Just wondered what peoples thoughts are on the 2.5, as some people don't rate it, any particular reason? Also why did subaru see fit to produce this engine as it doesn't seem to have any more power than the 2.0 in standard form. Is there greater tuning potential with it?

Cheers

 

Its a good engine up to a point, the biggest letdown is that its the same physical size as a 2ltr engine, which means that you have less metal between the bores, which makes it weaker, even if lined.
The driving characteristics are your next issue, the 2.5 is a lazier engine, more low down torque but not as revvy as the 2ltr, the 2ltr on the other hand is stronger, the 2ltr twin scroll is much more of a compromise between the 2, producing similar torque levels but also higher revving.

Tony

 

I think Tony forgot to add a big IMHO

Who doesn't favour it? (apart from Tony)- seems to be a common upgrade for those who have grenaded their 2.0 engines.

On like for like models, the 2.5 engine makes similar or slightly higher power, but quite a bit more torque.

Where fitted as the std engine (06> cars), the potential for making up to 400 lbft is far greater (and cheaper) than any 2.0 car I've had.

All IMHO

Nick

 

Bang for buck 2.5 is a best upgrade you can do IMHO. Well thats before the US to UK exchange rate went **** up. It s agood base for a good high perfomance engine with a nice wide power band.

Also means you can fit an even bigger turbo without it turning into an annoying pile of poop thats gutless below 3000rpm IMHO (unless it has anti-lag or a twinscroll ).

 

Now i have driven 2ltr single scroll cars, 2.5ltr single scroll cars and 2ltr twin scroll cars, and the best one was the twin scroll unit.
If you see what i put, the 2.5 produces more torque low down, which it does, its lazier, which it is because its a 2.5ltr, its not as high revving and is a weaker engine block, both of which are true.
You also forget to mention that when people go the 2.5 route they normally need to replace their gearboxes as 400lb of torque eats them but the 2.5 isnt the best engine subaru do, far from it, the twin scroll unit is, and it IS the best compromise, and considering on the standard turbo you can push nearly 400lbs of torque, not bad for a 2ltr is it

Tony

 

Horses for courses.

 

I agree im at 370bhp/405lbs.ft on powerstations RR and not a massive spec

 

JDM spec 2ltr twin scroll car, exhaust and remap, your pushing 390lbs of torque, what do you need on a 2.5?

Tony

 

What's wrong with "lazy"?

When you say the block is weaker, can you qualify that?

So its alright to put 400 lbft into a 5 spd box with a 2.0 engine, but not 400 lbft with a 2.5 engine

How on earth did a VF36 get to 400 lbft and how much did it all cost?

Don't be a Luddite and block the path of progress. Newer IS better

 

The 2.5 isnt newer the block has been around for years, the twin scroll unit is newer though
The block itself is weaker, the distance between the bores is less, which means you cannot put as much stress through it, they have a tendency to crack hence liners...
Now 400lbft on any 5 speed box is stupid, it will just eat it, doesnt matter if its a 2ltr or 2.5ltr, it will break

You can get to 400lbft of torque on a vf36/37 in under 1k, 650 for the remap and whatever the exhaust costs, a new one for 300 quid, but it does take some doing, most only reach the high 300's but i have seen one or 2 hit that 400 mark

Now lazy is the way it delivers its power, its lazier because its a bigger engine, so lazy describes it nicely

Tony

 

just a quick one - sort of related to this thread - is a jdm twin scroll (blobeye) able to be tuned up with mods to up to the 400 bhp mark - i heard this engines werent as good for moding

 

I thought the only real issue with the 2.5 was possible head gasket problems..? Due to the fact there's less material around the top of the cylinders and therefore narrower gasket area..?

That's the only thing that I've seen come up more often than on 2.0.

TBH, if my 2.0 did give up the ghost I'd go 2.5 without a doubt as I prefer 'lazy' power, for the road anyhow..

 

The same - 360/390 with an exhaust and map.

It really is horses for courses this one. We've been here a few times before. A lot is down to how you drive it and what you want from it.

 

Its more than capable of 400bhp with a turbo upgrade

Tony

 

For a road car, a 2.5 would be best IMHO. Torque is what you want, and a nice wide power band with something that'll let a bigger turbo get into it's stride without needing to thrash it.

