Tag: fuck wiseco

The piston debacle

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Sheesh! Finding proper 4A-G(Z)E pistons is a mess!

The following pistons are listed with 20mm pin and 30.68mm (1.208″) compression height

  • Wiseco K506M815
  • CP/Carrillo SC7653
  • Wössner 9035D050
  • Wössner 9191D050 is strange. It has a 30.6mm compression height. WTF?
  • Wössner 9278D050

…and following pistons have 20mm pin and 30.5mm (1.200″) compression height

  • Supertech P4-T4AG16-20-81.5-CR11
  • Toda 13010-4AG-001
  • Toda 13020-4AG-001
  • Toda 13040-4AG-001
  • Arias AP331669
  • Arias 3721070
  • Arias 3731220

If my current pistons can be shaved a bit, I’ll keep them. I’d love to get the compression height from 30.68mm to 30.5mm and shave a bit off the piston crown to get dome volume somewhere around 2-3cc. This would drop the compression rate little bit below 11:1.

Otherwise I’ll get the Supertech pistons. They’re pretty damn near perfect. 🙂

Difference in compression height numbers probably comes from two pin sizes. Early 4A-GE engines had 18mm pin, later models had 20mm. Some of the companies dont seem to care about this.

I promised myself that I wouldnt get any parts from a country, which still uses imperial units. Meh…

  • Supertech = imperial
  • Toda = metric
  • Arias = imperial
  • Wiseco = imperial
  • CP = imperial
  • Wössner = metric

Wössner would do, they’re from Germany, but why do they have that compression height error too?

Matrix Garage has some pistons too, based on their own design.

Guesstimates about compression ratio 2

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Well, I might have to buy new pistons. I made a mistake when doing calculations about compression ratio.

First of all, I dont know my current deck height. Internet says it is 191mm, but Wiseco uses 192mm. That one millimeter is going to make a huge difference. We’re talking here something above 12:1 compression ratio if the deck height is 191mm.

Also, Wiseco pistons have compression height of 30.68mm and as far as I can tell, stock pistons have 30,5mm. With a small end pin, I set a stock piston next to Wiseco piston to show the slight 0.18mm height difference. Hope the photo is clear enough:

I have to find a good source for either deck height or deck clearance.

Edit: New calculation

  • Bore: 81.5mm
  • Stroke: 77mm
  • HG thickness: 1mm
  • HG bore: 82mm
  • Deck clearance: 0mm
    • (this is a rough guesstimate. Many sites give a 0.38mm deck clearance. Wiseco pistons are 0.18mm taller than stock, which means 0.2mm deck clearance. Also, my block is shaved slightly (guessing 0.2mm) so total will be 0mm)
  • Piston volume: 5.9cc (domed)
  • Combustion chamber: 36cc (not measured yet)

With these values my static compression ratio is 12.3:1, which is slightly high 😀

If I change the head gasket to 2mm thick, CR goes down to 10.8:1. Only problem then is the squish cap, which is way more than optimum.

  • 1mm headgasket – 12.3:1 CR
  • 1.2mm headgasket – 12:1 CR
  • 1.4mm headgasket – 11.7:1 CR
  • 1.6mm headgasket – 11.4:1 CR
  • 1.8mm headgasket – 11.1:1 CR
  • 2mm headgasket – 10.8:1 CR