Honda D Series Forum banner

1 - 20 of 47 Posts

·
Registered
Joined
·
2,032 Posts
Discussion Starter #1
I recently destroyed the ringlands on my NPR p29's and I decided to switch to YCP's instead of NPR. I didn't base this decision on one being better than the other, it is strictly personal preference. I also wanted the YCP's before my build started but the NPR's were the only sets available when I was doing my build.

ANWYAYS, I noticed the piston heights are different. I ordered both sets from FJdistributors but have yet to inform him of this. Here are some pics to show you what I mean.



On the left we have the new YCP p29's and on the right we have the broken NPR (NOA) p29's. You can see that the dome's are similar but the piston heights are different. This was evident when I first assembled my block. I was expecting the p29's to sit 1mm below deck but they ended up at the same level as the block deck.



On the left is the old NPR the right is the YCP.



this shows the comparison with pm-0's. left = YCP p29's, middle = pm-0, right = NPR p29's

Sorry, I don't have any tools to measure the pistons accurately. I'm not sure how this ended up this way because I thought all p29's were casted the same regardless of manufacturer. But in this case, I mite say that the NPR's mite be better because they do not sit below deck? What do you guys think?
 

·
Well?
Joined
·
10,814 Posts
wow thats odd, im curious about this as well
 

·
Registered
Joined
·
2,032 Posts
Discussion Starter #7
So I think I'm the first guy to notice this? i bet u i was getting way more than the 12.2:1 C/R I estimated. I bet you I was probably getting around < 13.1:1 C/R. wouldn't zero deck p29's be the best tho?
 

·
Well?
Joined
·
10,814 Posts
yes and no. You do get your lost compression back BUT they still have the hughe dome on them so thats not great
 

·
Registered
Joined
·
2,032 Posts
Discussion Starter #10
well the only difference from the YCP's and NPR's that I noticed was that the YCP's have a teflon coating. Also, the NPR's have more oiling holes compared to the YCP's. When it comes to finish, the NPR's win. It just looks more refined if you get what I mean.

Albeit, the reason why my NPR's broke was due to too much timing advance and that's the only reason why it broke. It wasn't a faulty product at all. It was just my n00b dumbass ran a stock timing map.

I know the propagation of the flame front does get slowed down or interrupted due to the large dome but running flat top pistons with a p08 head (the head I'm using) requires machine work (i'm assuming more than .020") and no room for error to get enough compression to run a large cam.
 

·
Registered
Joined
·
873 Posts
Zero decked P29s? Whoever thought they were in the NPRs all along?
Damn that's actually real news to most of us!
What happened Giddeon? How did you end up running stock timing maps when you had Ectune at your disposal? I feel for you buddy, just concerned here.

Anyway, did Fort hit you up to say Hi?
 

·
Registered
Joined
·
2,032 Posts
Discussion Starter #12
well i semi broke-in the motor with the stock timing maps. I've retarded the timing since but still need to install the YCP's. Christmas season has been crazy. My mom and sister came out to visit me and my pops and we ended going to bacolod, cebu, bohol, boracay so I didn't have any time to work on the car.

I haven't seen fort in a long time. I haven't been going out much at all lol. Even tho iloilo is such a small city and you see everyone, everywhere. I'll make sure to mention about you when I see him.

Well the NPR's are specifically NOA's because to my knowledge there are Nippon Racing (japan) and NPR NOA (Nippon of America). I have the NPR NOA. I ordered them from francisco @ fjdistributors.com. I need to ask him if other NPR's are like mine because it might just be a fluke. It would be cool tho if all the NOA's were zero-deck. ~13:1.1 C/R with no machine work is great lol. I would pick the zero-deck p29's over the 1mm below deck just because of the compression but I already have the YCP's.
 

