I would like some thoughts on a 2.5 sti engine with standard internals running 400 Bhp. I was under the impression that anything over 380 was just asking for trouble especially when the torque wiil be more or less equal!

Here is the spec that helps get those figures-


- 2.5 STI short block
- Full Sti UK spec 6-speed conversion, including stronger clutch, flywheel, diff, driveshafts and hubs
- Andy Forrest TD05/06 20g Turbo
- Simtek installed and mapped by Jolly Green Monster (safe 400HP)
- SFS 55mm Silicon Inlet Hose
- RCM 3" heatwrapped Open Neck Downpipe
- Revolution 3" exhaust system and decat
- whiteline ARB, drop links and Anti-lift kit
- AP Racing 330mm 6-pot front brakes and Subaru 2-pot rear brakes with goodridge braided hoses
- Oil Catch-can
- Setrab top mounted oil Cooler
- Autobahn FMIC
- 740cc Injectors
- Walbro 255 Fuel pump
- Apexi Cold-air Induction kit
- GT spec headers (wrapped)
- Roger Clarke Motorsport Oil pump
- Hybrid Front mount intercooler


so is this asking too much for a standard engine??


P.s it's a spec from a car i am interested in

 

2.5 benefit from oil cooler as can run higher natural temps to a 2 litre
I'd also wait for standard clutch to start to slip

 

It's had a new clutch fitted when the conversion was carried out.

 

I would have thought the complete opposite due to the thin cylinder walls and dodgy pistons.

Tony

 

basically i was told form several peeps including bob rawle who did the race rom map, that a standard 2.5 sti engine will handle around 370bhp before the pistons start to become a problem. Anymore it becomes a game off some will last others dont, i capped my map at 370 as advised even though bob told me my harvey 20g had alot left in it.
IMO wasnt worth the chance until iam ready to forge engine, then the 20g goes out the window anyways, but since its a daily drive, i currently cant afford it to be off road with a blown engine

Just to add, since ur running a sti 6speed, torque isnt really an issue as long as ur clutch is good, they fairly bulletproof, 1 more thing, isnt a hybrid td05/06 20g more like a sc46 but not as good? Thought it was closer to 430-450 outta that , so its prob been pegged back

 

If its mapped properly and has zero det, i dont see why a stock 2.5 wont sit at 400 happy enough.

 

How does it have an autobahn and hybrid fmic

 

pistons are a bit weak on the 2.5, some fail others dont, having said that, they only designed to run 280 hp as standard so they dealing with a fair increase

 

Because the pistons are made of an alloy of chocolate andlead

Seriously, guy, they can't often handle that sort of power. The pistons melt, and the skirts can disintegrate. Ity's appartently all to do with clearances and poor skirt design.

When I told Harvey Smith I wanted that sort of power I was IMMEDIATELY advised to a) forge the engine and b) get a 6-speed conversion and stronger clutch.

David at API gave the same advice.

Now I'm not going to be the one to say THOSE two guys are wrong............

Mine is almost exactly the same spec as the OP.

 

was both harvey and bob who told me your playing with fire going above 370 and who am i to argue with those

 

So does the Rb320 have different pistons to a normal sti? I thought they were the same and there 316 out the box although most make 320 on the dyno.
From what ive heard the 2.5 is ok upto 400 as long as its mapped and not running lean. I guess we need honest examples to make a true judgment.

 

afaik they the same, just a diff base tune when released, as said ask around and the pistons are an issue on the 2.5 as much i hate to admit, since i have 1!
But id rather listen to the harvey and bob then some random on internet who says its fine ( not implying that here btw ) . I guess the issue comes down to " do you feel lucky " lol being dying to say that to someone

 

+1 to the above

API Dave said to me that he'd advise on limiting max power to below 370bhp in a remap on a std STi 2.5

 

I think the top pro's like the 2 you mention will always air on the side of caution for road cars. Its because of this im taking my car to Bob next week,

 

Standard Sti engine AFAIK.