I, personally, wouldn't want to get a significantly higher boost threshold and more lag than I have with the VF35 on a 2 litre car.

A well set up 2.5 with a MD321T would be an awesome car for the road.

If you want something you can rev the **** off on a track then maybe a really strong 2litre is the way too go?

When you get to the power outputs I suspect we're talking about, realistically, you have to assume that both a 2litre and 2.5litre set up will eat the std 5 speed gearbox, so not worth sticking with the litre just for that reason.

Ns04

 

Ive got an 05 WRX blobeye 2.0 ltr would that be a single or twin scroll thingy?????
how would I tell or are the twins only STIs

Must admit I asked the question re the 2.0v2.5 and the decission was split with goods and bads for both, so I just bought the 2.0 as the insurance was about £200 cheaper and as far as I was told there was not a lot of difference in the performance in either guise

 

Twin scroll is JDM (i.e. Jap import) only. If your car is not a JDM it will likely have a single scroll turbo. I would say there is a bit of difference between the 2.5ltr and the 2.0ltr both with single scroll turbos to be honest, but again it depends what you do with and want from your car.

 

I used to have the single scroll 2L UK STI and now drive the 2.5L UK single scroll STI,
IMHO the 2.5 is a far more relaxed drive (at same speed) due to more low down torque, requiring less gear changes, but it'll still rev quite high enough to gain the extra ponies when overtaking.. I'd still love to put an MD321T + remap on it thogh....

 

A quote by Andy Forrest about my 2.5 wrx, power run at powerstation, "400lbft of torque by 3100 rpm not something you see too often, especially on a maha dyno" as has been said above the 2.5 is such an easy car to drive on the road especially with a 5sd box .

 

Well that's kinda cleared some stuff up I asked because of this....
Subaru : Show winning impreza sti type-r I hope the acceleration isn't sluggish now due to the 2.5 conversion, cause that would kinda defeat the purpose of a Type R IMHO so much conflicting info..

 

Would be useful to find out which turbo that is running on and whether the block has more than just std US internals - it should be capable of much more than the 300 hp quoted

Nick

 

Tony Burns is right, and his knowledge is EVIDENCE based, not based on what he THINKS he knows. Factually, technically, mechanically, the 2 litre twin scroll engine is the best one that Subaru manufacture.

Why was the WRC car based on a 2.0 and not a 2.5?

In the case of STI, an STI engine is not a proper STI engine unless it redlines at 8000 revs. Oh it may have big low end torque, big deal, at the expense of paying through your nose fuel and tax costs?

The 2.5 engine was introduced on UK cars to compensate for variations due to Euro emission laws. It was not introduced as a 'hey, lets make a superb fantastic 2.5 engine for UK cars' How come the JDM even today still has the 2.0 engine? JDM only for the REAL STI driving experience.

 

Bad day at work Greg?

 

[QUOTE=GREGGYG;8514710]

Why was the WRC car based on a 2.0 and not a 2.5?

FIA REGULATIONS

 

I've had a 2l and now got 2.5 . As i understand it the 2l is a stronger engine . The 2.5 doesn't have forged pistons and can suffer with head gasket failure as mine did at 30'000 miles . But saying all that i personally prefer the 2.5 as it seems to be a lot more responsive at any point in the rev range especially at 3000 . Its a much more refined drive and you don't have to drop down the gears too much when over taking . I ve heard the 2.5 is pretty safe running iro 350bhp and 400ish torque on std internals which makes a very nice road car . I've not had the priveledge to own a twin scroll so can't comment but if it means anything to you a lot of people are converting to a 2.5 over the 2l so there must be something in it ?

 

You need to try a twin scroll car then they produce 80% of their torque at 2.5krpm, it makes for driving around town in 5th at 25mph very easy

As for the conversions of a 2.5 over a 2ltr, most are due to engine failures and the 2.5's are considerably cheaper to buy than a 2ltr short motor.

Tony

 

so if you were to buy either a 2.0 or a 2.5 wrx turbo what would you pick?

 

A 2ltr JDM twin scroll WRX

Tony

 

Based on what I've observed and been advised by some experts (e.g.Tony & Greg)...

2.0 Twin Scroll > 2.5 Single Scroll > 2.0 Single Scroll

 

can you not fit a tst to a 2.5?