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Discussion Starter · #1 ·
Hello All,
What are the advantages and/or disadvantages of using forged Gti-r (stock DET size) pistons as opposed to using forged 87mm (300zxTT size) pistons? Which would be best to use for 350-400 reliable hp? How about turbo lag?

I tried looking for an answer in the archives, but got more confused.

Anyone know the compression ratio of either size pistons in a DE block?

I would greatly appreciate any feedback. Thanks
 

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The 86mm forged gti-r pistons are "stock bore" good if the cylinder bore are with in spec. If there not then going with the 87mm would be the way to go by boring/honing properly with tirque plate 1mm over. Correct me if im wrong but a bigger piston/bore would give a larger area for combustion to take place?

Lawrence
92 se-r turbo
jwt 87mm block w/squirters
sitting in the garage
 

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Fmax Stg II B13
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358 Posts
Keep in mind the compression ratio of VG30DETT pistons that are not dished will be 9:1, GTi-R pistons will be.. 8.3:1 ? I went with VG30's due to the low cost.
 

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PDX S2000 said:
Keep in mind the compression ratio of VG30DETT pistons that are not dished will be 9:1, GTi-R pistons will be.. 8.3:1 ? I went with VG30's due to the low cost.
Actually, GTi-R pistons in a DE will give 8.5:1 CR. The GTi-R and the BB DET use the same pistons.... the GTi-R has a lower CR because it has a bigger combustion chamber (different head)
 

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Discussion Starter · #6 ·
Please forgive my ignorance, but what exactly does boring the cyliners 1mm over accomplish? If both 87mm pistons and Gti-r (or BB) pistons net 8.5:1 CR in a DE, which has the advantage? How does that 1mm over-bore benefit a turbo engine if it has the same CR as a stock (86mm) piston? Thanks
 

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Pistons

GTiR Pistons are Cast.....NOT Forged!
GTiR Pistons and Bluebird Pistons are exactly the same!
GTiR Pistons net 8.3:1 CR in a GTiR
GTiR Pistons net 8.5:1 CR in a BB DET or DE.

Factory Cast DE and DET pistons are 86mm

JWT/ARIAS pistons are 87mm which requires a .040" (1mm) over bore of the cylinder wall.

A 1mm over bore *REQUIRES* the use of a torque plate. A torque plate simulates a torqued head onto the block. The shape of the cylinder walls change when the ead is torqued onto the block, thus creating the need to use a torque plate to plateau hone the cylinders evenly.

Over boring the motor gives you more displacement as well.

More displacement =More power!!!!!
 

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Jah Rastafari
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Your motor is just a air pump bigger pistons move more air which inturn when added with fuel makes more HP.
 

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TurboJesus said:
If i do go 87mm pistion were do i get the torque plate ?

Richie
Have JWT do it. They have a torque plate, and have probably bored more SR20's than anyone else in the country.
 

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yes stock pistons are indeed 86mm



92 se-r turbo
90 talon tsi awd
Lawrence
 
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