Wiseco pistons for rebuild

[audiophile]

So I am rebuilding an 84' T with an 87 powertrain. To keep it simple there seems to be conflicting information on which Wiseco pistons to use. There are PT040 and PT120 pistons, Wiseco lists them as 85' and older and 86' and newer respectively, but it seems there are a few using 040s in 86 and 87 109 blocks. My question is which Wiseco piston is correct for an 87 street car build?

I am going for a somewhat stock build, but I want it to last...... FYI I am also considering running speed pros as well.....

 

[turbodave231]

What block are you planning to use?

The 86-87 "109" block has a lower deck height than earlier blocks.

 

[audiophile]

Dave,

Thank you for the reply! I am using a 109 block out of an 87 GN.

 

[dank GN]

I went with wiseco pistons .040" over and I'm happy . They where a lot lighter then my .030 speed pros. So to balance the assy was a Bi**h

 

[audiophile]

Dank, Thank you for the reply. I am assuming you are using the PT040 series pistons, correct?

 

[Lil Truck]

Both pistons work, they are different in compression height. 040 will be around 8.5 to 1 and the 12o will be 9.0+ to 1 compression ratio depending on rod length and head gasket thickness with stock CC.
http://www.wiseco.com/Catalogs/ProTru/BuickChryslerChevrolet.pdf

I used the PT120 in my current build.

 

[Lil Truck]

Both pistons work, they are different in compression height. 040 will be around 8.5 to 1 and the 12o will be 9.0+ to 1 compression ratio depending on rod length and head gasket thickness with stock CC.
http://www.wiseco.com/Catalogs/ProTru/BuickChryslerChevrolet.pdf

I used the PT120 in my current build.

Your 87 block is a Stage 2 block as listed on the Wiseco catalog for deck height ...... but they do vary a little.

 

[turbodave231]

The stock block is not the same deck height as a Stage 2 block. All Stage 2 blocks and 4.1 Stage 1 blocks are advertised at 9.535 the 3.8 Stage 1 is 9.560.

Production blocks prior to MY1986 are specified at 9.535

All the virgin 109 block I have measured fall somewhere in the 9.522 range. I am using a CNC mill with an electronic probe to take these measurements ( much like a CMM machine). I have probably done a couple dozen, so I think my measurements are typical for this block.

After line boring, line honing and square decking they usually end up around 9.515-9.510.

 

[audiophile]

Truck thank you for the reply! So I have always thought that higher compression ratios are bad for turbos, how are these cars different?

 

[turbodave231]

You can easily get away with 9.00:1 with these engines.


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[Lil Truck]

The stock block is not the same deck height as a Stage 2 block. The 4.1 Stage 1 and 2 blocks are advertised at 9.535 the 3.8 Stage 1 is 9.560.

All the virgin 109 block I have measured fall somewhere in the 9.522 range. I am using a CNC mill with an electronic probe to take these measurements ( much like a CMM machine). I have probably done a couple dozen, so I think my measurements are typical for this block.

After line boring, line honing and square decking they usually end up around 9.515-9.510.

Thanks Dave, I was not thinking just reading the catalog ..... sorry for the confusion!

 

[audiophile]

Thank you for all the input!!!

HMMM these waters are sure getting muddy lol! So is there consensus of which piston model for the stage 2 is better, for everyday use? I suppose not sense consensus is as foreign on forums as it is in congress.

My guess is that with the 040s that the boost can be turned up and the quench area is better, but the 120s are better "before boost engages"..... I just want a better street machine, but not want to run the risk of too much compression.... I will say that I am inclined to go with 040s from what I have read and what some builders told me, but I dont want to make a mistake, as this is all new to me....

 

[turbodave231]

No problem......Just want the OP to know what he might be in for.....I beleive the PT040A2 pistons would be out of the hole a substantial amount. The PT120A2 might be right at zero deck depending on what machine work has been done.

The wiseco pistons are a good choice. Its hard to build a higher compression engine using the JE's or Diamond shelf pistons. Mike at FT is offering a new Diamond piston that makes it easier to build a 9:1 engine.

Audiophile: If in doubt, take you block to your machinist and have him measure the deck height before you buy pistons. It shouldn't be an expensive or difficult task to perform.

 

[Lil Truck]

Sorry I confused the issue of a Stock 87 block with the Stage blocks.

You have an 87 Stock block as Dave mentioned at 9.522 deck height if it is virgin. The PT 120 will give you around 9 to 1 and you may have to cut the piston down to keep it in the block after decking.

The PT040 is a safe choice if you don't want to take the chance of extra machine work but lower compression is the result.

I am running 9.1 to 1 with aluminum heads and love the combo, it is not the combo in my signature.

 

[Lil Truck]

No problem......Just want the OP to know what he might be in for.....I beleive the PT040A2 pistons would be out of the hole a substantial amount. The PT120A2 might be right at zero deck depending on what machine work has been done.

The wiseco pistons are a good choice. Its hard to build a higher compression engine using the JE's or Diamond shelf pistons. Mike at FT is offering a new Diamond piston that makes it easier to build a 9:1 engine.

Audiophile: If in doubt, take you block to your machinist and have him measure the deck height before you buy pistons. It shouldn't be an expensive or difficult task to perform.

Dave the PT040 is 1.825 Comp Height and the PT120 is 1.860, would the shorter Comp Height be deeper in the hole?

 

[turbodave231]

Lil Truck, You are right......I was reading the Wiesco chart backwards. The 040 has the lowest C.H. and will be in the hole .035 farther than the 120.

 

[audiophile]

I just want to say Thank you for all the help, from everyone!

 

[audiophile]

So my engine builder got back to me and says that the "worst/biggest" cylinder bore size is 3.801, after he did a "simple" hone on it. He did say that all my bores are good I.E. nothing is tapered or out of round. That said I am tempted to throw standard size pistons such as Speed pro/TRW pistons in it and run it. I do want to run Wisecos, but he does not have torque plates for this engine. What should I do? Run (new) standard pistons with new rings, have him hone 20 over w/out torque plates or find a new machinist? I just don't want to pay to have this rebuilt again because it was done "wrong".

 

[dank GN]

My bore is 3.840 and used the PT040 model . Again I am very happy with them and they where lighter then my speed pro .030 over piston as seen in the pic

 

[audiophile]

I would prefer the Wisecos, but my machinist does not have torque plates for this engine, so if it is bored 20 over to fit the Wiseco pistons it will have to be bored without the torque plates. I really don't know what to do. Put in the speed pros and call it a day or...?