I have a stock d15b8 motor, and a messed up d15b sohc vtec motor sitting with a good head. I was wondering since the b8 is an 8 VALVE motor, will the pistons on the b8 match up with the valves on the vtec head? I know the d15b7's work pretty good, but i was wondering if i can do the same with the d15b8.

 

Some of the D15B8's have 2 valve reliefs per piston, and some have 4 valve reliefs per piston (same as D15B7 pistons). I think it's the earlier D15B8's that have 4 valve reliefs.
You need the ones with 4 valve reliefs.

EDIT: looked it up... 1992 CX and some 1993 have the 4 valve pistons

 

is the d15b8 block w/ the 4 valve reliefs basically the same as a b7?

would it make the same power after doing a mini-me as a b7 or is the b8 lower compression?

 

Yes and yes.

 

nice, may have to do it for some quick power while im building my ls/vtec.

 

My car is a 1993 cx, but i looked on the head where there is a year stamped and it said 92. So does it technically count that I have the 93 4 valve pistons, or am i still in the 92 range of having the 2 valve reliefs?

Are you going by the year of the car, or when the actual motor itself was built?

 

I'm not exactly sure. I am going by what I have read as consistent info. I'm led to believe it's based upon the year of the car.

 

I have a 94 CX and it has the pistons with 4 valve reliefs. Outside of the difference in pistons (which is debatable) the only other difference in the block compared to a normal DX is the water pipe on the back (I believe the CX has one coolant connection while the DX has two, difference being the CX doesn't have the Fast Idle Valve).

 

can i add the water pipe? or can i do without it? also, is the fast idle valve on the manifold, or on the block? Ive actually never heard of it before. Kinda new to certian elements during this whole tear down of a single motor.

 

I'll have some pics uploaded in a bit to better explain...

 

Here you can see the back of my block when I was rebuilding my 8 valve motor:



It's hard to see but on the water pipe itself there is only one outlet that comes off the pipe and it's right behind the thermostat housing. I modified this following pic so you can clearly see what I'm talking about.



Start at that outlet and follow the soft line to the EACV (also referred to as IACV but you get the idea). Another soft line comes out of the EACV and continues on to connect right underneath the throttle body. Continue on to a third soft line which connects to a hard line (which is attached to the hardline that goes from your valve cover to your intake hose) which then connects to another soft line that terminates at the intake manifold.

Now for the comparison, D15B7 and D16Z6 routing diagram:



Notice that this water pipe has two outlets? Again, follow the path only this time start with the outlet closest to the water pump end of the pipe. Soft line goes to the EACV, second soft line goes underneath the throttle body again but this time it attaches to the FIV (shown separated from the throttle body) and terminates with a third soft line at the intake manifold. The other outlet has a soft line that goes to a hard line (same one connected to the intake tube) and terminates with a second soft line at the intake manifold. Those last two lines honestly didn't make sense to me because they essentially just provide a path for the coolant to flow but don't connect to any sensors. Having said that, I decided to plug up this outlet on the intake manifold:



I used the CX water pipe and routed the soft lines just like normal except now instead of just connecting underneath the throttle body they actually connected to the FIV...

BUT

My car never fully ran correctly. I can't say it was because of that routing issue but since you have the other motor in your possession I would recommend switching the water pipes and routing everything correctly. Better safe than sorry. I don't know if the way I did it could've caused any issues because when you look at it those two soft lines really didn't do anything. Anyways, hoped those pics above help you better understand the differences between the CX and DX blocks (aside from the potential difference in pistons).