Back-to-back passes, chiller off vs on
Murphy's Law Garage took a Whipple-supercharged S650 on E30 to the drag strip at about 1,600–2,000 ft density altitude and made two back-to-back data passes with traction control on. The first was on the Whipple heat exchanger alone. For the second, the IC Chiller had pre-chilled the intercooler loop to about −15 °F.
With the chiller off, charge temperature was about 138 °F after the burnout and held around 128 °F through 3rd and 4th gear. With it on, charge temperature started near 70 °F, dipped to 60 °F, and ended the pass around 75 °F. That's a 65–68 °F difference.
The chilled pass was about 0.3 s quicker and 3 mph faster. The owner checked the logs and found the tune had not added timing, so the gain came entirely from denser air.
By the third pass in a row the car went into over-temp and pulled power, and it had to cool down and re-chill the loop. The chiller helps a lot on a pass, but it needs recovery time between passes.
| Whipple S650, E30 | Chiller off | Chiller on |
|---|---|---|
| Charge temp at start | ~138 °F | ~70 °F |
| Charge temp mid-pass | ~128 °F | ~60 °F |
| Charge temp at the stripe | ~138 °F | ~75 °F |
| Quarter-mile ET | baseline | ≈ −0.3 s |
| Trap speed | baseline | ≈ +3 mph |
| Timing added by tune | — | none |
Trap speed scales with the cube root of power, so +3 mph at about 135 mph means roughly 7% more power. Air density alone would predict about 13% for a 65 °F drop (598 → 530 °R). With a positive-displacement blower the realized gain is about half that, because cooler charge air also reads as slightly less boost at the same pulley. That works out to about 1% power per 10 °F of IAT2 drop, which is the figure used below.
Where my charge temps sit today
This chart shows the highest IAT2 (charge air after the intercooler) logged during each wide-open pull, in °F, against the video's chiller-off and chiller-on ranges. The two hottest pulls were evening sessions after repeated runs, when engine coolant had reached 99–100 °C. That's heat soak in the Roush intercooler loop, not hot weather: ambient intake air was actually cooler on those nights.
| Log | Ambient IAT °F | Peak IAT2 °F | Coolant °C | Knock retard ° |
|---|
Knock retard was essentially zero on every pull (one 0.4° blip), so the Roush tune isn't pulling timing for heat on 93 today. Like the video, a chiller would add power through air density alone. Any extra timing would take a retune to use the cooler charge.
What that is worth on my car
I'm assuming the chiller gets my IAT2 to the video's chilled range, 60–75 °F. That's plausible because the Roush S650 kit already has a large front heat exchanger, but it hasn't been measured on this car. The power figures also assume the car makes about 700 whp on 93, which is what a Roush P2 GT made on a dyno. My car hasn't been dyno'd.
Trap speed rises with the cube root of power. A 6% gain is worth about 2%, or ~2 mph on my 97 mph eighth-mile trap.
ET gains are smaller than the power gain suggests, because my launch and 60 ft are limited by the stock axle-torque table, not by air (see below).
| Scenario | IAT2 now | Drop | Power | ≈ whp |
|---|---|---|---|---|
| Cool day, first pull | 115 °F | 40–55 °F | +4–5.5% | +28–39 |
| Typical session | 129 °F | 55–70 °F | +5.5–7% | +39–49 |
| Heat-soaked, back-to-back | 150 °F | 75–90 °F | +7.5–9% | +53–63 |
My logs already swing 38 °F between sessions, which is about 4% power. A chiller would keep IAT2 near the same number every pass, as long as the loop gets time to re-chill. The video shows that limit: its third straight pass overheated.
A chiller can't help in 1st and 2nd gear yet
In 1st and 2nd gear, my throttle is held to about 34° and 68° by the stock Ford Transmission Axle Torque Limit table that Roush left in the Dark Horse calibration. That limit is a torque ceiling. If cooler air makes more torque, the PCM just closes the throttle further to hold the same ceiling. The chiller's gain only shows up from 3rd gear on, where the throttle is fully open.
For an eighth-mile car that matters: the launch, the 60 ft (2.05 s vs my son's GT at 1.75 s) and a good part of the run happen in the gears where extra air is thrown away.
- Fix the axle-torque table
This is the biggest gain for no hardware cost: about 0.3 s in the 60 ft. Ask Roush whether the GT value is safe on the Dark Horse driveline. Details →
- Add the chiller
About 5–8% more power once the throttle is fully open, and much steadier IAT2 in hot weather and back-to-back runs.
- Retune for the cooler charge
With IAT2 held near 70 °F, a tuner can add timing and use more of the density gain. Log again first to confirm the chilled IAT2.
Hardware, cost and trade-offs
Options
ICChiller (IC Chiller Interchiller) is the unit in the video. The maker lists S650 and Dark Horse kits at about $2,000. Its page doesn't say whether it fits the Roush kit specifically, so confirm the Roush S650 coolant routing before ordering.
FI (Forced Inductions) Interchiller is sold through Beefcake Racing and says it works with Whipple, VMP and Roush water-to-air setups. It splits A/C refrigerant between the cabin and the chiller, with a solenoid for a chiller-only “race mode.” S550 Roush Phase 2 owners report no timing pull or overheating in extreme heat.
Either kit ties into the A/C system and needs a proper A/C evacuate and recharge. That's a job for a shop.
• Cabin A/C is reduced while chilling, and off entirely in race mode.
• Recovery time: the loop needs minutes to re-chill between passes.
• A/C compressor load goes up, and drag mode runs it hard while staged.
• Forum concerns include condensation, parts cracking from extreme cold, and cross-contamination if a heat exchanger fails. The sellers say they haven't seen these problems.
• Warranty: it's an aftermarket A/C modification, so check with Ford and Roush.
Sources
- Murphy's Law Garage, Whipple S650 Track Day + IC Chiller Testing (YouTube)
- ICChiller Ford Interchiller (ICChiller)
- ICChiller install on a Whipple S650 (YouTube)
- 3.8-Liter Whipple Blower Boosts Evolution S650 To Bottom Eights (FordMuscle)
- 50 Degree Cooler IATs on Your Supercharged Mustang (Mustang7G)
- FI Interchillers Kit thread (Mustang7G)
- FI Interchiller 2015–2026 Mustang kit (Beefcake Racing)
- 2018 Roush Phase 2 heatsoak (Mustang6G)
- Roush SC cooling options (Mustang6G)
- Roush S650 Phase 2 kit description (Vertex Motorsports)
- My FORScan logs, 12 WOT pulls, 2026‑09‑16 → 09‑21: IAT, IAT2, ECT, knock retard