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Discussion Starter #1
Looking for some info that I haven't found so far. Basically, everything I can find on setting P2W for Boost/ nitrous pertains to forged piston expansion. In forged setups it seems the rule of thumb is to start with stock specs, and then add .001 to .003 if using a power adder, due to the extra heat.

With stock or type-S pistons, is this also a good rule to go by? I learned the hard way that ring gaps should be higher for nitrous use, and want to cover the P2W aspect as well when I have my bottom end at the machine shop.

Just for the info, I am going to oversized Type-S factory pistons, on my previous setup that used stock bore JDM H22A pistons, also swapping from H23A1 rods to H23A rods, same H23A1 crank, and a fresh hone, getting everything balanced etc.
 

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With stock or type-S pistons, is this also a good rule to go by?
Probably not. That rule isn't taking FRM sleeves into account, is it? My speculation is that the FRM sleeves match the expansion coefficient of the OEM cast pistons, in order to run very tight clearances to overcome wear issues inherent with the low rod-stroke ratio (1.48:1 for your build).

Cast pistons are less dense than forged, so they expand more, so the impulse is to try the loose end of your range. But, the wildcard is those FRM sleeves, so if you follow that impulse you may wind up with excessive P2W clearance under operating conditions.

What strikes me about the H motor, compared to those I've actually worked on, is the stock P2W clearances are way tighter than anything else I've encountered. This must be possible somehow, I attribute it to FRM. Sorry I don't have an answer for you, only some food for thought.

Just for the info, I am going to oversized Type-S factory pistons, on my previous setup that used stock bore JDM H22A pistons, also swapping from H23A1 rods to H23A rods, same H23A1 crank, and a fresh hone, getting everything balanced etc.
Good luck, can't wait to see how it turns out.
 

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Probably not. That rule isn't taking FRM sleeves into account, is it? My speculation is that the FRM sleeves match the expansion coefficient of the OEM cast pistons, in order to run very tight clearances to overcome wear issues inherent with the low rod-stroke ratio (1.48:1 for your build).

Cast pistons are less dense than forged, so they expand more, so the impulse is to try the loose end of your range. But, the wildcard is those FRM sleeves, so if you follow that impulse you may wind up with excessive P2W clearance under operating conditions.

What strikes me about the H motor, compared to those I've actually worked on, is the stock P2W clearances are way tighter than anything else I've encountered. This must be possible somehow, I attribute it to FRM. Sorry I don't have an answer for you, only some food for thought.



Good luck, can't wait to see how it turns out.
as far as P2W clearances, ill add this tidbit of info.

mahle gold series pistons say to make your P2w clearance (not 100% on this i don't have the instructions in front of me) but it basically says .001-.002" i believe. they add on top of that to add .001 to .003 for high output applications. there is also a section about ring gap for nitrous as well, which i think is just as important if not more than the P2w. if the rings get hot enough, the gap closes up and butts up against the other end of the ring, and if it expands enough, it starts to dig into the walls.

how much nitrous do you plan on running? this info is very important, because the amount of clearance will change depending on if you are running a 200 shot or a 50 shot, obviously.
 

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Discussion Starter #4
Yep, I had the ring gap in my last engine set at the tight end of factory spec, and one expanded enough to touch, looks like it not only grabbed the cylinder wall, but it broke the ringland on that piston.

I plan to run the same shot as before, 100 wet, maybe if it holds up for awhile, bump the shot to 125 just to see what it can do. Now that I don't have a local track, I will get even less chance to use nitrous, as I will have to travel quite a ways to race.
 

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If i m running mahle pistons, what should my oil ring gap be set at, should I go by the Honda service manual, if someone could shead some light, thank you.
 

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Discussion Starter #6
Mahles should come with a spec list for the gaps you should run, as they are different than stock. If you create a new thread it will probably get more help for you as well.
 
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