im thinking about buying the pm7 pistons. whats the compession on these. i heard it was pretty high and i might want a head gasket to lower the compession.

 

out of what motor?

 

not sure he just logged off. im thinking it might bout outa the crx if im not mistaking those came with them? they are connected to z6 rods if that helps any

 

Pistons are only 1 part of many that add up compression ratio.

Piston dome/dish, combustion chamber volume, piston to deck clearance, head gasket thickness, stroke, etc. etc. are all factors.

The PM7 is a DOHC ZC piston (same also as a 1988-1989 Integra P29 piston) with a +7.2cc dome on it - in other words it's a HUGE dome compared to any other stock D-series piston (barring the nat gas GX), so the CR will shoot up for certain.

Here's an example of how the same exact piston yields totally different CR in two different engines:

A P29/PM7 piston from a 1989 Integra D16A1 DOHC engine has 9.5:1 CR in it's stock engine, but if dropped into a SOHC VTEC D16Y8 the CR shoots up above 12:1. This is a general example, not to the decimal CR ratio.

Here's a fun CR calculator to punch in different engines, head, pistons, head gaskets, etc. for messing with CR:

http://www.knology.net/~jediklc/D.htm

The key is to know the correct numbers for EVERY catagory, including piston to deck clearances. This key number is where most people screw up their calculations.

 

BTW I have experience building my own SOHC non-VTEC engine with the PM7/P29 pistons:

For reference look at the stock dished piston:



P29/PM7 domers:





My engine is a D16A6 88-91 CR-X/Civic Si engine that started with dished pistons that only yielded 9.2:1 CR stock, but after the P29 pistons, metal 96-00 Civic EX head gasket, and a very minimal head mill (just enough to ensure flatness) I've got a nice 11:1CR and it's been running strong as hell for years now!


Modified by B18C5-EH2 at 10:34 AM 10/4/2007

 

so what are u saying i should do lol.. my mentor for my project owns a machine shop so i have access to pretty much anything i need. he has been building honda/acura engines for 15years now and been a machine shop owner for 25 now. im buying these he should know what to do with them and how much bore. how much was your car bored over? i want like .20 or .30

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by chadalac1712 &raquo;</TD></TR><TR><TD CLASS="quote">so what are u saying i should do lol.. my mentor for my project owns a machine shop so i have access to pretty much anything i need. he has been building honda/acura engines for 15years now and been a machine shop owner for 25 now. im buying these he should know what to do with them and how much bore. how much was your car bored over? i want like .20 or .30</TD></TR></TABLE>

You can't bore an engine AND use the pistons you're buying.

You bore cylinders to either get them round again, or you overbore them to match oversized pistons. You need to know if the PM7s are stock bore, and if they are then have the machinist HONE the cylinders.

I simply honed my cylinders to have a nice cross hatch design and it's been running smoke-free for over 3.5 years now:



What engine are these pistons supposed to be going into?

 

im putting them into my d16z6. buying them tonight from a guy...so all i have to do really is get it honed and im good 2 go

 

If you're going to rebuild an engine and you want it to really last then you might want to consider buying brand new factory pistons like I did.

I actually purchased new pistons, rings, rod and main bearings, timing belt, waterpump, head gasket, cam, crank, rear main seals, intake and exhaust gaskets, head dowel pins, oil restrictor orifice (non-VTEC engines only), etc.



If you do it that way you won't be worrying about anything since you know a good machinist.

 

i will need to buy new rings for the pistons 2 wont i?

 

i have the rod bearings,oem head gasket, a new water pump, block guard already i just need pistons and rods. and im buying th arp head studs tonight 2 i also am getting new headers and they come with the gaskets i need. i shouldnt have to remove my intake manifold so im good there. im almost done!

 

the pistons hes selling comes with stock z6 rods but i plan on putting eagle rods on them for extra durability. im not 2 worried about how the thing is gonna last me. i get a type s in february from my grandfather for graduating highschool ( what a joke eh) but anyways this is just for my senior project at school and i need something to do that i like and want to learn more about! thanx man u have been such a big help!!!!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by chadalac1712 &raquo;</TD></TR><TR><TD CLASS="quote">i will need to buy new rings for the pistons 2 wont i?</TD></TR></TABLE>

Yes buy them for a 1989 Acura Integra D16A1 engine.

Also what's the block guard for? Are you using nitrous on top of this engine? I'd never use a block guard personally, but if you must then keep in mind they can pinch the tops of the cylinders slightly, so it night not be a bad idea to have the machinist check the bore throughout the entire cylinders top to bottom, and have him hone the cylinders only AFTER the block guard is installed.

Lastly if you really are shooting nitrous on this engine with it's high-*** compression you really need to think about what you're going to do fuel wise to keep it from detonating and exploding.

 

Oh and I just realized the Eagle rod comment.

WHY?

If you're going all-out with Eagle rods then you might as well do it right and get some forged pistons to match. Eagle rods will do little good at all honestly, because the pistons will be the weak point still.

Either go budget with used pistons, or go all-out with new forged parts - I wouldn't go middleground and mix and match parts.

 

someone suggested to me that eagle rods i might want. i wont get them if i dont need them. i plan on running nitrous after i get my head and everything done. port and polish/intake mani/450cc injectors/ and a completely built head

 

his block was a .50 over. that shouldnt effect anything that has to do with the pistons right?


Modified by chadalac1712 at 8:31 AM 10/4/2007

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by chadalac1712 &raquo;</TD></TR><TR><TD CLASS="quote">his block was a .50 over. that shouldnt effect anything that has to do with the pistons right?</TD></TR></TABLE>

Okay dude someone's got some bad info here.

First of all the block might be bored .050 over, not .50.

Secondly Honda/Acura does not offer pistons in anything over .020 over, so someone's wrong here. Either the guy is wrong in saying his block is .050 over, or he doesn't have OE Genuine PM7 pistons to sell.

Lastly I'm trying to explain the best I can that piston diameter and cylinder bore go hand in hand. You cannot have .050 bored block with stock bore pistons 0 it's impossible.

I understand you're trying to learn, so I'm trying to explain things as clearly as possible.

If you are planning on nitrous then for your sake I'd steer clear of CR higher than 10:1 - those PM7 pistons will easily top 12:1CR which would be rediculous to shoot nitrous on top of.

Either go high CR, or go nitrous. Others will chime in and probably say "you can use nitrous with high CR" and you can, but you'd want a built block, all forged internals, stand alone ECU/tuning, more than just bigger injectors for fuel, etc.

 

ah ic where u are at. ill ask him when he gets back on. i was just gonna run nos if my caar could handle it fine and nothing would mess up where can i find oe genuine pm7 pistons?