I am building a 1990 GTU for Autocross and Track Day events. I plan to use Garrett Turbo on the engine after rebuilding. Which turbo would work best for minimal lag and a max horsepower of about 400 rwhp? I am leaning towards the GT30R or GT35R. Suggestions welcome.

 

GT30 is too small. The GT35R will work but you need to decide what manifold you are using first, as the GT35 comes with multiple turbine housing options (T3 and T4 in different sizes and configurations).

Are you installing a turbo engine or are you trying to turbo the n/a engine? turboing the n/a engine adds a whole host of complications. See the FAQ about that.

 

I am rebuilding a s5 Turbo II engine. I am planning on using a front mounted intercooler and stand alone EMS with additional injectors. Manifold options are still being investigated. Any suggestions are welcomed.

 

Talk to ASpec.

I would consider a 35r with a small A/R. Should give you pretty good spool.
FMIC - good
standalone - good
additional injectors - not necessary. switch out your secondary injectors for some bigger ones and you should be fine.

 

The only issue with a small A/R on the 35R is that it will come on explosively around 2500 RPM. Might not be the best for autocross.

 

Thanks for the input. What A/R would give a more progressive spool. I have heard the .82 is commonly used.

 

The .82 is too small in my opinion. It brings boost on around 2000-2500 RPM and by 3000 RPM it's flying towards the wastegate limit. It also is a cork up top. Then again, maybe this is what you want?

I'd stick with the 1.0 (1.06, whatever), use a lowish PSI wastegate spring and then rely on your boost controller to linearize the powerband.

On the street the .82/.84 is a good choice though.

 

84 is as small as u can go and not choke the engine id use about a 90 a/r i have a 1.15 on my t04b and it spools ok but around like 3300 and full boost by 4g

 

Big difference between a .84 T3 and a 1.15 T4. They really can't be compared.

I don't think any response will be lost by going to a much larger T3 housing on the GT35R to avoid choking the engine up top.

 

i suggest the .84 T4, my boost comes in fairly fast and i haven't tuned the boost controller settings yet. i got 18 psi by 3800 rpm, obviously i'm not running that much boost. i kind of want boost to come on faster so there would be more torque at lower rpms, but i am only running a cast manifold and i am sure the boost thresh hold would be significantly reduced with a divided manifold.

 

didnt know anything was said about t3 being usd?