In your opinion: do 2.5T's just "let go"?

[dr20t]

But 8500 rpm sounds too good to pass up

On a serious note - all very valid points

Don't really need revs uneccessarily, however revs do help

In all honesty my 2.0 litre with a big snail is laggy on the street - I personally don't mind it, but others would

My mates ej255 foz with a vf46, dump pipe and tune would shit all over me to 60/70km/h from a normal street start

Back on topic - 2.5's are good for everyday driving but there are some inherent design flaws that are only exposed or magnified once you turn the wick up a little

Piston skirt, position of gudgeon pin on the piston, stroke, rod angle at higher revs, head squish area, piston to deck height, ports etc

[Adrian2627]

Back on topic - 2.5's are good for everyday driving but there are some inherent design flaws that are only exposed or magnified once you turn the wick up a little

Piston skirt, position of gudgeon pin on the piston, stroke, rod angle at higher revs, head squish area, piston to deck height, ports etc

This is exactly my original point. Subaru start out with a well designed engine and then to better market it to trad V8 countries like Aus and the US they compromise that design in order to increase capacity. They did the same thing with the EZ30/36. Compromised the bore:stroke ratio, rod and piston design to gain what 10kws and a little torque. Made the farmers happy in their Outbacks but basically ruined a good engine.

If you follow trad engine building concepts, improve oil flow, cooling efficiency, and general component quality, rings, pistons, bearings, head studs etc, then focus on improving your induction/boost efficiency and keep everything to a reasonable limit then there no reason why it shouldn't be a reliable long lasting engine. It's the quick and easy approach, chuck in some boost, some timing, and rev the tits off it,just to get numbers that makes them go bang. Too much quantity over quality these days.

[bigBADbenny]

Love it.

No one has mentioned the GFC era parts bin specials yet.
The theory that things got very tight and the engine factory started cutting corners... In a variety of ways...
Check out the Wrx my08 failure threads on nasioc iirc. (I'll add a link)

Add that to that and that...
Some MY's probably do just "let go" more than others...

[GT-B Spec R Pilot]

Given this is a 'your opinion' thread, I will throw a few thoughts into the mix. To answer this question requires consideration of what the engine designers wanted to achieve & the limitations imposed upon them in the design phase. Secondly, what condition was the engine operating under when it let go? Finally, what's the difference in the two.
A designer can build an engine that would never fail under conditions that 99.9999% of engines will be operated & maintained under BUT, and it's a big but, that costs money to design, to build, to operate & to maintain. That is not what the majority of buyers want or can afford. So now a compromise is made.... If we take a road car & put it on a race track, it will not last long before something gives up. That is not because the design is inherintently flawed rather it is being used for something it wasn't designed for. Similarly, try driving a V8 supercar through Sydney peak hour traffic & see how far you get...again it's not because the car or engine design is crap...it's just not what it's optimised for.
When we mod engines or use the vehicle for something it was not designed to do, we move away from the original design parameters... This will always result in gains in some areas & losses in others. Reliability is often the loss as this is not something that is immediate, accurately predictable or easily quantifiable.
Perhaps the question ought to be, what were the design parameters & limitations that existed when designing & manufacturing the 2.5T engine? This would provide a starting point to compare how our forum posters usage differs from the intended design usage & that is where I suspect the answer may be more apparent.
But hey, it's only my opinion....
Cheers.

[bigBADbenny]

Good read

[Boostaddict]

Very good point GT-B Spec R Pilot.!!!

So of we knew the design parameters that would be a start...... But hard to get the facts on that I would say !!

Dr20T mentioned some of the limitations previously in this thread and also in the engine building thread!!

[Martymuso]

I would be interested to know what the failure rate actually was with regards to how many 2.5 engines made to how many failed seriously under the warranty period. If there were design flaws then most of the time this comes up in the warranty period. It is quite well known that nearly every manufacturing practise uses the consumer to fully test their products. That's why during lifespan of the range of products, there are model variants or 'face lifts' etc, which improve on known issue's.

