by the way, the s4 afterrun system does run the coolant through the radiator (i think that is what you meant by heater core, unless you really meant heater core for the passenger heating system)

on a side note, my "master" plan is to impliment the s4 afterrun sytem on the 1.8t A4. ive actually got all the circuit diagrams done, i also have some of the parts...maybe this summer ill put it all together.

[Modified A4]
2000 Audi A4 1.8tqmsx, K04'd
email:tfcwr at hotmail dot com

(click above pic for dyno video)
6.13 sec CAPS 60F 05/07/07
6.27 sec CAPS: 195 WHP , 186WT @AWE, 60F 10/07/06
6.40 sec CAPS: 220 WHP , 230WT @EPL, 64F 5/13/06
(stock exhaust, stock airbox, stock SMIC)

How does the performance of your A4 stack up? Get a CAPS time!
mod summary:
Performance: K04-15 turbocharger, GIAC K05 programming, APR Exhaust, 3.0bar FPR, 710N BPV, N249 bypassed, Audi TT180 injectors
Efficiency: ExtrudeHoned and gasket matched exhaust manifold, MAF screen delete, APR TIP, APR TBP, snow screen delete, upgraded passat vacuum lines, evoshield intake manifold spacer
Cooling: S4 oil cooler, a/c fan override, S4 vented wheel well liners(both sides), thermal wrapped coolant cross pipe
Venting: ATC valve cover, AWM PCV piping, TT225 pancake valve, second cam oil spash guard
Bracing: S4/V6 engine mounts, APR snub mount, urethane filled RS4/stock transmission mounts
Delivery: AWE stage 2 clutch
Braking: A8/TT font kit w slotted rotors, A6/B6A4 rear kit, Axxis Ultimate pads
Handling: S4/A6 front strut tower bar
Misc: heavy duty belly pan, alternate fog mod, boost gauge with firewall grommet, dentless trunk mod