Gt3071r - which A/R to go ?

[Tesa]

Hello everyone,

Im planning to go for modification with GT3071r turbo, but I dont know what a/r ratio should I choose.

Modifications installed :
3B engine with FSI coils
3" exhaust + downpipe
Larger intercooler
7A camshafts
(and all necessary bits to deliver enough fuel to the engine)

My car will be driven from 99,9% on normal roads.

Any suggestion ?
Thanks,

Radek

[A80Avant]

Wrong turbo for this setup, unless you mean the gtx3071.

Gt3071 is a smallish turbo to use with 7A cams, and you would have to use a 0.82ar at least to make use of the upper rev. Power band they deliver. If you do that then you loose the whole point of using a fast spooling turbo like the 3071 because you got a larger ar.

A GT3076 on 0.82ar will have similar spool and deliver more power than the 3071.

If you actually meant the gtx3071 then go for the 0.82ar and you should be fine.

[Jamo]

For a road car use .63 for better response and ditch the 7A cams, if you are going to track or trash it use the .82 with the cams

[prj]

.63 + 3071 + standard cams + standard head = mega SURRRRRGGGGEEEE. Don't do it.

.63 + 3071 + 7A cams = almost no surge, and still 440hp

[filip.krticka]

Tesa,
Do you know who Beda is? www.Audi-sport.cz
He is familiar with this application in our region.

Btw. Check my tread. Don't have time to post right now.

http://www.s2forum.com/forum/showthread.php?t=68186&highlight=s2+spirit

[Guslotti]

.63 + 3071 + standard cams + standard head = mega SURRRRRGGGGEEEE. Don't do it.

.63 + 3071 + 7A cams = almost no surge, and still 440hp

Dmitri,
do you have figures about GT3071R .82 + 7A cams?

[prj]

Dmitri,
do you have figures about GT3071R .82 + 7A cams?

Never dynoed, but by butt-dyno, the top end feels somewhat stronger
With 0.63 and 7A cams it still surges a little in high gears, but not too much and can be mapped out. With stock cams and 0.63 it is pointless. After mapping out the surge you end up with almost same spool like 0.82 A/R. Transient spool is a bit better, but with a BB turbo it's close to instantaneous anyway.

[Tesa]

Thanks all for responses.
I think I will go with PRJ suggestion, because he has a lot of experiences.

filip: I will try to contact them and see if they are able to map my car.

Prj: Do you think is it worth to thinking about 0,83 A/r or not ? just to mention, I have a really short gearbox (140km/h - 4000rpm) - I have to change it, but it wont be soon.

Thanks,
Radek

[A80Avant]

The 3076 on 0.63ar surges a tiny bit less than the 3071 and makes more sense for 7A cams.
Not worth using a turbo that would have the potential to spool fast and have minimal wot to full boost time if you are going to have to map it in a way that a bigger turbo works anyway.

[Tesa]

And .. with if the 3071R will have 4" anti-surge inlet ?

Please be patient with me

[Rusty]

What about with NM cams?

[prj]

Prj: Do you think is it worth to thinking about 0,83 A/r or not ? just to mention, I have a really short gearbox (140km/h - 4000rpm) - I have to change it, but it wont be soon.

With 7A cams and 0.82 A/R the car will not be nice to drive. There will be too much lag.
If you fit 0.82 A/R, fit standard cams.

With 0.82A/R and standard cams you will get slightly more power, and a more linear power delivery.
With 0.63A/R and 7A cams it will be more on-off, but snappier.

Anti-surge inlet or not, there will be some surge issues, and even if the anti-surge helps, it just does this by slowing down spool.

3076 spools more than 300 rpm later than 3071, and on a 3076 the 0.63 A/R hotside chokes it a lot more than on 3071R, as on the 3071R the compressor is closer to running out before the hotside is saturated, than on the 3076R.

As for mapping - I have someone who has full access to all my mapping technology in Katowice in Poland, and he can also send me logs. So maybe this is interesting for you. I would recommend with this turbo to use the RS4 MAF or MAFless solution, because with standard MAF you may have problems with it breaking all the time.

[Guslotti]

We are talking about 7A cams only for exhaust or for intake and exhaust?

I thought that GT3071 0.82 A/R and 7A only on exhaust would be a nice option.

[prj]

If you fit 7A cams, then you always fit both.

Any other combination just massively kills mid-range torque for not much gain.

Then again, if you would ask me what I would do - HX35 Super and tubular manifold.
Full boost in 3rd at 3700 rpm, which is 100 rpm sooner than a GT3071R/0.82, no surge issues whatsoever and you won't need a new turbo every one-two years either.
Holds 1.9 bar to redline like a 3076R, over 500hp with w/m injection.

[Guslotti]

I was thinking to use GT3071R 0.82 + 7A cams but the car that I'm built will be lighter than S2 and RS2 (approx 1.000 kg or less ~900/950kg). In this case the lag will be reduced, right?