·
Registered
Joined
·
873 Posts
Yah they'd be really great for a 13:1 on a P08 head.
I just finished my P29/Y8/crower2 rebuild this Jan. 3 and everything was like CRAZY slow before i got everything done LOL! Xmas really brought a halt to everything for me. (i never knew eating could be such a "bother" LOL)
I thought I'd be finished before the 25thDec but i just had to give way to everything and everyone. I was porting my head ONE port a day, would you believe! geez!
I'm tuning it now and I'm LOVING 13:1!! You just have to really be generous with everything that the engine will want. As of now I dropped ~6 degrees of total timing from my previous 11:1 tune on the PM6 pistons. You can feel that the engine is VERY efficient now coz even if I added ~15-25% more fuel on all the driving ranges to get to stoich values compared to the 11:1's lean (i.e. 15.8-16.2:1 part throttle) tune, it needs much much less throttle input to accelerate my heavy ass 4dr with full interior and power everything so I'm really happy.
And it's doing it at 14.1 to stoich values at cruising and at 12.5ish at WOT to keep things cool, conservative and safe.
I'm def wanting a much bigger cam with this.

Btw, why don't you sell those YCPs and go for another set of NPRs?
 

·
Registered
Joined
·
857 Posts
Very interesting stuff. NPR piston clearly is "racing" version of stock piston. It has taller compression height to get it closer to deck and more compression, it has clearly bigger valve reliefs and it also has 5+5 oil draining holes compared to stock's 3+3.

Does these come in 76mm? Damn I should've got these for my D15..

Any idea what broke the ringlands? Was it detonating, used poor fuel or something? How much timing?
 

·
Registered
Joined
·
873 Posts
Out here we have 96 RON Petron "Blaze" - i'm willing to bet he used that.
But i guess the stock timing maps plus some high-rpm passes was what did it.

IDK, hope I'm not butting in prematurely Gid. You might wanna answer rushi's Q man...
 

·
Registered
Joined
·
163 Posts
Just reading this post again, I read it before but it haddent come to me that I have the same pistons as you installed now and I am guessing my comp numbers won't be what I exspected. I just posted a similar topic to this above but one of you may have my answer.

The NPR p29's that I installed from fransico at FJ are std bore but in the block they are at zero deck height as well or close. I have to do some more reading but I am guessing from this post that they are supposed to be under the deck not at "0".

From the one compression calculator http://www.zealautowerks.com/dseries.html

If I use my setup A6 head and block with y8 headgasket .037" apparently they are actually all .027" thick (not 100%) No milling or anything compression should be 11.1:1

If I use this calculator http://www.knology.net/~jediklc/dcalc.htm

Same exact info except it states your piston to deck height. My compression ratio ends up being 12.3:1 again with no milling.

It says that the stock A6 piston to deck height should be .002" which in my case could be correct to what my block looks like. I have yet to measure it exactly but it is close to zero.

Before I mill my head I need to know what the propper specs are?
 

·
()*#$(*$
Joined
·
11,404 Posts
Stock MLS gaskets ARE DEFINITELY ~.027" compressed.

The problem with the NPR pistons is that if they have a raised compression height from stock P29s, we don't know if they kept the stock dome size or if it is reduced in volume to compensate from the raised compression height. No one, to my knowledge has had them CCed to make sure of thier dome volumes. We can't just speculate by the picutres teh OP posted.

Stock PM6 piston to deck height is .020", not .002". Choo need to watch your number places, meng!

Get the NPRs CCed, measure the compression height, and then you can finger out the rest of your stuff.
 

·
Registered
Joined
·
163 Posts
I only wrote .002 because that is what the knology calculator states for an A6 but I was pretty sure that wasn't right.

Next friday I will measure the exact deck height clearence on the piston but from the look of the piston, I would say that they probably have exactly zero deck height. I am going to clay the pistons when the head is finished to see my clearence before I mill the head down.

I really don't want this engine above 12.5:1 and I was shooting for 12:1
 

·
()*#$(*$
Joined
·
11,404 Posts
*sighs* Zeal>knology for the eleventy billionth time.

Stop worrying about the compression numbers. Static compression ratio isn't much to be feared if you plan for it and just build the whole engine right.

Please do let us know the results of your measurements!
 
1 - 20 of 47 Posts
Top