Lightweight EJ25 Engine Internals

[LaszloT]

Is there significant advantage to tailoring an engine rebuild with lightweight engine components, even if you're not building a big-power motor?


AMS EJ25 Basic Engine Rebuild Kit

Developed for power levels from stock to 500whp and a 7200rpm rev limit, this Engine Rebuild Kit features upgraded JE pistons, Clevite main and rod bearing sets, and an OEM Subaru engine gasket kit.

[STeveD]

The OE gaskets that come with that kit are a good idea. Likewise the stock head gasket, assuming you're going to aim for <400 whp.

The obvious benefit of lighter weight pistons is that they take less energy to move and put less stress on the components (crank, rods, bearings) when they are moving around. Rods aren't necessarily where you want to go light. And lightweight cranks are expensive.

Those JE's aren't actually very light for a 2618 alloy, unless they're the billet FSR. Wiseco's are lighter in the same 2618 alloy.

For a reliable street car like you want... assuming under 400whp, it is more beneficial for you to get a 4032 alloy piston with factory moly coated skirts, offset pins, and then have them bore matched to keep knock / piston slap to a minimum. 4032 can run tighter piston to wall tolerances because it expands less which helps keep cylinder wear down. Joe's happy with his 4032 Wossner pistons. Diamond can also be ordered in 4032 (sold by Canjam locally). My 4032 Mahle's slapped, but they were built to high clearance and didn't have offset pins.

Next, think about rods. 350whp and less, those STi rods that would come with the EJ257 short block you're considering should work fine. A mild and inexpensive upgrade is to Eagle rods, and those will take significantly more stress. Most builders prefer to go to Manley or better, but Joe and I never had an Eagle rod fail ... only spun bearings.

Whatever rods you choose, most builders prefer to upgrade the rod bolts to ARP 2000 as a minimum, and that isn't as cheap as you'd think.

[LaszloT]

STeveD,
When the time comes I'll start by getting your help with developing a performance build outline with some sort of budget. If my shortblock is fine, I'd probably try to rebuild that [overbored] strong enough for Stage2, and go with your suggestions about internals (like above).

Are valves and valvesprings required for a head rebuild, and are the WRX stock cams adequate if the stock turbo is going to be used? I read that for the WRX, the torque peak is 4000 rpm, power peak is 5000 rpm and redline is 7000 rpm.

[STeveD]

Stock WRX valves are pretty reliable, just change the springs and retainers. Stock cams for stock turbo or moderate upgrade.

The specs you give for peaks... are you referring to cam profile? You can move your torque peak downwards when you go stage 2. Is your uppipe already catless?

[LaszloT]

The specs you give for peaks... are you referring to cam profile? You can move your torque peak downwards when you go stage 2. Is your uppipe already catless?

STeveD, I listed the stock performance curve peaks above and I have a catless turbo up-pipe in my trunk that just needs to be installed.

Assuming you've rebuilt a suitable long block, how do the performance curves peaks get adjusted along the rpm range? Is it just ECU (a "Tune") or ECU, exhaust and/or cams?

And why would you need to adjust the performance curve peak rpm, if better breathing and more boost will raise power and torque levels up anyway? Isn't higher rpm more demanding on components? I'd hope to get engine responsiveness out of lightweight internals, rather than higher rpm.

[Lloyd]

I would be surprised if there is much responsiveness improvement that is noticeable from a motor with a laggy turbo attached. Lighter components are good for high RPM life, but I imagine the incremental reliability improvement when used in a OE RPM range would be more than offset by using aftermarket components, which seem to frequently have much looser clearances than OE, and to that extent, should result in fewer KMs between rebuilds.

[JoeT]

For the power levels you're looking at with stock turbo, you're wasting money going with forged internals. The stock WRX 2.0Litre pistons do not suffer from the ringland problems that the "Hypereutectic" pistons on the EJ25's have. Lighter internals will do nothing for you unless it's drastic and you invest over 10K for titanium connecting rods and very exotic metals. Note, the farther "off" stock that you are, the more TLC the engines will require.

