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Discussion Starter · #1 · (Edited)
I'm building a D16Y8, presently stocking up on parts. I've come to the point where I have to decide on pistons. From the tons of research I've done on this forum/google it's PM6 or PG6 pistons. Nobody I’ve read about has my situation thus far, so I'm guessing PM6 pistons will be the way to go to bring me to a sensible ~11:1 static compression ratio.

Well...it seems simple. I don't know my way around tuning and building engines (which is why I'm having it rebuilt by a professional--no substitute for experience) BUT I can safely guess that more fuel=more emissions. I want to build a high compression engine, but it needs to be smog friendly for Cali.

I bought a rebuilt Y8 head with mild intake porting and a zex 105300 camshaft. It had Isky springs but according to the numbers and from what people here say, I'll have coil binding. I've got supertech springs and retainers to replace them. It's milled .018", though I need to have it checked out...there is some wear on the valvetrain/rockers (?).

What I want is a DD with some zip, handles the corners and has plenty of torque so it doesn't choke on hills. I've rebuilt the suspension and brakes, and it handles great! (with some minor bugs I've yet to figure out) I just need some power behind it. Just throwing in a D16Y8 engine would do, I'm running a D15B8 now, but why rebuild a stock engine with stock parts when the labor costs a little more to do better? Besides I made mistake of starting a turbo build and I've already got a bunch of parts I can't use so I'm scavenging what I can.

PG6 pistons will punch me up to 13.18:1 static compression, as long it can be tuned to be smog friendly that’s great. I can get the machinist to clay for P2V contact, clearance the valve reliefs, zero out the deck, etc. I was told 11:1 is feasible for smog...what I need to know is how far can I go?
 

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Discussion Starter · #3 · (Edited)
Shoot...PO6 chipped and tuned on an EG hatch...shoulda said that.

...and by smog friendly I mean smog test. Not CARB gestapo compliant.
 

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That changes things. My usual advice for people who deal with smog is to move out of cali, drive anything other than a Honda, or hope the fault drops.

Your cam will be the determining factor in emmisions compliance. Talk to bisi.

I would do a nice lil' build with a Bisi cam and PG6s.
 

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Discussion Starter · #5 ·
Update for those in a similar situation:

I wasn't able to talk to Bisi directly (corporate network experience took me four days to get in touch with someone), but found that 11:1 compression is possible for smog, but it's on the edge---meaning that a 12:1 won't be possible, so I'll have to stick with PM6 pistons to get 11:1 without crazy head gasket sizes. As I've read countless times before, getting it to pass smog will rely on a good tune. I was told some people were able to pass smog with a 1.2 grind but it isn't suggested.

I'm going with a Level 1 camshaft and cam gear from Bisi. The supertech springs/retainers I bought not too long ago for the Zex 105300 camshaft should be fine with it.

I got a new question though:

For 11:1 compression should I be looking for other than stock pistons? I sure as hell don't want to waste money on forged pistons or for that matter, stock pistons from honda parts deals (>$300). I could get a set really cheap on Ebay...don't know if that's a good way to go though. If I were going with PG6 pistons I could get them from FJ Distributors for only 130 bucks...
 

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Compression doesn't matter, the cam does, at least for passing emissions. I know people who have passed stringent emissions tests with a 2.2 level cam. A lot of it does come down to tuning.

Just rock some 75.5 or 76mm PG6s and a nice cam from Bisi. That will pretty much get you a very good increase in power, without spending a whole lot.
 

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Very interested to see how this works out for you. I'm in a very similar situation, where I don't know exactly where to go with my build for this reason. Keep us updated, and good luck!
 

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Discussion Starter · #8 ·
Hope you haven't wasted as much money as I have. I've been able to get somewhere with every hobby I've had. This car is turning my wallet into a black hole.

Compression doesn't matter, the cam does, at least for passing emissions. I know people who have passed stringent emissions tests with a 2.2 level cam. A lot of it does come down to tuning.

Just rock some 75.5 or 76mm PG6s and a nice cam from Bisi. That will pretty much get you a very good increase in power, without spending a whole lot.
Is this the same stringent emission requirements as Long Beach? The guy from Bisimoto gave me an entirely different opinion. He said too much compression would heat the emissions past the point that a catalytic converter could handle, and it would fail smog.

What's the science behind this? Why doesn't compression matter? I thought more compression = more fuel = more emissions...? If I were to use 75.5mm PG6 pistons my static compression would be 12.17 with a .060" head gasket.

I'm all for power but I just spent five hundred on a head with a camshaft I can't use, three hundred on springs and retainers I didn't need. Just spent another five hundred on a camshaft/cam gear to keep in line with emissions requirements. Before that I wasted a bunch of money on turbo related parts. Cheap went out the window a LONG time ago. I'm to the point where I just want to get this done.
 

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Do your homework, make a plan then stick to it.

Every time you change your mind after buying parts you put yourself in a deeper hole.

You absolutely do not need forged pistons.

Compression certainly does matter for smog as the higher the compression, the higher the cylinder pressures and the hotter the charge. Heat makes nitrous oxides.

Re tuning to pass emmissions, you get into a balancing act betwen NOx and HCs and CO.

Generally what helps one, hurts another. To much compression or to much cam overlap or to much cam duration all start to paint you into a corner.

A good well positioned catalytic converter helps, but can only do so much.

Without direct experience with your set up, I would think pistons with a similar dome shape to those offered on the newest model with a similar head casting to yours would be best. I would not give any consideration to high dome pistons

Removing hot spots and sharp edges so as to reduce chances of preignition or onset of detonation will help if you want to push limits.

