Here photos of a GT3071R i've just bought :




Another pics :

http://924cup.fr/doc/turbo/turbo9.JPG
http://924cup.fr/doc/turbo/turbo10.JPG
http://924cup.fr/doc/turbo/turbo11.JPG


This turbo should have 2000 km are this turbo weak ?... how can i control bearings ? there is no oil in the compressor.


And now what turbo should i use ? GT3071 ou 76 ?

My engine has new pistons rings, line and rods new bearing, 9R cam (944 ph2) but stock valve springs, stock turbo head...

My aim is to reach about 350/360 euro horsepower and to have a track car that i can use on street....

 

i've got a GTX3076R (which is the same as a GT except new compressor blade technology) with a .82 a/r

The way the car feels, there isn't much back pressure in the X-over at all. i've got power up untill 6200 rpm.
Realistically if i got a cam that moves my power band to the right, the turbo has no problem to keep up to 420 rwhp with a stock head.

 

You might be surprised if you measure the back pressure.

 

Vic from pauertuning, he's running a gt3067R .63 at ~18.5psi making 360 rwhp and has 22-24 psi of back pressure. so my guess with mine it should be a few psi less.

Oneday i'll have to measure my back pressure. it's on the To-Do list

 

It rises with boost so yours would probably be similar, but still in a good turbo system, you want less back pressure than boost, I don't think that is possible with a 951.

 

to get more boost pressure the exhaust pressure, isn't that more F1 technology?
I haven't really seen this happen before.

a 1:1.2 pressure:back pressure ratio is pretty ideal IMO for a 951

 

Back pressure is lost energy, so as it rises with boost you are losing efficiency. I dont think having less than boost is that unusual,it just isn't that common, but it is possible if things are sized right. But that said 1:1.2 is pretty reasonable.

 

have you measured your back pressure? yours would be quite interesting as it's a twin scroll IICR

 

Of course I have, it is not that different to vic's numbers, with a slightly larger crossover(the twin pipes) the back pressure went up, so there probably is potential for improvement, but it is lot of work to experiment with pipe sizes, and results can be unexpected.

 

Rod, I'm wondering if the slightly higher backpressure you saw with your twin scroll set up isn't simply explained by having completely removed the possiblity for gas reversion that might always take place with the stock, single scroll set up...?

Did you measure back pressure in both scrolls or just in one?

 

I didn't say the twin scroll had higher back pressure, we tried two different size pipes for the crossover to turbo, the larger diameter pipes resulted in higher back pressure. We measured one scroll, but pressure is pressure.

 

Buy the way how do you measure exhaust pressure ?

 

I had the same thing with larger ts pipes. The back pressure was through the roof. It was foot to a point then took off...

In regards to ratios, I havnt seen a turbo that can spool reasonably for a street car not have higher Bp than map.

The only cars I've seen with anything close to a 1:1 are designed to make power high in the rpms and are very laggy otherwise.

 

Weld a bung in the crossover and use a fitting and copper tubing to dissipate heat. Then you can either log it using a 5bar map or use a gauge that can hold highest pressure. A compression gauge works with the right fittings

 

something like that ?