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Discussion Starter #1 (Edited)
Long time no speak gents,

Currently refreshing my engine for what I hope to be the last time and had a few quick questions. All regarding my D16Z6.

My block has been decked twice, at least I'm 95% sure it has been. From what the guy at my machine shop tells me, he only decks .005" at a time, which would equal .01".

After the first deck job, I used an OEM gasket and was tuned on that gasket. My question now, is since there's been another .005" shaved off should I go with another OEM or look into a Cometic? The problem there is that Cometic only offers a .027" and a .030". And correct me if I'm wrong, I believe the OEM is .028". Please bear in mind that I'm looking to reuse my current tune and that's where all of my concern comes in to play as I'm worried about my compression changing slightly.

Next, how will the correct HG choice affect my mechanical timing? And will this HG choice affect how much I should torque my head studs?

Last question, I've read that some people like to go .5mm over bore size on their head gasket? Any validity in this? I've always matched my HG's to my 75.5 bore size.

Thanks gents, looking forward to posting photos of my rebuild soon!
 

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Brokedick Millionaire
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not enough decking to worry about.

More slop in the crank drive gear that you are dealing with just from the milling. What little milling there is would retard the cam timing and lower cylinder pressures anyways.

There are registers to check amount that has been milled. Cometic has thicker gaskets is needed, esp. for the thicker 88-91 spec (.046" IIRC) but an .080" was possible when I though about it for clearance on a special build.

ROUGHLY 1 MM (.039xxx") will alter cam timing (1/2 crank speed) by 1 degree.

HG's that I've dealt with START at 76mm, even OEM's.
 

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Discussion Starter #3
not enough decking to worry about.

More slop in the crank drive gear that you are dealing with just from the milling. What little milling there is would retard the cam timing and lower cylinder pressures anyways.

There are registers to check amount that has been milled. Cometic has thicker gaskets is needed, esp. for the thicker 88-91 spec (.046" IIRC) but an .080" was possible when I though about it for clearance on a special build.

ROUGHLY 1 MM (.039xxx") will alter cam timing (1/2 crank speed) by 1 degree.

HG's that I've dealt with START at 76mm, even OEM's.
By "not have to worry about." Does that mean I'll be fine using another OEM?

What is the advantage of a slightly larger HG bore size?
 

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Brokedick Millionaire
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By "not have to worry about." Does that mean I'll be fine using another OEM?

What is the advantage of a slightly larger HG bore size?
Carbon fills the tiny gap.

Unless going above 300 whp, no reason NOT to run anything other than OEM Y8 HG and many have went beyond that threshold.

If you are truly worried after a "deck and slap" of the head and new gasket, pull 1-2 degrees at the dizzy and work your way back watching for signs of issues.

IF you pay attention to the plugs, like old school tuners did and I will ALWAYS do, reading the tip and heat stripes, you can sneak up to the max of the tune already locked in the ECU.

How much wiggle room did your tuner leave in the tune?

I know on my old Blundell tune I had an extra +6 initial (MPG) base timing that I forgot to work around went I stepped up to 100 shot on my Z6.

85 shot to 100 shot, +6 timing, still kept the rods and slugs inside the block without oil leaks, but it wasn't happy!
 

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not enough decking to worry about.

More slop in the crank drive gear that you are dealing with just from the milling. What little milling there is would retard the cam timing and lower cylinder pressures anyways.

There are registers to check amount that has been milled. Cometic has thicker gaskets is needed, esp. for the thicker 88-91 spec (.046" IIRC) but an .080" was possible when I though about it for clearance on a special build.

ROUGHLY 1 MM (.039xxx") will alter cam timing (1/2 crank speed) by 1 degree.

HG's that I've dealt with START at 76mm, even OEM's.
More info on where on the head these registers are ?

Stratton.
 

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DIY Guru
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Transzex... Those are not mill stop points, they are injection points from when the head was cast.

General rule of thumb is for every .007-.008 milled the combustion chamber closes up by 1cc

So by the time you hit the first point you have lost 4cc in the combustion chamber

According to AREA (Automotive Engine Rebuilders Association)

The Honda D16Z6 head

New thickness 3.659-3.663 (92.939-93.04mm)
Min Thickness 3.651 (92.735 mm)

So By the Book there is .008-.012 that can be safely milled from the head.

It is common practice to mill heads more than the AREA or FSM spec

But when you do, the Head should be CC'ed and CR figured and anything much more than stock.

Also, OP, Once the short block is assembled, I would check for piston protrusion above the deck surface.

You can get away with about .010 above the deck, but much more than that you may need a thicker head gasket.
 

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Discussion Starter #8
I've got to be completely honest, a lot of what you guys are telling me is going far beyond my level of comprehension. And allow me to thank you for helping me this greatly.

The only facts I can provide are the motor makes roughly 330whp, the block was taken down .005" on the first tune and ran with OEM HG. Now it's been taken down another .005".

I hate to be that guy, but can anyone put into idiot terms which gasket I need to run in order to be safe?
 

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Brokedick Millionaire
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Transzex... Those are not mill stop points, they are injection points from when the head was cast.
They are used along with the deck surface to check amount of milling from stock. SCCA/NASA uses them to check this when looking for rules infractions.

Andy Hollis clued me in on the info, esp. when figuring out headgasket thickness and the "newer" 5 layer replacement to the old composite, both OEM.

RedShift ST Civic Tech

Jason Tipple's car pictured, 2001 STS National Champ, Chris won with it the next year.
 

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Meat Popsicle
91 CRX Si
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Transzex... Those are not mill stop points, they are injection points from when the head was cast.
You're right, the FSM makes no reference to these points. Bone knows his shit though and this info goes back many years. I recall the same info and image being sent to me at least 5 years ago by bone and I have no doubt in my mind that the info is correct.

So while it may not be the Honda approved method for measuring head thickness, it's a quick and dirty way of seeing if you need to adjust your cam year or if you've bought a head that's been excessively milled.
 

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I am not saying that Transzex is wrong, he is quoting his source.

If sanctioned race bodies want to use that point for tech ...so be it.

I am pointing out, what is believed to be common knowledge, is inaccurate.

No way is a rough cast mark going to be accurate,

By the time you get to it you will be 3 times past the service limit.

If you want a high compression race engine that's fine, but on grandmom's grocery getter it does not be used.

By the OP asked what the specs are on a D16Z6

So In my book published by AREA

New thickness is
3.359-3.663 (92.939 to 93.04 mm)
Min thickness of 3.651 (92.735 mm)

This spec is measured from the VC rail to the HG surface, anywhere around the head.

I could set up a head and mill the same head on a tilt and/or angle, and still leave that casting injection point with in the spec the race body is looking for, but till gain compression.
 
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