Manufacturing these days is a pretty consistent process, and it has to be to ensure speed of manufacture and reduction in warranty failures. As was mentioned before the unit is designed for a specific market, and whilst the product is used within that which is was designed for, and good care is taken of the product, the lifespan usually meets expectations.

Of course there are many variables which can't possibly be worked out to an exact science so selection of materials must meet certain standards before selected for a product so they can cope such things. One day we might fill with some contaminated fuel without realising it, and sure enough once it gets inside your engine, bad things happen.

The Subaru brand has been making these types of engines for many years and they will know intimately what they can and can't do. Unlike some other manufacturers in the automotive world where they have used several engine designs through the life of their ranges, Subaru have been perfecting the Boxer.

It is only logical that you can only push the limits so much before failure. I am sure some people have pushed the 2.5T further than most people thought possible, but in doing this have most likely upgraded almost everything which made it a stock engine!

So to answer this question posed... Anything will 'let go' if it is not treated with the right respect.... just like my waist line

[Newbie GT]

What do you call pushing the limits ?

Bigger turbo like a vf52? And a tune or is this considered baby steps

[bigBADbenny]

Pushing the limits is more letting it knock, over revving it, using max boost for extended periods eg on track and so on IMHO.

Tuned sensibly with supporting mods, maintained and driven intelligently wouldn't be much less reliable than stock IMHO

[Boostaddict]

Pushing the limits is more letting it knock, over revving it, using max boost for extended periods eg on track and so on IMHO.

Tuned sensibly with supporting mods, maintained and driven intelligently wouldn't be much less reliable than stock IMHO

Pushing the limits ...... REALLY depends on the tune.

You could baby your car ( like 80% of the time my car is driven ) and have a tune that is too close to the edge and pushing the limits and BANG.

Or the actual tune could be really lean on light throttle and because thats where most people drive in our shit Sydney traffic you could be doing damage by cruising !!!

You could have a really good tune on WOT and drive it hard and it will never break !

So too many options for "pushing the limits" really!!

[kiahatsiu]

I think we just need to accept that over say (and i am making this number up, it isn't scientific) 240kw at the wheels the cylinder pressure is too high for the old stock 2.5, and that is where shit goes wrong.
My theory is the bearing issues were manufacture issues, the head lifting issues are people asking too much.
Keep it to 220 at the wheels and you will be safe as houses.

[Boostaddict]

I think we just need to accept that over say (and i am making this number up, it isn't scientific) 240kw at the wheels the cylinder pressure is too high for the old stock 2.5, and that is where shit goes wrong.
My theory is the bearing issues were manufacture issues, the head lifting issues are people asking too much.
Keep it to 220 at the wheels and you will be safe as houses.

Shit..... I only made 203kw atw on my stock motor!!

My new motor is gunna laugh at that power!!

[Monkey]

I have a question which might seem a bit stupid - don't flame me please.

Given some of the HG issues which have arisen on here, if one has any early indications of HG problems, what can be done?
eg. would it be advantageous to get a new set of head studs (eg. ARP2000) and lock down the head tight?

In my case, I have noticed the occasional bubbles in the expansion tank and sometimes fluctuating levels outside the min/max line. But no other issues (no overheating, milky oil, oily coolant, steam on startup, coolant burning/consumption, increased fuel consumption, etc) - the car otherwise runs perfectly (as it should with only 70,xxx kms). It may well just be an airlock in the system which will take a few more flushes to remedy. Ross at Cromwood doesn't think it's an issue, but I can't help feeling concerned about the possible $3k+ spend.

So I would much rather spend $300 now if that potentially saves $3k in future. Are there any advantages/disadvantages in doing the studs as a preventative measure?

[kiahatsiu]

Head studs are an engine out job. I would imagine your 300 buck studs would be a 3k job.

[Monkey]

Ah ok, I assumed it was like changing spark plugs - 4 to screw in and under 10 mins.