[torsen] Re: [s-cars] RE: RS2 turbocharger

CaptMagu at aol.com CaptMagu at aol.com
Mon Jun 17 13:01:45 EDT 2002

Greetings turbo fans,

I have watched this thread develop with some interest and will chime in with 
my impressions. Big turbos are not a cure all for big performance. If you do 
go beyond the RS2/Garrett hybrid sized turbos there are some very important 
and very very expensive requirements to take advantage of the flow that can 
be obtained from such a turbo. 

First would be intercooling. The bigger the turbo the quicker it can pump the 
charge air through your I/C and the sooner your stock I/C becomes heat 
soaked. Brian Billotti's trip to the land of the s-car mafia this spring 
proved to him anyway the need for an adequate(as in BIG) I/C. As he drove 
Mike P's and my car he just couldn't believe how efficient our big Garrett 
I/Cs were. He was continually amazed to see I/C out temps at or just above 
ambient. The last I heard he had begged off the very last short radiator core 
from Mike to allow a big front mount I/C. Speaking of charge air temps, 
another benefit from a larger turbo that is operated short of its efficiency 
peak is lower charge air temps to the I/C to begin with. This is the primary 
reason I went with the size turbo that I chose. Oh yeah, that and the mid and 
high end power.

As Rod so elloquently put it, no I haven't given up on drivability, its just 
located a little farther up the tachometer. One thing I have noticed is that 
my turbo is very sensitive to back pressure. We had removed the kitty and 
tried a test pipe and I lowered my full boost rpm to about 3800. The 
exhaust(Stromung SS) was real loud when I did this so I substituted a Borla 
racing muffler for the test pipe. That threshold jumped up to 4100 rpm. I 
think this is somewhat related to my RS2 exhaust manifold/Garrett big turbo. 
My next step will be either the Sport Q or Spaghetti manifold and a big MAF 
intake to go with the RAIS(ram-air intake system).

One last thing about drivability. With a big turbo you can't drive the car 
looking at the boost guage. The flow off my turbo at 5 psi is significanly 
greater than a K-24 or RS2 or T3/T4. The other given is that I'm getting a 
lot more flow for an equivalent boost level and my IN I/C temp and resultant 
OUT I/C temp are all much lower. The seat of the pants feel to my car is 
rather invisible. You just don't realize the big turbo is there until your 
foot is in it. Big turbos are not an easy answer to all the challenges of 
life with a urS4/6 but, they aren't hard to live with either if you do 
everything else that is required. 

Hap, keeping my charge air cooooool in Evergreen, Maguire

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