22 replies to this topic

[tamastar]

Okay so I know this has been gone over... And I've read you guys tear people to shreds about this, but hear me out with this!

 

I understand that the 2.5 isn't suited to turbocharging because it's high compression, easier to swap in a WRX engine yada yada ya.

 

But, I have a spare 2.5L engine lying around, that I was going to rebuild anyway. If it's going to be pulled apart, why not rebuild it with low compression pistons, and a TD04L or something like that? Then you'd still have the torque of the N/A, which would be awesome for towing and whatnot, plus the power of a turbo.

 

Convince me this is a bad idea. Go

[Cam.]

This is a bad idea.

Buying a healthy MY01-MY05 WRX donor or halfcut will be cheaper, easier, more reliable and go better.

[alexGT]

-blocks are open deck (semi closed on ej255/257)

-what compression are you going to run? what headgaskets? etc etc.

-engine management will be extremely expensive 

-gearbox will eventually go bang

-risk of not building engine properly then going bang will cost you even more

[allpaw4]

Agree, the 251 (or anything other than the already mentioned 255 or 257) will need more work than its worth to reliably turbocharge. The 2.5 route might be worth it if you had the supporting mods already - brakes, gearbox, late model turbo 2.5 ECU, etc, but without it, you could do it, but it just wouldn't be very reliable.

You're more than welcome to try it, but I think you'd be better off finding an old used 207 block and using the 2.5 crank to make a frankenstein 2.35L or something, but again, you'll run into engine management issues etc.

[JRod]

I'm using a gen 3 2.5 na block. Bores have thicker walls and we are only running 20psi from memory. All forged internals and ACL bearings were used. Getting 216kwatw. Current restriction is the turbo - GT3071. Exhaust housing is too small.

And a 2.0lt block with a 2.5 crank will only give you a 2.15 motor. 2.2 block with a 2.5 crank will give you the 2.35.

[Richo]

this is why you don't typically turbo charge an N/A 2.5ltr

 

 

That was DTRally's old N/A 2.5+T

 

If you go down the path of what JRizzle has done, then yeah ok, should be fine.. But shit. Just get a 257 + 20g + ecu, smash ~17psi in it and have easy and reliable 200+kw

[JRod]

My block was $100 from memory Mick. I was doing it on a budget as apposed to the drag block lol. If this one pops, I'll use my big one. Just a shame the V3 heads will be restrictive lol.

[RX25SE]

@ OP

 

The members posting here have done the hard yards and know the ways of getting reliable power without wasting cash.

 

Sometimes what seems like a cheaper option at the start, ends up be a compromise that is costly and problematic.

[Grahama]

If it's going to be pulled apart, why not rebuild it with low compression pistons, and a TD04L or something like that?
Then you'd still have the torque of the N/A, which would be awesome for towing and whatnot, plus the power of a turbo.

You have a misconception here - the torque of the N/A comes from it's high compression. By lowering the compression you lose that torque.

[Miguel]

Just shove the Td04 on it, low boost and run it till it pops. Work out something better to chuck in when it does go

[alexGT]

Just shove the Td04 on it, low boost and run it till it pops. Work out something better to chuck in when it does go

 

this is all good but what are you going to do for engine management???

[Barbbachello]

 

this is all good but what are you going to do for engine management???

The yanks seem to be able to run low boost on 25D ECUs with no issue. Might be the same for 251 ¯\(°_o)/¯

[El_Freddo]

Just shove the Td04 on it, low boost and run it till it pops. Work out something better to chuck in when it does go

I'd be doing this. Only stick with a small turbo and low (stock) boost for a real power house. Being an ej25 the worst thing that will happen is popping a HG if you're not redlining it every week. Drive it neatly and you'll be good.

Get a monitor/gauge that taps into the O2 sensor to make sure the factory tune is not leaning out the mix. A Hotwire airflow meter will cope better with boost than the other pressure sensor thing from what I've read - but don't take this as gospel.

A mate of mine stuck a SC14 on his Ej22 and monitored the O2 sensor with the factory tune and all worked very well at 6/7psi. An intercoolers would've made things even better.

Have a go, the worst that can happen is that you've had some fun before the engine pops (if it pops)!

Cheers

Bennie

[El_Freddo]

Also forgot to add that the gearbox strength is negligible - it comes down to the driver and the abuse they give their drive train.

If you've played open gearbox surgery you learn quickly that from the L series (if you're going back that far) to the wrx you're looking at geadsets with the same thicknesses and treatments from the factory. Ratios may change for the different applications in each vehicle but the builds we essentially the same up to the 8 bolt boxes.

At this point Subaru beefed up first and second gears and changed the ratios to the typical 4 bolt gearbox builds. These boxes are stronger in gearset and casing build. If you want a stronger box but don't want to go the whole hog on a 6 speed conversion this is the way to go IMO.

A stock boost turbo on a NA built engine should be fine if driven without abuse.

My 20c

Cheers

Bennie

[duncanm]

   If you've played open gearbox surgery you learn quickly that from the L series (if you're going back that far) to the wrx you're looking at geadsets with the same thicknesses and treatments from the factory. Ratios may change for the different applications in each vehicle but the builds we essentially the same up to the 8 bolt boxes. 

 

stock gearbag will work fine with what the OP is proposing...  shit, it's reasonable behind STI or EJ208 (for how long remains to be seen).

 

I say go for it - plenty of crazies in the US who have turbo'd or supercharged their EJ251's with low boost levels and std ECM's.

 

As you say El_Fre - keep and eye on the det and get a wideband for monitoring seems to be the go.

[duncanm]

Here you go: Raptor sell a bolt on SC kit - seems to run about 7-9psi and uses a piggyback.

 

 http://www.raptorsc....au/subaru1.html

[allpaw4]

It basically comes down to if you want reliability or some fun. If you're doing this for fun, then why not. But if you want reliable power all day every day, this is not the best way to go about it. Just make sure you watch the wideband like a hawk.

[Barbbachello]

There was a thread on facebook the other day about a wideband that can also retard the heck out of timing if it senses it leaning out past what you set it at. Would be perfect for this setup. I think it was an AEM one

[Josh.]

The AEM fail safe gauge. It is also a boost gauge.