2.5 shortblock 2.0 heads - who's done it?

[sultan]

I'm looking at doing a 2.5 SB with 2.0 heads with a power goal of around 260kw at 22psi. I'm wanting to keep HG the same for high compression and will use forged pistons to safegaurd the extra chance of det. The motor will otherwise be std (i.e rods/crank/reconditioned std head - probably v4)

Has any one else done this combination? What are the successes/failures? I've read a fair bit on people in the states doing this, but would like some local feedback!

[Koom]

http://www.clubsub.org.nz/forum/index.php/topic,1835.0.html

RAC who is second on that list has EJ257 bottom end and V3? STI heads from memory. + a large turbo.....

[sultan]

i imagine he would have had to have cnc port matched or run a thicker head gasket for that much power. i'm wanting to keep it high compression as my 2.0 already lets me double the speed limit within seconds, i just want something that feels alot nicer to drive, and has balls when needed. so i guess my questions are specifically around high compression 2.5 builds. would be interested to find out more about RAC's though if he still posts here?

[Koom]

Haven't seen anything from him on here in a while, possibly lurks from time to time though. From what I can gather, he's possibly used normal V3 STI heads and bolted them up to a std 2.5 bottom end. Not sure what headgasket was used though. I do remember him mentioning adjustable cam wheels to ensure the cams were degree'd properly.

There's a few guys around that use the EJ257 bottom end so hopefully some of them will spring up at some point soon for you.

[99GTB]

I got a ej257 in mine using 99 gtb heads, similar to v5/v6. Using a 1.6mm headgasket from memory.

All standard internals, been going fine for a year but is off the road for upgrades atm.

[Optical]

there is no need for high compression with a 257

[sultan]

 Optical']

there is no need for high compression with a 257

care to elaborate?

I would have thought it would give a bit more torque and response when off boost, which can't be a bad thing. Also surely it would aid in spooling the turbo quicker. remembering that my power will be 260 as opposed to 360kw so it won't be a knife edge hand grenade

[quote name='99GTB said:

I got a ej257 in mine using 99 gtb heads, similar to v5/v6. Using a 1.6mm headgasket from memory.

All standard internals, been going fine for a year but is off the road for upgrades atm.

cool. what upgrades are you doing? i imagine you don't intend to push it too hard with the pistons in it? yours must be fairly low compression with that size HG, any idea what it is?

[Koom]

 sultan']

[quote name='Optical said:

there is no need for high compression with a 257

/quote]

care to elaborate?

I would have thought it would give a bit more torque and response when off boost, which can't be a bad thing. Also surely it would aid in spooling the turbo quicker. remembering that my power will be 260 as opposed to 360kw so it won't be a knife edge hand grenade

The 2.5L engines spool reasonable sized turbo's much faster than the 2.0L engines so the boost threshold is naturally low and they are more "driveable" for a similar power level. If you try to keep the compression ratio too high you will become knock limited earlier than if you put a thicker headgasket on it and kept compression ratio to a normal level. And unless you're using V5/6 heads (or pistons with a better shaped dish) the quench region gets messy with 2.0L heads on an EJ257 which could also mean you reach detonation earlier than expected.

[Guest]

RAC started out with that combo making less power on smaller turbos. AFAIK he didn't change headgaskets.

What sort of turbo are you thinking about using ?

[sultan]

I have a UK made turbo that cosworth use on their rally car builds, t04e 500hp rated. on the current 2.0 with twisted setup, and headers, it spools circa 4500 and makes good power 4800 and above (240kw). 1st gear it doesn't do much until 5500rpm. I realise I could change to a more appropriate turbo for a 2.0 and get the same/better result, but the turbo setup is already done, and my cast piston block is getting old now and could do with a replacement any way.

This is also why I want to use v4 heads, as I already have the manifold fuel rail injectors and computer to suit.

[Guest]

RAC found with his combo its was rather sensitive to EGBP and needed to go larger with exhaust housings.

Its possible you might have the same issues.

[sultan]

sorry i'm not familiar with that acronym?

[Koom]

Exhaust Gas Back Pressure.

[sultan]

ah right. I've done a fair bit of reading on this topic, and haven't come across anything like that. Most of the cases i've looked at haven't been pushed as far as his power wise though, so perhaps it was an issue for him because of his power level. (that sounded a bit like dragon ball z or something ;D)

[Guest boostin]

It may sound dumb but I've seen it done, make sure you use 2.5 head gaskets, not 2.0!!

[99GTB]

I was running a td05h on ~14psi with yellows at ~85% duty cycle. It could light up all 4 in the dry on pirelli pzero rosso's at pretty low rpm. ~3500. Ran a possumlink.

It is getting a big change... g4 xtreme, 8 injectors in dual stage sequential, full 3" exhaust, 44mm wastegate, flipped v7 manifold, FMIC, 'large' turbo, walbro, permanent wideband O2 install and lots of custom crap.

Can't remember what CR it was i think ~ 8.2-5 :1

Going to push it reasonably hard on the stock pistons, but have lots of safety built in ie g4 xtreme with dual knock sensors, a/f ratio and a few gauges to keep an eye on things.

Hoping to get 260-300atw, will have to see how it goes when I tune it, will tune pretty hard then pull it back to keep it safe. Won't know until a dyno day what sort of power it will be putting out though.

Hoping to get at least a year out of it until it blows and I forge it and wind the boost.

[sultan]

sounds pretty similar to my current setup, although i'm not as brave as you to tune it myself. are you using a 6spd to handle that power? that's the sole reason i'm limiting myself to 260kw, my setup should be able to do over 300, but i don't want to have to upgrade gbox and clutch

good luck with yours, i'll be interested to see your result. personally i'd be very nevous about your pistons, maybe water/meth injection could be a good idea

[99GTB]

I'll be using a v3 sti box for now, 6 speed is a definite later on. But 5 speeds are cheap and will be fine as long as I drive it nicely.

Not going to bother with water/meth should have enough safety and worst case I'll just have a bit less power but there should still be plenty. (real worstcase is rebuild time ;D)

[Guest Oscar]

I've read up that guys have done it in the US and their dyno plots are really funky like.

More to do with the EJ205 heads they use more than likely.