pnebbs

I apologise for thius not being about impreza's but thought as the legacy is related, nobody would mind.

I have just bought a an automatic 94 Legacy GT estate with the sequential twin turbos (I needed a big estate). It seems much slower than my last car (a 93 supra with 290bhp).

It has two problems

1) Gap between the two turbos, the low end turbo boosts at 10 psi from about 2300, then drops down at 3700, and the big turbo doesn't hit 10psi until 4500, and then keeps going strongly to the redline, any ideas on how to bring the 2nd turbo in more quickly, or make the first last longer (or a combination). This isn't a huge problem because the auto box masks this problem quite well.

2) Max boost is only 10psi, this seems rather low, particularly as all your imprezas seem to boost between 13 and 17psi, any ideas on increaing the boost. I tried a bleed valve with no success, even removing the pipe to the wastegate completely only increases the boost to 11psi. Could the standard exhaust, downpipe and air filter be casuing this restriction (I have plans to change these parts in the relatively near future)

Thanks (in anticpation) for any help

Benny Boy

Hello Mr pnebbs

Do you know what compression ratio the car runs? If it is higher than 8:1 then you want to seriously think before doing any major boost increases. Even at 8:1 you don't really want to start increasing it too much.

If you fit a high flow de-catted exhaust then you will free up the turbos a bit which will give you some more boost.

By doing this the car will try and suck some more air in and as long as you don't exceed the parameters of the airflow meter, then an induction kit or higher flow panel filter will help.

Anything that you can do to improve the flow of gasses through the motor will improve response and supply a little more boost.

So, my advice would be to improve the air intake and fit a highflow exhaust. This might solve your issues and you will enjoy the mods anyway. If it doesn't then there are other ways but can get costly.

If you are still hankering for more, mail me direct and I'll help you out.

I would like to think though that the exhaust and filter will do the trick.

kind regards

Ben

pnebbs

Benny

The compression ratio is 8.0:1, what is the compression ratio on the imprezas, baceause they seem to run more boost than the legacy, although the legacy is stated to produce 260PS (250bhp) which is more than the UK impreza.

Is this because the boos doesn't tail off as early. The plan is for a scoobysport backbox and downpipe (for the second turbo) and a K&N filter.

I was intrigued why the boost didn't really increase with the wastegate disconnected - you think that there is simply not enough airflow currently to support more boost, but surely if it can boost at 10/11psi at 6750rpm it ought to be able to boost more than that at 5500.

Paul (confused)

Paul

Subaru doctor

Would a dumpvalve help to smooth it out?

clarence

Sure it's not because of your previous Supra that caused u to feel slow in your Legacy?
The 94 Legacy GT only has 250ps and 31.5kgm of torque, and it weighs at least 1500kg in estate form. The 4-speed auto doesn't help at all.
Are there any problems with the wastegate on the smaller turbo?

clarence

Sure it's not because of your previous Supra that caused u to feel slow in your Legacy?
The 94 Legacy GT only has 250ps and 31.5kgm of torque, and it weighs at least 1500kg in estate form. The 4-speed auto doesn't help at all.
Are there any problems with the wastegate on the smaller turbo?

Benny Boy

Paul

The reason that the car will not have produced more boost when you totally shut off the wastegate could be down to the size of the turbos.

If the volume of the turbos is too high for the amount of exhaust gas the motor is producing then there won't be an increase. That is to say that if shutting off the wastegate does not give you mor boost then that would inicate to me that the wastegate isn't being used much anyway.

In that instance then a slightly smaller turbo would generate more boost. This is only logical thinking and I have no real evidence and no particular knowledge of the Legacy.

Ben