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Im gonna do a full rebuild of my vortex motor and seing im gonna have the pistons out- 7.7:1, i was considering getting pistons from the NA motors ~9.5:1 and putting them in.

Obvious upside would be better low end torque and off boost power.
The downside i see is more prone to pinging, but i will be running an intercooler and probably premium juice.

There are quite a few Yanks doin it on ultimatesubaru.net, and i was wondering if anybody here has done it and had success with it.

All coments welcome


Gannon

I did this with an ea81t, but had the piston crowns faced down a little to bring it back to an 8.5:1 comp ratio. The aim was to achieve the outcome you were looking for. It didnt work to well. Had a habit of blowing headgaskets. This engine was running an ea82t computer btw.
If I dont believe its worth it given the ea82t is quite torquey for a turbo motor producing its max torque of around 134 ft/lb @2800 rpm (according to the chiltons manual).Whilst a Lib2.2 produces marginally more torque at 137ft/lb @2400 rpm. In the ea81t I found that my boost would come on to early and result in spinning tyres at revs where I was trying to take care!.
My thoughts anyway

Had my EA82T built with custom forgies & is running at 8.1:1 and runs 18psi boost for the street but also have a fuel map for 21psi which rarely gets used. New pistons are a fair bit heavier so has increased torque also.
Can't comment if it'll ping or not as is hard to compare cause my whole fuel system is aftermarket.
Having a decent intercooler will definately help but not sure if the increased comp ratio will ping on the stock boost.
Would say 9.5:1 is a bit high & wouldnt want to do it unless had a programmable ECU.
Not sure if anyone else here has raised the CR on an EA82T so might be hard to find someone with firsthand experience with the exact setup your refering to....
Hope this helps!

Thanks guys

What comp ratio does the Mpfi and carb blocks run, cos thats all they use, just bolt the turbo heads onto the NA block.

Im not chasing huge horsepower figures, i prolly wont run anymore that stock boost, i just wanna improve its drivability

Keep those comments coming

There was an EA82 that came with around 8.5 compression, it was a motor around 85-86 vintage, you could try to get those pistons as they would be cheaper than some made to order customs. In saying that the EA82T doesnt have a bad bottom end power range compared to the NA version anyway

someone mentioned in here some time ago that that USMB bods had been doing this, I have thought I may try same thing (one day when all is going well) but on LPG for its higher octane rating

Having read the attempt on USMB, id consider it a waste of time if you just want power. you'd be better off putting the benefits of intercooling into the standard comp.. you'll get much better and more reliable results.
The engine isnt efficient enough to work well with high compression+boost.

If you jsut want a grunty engine though, go for but keep boost really low.

I will see what selection of pistons there are.
Something between 8:1 and 9:1 i suppose.
Im not chasing big ponies, (if i did i will probably injure myself )
Im mainly after off boost power and lower end grunt.

I remember seing somewhere a calculation that shows equivilent compression vs boost.

For example... 7psi at 9:1 comp at boost is the same as 11 psi at 7:1 comp at boost
But dont quote those numbers, that was just a guess.


Thanks for the input


Gannon

Might help or might not, but if you can source some SPFI EA82 pistons they are only 9.1:1 I think? Wouldn't think shipping would be too much. BTW we didn't get the SPFI EA82's here...