It's the boost required to achieve the levels that are being talked about here and the relative fragility of the pistons that is the problem with the 2.5. 1.3 bar is all they're good for by all accounts (Not my advice: APi's and Bob Rawle's.... Experience has shown me that they are very rarely wrong

If you can afford to chance it, why not. But I wouldn't expect it to last and if you do break it, you're going to be forking out for a new block amoung other things. Stick to the standard turbo with decent supporting mods and a professional remap and be happy with around 350-380 and slightly higher torque (it's a very nice road car at those levels and spools from nothing), or get forged internals IMHO.

I did the latter and am now very happy with 470/480

You play, you pay!!

 

If it bothers you enough, get it wound back a bit to 370 ish? Personally I wouldn't worry at 400 if it's mapped safe with zero det.

 

My understanding is that's it's the boost pressure that's issue here, not the bhp per se!

If it's much above 1.3 bar, you're on dangerous ground!

 

Im not about to risk my car. I love the power and torque it has to be honest and mines standard apart from 100 cell sport cat japspeed full system and panal filter, was mapped by FB tuning at the time. Im taking it to Bob to have RaceRom with 2 maps. If anything i may have it turned down in power on the first map for daily driving and to be kind to the engine. Map 2 will be anti social but only used on occasion.
My car has only just clocked over 20k so not looking to forge yet. Once its done a few more miles and starting to get tired i will forge it. Im hoping by this time lots of 2.5's will be getting re-built so the parts price may come down in price due to supply and demand. I was told that the forged pistons are cheaper than the standard subaru pistons anyway.

 

1.3 bar from what though? A vf30 or a gt35r?

It's all about cylinder pressure, which is torque related. If temps and det are kept sensible, I seriously fail to see a problem.

 

i personally had a vpower map done and a meth map done on race rom, hey 60p a ltr for meth saves alot of money

 

Im concidering this at a later date and im an avid reader of threads here on the subject.

 

I recently built a mostly standard engine using standard internals I was advised to use a 2 litre late sti short motor, sti 3 or 4 heads (my car is a version 2) and a 6 speed gearbox etc. It's now making 420bhp and although the turbo is late spooling (my fault) it's probably more reliable than a 2.5!

2.5's at the moment are too fragile, I'm certain someone will crack it though just like when we thought 2 litre Impreza engines were fragile, we now know they aren't

 

i do agree, 2.0 are more reliable, 2.5 have good points upto a certain level, but massive power requires a cbd, the 2.5 dont have that, however if you dont want 550 + the 2.5 can be made to suport that, but in standard form dont go above 370 !

 

I disagree. All 2.5s are not built and tuned equal.

 

It's the 2 litre newage that tuners says ok for 400 mate
As above 2.5 are not
I'd still say it needs a oil cooler

 

Even forged 2.5 usually kept bellow 500 hp
I thought .....
Warning all things I've said are from memory and my memorys ****

 

No mention of what heads are fitted, comp ratio, head gaskets, etc this will have a big effect on the std 2.5 STI internals.

 

It seems the general view is that 400 is asking too much. This setup is on a p1 that i have seen for sale and to be honest if i was to cap it back to 370 it would still make for a decent road car with the torque from the 2.5 in a classic imho. I guess i have to decide if iwant the worry of the 2.5 failing.

I have someone viewing my bug Sti over the weekend and i am pretty sure i will be needing a new project soon.

 

The 2.5 engines vary very much, if they are going to have an issue they usually do in standard form or tuned regardless.

I was lucky to spend a fair bit of time mapping a hawk wrx 2.5 when it was brand new to 420bhp and it is still running now.

Generally 380 is a good stopping point but they will take more, lost count of the number out there running 380 to 400.

If you send me a link to the advert I can refresh my memory on the car in question.
It might have been road mapped and the power output an estimate from the current seller.
If its the car I think it is, it has changed hands a couple of times since I mapped it so the power figure might be different.

Simon

 

ok mate i will pm the advert when i get home from work.


Thanks for the help