[s-cars] RS2 TURBOCHARGER

[QSHIPQ at aol.com]

In a message dated 10/18/2004 5:06:51 AM Central Daylight Time, 
mihnea.cotet at easynet.be writes:
>Scott, I'm not giving up on this, because I do think there's something 
>wrong with your maths.

Yup, caught it from my own posts to the main list years ago...  I guess I've 
been away from this stuff too long, thanks Minhea...  So, let's try it 
again....

For 6000 rpm
135.8ci * 6000rpm * .85VE/1728
200cfm with no turbo (PR = 1)
Assuming a DR of 1 (DR = 1) and no restrictions elsewhere, you multiply
200cfm * 3PR (29psi)
600cfm

Now over to the RS2 MAP (2672 cold side)
.20m^3 (* 35.315 * 60) = 423cfm
.22 m^3 = 466cfm
.25 M^3 = 529cfm (the absolute peak of the RS2 at 70% Turbo Efficiency)

yuk we "appear" 70 cfm short...  However, all is not lost, since DR becomes 
an important factor to coming up "short".  DR strays further from PR as PR 
increases, even accounting for intercooler recovery.  There is no doubt in my mind 
that the RS2 is at it's limit at 6000rpm Minhea, but I'd argue the DR is 
probably far enough away (and now climbing) that it's not a factor.  I also 
believe that what saves all these motors from schrapnel is CAT temps (I'll hold off 
knock for now).  Very few RS2 turbos stick 26psi and hold it.  In fact, most 
stick 26 and quickly dive to the 22psi mark (2.5PR).  This turbo acts the same 
way as a "stage III" k24 in fact.  Those running 2.4-2.5PR in the k24 live 
with this "feature" daily.  2.4 isn't even on the K24 MAP!  Some (Chad) have more 
luck than others (me).  So, my claim is, thank goodness for CAT/knock sensors.

Minhea, before I took a fully RS2 equipped Scar to the dyno, I did a bunch of 
calculations on expected HP (25psi based RS2 software) and HP.  I used 
70ambient temp, a realistically observed 150F IC (stock IC) outlet temp, with actual 
engine swept volume of 236cfm at 39lb Airflow (at 6000rpm).  I got a 
theoretical 400hp with 348lb/ft of torque.  I hit HP on the nose, and actually picked 
up 20lb/ft of torque.

I'll also claim that 300rwhp (400 crank) is quite doable on the RS2 S cars.  
The question is really, how would you like your number?  If you track a car, 
and want *continuous* HP, then the RS2 isn't for you (I freely admit that I 
stood in front of the dyno with a ice filled sprayer), it'll heat soak quickly 
(read reduce power output).  However, for midrange torque in a stock motor, it's 
right at the 400hp mark.  At altitude a better IC might be in order...

Minhea et. al., I'm *not* claiming that those over 400HP shouldn't consider a 
different turbo, I just claim that the RS2 is quite capable of producing that 
number on a dyno, and in real life street driving, not track or race.  It's 
forte on the I5 20vt is TORQUE without giving away the HP hump.   

Minhea, Ned probably has more of these MAPS handy than I do these days, but I 
know he and I have had many discussions over the years on these turbos.  The 
GGCAA 2672 6.12 (common JujuB RS2) has a continuous rating of ~320cHP, with a 
couple up better cold sides getting to the ~350cHP.  Considering I have seen 
400hp (corrected) off the GCCAA, "peak" HP off the RS2 2672 10.11 (350HP cHP) 
should catch the 450+HP in "peak" terms.  Then we could ask Ned has bolted up 
that "RS2++" (K26 3472 rated at 450cHP!), that should be capable of 600peak.

Ok, so the PP and the really wild 600HP+ audisport cars used k27 and even 
larger.  But as James B knows, that wasn't without some serious antilag action, 
and it was still a slug below WOT.

Fear not my friend, I have acquired some neat toys of my own for my urq as 
well, so my SQ manifold has a big dog bark.  Darn that Everboost guy!

Maybe we can bring Lawson out of the woodwork to really nerd this up (for 
more read his 06.20.97 audifans post)

Best Regards Minhea, off for my math tutoring with my own homework....

Scott Justusson
QSHIPQ Performance Tuning
Chicago