K24 vs K26 vs RS2, more nerdy stuff (long)

[QSHIPQ@aol.com]

Some interesting "newbie" discussions on turbos recently has perked my
interest (hardly conflicting, but vested certainly)....  Some interesting
stuff on turbos will follow here.  In deference to the list, I will say up
front, that I have been selling modified K24/26/27/29's as a sideline
business for some time....  Here are some specifics of the k24 vs k26 vs RS2
debate:

*  The addition of water cooled bearing housings is a must for a k24, and I
don't supply k24's or RS2 without it...  There is some serious heat generated
by these units, that the oil alone cannot siphon off.  Especially in the Urq
body, heat is a major problem, and a fast spinning turbo will puke it's guts
with just an oil cooled bearing housing...  There is a SAE paper on water
cooled turbo housings, if anyone is interested in the specific number, let me
know....  
The conversion is not impossible, but requires different oil feed and water
feed and return lines, not an easy project...  But worthy

*  K24's are mean to spin very fast, generate lots of boost (in fact peak
torque is at 1950 vs 3300 for a k26), it's primary job was to make a I5 feel
like a V8.  A job it accomplished very well.  Unfortunately, tweeking a k24
has limited options, and btw, the MTM 1.8 286hp is a k24 HOT side, not cold.
 The bearing shaft is very small, almost half the size of the k26 based (RS2
included).  As soon as you hang a larger wheel on it, it tends to shrapnel,
as in break the shaft (btdt), it wasn't meant to be tweeked.

*  The RS2 on the other hand, being a k26 based turbine, has a plethora of
options on the cold side, with a much sturdier center bearing shaft and end
bearings, and gives little to the k24 based RS2....  Full boost, as a general
rule is achieved in a stage II (2.0 bar computer mod) by 26-2800 depending on
application.....  The downside to it, is that the Catalytic converter becomes
a restriction quickly on the early 44t cars...  The k26 hot sides go as
follows:  -2, -1=RS2, +0 = k26, +1....  The k26 cold sides are prolly 5or 6
legitimate ones, 6 flowing in the mid 600-700cfm range, almost double the
stock k26 found on early 44t's

*  The k27 range really requires either a love of 4500>rpm enjoyment, at the
expense of sub par enjoyment below, or a bump in displacement....  Even the
smallest bump in displacement (2.3L>) almost dictates the use of the k27 or
larger turbines....  Not many here that need to explore this region, if you
do, I can still help you out, but e-mail me directly for mor info...

*  The RS2 is one of the best B4B (bang for bux) on the turbo cars below
~375hp....  They, in unmodified trim (stock hot and cold sides) are good for
about 310 or so HP on the 20vt cars....  Beyond that dicatates a larger cold
side...  Be advised that RS2 exhaust manifolds are required for the 20vt
cars, the 2 piece exhaust manifold is "suggested" for the 10vt cars......
 RS2's benefit from larger exhausts too, they are meant to run with low
restriction systems....

*  If you are running a 2 bar computer that is using resistors to divide the
voltage from the Pressure Transducer (PT), be advised that Kaboom is a real
risk esp if you are in the mid 100k> mileage....  I have done many "actual"
pressure measurements on stage II boxes that show PT getting whacked with
upwards of 20psi....  That's a Pressure Ratio of 2.5 Bar on a component that
only measures 2.0 bar with accuracy, and loses accuracy over time....  Not to
get too nerdy here, but suffice it to say, a stock K26 really isn't giving
you big performance gains beyond a PR of 2.0, or 15psi at sea level....  At
about 18psi the air pump becomes a heat pump, and your gains are outweighed
by your heat generation...  Add to that the propensity for k26 units to pop
the plastic end caps of the IC's, and the problems mount....

*  The RS2 k26 based unit is spec'd by Porsche for the Audi RS2 cars....  It
is commonly available, and has upgrades that really kick this thing pretty
well....  Anyone that is claiming more performance than the RS2, already
addressed the fuel issue that holds back the Urq's from going 275hp> and the
5ktq from popping the 300 mark....  The 91 200tq and the S4/S6 has
capabilities in the mid/upper 300 range before real fuel issues need to be
addressed....  

*  A point of reference:  The 20vt Sport quattro achieved it's 305 hp @ 1 bar
PR....   Hmmmm

*  A turbo is a performance upgrade.  Understand what you need to do to get
the big benefits from the big dollars it needs...  Boost is the easiest
upgrade, do it first...  Addressing the turbo is a combination of upgrades
and some creativity in finding the right equation.  Personally done 10 swaps
to date, all with different combos and characters...  Now I have a vested
interest in the tweeking side.  The amount of upgrades beyond the RS2 on
audis is not the majority, and has tradeoffs that outweigh the benefits...
 Remember the k24 is a v8 design "feel" no more...  You will get more power
from an RS2, but be advised you need to give up some of that sub 1900rpm
torque for the power.  Depending on your other mods, you won't be
disappointed....

If anyone wants to discuss any of the applications further, please E=mail me
directly at QSHIPQ@aol.com.  To date I have done dozens of configurations,
some right here on this list, and can address mild to wild.  Be advised Urq
owners, that I require WC bearing housings on all turbo upgrades....  

Hope this helps weed out some claims and adds something new to my archived
posts on turbos....  And there are several....  And prolly more....

Pocket Protector shined

Scott Justusson
QSHIPQ@aol.com
'87 5ktqRS2
'84 UrqRS2