Ok, i have a d15z1 motor in my car right now, i want to swap the head to a y8 because i have one.

When i do it, i want to put a thicker headgasket in it to lower the compression ratio becasue i plan to turbo this summer. I would like to know what to do to keep it around 9. I think the stock VX motor has a 9.1:1 CR anyways, but when i swap the head it will change, because i think the Y8 has less volume in the combustion chamber?? im not sure

thanks for the help

 

https://honda-tech.com/zerothread?id=789586
https://honda-tech.com/zero...age=4

It doesn't matter what you do, you will have to RAISE the compression massively, or just get another set of pistons. Possibly a set of CX/DX pistons would be called for.

 

The D15z1 already has Vtec Correct? If So it has dish pistons like the JDM D15b So Basically you would be making a d15b That has a Comp ratio of 9.2:1 Just with a less agressive cam. If its a not a Vtec Motor than yes you well need to try to raise compression.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MENACE &raquo;</TD></TR><TR><TD CLASS="quote">The D15z1 already has Vtec Correct? If So it has dish pistons like the JDM D15b So Basically you would be making a d15b That has a Comp ratio of 9.2:1 Just with a less agressive cam. </TD></TR></TABLE>

No....it'll still be ridiculously low.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dr_latino999 &raquo;</TD></TR><TR><TD CLASS="quote">

No....it'll still be ridiculously low.</TD></TR></TABLE>

Its funny cuz i didn't no My D15B vtec Has a comp ratio that low. Ive pulled the head since i had it i also have the same dish pistons that are used in a vx block. why because the Vx Bottom is the same as the D15b bottom. I wish i would have snapped some pics when i pulled the head 2 weeks ago. Also the casting on the head is the same for a D16z6 as a D15b Both are P08 heads Now i have heard the Y8 does have a bigger Combustion camber but it not that big where it would cause such a low comp ratio.
Also if someone can get me the piston numbers for a VX then i can compair them to my pistons and make sure they are the same.
I know i would like to figure this out since i know i have never heard of it befor. And i would like to settle this once and for all. if my pistons are different from a Vx's then you all are right if not then we need to figure out how this got started.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MENACE &raquo;</TD></TR><TR><TD CLASS="quote">

Its funny cuz i didn't no My D15B vtec Has a comp ratio that low. Ive pulled the head since i had it i also have the same dish pistons that are used in a vx block. why because the Vx Bottom is the same as the D15b bottom. I wish i would have snapped some pics when i pulled the head 2 weeks ago. Also the casting on the head is the same for a D16z6 as a D15b Both are P08 heads Now i have heard the Y8 does have a bigger Combustion camber but it not that big where it would cause such a low comp ratio.
Also if someone can get me the piston numbers for a VX then i can compair them to my pistons and make sure they are the same.
I know i would like to figure this out since i know i have never heard of it befor. And i would like to settle this once and for all. if my pistons are different from a Vx's then you all are right if not then we need to figure out how this got started. </TD></TR></TABLE>


so.. your pistons look like this?

 

Yes they do. I was sent a D15b Vtec Motor but it was The Econo version Vtec only opens up the second set of intake valves. Ive Since swapped a D16z6 head on it. Still using the dish pistons. If i remember right the piston were also marked po7 and not po8 like the Regular D15b vtec. When i swapped heads i had no prob with compression, and the motor runs like it always did just now with more power. I would have gotton rid of the pistoms for some PM5's (flat top kind) like in my old motor but i just bought the dam thing and i was pissed when i got the econo and had to swap heads. I really didn't want to have to build a new motor to ya know. I really want to get it on a dyno and see what im putting down. But im gonna wait til i can find a Si Tranny local. Even with my 4 speed i still keep up with my friends Ex's and even give them a good run. So i know my comp cant be noy 7:1 ratio. It wouldn't run right.

 

I feel like somehow weve opened a can of worms. Im must say if the D15b vtec thats not econo doesn't have dish pistons im gonna be pretty mad agian. Maybe theres a difference in dish size between the 2. I really would like to know the numbers on my pistons. I really wish i would have takin a pic. Pulling the head is easy on and off in an hour i just dont wanna lose my oil and coolent to see some number.

 

P07-010 is the number for the D15Z1 pistons as referenced at http://www.knology.net/~jediklc/D.htm. I will have to look for the D15B piston specs.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dr_latino999 &raquo;</TD></TR><TR><TD CLASS="quote">P07-010 is the number for the D15Z1 pistons as referenced at http://www.knology.net/~jediklc/D.htm. I will have to look for the D15B piston specs.</TD></TR></TABLE>

I know im having a hard time finding the number for them.

 

The D15B uses PM3 pistons if I am not mistaken.

 

I think it should still have some sort of Dish with a flat top piston the comp would be closer to 10:1. Maybe they use some like a P28 it has a slight dish.

 

Ok, It isn't the PM3 as I thought, you're correct with the 10.1 CR. The P28 though would drop it to around 8.3 though. Still looking for that magic piston; I have figured out that to get a 9.2 CR you would need around -4.5 cc piston displacement.

 

I found some more specs https://honda-tech.com/zerothread?id=585043 seems like it would defenatly use its own piston.

 

d15b7 pistons:

 

Yeah that D15b7 is the same as the piston in my pervious motor its a pm5 or pm6 or something. that piston will give you the 10.1:1 CR I really think it uses its own piston. Next time i pull the head ill be sure to look. As far as mine goes if i have the VX pistons oh well the motor is very powerful even with them. I still cant belive it would yeild a 7.1:1 comp ratio. Also from what i got the Vx pistons extend out of the block 3mm if you take into account for this it raises the compression to a 10.5:1cr Maybe i was reading it wrong who knows. All this piston talk got me all confused beacuse i know my motor wouldn't run as good with a comp that low.

 

the B7 pistons are labled PM3 but the oem part number is P03, weird
edit: oh BTW i noticed in one of your first posts you said the Y8's chamber was bigger, it's actually smaller then a D15B/Z6 head