borat52

I'm looking into options with regards to building up an 2.5l block. What will be needed to fit sti3 heads to it. Will sti 6 heads go on easier and if so are sti 3 heads really that much better than sti 6 heads?
thanks
will

Slowboy Racing

STI 3 Heads have the wilder of the cams, I believe the v6 heads flow better as standard. Much of a much really. I would say if you have the option of the two and plan to bolt them on with out any head modifications “which is fine“ I would go for the V3STI.

With regards to fitting the heads onto the block there is no difference, the difference is in the manifolds and bolt ons, one is phase 1.5 and the later phase 2. If you have a version two set up then I would suggest going for the V6 Heads and if you have the earlier set up Stick with the V3 Heads

borat52

I think I am following now, so if I were to replace the cams on the ver 6 heads with some uprated ones (been looking at helix DNA) then this would negate the advantage of the ver 3 heads anyway.

Is there any real advantage in the helix cams over the stock sti.3 cams?
Also is there any real advantage in a phase 2 intake manifold over a phase 1/1.5?

thanks,
Will

Slowboy Racing

For your original planned spec, I would stick with a standard STI cam/head set up this would be fine to reach your target assuming other modifications are sufficient, gear towards the STi 3 heads.

If you where to add cams then you would also be wise to add double valve springs and solid valves etc, it wouldn’t be a case of just fitting the cams and the costs would add up.

The early phase one manifold seems to be the best choice as it has a larger plenum and better flow characteristics over the later STI manifolds, this will also only fit the early phase 1-1.5 heads and not the later phase 2.

borat52

I think the sti 3 heads are the best bet as you have said, as for the intake manifold are there any differences between the sti 1/2/3 intake manifolds and the wrx 1/2/3 intake manifolds? I've got a ver 1 WRX at present which this engine will end up going into so could I use the intake manifold from that?

Slowboy Racing

The manifold you have is Phase 1 I would use this.

STI versions 1 and 2 also use this manifold, version 3 was different.

Its worth pointing out that the STI manifold was blue printed i.e the manifolds are matched to the head inlet almost exact. Other non STI manifolds I have seen have been matched rather poorly to the heads as they are non blue printed. It would be worth while matching your inlet manifold with the gasket so it fits the head inlets perfect this will improve the flow.

borat52

Thanks for the advice, having looked around a pre built short motor looks like a much better option than getting the parts myself, then a set of sti3 heads and intake manifold from my current engine. Also already have an FSE fuel pump and FMIC which should save a few pounds. So on top of this I'm probably looking at:
gaskets, injectors, turbo, parallel fuel rail, fuel reg, ECU, oil pump, water pump(can I use my current water pump? Only replaced 5k miles ago).
What about the exhaust system. I currently have a scoobysport sports cat downpipe and fujitsubo titanium back section. Would this all have to be replaced?
I'm also still in the dark over the ECU, I'll be pulling out my 1993 wrx engine and putting this built ej257 in - will all of the sensors fit from the existing ECU wiring? I was looking at getting an apexi power FC for the ECU, will it wire in as a 1993 car or will it have to be custom wired?