Here we go.
My motor was bored .040 over and Honda dosent make anything larger than a 81.25mm piston. So my motor seems illegal. Now my car is a GSR with a GSR motor and trans at 2465# so it is H3 legal other than the valve springs and retainer. In H3 .040 is legal so if I change the valve springs and retainers making the car H3 legal can I run it in H2? If not I guess I'll change the cams and run H1 or PTC

Here is the rule that seems to be overlooked by more than just me:

10.3 H2 Limited Preparation Vehicle Engine Preparation This section is intended to clarify the engine preparation rules specific to Limited Prep Vehicles: a) The entire engine assembly, (cylinder head and block) MUST be constructed entirely of Honda/Acura OEM parts. Cylinder head and internal engine parts must be OEM parts for that particular engine code. Updating and backdating of parts for that engine code is permitted. No aftermarket parts are permitted in, the “bottom end,” of a Limited Prep Vehicle engine (except were specifically stated). Example(s): 1) A USDM D16A6 may not use pistons from a D16ZC engine and a head from a D16Y8. 2) A USDM B18C1 may not use ITR crank and pistons with ITR head and call it a B18C5. 3) A JDM B18C (GSR) may use ITR crank, pistons and ITR head and call it a JDM ITR engine since that is the proper engine code for both engines.
b) “Aftermarket OEM” replacement pistons and rings are allowed but must be identical in every manner to the OEM Honda/Acura part. Note: Piston size must not exceed OEM sizes.

 

Correct.

You can't run 40 over in H2.

This has been long debated. But its the rules.

incorrect info- deleted

This is from my memory... Though.


But the deal is that, you can run OE standard, OE 20 over, aftermarket standard, aftermarket 20 over.

This goes wayyyyyy back in day to the fact the HC came IT, IT has many many different types of cars, with some factory pistons offered in 40 over.

Since some cars could legally go 40 over, ALL cars have to be able to go 40 over.

This transfered over to HC.

The RC changed this for H2 (adopted H1ish rules), as no factory pistons were offered in 40 you really have nothing to compare it too (legality).

40 has never been "new H2"

Scott Brewer from AZ had this issue when he tryed to take his 40 over H4 92 DA, to H2.

 

Dammm it ! now we both agree on a topic !!

 

its ok Benny it had to happen sooner or later.
Sometimes the rules read like bad stereo instructions.

 

Not all engines can go 20 over though, only the ones that had 20 over OEM pistons available at some point. My understanding is that the B16A only had 10 over pistons available from Honda, making that the largest piston you can legally run.

 

lol i'd bet it happens a few more times!!!


Andy- the 20 over 40 over are in inches. Which honda doesn't use, so i just use the 20 and 40 as equivalent 25 and 50 over.

A quick search shows that the gsr/b16a/b18b/K20a3/b18c5/h22a/h23a all come in .25mm OS piston sets. One size bigger.

But if i did my math right .25mm = .01 inches or 10 over...

 

Ok I undrestand. I do question the part about H3 that is .040 over not being legal. Like i said I cant find anything in the rules other than my valve springs and retainers that are not H3 legal. So I guess if I want to race with no one I change the vs and retainers and get in the H2 guys way SWEEEEET

 

I got out of the B series game a while ago.However from my personal experience 81.25 or .010 is the most common OS from Honda,I rarely see Honda selling a .50mm over piston,but they have.Now .040 is 1mm over and that is not legal as Honda never made a 1mm OS piston for any engine I know of.Aftermarket nippon does,but those are only legal up to 81.25mm or 81.50 if Honda had a .020 over avail. in that model.

Normally for most engines,they only offer a standard size A bore,standard B bore and .25mm over.

Rule 10.3 is fun.

 

Jimmy, I'm not sure I understand what you are saying here?
In H2, the only piston sizes you can use are what Honda offered. In all the motors you explained, they were only offered in Standard and oversize (.25mm).
So, standard and 10 over are the only allowed sizes for H2.

Equivalent .25mm over and .5omm over would be "10 over" and "20 over".



Also, this actually wasn't the case Jimmy. The rule was put into place the way it is to help even the playing field between the people with "stock" untouched bottom ends and the people that went ahead and "built" them. The idea in H2 was always to have people buy used engines and plop them in to start racing. The power difference between a .25mm over engine and a stock one should be very minimal and something not worth doing unless there is already a problem.
That was the thinking anyway right or wrong.


Just wanted to clear that stuff up.

 

Sorry for the confusion.

What i am trying to get at is way to complicated to try and type out. But in simple terms "20 over" is a generic term for the first OS piston, for me at least.

Like i'd say my motor is 20 over, but in reality it isn't it has .25mm OS OEM pistons in it.


I know that technically its wrong, just the way that i use the terms and i have heard others use it too.

correct jeremy, here is the thread i was thinking of. http://nasaforums.com/viewtopic.php?f=11&t=21652

 

Anything besides the rear wing that makes your car not ITS-legal?

 

As of right now I think the flywheel (if you cant run a lightend one). I plan on talking to the guys in my region and seeing what they think. And if they will let me I will run the bottom end for a few races and then build another shortblock with the correct pistons so the car is 100% H2 legit.