The full round design is not as stiff/strong as a strutted piston. When you're talking about 550-600whp in one of these cars, the engine is making ~175hp/cylinder if you take away all drivetrain and other parasitic losses. Its really doing A LOT of work.

 

Non strutted pistons are fine for anything under 800whp. If the factory pistons can handle 600whp then it's pretty safe to assume a forged pistons will be able to handle more.

 

aren't the factory pistons forged?

 

They don't really "handle" it for any length of time, since the rods don't either. A few "hero runs" on the dyno and a handful of 1/4 mile passes here and there doesn't count. Just because the piston doesn't fall apart doesn't mean it not in there distorting, overheating, and doing things it shouldn't. There's really not even a price difference between the two (I think for Wiseco it's like, $100-$150), so not running a strutted piston is really just silly.

Theyre like hypereutectic or something. Not forged, but not same as cast either Strength falls between cast and forged.

 

Huh..TIL, thanks. I remember when ford adopted hyperexplosive pistons. I guess Mitsu has a better process cause there is no way the hypereutectic that I knew could survive what these do.

Edit: And im sure ford / others have improved the process too. My impressions of it are holdover from the 90's so.... yeah lol

 

Every piston and spec'ed wall clearance and ring end gaps are designed around its intended use. I'm sure the ofrds you saw exploding were OEM engines that were having power adders put on that thay were never meant for, on top of the extremely rudimentary tuning solutions of the 90's and earl 2000's.... it was always a recipe for disaster

 

Yeah it was basically required to swap out the pistons if you wanted power adders. Ford used forged pistons in the terminator and lightning, which are basically the same era as the evo 8/9 4g63. I guess having never seen my evo pistons outside the block (side effect of a still running stock shortblock) I just assumed they were the same. I would have never believed you could push the kind of boost a stock evo does on anything less than forged. Let alone what people push these things to.

 

Thats part of why the 4g63 has oil squirters, keeping a cast piston alive hinges on keeping it cool, where forged doesn't care so much about that and doesn't need squirters. Also, far superior engine management.

You can see the casting lines in this EvoX piston if you go to the pic that shows the bottom/inside of the piston. 8/9 pistons look basically the same.

https://www.ebay.com/c/1516204651

 

Hah! My whole import life has been a lie Well that just makes me even more impressed with the engineering of these little engines.

 

There are actually 3 different types of cast pistons. Hypereutectic is the most common but there are also Eutectic and Hypoeutectic. All three have a different blend of silicon. Not sure what the Evo has though haha

 

Nearly every factory "performance" engine has used hypereutectic pistons for the past 20 years.

The term hypereutectic denotes any cast piston with a silicone content above 17% (that number may have changed). High silicone content means low thermal expansion which means small piston to wall clearances can be run.

With that said, hypereutectics are not an easy pistons to produce. If the heat treatment process isn't done correctly they can literally disintegrate in a matter of hours (on a dyno). It's rare to see them fail nowadays but not impossible.

Also, don't be quick to write off piston squirters with forged pistons. I've seen data between 2 nearly identical engines with on engine dynos with the main difference of one having squirters and the piston core temps were anywhere from 30-50F cooler with squirters. Consistent piston temp means predictable knock behavior.

 

The main problem with keeping squirters in the 4g63 (especially) with stroker cranks and aftermarket rods and pistons is you have to bend them to clear the rotating components. And once I've bent them, I've never had them not break off (even if I warm them up and be gentle) and then they're just a small internal oil leak that isn't doing anything for you, and you waste an hour or two installing everything, check clearance, removing, bending, reinstalling, repeat...lol

30-50* of piston temp I'm sure helps greatly with more consistent knock behavior in an OEM app with an ECU that is always trying to run at or near MBT timing (or more, especially in cruise). But generally when tuning a racecar, we aren't that aggressive on timing so it isn't as critical (IE you "can" pick up 20-30whp in an 800whp evo by running 19* of timing instead of 16*, but we don't do it). And then you add high octane and high latent heat fuels (ethanol) and it really becomes less of an issue.

 

I went ahead and contacted Diamond about the strength/rating of the pistons and they said;

"With the std Wrist pins I would say 600hp and with the H13 pins 800-900hp, the rebel series parts have a longer tool steel pin, and uses buttons to retain the pin, and uses total seal rings.

The rebel series would be for more of a race only application, if it is a street/strip application the 82022-4 would be better for that."

Here is a good blog post from Wiseco about the differences and pro's/con's between the two

http://blog.wiseco.com/what-is-a-strutted-piston

anywho, I'm doing some intercooler piping and exhaust fab and once that's completed the motor will be pulled, head sent out to be worked (and cc'd) and block sent to the machine shop. once that's done ill know what pistons/dish I need to get to the desired comp ratio.

 

I have a brand new set of Diamonds laying around (PN 82004) if you're interested I can shoot you some photos of them. They're a 9.6:1 comp ratio so just a mild bump over stock, still very pump gas friendly.

 

thank you for the offer but the 82004 is the wrong CD for 94mm stroke and 153mm rods