The earlier the inlet valve closes, the less compression you can tolerate without going over the top with NOx. Shorter duration or advanced cam timing closes the inlet earlier.

Narrow lobe centres or longer duration increases overlap and increases hydrocarbons.

Rich mixture to suppress detonation and reduce NOx increases CO.

Flat top pistons and small chamber heads to give about 11:1 shuld work fine.

Take Bisis advice on the cam.

A small cam should be fine on stock springs and retainers, but if you have better springs they will do no harm.

The Supertec springs might br OK with the Bisi cam? Check it out.

Milling the head and changing gasket thickness or milling the deck all influence cam timing and therefore emmissions.

Using high octane unleaded petrol can help with emissions as you can then tune for emissions instead of suppression of detonation.
 

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yEaH tHaT gUy!!!
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smog what is smog?


you mean u actuall y take your car to get tested kind of smog?


SCREW smogs lol
 

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Discussion Starter · #12 ·
Do your homework, make a plan then stick to it.

Every time you change your mind after buying parts you put yourself in a deeper hole.

You absolutely do not need forged pistons.

Compression certainly does matter for smog as the higher the compression, the higher the cylinder pressures and the hotter the charge. Heat makes nitrous oxides.

Re tuning to pass emmissions, you get into a balancing act betwen NOx and HCs and CO.

Generally what helps one, hurts another. To much compression or to much cam overlap or to much cam duration all start to paint you into a corner.

A good well positioned catalytic converter helps, but can only do so much.

Without direct experience with your set up, I would think pistons with a similar dome shape to those offered on the newest model with a similar head casting to yours would be best. I would not give any consideration to high dome pistons

Removing hot spots and sharp edges so as to reduce chances of preignition or onset of detonation will help if you want to push limits.

The earlier the inlet valve closes, the less compression you can tolerate without going over the top with NOx. Shorter duration or advanced cam timing closes the inlet earlier.

Narrow lobe centres or longer duration increases overlap and increases hydrocarbons.

Rich mixture to suppress detonation and reduce NOx increases CO.

Flat top pistons and small chamber heads to give about 11:1 shuld work fine.

Take Bisis advice on the cam.

A small cam should be fine on stock springs and retainers, but if you have better springs they will do no harm.

The Supertec springs might br OK with the Bisi cam? Check it out.

Milling the head and changing gasket thickness or milling the deck all influence cam timing and therefore emmissions.

Using high octane unleaded petrol can help with emissions as you can then tune for emissions instead of suppression of detonation.
Thank you very much. This is exactly the information I needed.

As for the other comments, I got enough to worry about. Given the history with CARB and bias from state officials, it won't be long before they start impounding hondas that aren't smog compliant. I'm planning for the next ten years, not the next 13.** seconds. Just my prerogative.
 

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The reason why I say compression doesn't matter is because if the compression level is achieved with a good combustion chamber, everything all rests in the cam and tuning.

Pat is certainly correct about most of this, but, I have knowledge of several high compression builds that pass rolling road inspections in Europe with large cams, including a Bisi 2.2.

I also have no faith in any of Bisi's sales monkies, especially after the disgustingly poor service I have received with my last order. I won't know Bisi's products. They perform. However, I doubt I will be ordering from Bisimoto again.
 

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I agree that chamber shape including piston dome shape has a huge influence on just how high the compression can go.

Good quench helps with NOx but tends to hurt CO and HCs a bit.

Quench and squish gets real complex real quick as quench extinguishes the flame as the gap between the head and piston gets tight enough so that the heat conducted out of the charge puts the flame out, but the squish as the piston and head get real close generates turbulence and tumble that suppresses detonation and increases flame speed to help burn up the charge that was extinguished by quench. Bottom line is results can be a bit unpredictable as opposing trends each have their influence.
 

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Discussion Starter · #15 · (Edited)
Hmm...the head was already milled to .018", have a .030" head gasket on hand and the PM6 pistons are .02" to the deck. So PTH would be .032"

Now it's the question of balancing quench/squish. Should I increase (larger head gasket), decrease (zero-deck/mill the head even more/smaller head gasket) the quench, or just let it be?

What effect (if any) would a high flow catalytic converter (using magnaflow) have in the process?
 

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The better the cat, the more hydrocarbons it will soak up.

I would run it as it is.
 

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Your math is wrong. .020" in the hole, and a stock MLS headgasket that squishes to ~.028" is a quench distance of .048". That's well within my theoretical maximum effective quench distance of 3.5mm (about .138").

You want to have a minimum of .027" piston to head clearance simply because no one I know of has ever run tighter to see how much the stock rods stretch at any reasonable rev limit. I suspect one COULD go a bit tighter, but, headgasket thickness is a very decent safe limit for stock rods.
 

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Discussion Starter · #18 · (Edited)
Doh! Well it would help if I knew what the formula was. :mrgreen: I pieced together that from my search on calculating quench. What about how much the head is milled, does that not also count?

The gasket is from FJ Distributor's turbo kit, don't know if that changes anything.
 

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It'll squish to about .030" then. I doubt anyone has taken the time to measure squished height.

You have to measure the depth of the quench pads to figure that out. Most heads are rather imprecise, which is why it is better to spot face the chambers to a consistent depth like Endyn does when building a performance engine.
 

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Thanks for all the information, I really enjoy reading all these posts about rebuilding an engine. I currently have a D16Z6 which I am planning on rebuilding this summer in my garage and I've been lurking and reading up as much as I can. I'll be sure to have a rebuild thread just to ask questions about my future smog compliant rebuild.:yes:
 
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