JE pistons, from 81 mm to a 81.5 bore Question!

[Shago!]

Hello!,

Im currently building my engine from scratch.

just got new JE pistons with a 0.5+ overbore from stock..... everyting else is stock (URS4 AAN 2.2T) .

I was wandering where can i find any recomendations on clearance Cylinder/piston with this set up?, does anybody have tryied this?

Any recomendations before puting it together? .

PS: in my country there are only 2 other cars with 5cyl AAN engines.. so there is not mutch experience on it..... i really would apreaciate any help!

Thank you!

[Error404]

Depends on what alloy they are, and your use for the engine and expected boost / power level really.
If they are the 2618 I would go on the tight end of the spec unless you are going for lots of power or dedicated track car, since JE's spec is already quite loose due to the relatively expansion ratios of the 2618 alloy. I think 0.06mm is as tight as you want to go really, for a pure road going car with fairly conservative power/boost levels. (Factory clearance is just 0.02 for reference!) If you run at the looser end of the clearance range you will burn a lot of oil.
If they are the lower expansion 4032 alloy then you can run tighter again, 0.05mm I think would be around the minimum I would run. This is the material I would choose on a road car

[Shago!]

Depends on what alloy they are, and your use for the engine and expected boost / power level really.
If they are the 2618 I would go on the tight end of the spec unless you are going for lots of power or dedicated track car, since JE's spec is already quite loose due to the relatively expansion ratios of the 2618 alloy. I think 0.06mm is as tight as you want to go really, for a pure road going car with fairly conservative power/boost levels. (Factory clearance is just 0.02 for reference!) If you run at the looser end of the clearance range you will burn a lot of oil.
If they are the lower expansion 4032 alloy then you can run tighter again, 0.05mm I think would be around the minimum I would run. This is the material I would choose on a road car

yup they are 2618.

its a daily fun car... its all stock (turbo...and everything else) ....so you think 0.06mm its propper?

thanks in advance!

[_ShurikeN]

Factory clearance is just 0.02 for reference!

Factory clearance is 0.03mm actually, but still considered to be rather tight. There is an opinion that 0.05mm is preferrable even for stock pistons when one builds such engine.


As for me I would not choose forged pistons with lowered CR for a street car and near-stock boost, but there seems to be no choice.

[Thuppu]

I wouldn't dare to use 2618 with under 0.09mm clearance. 4032 may be ok with 0.06mm.

[Simons]

For a stock set up I'll don't change the pistons...they can manage +450bhp without problems. I prefer fit a good forged rods.

Also for a stock setup, you don't need to change pistons or rods

[twenty valve]

You should have a sheet supplied with the pistons regarding bore clearances, so work from that. From memory, the standard 81.5mm pistons from JE have a MINIMUM clearance of 0.0035" / 0.09mm. This is typical of most 2618 pistons of that diameter. As a rule of thumb, most pistons of this material would need 0.001" / 0.025mm clearance per inch in diameter. You can go a bit extra if you plan to run high boost, personally I did mine to 0.004" / 0.1mm, which was for an engine planned for 650hp+