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93 Civic HB SI
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378 Posts
Discussion Starter #1
Hi all,

I have some questions that I hope someone with knowledge/experience of using 'much thicker than normal head gaskets' might be able to answer.

My original build and hard facts:

In my original build, I used Vitara dish style 'turbo' pistons with 'custom length' I-Beam forged rods, beefy SOBs. Stock rod length on a D center-to-center is 5.394", and these 'custom length' rods are 5.458", difference of 1.6mm/0.064". The reason for the rod 'custom length' in this Vitara piston application appears to be the wrist pin bore hole-to-piston crown distance on the vitara's compared to a stock piston. On a stock D piston, the crown-to-wrist pin hole distance is longer and the Vitara is shorter. Hence why if you use stock length rods with these Vitara pistons, the final piston/rod assembly is shorter, your CR is in the 7s and the peak crown height at the diameter edge of the piston is actually quite a ways below the top of the cylinder. Adding these 'custom length' rods with the Vitara's brings the piston outer diameter edge back up to deck height, as well as CR back into the 8's. With the combo together, piston/rod assembly length is the same as a stock piston/rod assembly, meaning a stock head gasket can be used. All is good with the world.

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The situation facing piston upgrades using these rods:

Everyone and their mother appears to offer pistons for strictly stock rod lengths on D series applications. Everything in Wiseco, CP, Arias, Supertech, etc. all offer off-the-shelf pistons with rod length requirements of stock (5.394").

I don't have the money to ask for custom built pistons, but I am somewhat prepared to purchase new stock length forged rods if the will of the D series gods sway me in that direction.

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My question with some facts:

My 'custom length' rods are perfectly fine right now, nothing is wrong with them. In hopes of being able to continue to use them, I have envisioned a couple scenarios, and each have potential problems associated with them:

1. Getting stock-length-rod piston offerings from Wiseco, etc. and using them on my custom length rods. Having a machinist mill the piston tops down 1.6mm (0.064").

1a. My personal issue with this is that is a LOT of material to remove from a piston, which exposes a huge number of problems in and of itself. I have already talked myself out of this. No point in buying nice pistons to purposefully fuck em up shortly after.


2. Getting stock-length-rod piston offerings from Wiseco, etc. and using them on my custom length rods. Using a thicker head gasket to overcome the reality of having pistons protrude 1.6mm/0.064" out of the cylinders.

2a. I don't have a lot of experience with overly thick head gaskets. My concerns with choosing a head gasket to provide a near-0.064" final thickness after crush would be the wrong way to attempt to make up for 'missing cylinder height'. I don't think the head gasket itself would like having so much of its own material exposed to combustion temperatures, although I could be wrong here I just don't have the experience with thick gaskets. I know companies like Cometic offer some crazy thick head gaskets, but I question longevity of the combustion chamber seal over long periods of having so much head gasket material exposed to the combustion chamber and its temperatures. Thin gaskets have the benefit of being able to rid their heat through the block/head quickly, not too sure if heat sinking becomes a concern with thick head gaskets exposed to combustion temps for so long. I'm not too concerned about a thicker gasket's ability to seal the chamber pressures, as I'm sure the gasket companies wouldn't offer gaskets so thick that couldn't provide a proper seal. I'm sure sealing is well tested, but I do question the heat sinking concern as I'm just not too familiar with guys who frequently abuse thick head gaskets to know the long term results.

2b. If guys who have experience with thick head gaskets being used and abused could comment on longevity after reading 2a, I would greatly appreciate it. If results are positive, it might sway me to attempt this, picking a gasket that provides proper cylinder head clearances after crush coupled with the piston protrusion. It would save me a few hundred bucks that could instead go towards bearings, other gaskets, etc.


3. Shelving my 'custom length' rods, or offering them up for sale with an explicit note saying they MUST be used with Vitara's only! Then buying brand new pistons from Wiseco, etc. along with new stock-length forged rods.

3a. This will prevent all issues I'm facing, but at the expense of buying new rods. If I could use my 'custom length' rods, I would love to in attempt to save some money, but I'm not going to chance it if people unanimously agree that I should just buy new rods/pistons together and be done.

3b. If the vote swings towards new rods, would anyone be interested in my 'custom length' rods for their Vitara build? You would only need to get pistons if you bought my rods! I would price them to help save you more than half of buying a full Vitara piston/rod kit. These rods do require block notching though!



Thanks for any feedback!
 

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Registered
93 Civic HB SI
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378 Posts
Discussion Starter #3
what about using a d17 forged piston ?too low?
Holy f***in shit, I didn't even think to look at the D17 piston specs in the Wiseco catalog!



The compression height is actually 0.085" lower than the same style piston for the D16Y8, but offers 8.8:1 using the D17 crank stroke instead of the D16Y8 8.5:1!

Following the specs posted in the Wiseco catalog as well as using information I already know about the D16Y8, I should be damn close to what I had with the Vitara's.

Just did the maths and those will actually work and I won't lose too much comp as I'm going to get the head milled again for flatness anyways! I'll wait to purchase the HG once the bottom end is complete, but I feel through the math that if I couple it with a thin HG like this:


I should be able to stay around 8.5:1 which is OK by me. The D17 pistons will end up being just slightly below the cylinder, 0.021" or half a mm! That is perfect, and will let me save $300 bucks!

Wiseco also seems to be the only player for the D17? I can't find any other brands just by quick google search.

Dude I can't thank you enough for pointing this out, that is the route I'm going to take.

This needs to be a sticky "What to do if you bought Vitara pistons and custom rods, but want to upgrade pistons"
 

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Never finishes (TWSS)
91 Civic SI hb
Joined
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1,880 Posts
I didnt read the whole thread, although i do see d17 pistons willl work for you. Another simple option is counter boring the head to allow the pistons to come up out of the block. Ideally you would run a oem thickness headgasket aswell. But milling the tops off the pistons is a simple fix aswell.

In my build i need to take 0.080" off the tops of the pistons. Or counter bore the head. Still not sure what was im going. Probably will be taking the tops off the forged b16 pistons though.
 
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