Miggs Posted February 12, 2014 Share Posted February 12, 2014 Originally I wanted an Impreza turbo. However, as a family man, I knew I would have to get a wagon version, which I have never found too appealing, so I looked at what else was out there. At that point I came across the Legacy range and settled on a 2.0L normally aspirated estate. Loved it to bits and joined a forum to figure out how it worked. (My first foray into flat fours). Ended up going to an organised meet in Wales. Mine was the only normally aspirated there. (At that time, I didn't even know about the turbo versions). At that point the search started for a suitable twin turbo Legacy. I figured if an Impreza has a single turbo, a twin turbo Legacy must be better. Despite needing an estate, I ended up changing the wife's car to an estate family car so I could get a twin turbo legacy saloon. Not looked back since. Had the twin turbos ever since. I just think they are more of a sleeper than an Impreza, plus, from the factory they have more power but are less tuneable. Hence my current project :) sorry to go off topic but i have to ask or i'll forget later, is it possible to go single turbo with a leggy? would it just be a case off impreza fanimold and ecu or would it be a bot more complex? Quote Link to comment Share on other sites More sharing options...
Jay762 Posted February 12, 2014 Share Posted February 12, 2014 New thread created from a question in an alternate thread Quote Link to comment Share on other sites More sharing options...
Tlag Posted February 12, 2014 Share Posted February 12, 2014 It's a bit more complicated than that. The turbo oil feeds on one head need blocking off, the entire vacuum system needs ripping out and an Impreza one fitted, the entire exhaust system is different, the wiring loom needs modifying as the legacy ecu won't work with only one turbo. Is it worth it? Good question. A standard classic type turbo Impreza has what from the factory? 220-240bhp? A standard twin turbo Legacy has 280bhp although they are Jap import only. With a lot of work, the maximum you can get from a Legacy will be 330-340 bhp. Whereas as an Impreza can be made to push out double that. The other BIG downside with the legacy is the VOD (valley of death). The primary turbo comes in quite early at about 1500rpm and runs out of steam at about 3800-4000rpm. The secondary turbo, comes on line at about 4300rpm. That gap of 300-500rpm is known as the VOD. It's fine when pushing on through the gears. You just feel it as a 'pause for breath' and it's no problem. The big issue is when you drop down a cog to overtake. If you are relatively new to the VOD, it comes as a bit of a wake up call, when you have indicated to pull out, moved over the white line, dropped the gear, and .......... No power. You have just dropped into that rev range that offers no boost. You learn to live with it and drive around it. It can also be mapped out to certain extent which rings us on to another problem with the twin turbo set up. In standard form, the ecu cannot be mapped. In fact, it's only in the last 2yrs that a solution has been found for this. A company will adapt the ecu to allow it to be mapped. So, is it worth it? If you want a standard, 280bhp car the it's probably a cheaper to buy option than an Impreza. If you want to get more performance, converting to single will cost a lot but the gains are potentially great. The cheaper option to performance is buy an Impreza and upgrade parts accordingly. For me, I'm lucky at the moment in that I have a mildly tuned twin turbo legacy and I have a project on the go (see the projects section) which will be single turbo. Best of both worlds. :) Quote Link to comment Share on other sites More sharing options...
Jay762 Posted February 12, 2014 Share Posted February 12, 2014 Would it be possible to address the VOD by changing the spool up characteristics of the turbos, different blades, profiles etc Quote Link to comment Share on other sites More sharing options...
Tlag Posted February 12, 2014 Share Posted February 12, 2014 That would be the holy grail to be honest. The twin turbo system was designed by Porsche, for Subaru. We know that they didn't want a 5 dr family estate car to be quicker than the 911 of its day. For that reason, we think it was probably a deliberate attempt to inhibit the turbos. I don't know what the performance figures were of the 911 of the early 90's but a twin turbo Legacy, according to the literature would get to 60 in just over 5 seconds and go on to 172 mph. The turbo control system is stupidly complicated with over 9 metres of vac hose. Quote Link to comment Share on other sites More sharing options...
Jay762 Posted February 12, 2014 Share Posted February 12, 2014 Ahhh that does potentially explain it - I know the twin turbo toyotas and Nissan dont have that characteristic so it might be possible then - I would have to start researching the legacy plant as well - only just starting to get my head around the impreza one :D Can the Vac system be simplified? Quote Link to comment Share on other sites More sharing options...
Tlag Posted February 12, 2014 Share Posted February 12, 2014 The problem with the vac system is that it is controlled by the ecu. It's only recently that it's been a. Possibility to map the ecu, and only then with the addition of a daughterboard. I suspect that in time, altering the vac system may be a possibility but with the cars getting increasingly older and the twin turbo evolving to a twin scroll turbo, I suspect the R&D costs would outweigh the number of people who would take it up. Quote Link to comment Share on other sites More sharing options...
antlockyer Posted February 12, 2014 Share Posted February 12, 2014 964 turbo did 0-60 in 4.5 with a 174 top speed. Quote Link to comment Share on other sites More sharing options...
Tlag Posted February 12, 2014 Share Posted February 12, 2014 So it's not very much above what a 5 door family estate car could do. The theory makes sense Quote Link to comment Share on other sites More sharing options...
BlackBosh Posted February 12, 2014 Share Posted February 12, 2014 I'll back that theory, look how Toyota undercut Subaru With the gt86, better warranty better finance deals, more availability yet the car was a joint project. Subaru should've got their own back with an sti version. I imagine this sort of thing happens all the time with car manufacturers. It's just none of it will be instantly obvious Sent from my iPad using Tapatalk 1 Quote Link to comment Share on other sites More sharing options...
Gambit Posted February 13, 2014 Share Posted February 13, 2014 It wasn't a joint project until Toyota see the idea it was just going to be a Subaru BRZ originally :( But agree fully with an STI version :) 1 Quote Link to comment Share on other sites More sharing options...
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