Stock bigport piston "dish"

[biGtai]

Do they look like standard ?

the depth on the dish is under 4mm at the deepest point.
I think compression height on them might be around 29.3mm, does that sound right?

basically i just want to be able to tell whether they're high compression or standard

cheers


forgot, also they're 1mm oversize

[Fozz]

Are thoose acl pistons? they look just like mine pretty sure there standard compression not high

[rthy]

they don't look like stock pistons to me, by memory the squish shaped part of the piston on the OEM bigport and not machined

[SpotterOne]

<div class='quotetop'>QUOTE (Sam_Q @ Aug 21 2008, 04:57 PM) </div>I thought the same thing too, but I just ducked out to the garage to have a look at a set. They don't look like they are machined, but only because they are covered in carbon!

Those pistons could be toyota pistons because they look like they are standard compression, and they have the dimple to indicate forwards the same as stock pistons do. They are also very close to the same shape as standard ones.

I've been hunting around for standard compression 16v pistons for a week or so, and can't find anything aftermarket. All the aftermarket ones are either High Compression (they have a big lump on top) or GZE (with a big dish in them). Those pistons look like neither, and I've checked out quite a few manufacturers recently.

I don't have a picture of a 4agZe piston here, so I can't be sure of what they look like, but it might be one of them. How far below the deck of the block do they sit when connected up properly and are at TDC? The difference only needs to be in the location of the gudgeon pin to lower the compression ratio.

[rthy]

maybe my memory is off but I remembered mine wasnt machined there, mine was cleaned before I chopped it into 5 peices for my engine build research. Have you seen a picture of an acl piston before?

[SpotterOne]

<div class='quotetop'>QUOTE (Sam_Q @ Aug 21 2008, 10:03 PM) </div>Yeah, mine are definitely machined around the outside rim. The squish area looks like it could have been machined, but I couldn't tell through the carbon so you may be right! :2thumbs:

I had a look at the ACL website, and the picture is definitely different. In fact, the only 16v piston they list on there is a GZE version.

edit - I found a pic of some GZE pistons, and remembered that the easy way to tell them apart is the ceramic coating, so the pistons in the pic definitely aren't from a GZE.

[rthy]

acl did sell a 16V piston, the guy told me it had 0.5 lower compression ratio across their whole range to allow for machined decks. I may have a crap photo of it somewhere, I need to do some digging.

[SpotterOne]

<div class='quotetop'>QUOTE (Sam_Q @ Aug 21 2008, 11:02 PM) </div>Wish they still did them! I could use a set right about now!

[rthy]

heres a pic i found off my hard drive that I keep for my 20v/4afe build:



I didnt end up considering it because they have a pretty bad reputaion amoust people for breaking and one guy said it was they expanded unevenly.

Bigtai: I will look to see if I still have those piston pieces so I can tell you if its the same

[biGtai]

<div class='quotetop'>QUOTE (Sam_Q @ Aug 22 2008, 06:58 AM) </div>
thank for the replies.
They are aftermarket pistons, not ACL though. Some NZ manufacturer.
I just wanted a rough idea whether the dish was the same or not though i'm not entirely sure how to calculate it or what the stock one is like.

They look similar enough to the ones you posted. If they're 20v pistons & mine are they same that would suggest they're give a higher compression than stock bigport pistons?!

edit: i figure it might juust be easier to call them when i find their details.

I also found this info about them too:
New set NEW ERA pistons 4NE25160 with gudgeon pins and Grant chromed top ring set. Available in Std or +1.00mm. Suits Toyota 1587cc DOHC 16valve engines from Carina, Corolla and Celica cars 1983 on, 4AGEU (or 4AGE-LU?) and increased compression for 4AGE engines. Have shallow dish (1.2mm) in top with 4 valve pockets. Normal 4AGE pistons should have 2.5mm dish. These pistons have 18mm press fit gudgeon pins.

any idea on how to calculate dish area so i kno an accurate comppression ratio?