Low compression 3.2 forged pistons -$400 obo

[MerkXRTurbo]

Hey guys, I had a custom set of forged CP pistons made less than a month ago, but they messed up on them! They mistakenly increased compression height (the distance from center of wrist pin bore to piston crown) by ~.2". They honored their mistake and sent me replacements, but now I have an extra set of low compression pistons that I would like to see go to a good home rather than be a VERY expensive set of paperweights!

Info:
-3.642 bore for a 3.2 SHO

-1.53" compression height (wrist pin center to crown), OEM rod requires 1.309 compression height. All these need to work in a 3.2 are a set of rods that are .221" shorter than OEM.

-Accepts stock replacement rings

-Accepts stock diameter wrist pin, however the length of the pin is shorter than OEM. The OEM wrist pin should suffice, provided that the length was machined down .192".

-The dishing of the piston is designed with a smooth radiused transition from the bottom of the dish to the crown of the piston, that way there are no sharp edges that tend to cause detonation due to the fact that sharp edges trap a tremendous amount of heat. These pistons were designed with detonation resistance as the primary goal in mind!

- .003"-.004 " thermal expansion rate. Similarly available forged pistons for the SHO V6 have a thermal expansion rate of approximately .008"-.012", which make an engine prone to mild piston slap when cold. Also, due to these high thermal expansion rates, rings will not provide a very good seal except when the pistons are at their hottest under WOT, so they are not the best for a vehicle that spends any time on the street, IMHO. These CP pistons, however, are great for any intended use!

-These pistons cost me $1100 with rings and wrist pins. Anybody who buys these is getting a steal and a set of pistons of absolutely uncompromised quality.

-8.0:1 compression

-These pistons are brand new! They have not been installed in a block, and they have not had rings installed in them. They are as brand new as you can get! They don't have a scratch or a nick on them, and have barely been handled but a couple of times.

Showing difference in compression height, left piston designed for an OEM rod, the right piston designed for a rod .221" shorter.



Showing the difference with the pistons right side up. The mistake piston (right) has a longer skirt, due to extra material needed to place the wrist pin lower.



Showing the dish of the piston:



Pic I took with a MUCH better camera when they 1st arrived a few weeks ago before I noticed the error:



Data sheet. This contains all the info a machinist needs:







Asking $400 or best offer! You won't find a better deal anywhere!

 

[Ict_Lx]

Oooh! Those are pretty! Doesn't look like they would fit my v8 though...and missing a couple. Free bump for a good deal.

 

[Brett]

what a deal man.

 

[CademiaX]

bump for a heck of a deal!

 

[HotRodKid]

2JZGTE rods seam rather promising for these

any idea what the clearance between piston and head will be with the proper pistons on stock rods? that might make all the difference.

i wonder if a small amount of material could be taken off the top of these pistons if someone cant find a rod thats exactly .221 shorter then stock, you would be able to apply a thermal coating to compensate for the otherwise quicker heat transfer to the rings that would result

 

[MerkXRTurbo]

The OEM pistons stick up .005" past the deck, and these pistons were designed with the intent to do the same. Yamaha knew what they were doing when they designed this.

The SHO heads have a lot of quench area, which is the area between the deck surface of the heads and the top of the pistons (basically anything above the piston that is not a part of the combustion chamber). What this does is squishes the air/fuel mixture into the center of the bore, into the combustion chamber, pushing everything toward the spark plug, greatly reducing the risk of detonation simultaneously. More quench area means more boost and/or timing and/or compression on the same fuel, which is why SHO guys can run boost pressures beyond what anybody else can dream of on stock 9.8:1 compression!

Anyway, by going with an even shorter rod than .221" shorter than OEM one would be reducing the quenching effect, which is a VERY bad idea for a boosted motor IMO!!! 1-2 thousandths would probably be okay, but any more than that would be a major no-no.

The pistons could potentially be machined down in height a small amount, or a SLIGHTLY longer rod used, however two things could potentially happen:

- Raising the compression, which may be okay. I am running a lower compression than anyone I've ever heard of with a SHO V6, but I did so because the 8.0:1 will only cause a negligible change vs 8.5:1 (which has been done quite a few times), but will provide more safety margin against detonation.

- Possibly creating an interference motor! The valve clearances are cut the same depth of the ones in the OEM pistons. By trimming the crown or using a slightly longer rod, and moving the piston up farther, you have effectively made the valve clearances shallower.

It's doable, but the above 2 items will need to be taken into account. As I stated before, the stock pistons rise up .005" past the deck, which these were also designed to do. The OEM head gasket is .045" thick, meaning that Yamaha left .040" clearance. How much of that .040" do we need to retain non-interference status? That is the million dollar question for someone wanting to push the piston up further. I certainly wouldn't want to try it on my own dollar!

One could also have custom rods made. My retailer buddy that I went through for the pistons can have rods made for $180/ea. That piston and rod combination would easily handle 1000+hp... maybe then the buyer could find out for us how far the block and crank can be pushed!

 

[HotRodKid]

sho rods:
length: 5.780"
big end: 2.047"
pin bore: 0.9122

2JZGTE rods:
length: 5.590 in.
big end: 2.000 in.
pin bore: 0.787 in.

length is .031 to long, that could come off the top of the piston
big end of the 2jz rod get bored out a tiny bit
pin bore: to small but idk ...

 

[zak]

MerkXR, these might be of considerable interest to anyone messing around with 3.0 Vulcans, compression height seems about right for that engine from what I recall.

Maybe post them on Tempo/Topaz forum - zak

 

[MerkXRTurbo]

HRK, here are the proper dimensions for the 3.2 SHO rods. I have a 3.0 rod somewhere as well, out in my garage if anybody would like me to measure it (3.0 and 3.2 have different rods, right???):

Length: 5.817"
Big end: 2.155"
Pin Bore: .866"

I have a rod, pin, and piston here in front of me right now measuring with my calipers. It looks to me that the 2JZ rod is even closer than you thought, but .006" too short. Maybe a slightly longer rod is available for the 2JZ?

ZAK, thanks for the recommendation. I will look into it. I didn't know there was a Tempo/Topaz forum... I thought people had to actually like a car to want to start a forum for it.

 

[Toolman]

I didn't know there was a Tempo/Topaz forum... I thought people had to actually like a car to want to start a forum for it.

Not true. There is even a forum for Taurii I have heard.

 

[HotRodKid]

theres definantly rods out there that can be made to work with these pistons

now im really sorry i didnt jump on those titanium rods for my project, they would have been perfect for these pistons, but at the time i couldnt find rod specs

 

[MerkXRTurbo]

Bump. Cheap pistons anyone? Won't find this good of a deal ever again!

 

[NovaSS]

Its a great deal but the cost of getting a rod that would work with them would destroy any savings.

 

[MerkXRTurbo]

True, but then one could have an even better built bottom end for just the cost of a set of pistons normally.

 

[Phoenix]

From what I understand if you hook these up to 3.2 rods you have high comp pistons ya?

 

[MerkXRTurbo]

No, they require a shorter rod. Compression can never be reliably changed by changing the length of a rod. There are a number of reasons why that is a totally awful way of doing it, but I won't get into that now.

The OEM pistons stick up past the deck .005". On stock rods, these will stick out of the bores around .205"... way more than enough to smash it into the head, and to uncompress the ring pack without the heads on. These can only be used with different rods.