MileHIFcar

Like the title says guys, what are your thoughts on the fact that Lexus engineers decided to use cast pistons in the 2UR-GSE instead of forged pistons?

I think I only remember seeing here on CL 2 ISF's that cracked their pistons: 1 was because of too much nitrous (I think a 200 shot) and the other one was because of the S/C that honestly cracked a piston(s) within a couple hundred miles so it sounds like that one was heavily tracked or abused prior to the S/C install and the small amount of boost (7psi) was all that was needed to seal the fate of one or more of that particular examples pistons......

I know the motor was designed to be NA with maybe little thought to the aftermarket coming in and providing boost to a high compression motor, so I don't know if it was a cost saving measure per motor? If not why not just add in forged pistons to accommodate the other robust features of the 2UR-GSE that are already beefed up?

I'm not saying it was a mistake, so no right or wrong answer here from an engineering perspective. Just curious to see what some members thoughts are on this particular aspect of the motor or lack there of now that there are boost options for this motor and the longevity of a cast piston to handle 100k+

By the way I would love to get the RR S/C kit when finances allow if I still have the ISF down the road!

jdmSW20

iTrader: (12)

Im almost positive its a cost saving measure to be honest. Not many performance cars come with forged pistons, even in factory boosted applications, some making far more power than the 5.0L in the ISF. Just comes down to the tolerance you are willing to push, you gotta pay the cost to be the boss

lorenr

iTrader: (1)

Depends on what they are cast from. Same for the forged pistons. Depends on the raw material.

Modern cast pistons can be a great product if they are not subjected to to much heat, like turbo charging and super charging (read that as compression or boost). Nitrous oxide is really, really hard on pistons and can easily melt them.

I'm sure if you run this motor as it was intended, the piston will last a really long time. If you boost it your just screwing the next owner of the car. If you need something fast, get one of Toyota's 5.4 liter engines with the good heads and I'll bet they come with forged pistons.

Loren

tas02

iTrader: (2)

Cast expand less than forged. Allowing for tighter piston to wall clearance. And greater efficiency.

Also the reason for all those knock sensors.

MileHIFcar

^^^^Interesting break down! Thanks for the explanation

Helo58

Thanks for this. I learned a little something tonight. One caveat to this though, Although cast pistons do expand less than forged pistons typically, it has nothing to do with the processes of casting or forging. Thermal expansion is an intrinsic material property (same properties regardless of process) that varies by temperature and isn't typically linear. This means that different alloys lend themselves to casting and others to forging. In aluminum alloys, one of the alloying materials is silicon. Thermal expansion rates are related to the amount of silicon in the alloy. Casting alloys require more silicon than forging alloys. A very important note of consequence: although thermal expansion is lower for cast alloys, they are also harder and more brittle relative to forged aluminum alloys. Although forged aluminum has higher thermal expansion than cast, it is also far stronger. As a result, a similar strength forged piston can be made using less material resulting in lighter piston. Lighter forged pistons are often sought for higher rpm applications for this reason.

lobuxracer

iTrader: (2)

And because forged pistons need to be fit with greater tolerances than cast pistons, controlling NVH especially on cold cycle, is a huge challenge.

You'd be amazed how many things the OEMs do to control NVH.

So forged pistons are extremely rare in production vehicles.

One of the really good things about these engines is the oil jets underneath the piston crowns. The engine sprays oil on the bottom of the piston constantly to help remove heat from the piston crown. This dramatically helps with a whole host of things related to service life and engine tuning.

tas02

iTrader: (2)

OEMs also have issues like cold start emissions and oil consumption to consider.

MileHIFcar

Thanks Lance for the feedback

Is that part of the reason why the 2UR-GSE takes an enormous amount of oil (9.8 qts) for the oil jets? Also, do the oil jets under the piston crowns spray all the time or only on WOT or after a certain rpm?

Didn't realize how rare forged pistons are on a production based sports sedan/coupe etc...... off hand does anybody know which production vehicles come with forged pistons from factory?

ultimase

probably not, even the old ka24de nissan engine had oil squirters stock, and was only 4 quarts stock.

liquidtek

S2000 motor came forged from the factory.

TURBO5DAVE

iTrader: (1)

03 ford mustang cobras have forged pistons.

MileHIFcar

No wonder guys are able to push out big power on the S2000 without any beefing up of the internals

I knew the terminator motors were stout but didn't know that they had forged pistons as well! Thanks for that tidbit of info

jdmSW20

iTrader: (12)

yeah all those guys go big turbos and crank out power no issue on the S2K, now I see why

yeah on mr2 it has oil squirters as well and that's a 92

lobuxracer

iTrader: (2)

As did the 2JZ-GTE, but not the 2JZ-GE. No, the reason for the large oil capacity is to help insure there is always a supply of oil for the engine. I learned this years ago with circle track racing. The oiling systems for small block Chevrolets can get pretty exotic on dirt track cars. Thumb through a Moroso catalog and you'll see what I mean.