find any earlier GCR's on-line. GCR's for 2010 and 2011 show the pin height as 1.737" +/-.002"; 2012 thru 2016 show the pin height spec as 1.702" +/- .002". In either case, the pin height spec is wrong and should be revised. Ditto for overall piston height.

[Art Smith]

Bob-

per my 2002 GCR (hard copy #5675; FCS - 50 (ie: page number))

Uprated Engines:
Maximum diameter: 3.189"
Depth of Bowl (+/- 0.005"): 0.500"
Maximum diameter of bowl: 2.44"
Centerline of wrist pin to crown: 1.737 +/- 0.002"
Overall height: 3.30"
Minimum weight w/rings & pin: 525 grams
Minimum weight of pin: 115 +/- 2 grams

"technical" problems are all too frequently created by "lack of process" problems....! it was my experience in industry if the "lack of process" (ie: configuration control) problems are solved, there wouldn't be nearly the number of "technical problems"..................

Art
artesmith@earthlink.net

[Albatross]

Not to steal the thread: But I always adjusted the valves in my Kent engine when it is already bolted in the FF and Hot.