The only thing that I would fix on a 2.0 litre engine is the Oil passages in the stock crank, or just replace the stock crank with the forged EJ25 cranks for a bit more displacement and better oil passages.

The cylinder walls on the open deck 2.0 blocks are super thick and do not walk like the thin walls of the EJ25's.

To summarize for your build:
Use Stock Pistons stock rings
Change to EJ25 Rods and Crank
Stock oil pump
Stock oil pan
Modified Oil (toilet seat) pan baffle

Then go have fun!!

[LaszloT]

Then go have fun!!

Perfect summary, JoeT. Thanks so much.

Did I mention how happy I am to be in the SPDA? : )

[STeveD]

I didn't see you sticking with a TD04.

[LaszloT]

I didn't see you sticking with a TD04.

TD04 is the stock turbo, I believe. What would be a modest upgrade from the TD04, STeveD?

[JoeT]

Modest bolt in Turbo is the TD05H-16G XTR.

[LaszloT]

Modest bolt in Turbo is the TD05H-16G XTR.

Got it. Here's a TD05H-16G XTR available at Touge Tuning:

http://www.tougetuning.com/store/blo...rx-p-2470.html

And some comments:

"Product Info
Blouch WRX/STi TD05H-16G-XT Turbocharger

Application: Subaru WRX/STi
Horsepower: 410HP

Most bang for your buck in a 16G upgrade platform, the Blouch TD05H-16G-XT features the new aero of the Blouch 41 lb/min fully machined billet XT compressor in a TD05 compressor housing combined with the quick response of the Mitsubishi TD05H turbine in a 7cm2 nozzle area turbine housing. Standard wastegate actuator is calibrated at 9 PSI.

If you own an EJ20 in a WRX, the Blouch 16G-XT is an awesome upgrade turbo for you. The WRX/STI TD05H-16G-XT is a direct bolt on upgrade shipped complete with coolant pipes and turbo oil drain tube installed and requires no modification to intake, exhaust, oil and coolant connections for installation."

[LaszloT]

To summarize for your build:
Use Stock Pistons stock rings
Change to EJ25 Rods and Crank
Stock oil pump
Stock oil pan
Modified Oil (toilet seat) pan baffle

Then go have fun!!

Are the EJ25 Rods and Crank a direct no-mod swap, in the EJ205 block I have? And if not, are suitable pistons available for that combination?

Phase 2 Engines
-75mm stroke with 52mm rod journal
-79mm stroke with 52mm rod journal
-130.5mm rod length & '05+ EJ25 NA(exception '99-'04 EJ25 NA 131.6mm)
-thrust bearing is main bearing #5
-6 bolts top to bottom with 2 studs at the bottom


BORE x STROKE
EJ20 - bore/stroke
- 92mm x 75mm

EJ25 - bore/stroke
- 99.5mm x 79mm

[STeveD]

Wiseco actually made 79mm stroker pistons for the 1998 and earlier 2.0L blocks as a standard order item. Not sure what would have to be done to them to make those pistons work on the 2004 2.0L. Custom pistons aren't usually that much of an up-charge.

Wossner makes them as well, but they're listed as a Version 7 stroker kit, and it states that they're compatible with up to 2003 WRX. Probably also the 2004, but best to check.

http://www.wossnerpistons.com/produc...m-bore#reviews

[STeveD]

Remember the 2.0L tips in this article... http://www.importtuner.com/tech/impp...h/viewall.html Pistons, rods for better oiling, head studs. The 92.5 Wossner or Wiseco pistons should allow piston-matched bore/honing on your own block. But... plan to be down for a few weeks if a good engine builder will be working on your current engine. (All the better if they're done early, but don't count on it.) Plan for winter if convenient so that they are in less of a rush. If you pick up a spare block, they can do the short block machining and assembly offline, then it's just head freshening which can be done within a week.