alessio

iTrader: (3)

Hi everyone,

As things usually happen with this car, my headgasket replacement has turned into a full-on forged build that includes going from an open-deck to a closed deck 2.0 block as well (the ODB had crank saddles out of limits and the CDB is good to go in that regard).

The car is a V4 MY98 Impreza Turbo (non-STI), the cylinders will be bored to 93 mm, the cranksahft will remain a 2.0 and the heads will receive some attention but I'll stay with the non-STI V4 heads for now. Leaning towards CP pistons and Manley T-tuff rods for this build, will run a VF34 at around 330 hp for the foreseeable future as, well, this is an unplanned expense all of this. The pistons will be 2618 but with coating on the skirts to help with the piston slap a little.

The thing about CP pistons, however, is that by default they are for 8.5 CR. I understand that stock is 8.0 and I'm sure CP will be able to custom make the pistons to suit my needs. I don't have an engine builder as such for this project so I'm hoping for some advice from the community here.

In short, what CR should I go for with these settings and why? Stick with 8.0 or go for 8.5? All advice is, as always, greatly appreciated.

Thanks,
Alex

MOTORS S GT

iTrader: (2)

Main concern on deciding comp ratio is, what fuel do you have to run it, if you have fuel readily available to run 8.5:1 that will help spool, & give a better overall performance package, getting it mapped correctly also.
If going with CP pistons, double check the gudgeon pin wall thickness, some are thinner than others, & have failed.

alessio

iTrader: (3)

Thanks for the reply.

The fuel I have access to and am planning to run is 98RON. The car, by the way, is a street-legal car that is sees many track days. So there...

As for the pistons, they don't really have to be CP, it's something RealStreetPerformance have recommended. I'm also considering Mahle 2618 pistons and I'm waiting for a price offer on those Heard failure stories about all of the brands, unfortunately, and this selection process is a real head ache

Cheers,
Alex

merlin24

iTrader: (1)

On pump fuel, I generally aim between 8.2:1 ~ 8.5:1 Static depending on what the engine is being used for and as in post #2, a good map is essential as even the best forged pistons are not det resistant.

Mick

alessio

iTrader: (3)

Hey, thanks for the feedback, guys.

I'm quite glad that I've started looking into this in detail as I did not end up with "newer" EJ20 pistons that would have left me with a wrong CR and squish...

Somewhat surprisingly neither CP nor Mahle have off-the-shelf pistons for V4 EJ20 enignes so I can either go the custom route (having a very vague idea how to spec them) or look at other manufacturers.

Wiseco is starting to look more and more attractive now and I should be fine with them as far as my needs are concerned, right? Using the OEM subaru piston pin locking rings

Has anyone got any ideas/suggestions on this? What would you do if you were building a V4 engine with V4 heads and stock thickness HG?

Thanks again,
Alex

merlin24

iTrader: (1)

Have a look at the Supertech range of pistons ( yes,they make pistons too ) to see if they have anything suitable for your needs.


Mick

alessio

iTrader: (3)

Mick,

They make them for the later EJ20 engines only. And the material is 4032 alloy and I believe 2618 is the way to go.

Cheers,
Alex