Jump to content
Ultimate Subaru Message Board
tallwelder81

ej18 upgrade. better pistons?

Recommended Posts

Rods are the same.

 

Crank is different.  Shorter stroke in the 18.

 

Interestingly though,  EJ18 and NA EJ20 share same piston size.....hmmmm???

 

And Also,

NA EJ20 and EJ22 share cranks (same stroke)......Hmmmm? 

 

MAybe a 2.2 crank w/ NA 2.0 pistons in the EJ18 block?  I guess you could just get a JDM NA 2.0 at that point :rolleyes:

I did some looking around after you posted this.

 

Everything I see says the ej18 is 3.46x2.95 (87.9x75mm) and the ej20 is 3.62x2.95 (92x75mm)

Share this post


Link to post
Share on other sites

Rods are the same.

 

Crank is different.  Shorter stroke in the 18.

 

Interestingly though,  EJ18 and NA EJ20 share same piston size.....hmmmm???

 

And Also,

NA EJ20 and EJ22 share cranks (same stroke)......Hmmmm? 

 

MAybe a 2.2 crank w/ NA 2.0 pistons in the EJ18 block?  I guess you could just get a JDM NA 2.0 at that point :rolleyes:

 it is not often i correct knowledgeable folks here, but,  i think you may be mistaken or confused.

 

links below for the impreza ej18 and the impreza je22  crankshafts, item # 2 in each diagram. both use the 12200AA042 crank.

 

ej18 - http://opposedforces.com/parts/impreza/us_g10/type_43/engine/piston_and_crankshaft/

ej22 - http://opposedforces.com/parts/impreza/us_g10/type_56/engine/piston_and_crankshaft/illustration_1/

 

so while i'm not saying you are wrong, i am saying there is evidence that the cranks are the same.

 

ej18 and ej 22 use the same cranks and rods.

ej18 and ej20 use the same pistons. crank must be different.

Share this post


Link to post
Share on other sites

 it is not often i correct knowledgeable folks here, but,  i think you may be mistaken or confused.

 

I believe I was mistaken.  My bad.

 

The cranks are all the same.  EJ18,EJ20,EJ22

 

The pistons are different.

 

I think I was thinking about EA81/82 pistons sharing bore size with the EJ20.  Which they do...92mm

Share this post


Link to post
Share on other sites

All engines are basically just an Air Pump a 7 litre V8 just pumps more air to make more power, Ditto turbos just another way to pump more air.

 

Where things get interesting is when you talk Torque all engine measurements are in torque, Horsepower is the work done so it is derived at by using the Torque figure in relation to a timebase , Ie RPM where this bewcomes interesting is when people start arguing about what constitutes a torquey engine build with people prattling on about long stroke engines or rod length to stroke ratios.

 

In every case one must first put into the equation of ones thinking BMEP or Brake Mean Effective Pressure that is where the EJ 22 wins over the EJ 18 or EJ 20 all have the same stroke and unless aftermarket skulduggery is involved with Pistons and Rods the same rod stroke ratio's so the real difference we see amounts to real estate not so much capacity.

 

Real estate ?? I see the thought bubbles by real estate something to grab your attention I mean the exposed area on top of the piston the EJ 22 has more area because of it's bigger diameter and therefore say you have 1500lbs/sq/ inch pressure on the piston top then if an EJ 18 or EJ 20 has say 6.5 square inches of piston top seeing 1500 lbs/sq /inch and an EJ 22 has 9 square inches of piston area seeing the same 1500 lbs pressure then there is two and a half square inches of piston seeing an additional 1500 lbs of pressure.

 

If you can follow that it shows that Torque does not always relate to long stroke engines or rod stroke ratios they do make some difference regarding leverage as our torque or twisting force can be multiplied by leverage, But Torque can also be increased substantially with more surface area for cylinder pressures to work against and that is why the EJ 22 is so torquey.

 

EA 81's gain torque through both piston area and long intake runners that maintain good port velocity despite less than optimal port layouts even with the rare factory reverse valve layout which is a massive improvement on high speed cylinder filling.

 

So Stroke is not the be all and end all of making a good torque monster of an engine suitable for off road use.

Share this post


Link to post
Share on other sites

Coxy you resurrected a dead thread.The OP hasn't posted in this in over a year.However, with that being said, the magic of internal combustion happens with the cylinder heads.The more the heads flow the more power that can be produced.Subaru heads are notorious for not flowing well,and short of changing the shape of the runners in the heads I don't know how much of a gain could be made by simply porting and blending.More compression gives a better bang but there is a limit to how far you can go if you still want a non interference engine. Although with various engine voodoo, if you were to put longer rods and keep the compression height the same the longer rods would "mask" the effects of poor flowing heads.Look at mopars-they have some poor flowing heads but because they all have long rods compared to the stroke they can still make decent power.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×