I have done the searches, but i want your opinion on which turbo to upgrade too, and any advice on how to do it? Ecu? can i use an existing one from a impreza ready mapped that plugs straight in, like the z4 for td05? VF turbos?, are there ecus that correspond to them?, which models? VF24 etc?,car is my94 wrx wagon, looking for about 300bhp minimal lag of course.

 

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My scoob, MY00, went from a TD04 to a VF28...
at the same time, uprated the intercooler to an STi one, improved the induction kit, uprated fuel pump etc....

oh and had it remapped, TEK2 to TEK3 at ZEN.
once you start on the turbo upgrade, it opens all kinds of other doors that you start to think about...

 

Been there and done it with a 1993 WRX wagon. Easiest and least costly route is a used TD05 from a pre facelift classic. Pciked mine up of someone on here for £175 about 12 months ago now. This should pop straight in, however you will need a new ECU with the TD05 as your current map will be for the TD04. The best stock map is the Z4 from a 1995/6 saloon. Stay away from sti maps as they are incorrect for your car. A Z4 will be fine - prodrive even used it as a base map for their tuning.

Even better than the Z4 is a scoobyecu or an ESL chip. I went for an ESL chip as there was a group buy running at the time. These are add in chips which contain a map and you solder them in to a spare socket in the ECU, they replace the stock ECU map completely whilst retaining the ECU's features. They are based on the Z4 map but are mapped for 1.1 bar boost and adjust fueling appropriately. One of these with a decat and decent panel filter should see you to 280-285 bhp.

You will not really need a Z4 if you get one of these but a word of caution as apparently the wagon ECU's sometimes don't take kindly to the ESL/scoobyECU chips (from what others with a lot of experience told me at the time) so even if you get one of them you should also get a saloon ECU just to be on the safe side.

If you want any more than that then a FMIC and 440cc injectors along with ESL's upgraded map and a boost controller set to about 1.2-1.3 bar should get you 300bhp.

I have just completed all of that, FMIC, 440cc's, decat, induction kit and dawes device. Currently have a leak in the intercooler piping so only managing to run 1.15 bar but its very quick. A lot of extra effort and expense just to get from 280bhp-300bhp though.

And just to add insult to injury my air conditioning decided to spring a leak today so the gas has been slowly seaping out all afternoon (Dont tell Geldoff) - at least its not hot at the moment.