I've been looking at these blocks recently.

How much bhp/torque can these handle in standard form?

I know STI 5/6 heads are ideal but they are quite expensive is there still going to be significant gains if i use MY99/00 UK heads?

I'm looking to get around 450/450 using a MD321T turbo.

I've got a UK STI 6 speed gearbox aswell as all the other suporting mods sorted i.e fueling,induction,exhaust,FMIC & uprated oil pump.

I'm not looking to do this on the cheap but i am looking to make savings where possible

 

I'm suprised that you haven't been bombarded with tech info. Come on chaps whats your view?

 

The semi closed deck 2.5 themselves seem to be capable of running up to 500; however this would not be running standard rods and pistons at least this being the safest way. Using a standard unit 400-450 is achievable retaining reliability if done right.

The uk99 head casting I believe are the same casting as the sti5 the difference being the springs and cams, in theory you could use uk99 heads with sti cams and springs you would just need to re shim the to obtain the correct clearances.

I personally would look towards the above or replacing with v3sti onwards. However I am sure there will be more specific info regarding the 99 cam profiles etc.

 

I wouldn't want to rely on a standard shortblock doing 400-450hp. For 450/450 I would definitely go with uprated rods and pistons, and even then, there are good and not so good parts to fit.

The UK99 head castings are the same, but that's it, everything else is different, cams, valves, springs, retainers followers. To do the job properly I would get proper STI heads, or build some UK heads with all the trick gear. A fully built set of heads though can esily cost £2.5k so you want to be sure you need all the nice bits inside.

V3 heads are not really a useful option if you have a v5/6 car. The inlet manifold doesn't fit, and you can't transfer the throttle body with integral ISCV to the v3 manifold without modifying. Aftermarket valvetrain parts are also more readily available for the v5-> heads for sensible money.

I would put the money into the engine and heads now, but save the money from the turbo till you're later.

Paul