45 replies to this topic

[legacy rsk]

yeap just got a new engine (sti short block) and my old jdm engine did not have forged piston

[B4TT]

How could you tell Shane? They physically look no different, forging is just the manufacturing process used to make them as apposed to cast. B4's from Factory have forged pistons, yours would have had them just not to the quality of what you can buy aftermarket. There are different compositions of aluminium/silicone and various other materials available which dictate the strength and how much they expand under heat, this is why it is suggested when you have certain forged pistons you need to warm the engine up well before driving as the pistons need to be allowed to expand under heat (like the ones I used after my rebuild)

[Trent]

I thought they would have just used the sti forgies, and while they are not the same as aftermarket ones, they are still pretty good. Does any one have the B4 piston part number?

[legacy rsk]

How could you tell Shane?

They physically look no different, forging is just the manufacturing process used to make them as apposed to cast.

B4's from Factory have forged pistons, yours would have had them just not to the quality of what you can buy aftermarket.
There are different compositions of aluminium/silicone and various other materials available which dictate the strength and how much they expand under heat, this is why it is suggested when you have certain forged pistons you need to warm the engine up well before driving as the pistons need to be allowed to expand under heat (like the ones I used after my rebuild)

the guy who built my engine worked in japan at subaru for 3 yrs. he told me that the piston are not forged or semi forged. only the sti engines get forged pistons. i guess he should know he worked in the engine assembly for a short period.

[alexGT]

I thought they would have just used the sti forgies, and while they are not the same as aftermarket ones, they are still pretty good. Does any one have the B4 piston part number?

exactly. like the proper forged pistons in the ej207... you can run 22-23psi through those bad boys all day long! thats a tough oem motor!

[legacy rsk]

I thought they would have just used the sti forgies, and while they are not the same as aftermarket ones, they are still pretty good. Does any one have the B4 piston part number?

piston set part numbers

12006AC190 or 12006AC200
12006AC210 o/s 0.25 or 12006AC220 o/s 0.50