What, if any, would be the likely advantages of swopping a TD04 with a VF23 turbo, on a UK MY00?

Adv:

Lower exhaust back pressure for same airflow
Lower temperatures pre and post intercooler
More boost at high revs especially, but across the range if you want

Dis:

Need to remap ECU to make most out of it
Higher boost threshold
Probably benefit from new fuel pump
Need high pressure intercooler hoses (ideally)
Insurance woes
May well stress your original clutch and gearbox excessively

I went for a Turbo Dynamics MD297 which is an exchange for your TD04. It is somewhat "smaller" than the VF23 but a good compromise. Supplied through Mark Aigin (R19KET). Not ideal if you want to go well over 300 BHP/300lbft which you might just scrape at PE on a cold day. However, for a road car it is very nice. Also consider the newer VF30 which I understand has some of the advantages of the larger VF22 as well as the VF23 with good spool up. The VF24/28 are what were fitted on the last of the old STis and also seem quite a nice compromise.

Food for thought. That ECUtek remap can't be far away!
Cheers John.

What about if you mix up a VF23 with a Prodrive ECU, wont that
give the same benefit as a remap, but keep all the cold start,
knock correction properties of the "STD" (PPP) ecu ? Whats the
difference between boosting a TD04 at 1.2 bar and a VF23 at 1.2
(or whatever the PPP runs ?) I think the VF23 will take another 500 rpm to get going (lag), but after that, wont is all be good ?

There is a big difference between a VF23 and a TD04 at 1.2 bar in terms of airflow. Firstly the turbo outlet temperature and the charge temperature will be lower. Secondly there is less back pressure from the VF23.

With a remap you can keep all the cold start and knock correction properties - see my profile for info. The PPP ECU map is not suitable for a VF23. Besides running excessively lean and retarded during spool up which will particularly hit off boost performance with a turbo with a higher boost threshold, it arguably runs far too much advance at the top end - at 7000 RPM the standard turbo is at or under 10 PSI, the VF23 could still be at 17 PSI (with boost control), the airflow that will be made will lead to the ECU taking points right on the end of the map which were never designed to be hit with the PPP ECU. These areas for fuelling and timing are not mapped properly. At best you will lose performance as they are inappropriate. At worst the timing is too advanced for the expected lower boost and detonation could result. The PPP ECU tapers the boost far earlier than you would want to with a VF23 and leaves you with a 19.6 PSI fuel cut.

Have a look at the AE801 fuel and ignition maps on the Ecutek site (the Prodrive ones are similar with the column headings for load points adjusted a bit) and you will see some of what I mean.

VF30 on a 00MY UK.

Lost about 400rpm in boost threshold (2700 Vs 2300)on the TD04, and there is slightly more lag, due to the slieved type bearing I believe.

Some gains at 3000-4000rpm. Kicks at 4200ish, kicks again at 5800, carries 1.3bar to 6500 no problem. I reduce to 1.1ish at 7000rpm. Going by the duty cycle on my EBC it would still hold 1.3bar at 7000rpm no proplem. I suspect above 7000 flow is not as good as the VF23/22.....not sure??????

Suffice to say 4500rpm+ performance was significantly improved!

A friend here has a VF23 on a my99, and mine goes on next week...enough said really! It pulls much, much harder once on boost - even though it's running the same boost, the charge is cooler and there's less restriction.

However, as stated, to get full benefit (and be safe...) you need a remap and the high-flow fuel pump.

Ask me again this time next week :D

Richard