Back-to-back dyno: Recirculated wastegate vs open dumptube, highest boost setting
The goal was to see if a well sorted recirculated setup will make the same all-in power across the board, highest boost being a key factor.
Tylor’s 2.0L Evo 9 with a HPT 6466, 1.07A/R v-band, MF v-band manifold with either recirculated O2 housing or O2 housing with dumptube, 44mm MVR, 3” MF downpipe, 3” to 3.5” ETS catback exhaust. E85, tested and tuned on Haltech by Roni at SpeedLab.Inc
All pulls were at the highest boost setting in the 850whp range (~46psi).
3 first runs/traces with the recirculated O2 housing/bend off the turbo, and 2 last traces with the O2 housing/bend using a separate dumptube.
Regardless of the setup, each trace tracks with the rest; some a little more, some a little less, but mostly run-to-run variance from slight boost differences or time sitting between pulls (which affects how much energy goes into heating the turbine housing back up vs driving the turbine etc). The dumptube setup showed a little quicker spool in one pull, and the recirc had the highest power pull, but only due to the factors above in this case since recirc isn’t going to actually increase power, only be quieter under full boost.
Boost traces:
Ultimately, when the setup was being pushed, there was no discernable difference in the dyno graph. When you can max the turbo out, the power was still there. More boost= less wastegate opening= less potential difference.
This was only the initial test though, added in just after dialing in the new setup on the dyno, with more back-to-back testing planned at lower boost levels where differences between the two configurations are more likely, due to the larger proportion of exhaust gas being bypassed through the wastegate. When the wastegate opens near target boost on a recirculated setup, all of the bypassed exhaust gets re-entered into the main exhaust whereas the open dumptube takes a little load off the main exhaust, essentially acting like a larger exhaust overall. These tests at the highest boost setting have the highest total exhaust flow, but the smallest proportion of wastegated exhaust flow, keeping the differences between where the bypassed exhaust goes negligible. The lower amount of exhaust being bypassed/wastegated around the turbo is exactly what increases/maintains boost to begin with (wastegate nearly closed).
The setup made 900whp with some more boost, so near maxed out in this comparison with boost still falling at high rpm. Some of the main factors are exhaust size (post turbo and if undersized for the potential power/flow), engine vs turbo size/efficiency which greatly affects the amount of exhaust gas that needs to be bypassed at a given power/boost level, and how the re-entry is handled into the main exhaust (the more potential losses if not done well when recirculated, mostly at lower boost).
A huge thank you to Roni and SpeedLab.Inc for doing the dyno tuning/testing and Tylor for coming to us to being with and offering his setup for testing!
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Original write-up before testing:
Something often asked- The main reason for wastegate recirculating vs open dumptube is often noise preference under full boost. When boost builds and you get near your target psi, the wastegate will begin opening and either recirculate back into the muffled exhaust or straight out the open dumptube. Recirculating will keep a quiet car subtle at WOT without masking turbo intake noise, and a dumptube will abruptly scream at full tilt. A car that already has a loud/minimal exhaust won’t have as stark of a difference and a dumptube can sort of blend in overall. It’s still pre-turbo exhaust coming out, and keep in mind that at low target boost and power levels, the wastegate will open fairly early and you risk making more decibels than horsepower 😉
Performance wise, there are things to keep in mind on a recirculated setup. It’s important to keep a good re-entry angle when recirculating back into the main exhaust to avoid disturbing the flow coming out of the turbine when the wastegate is open/bypassing exhaust. You want it aimed in the same direction as the main exhaust flow and so it can smoothly join it, and also follow the swirl direction coming out the turbine wheel itself when applicable.
A recirculated setup always has the entire exhaust flow going through the full exhaust, vs a dumptube that just dumps some of the exhaust ahead of time. So a recirculated setup may not be able to get away with an undersized exhaust as well. But, the higher you raise boost, the more the wastegate is held shut, so the overall difference between recirc/not may become less when you push things anyway.
If it’s done thoughtfully, there shouldn’t be much difference/concern in performance, and usually just comes back to preference and/or intentions with the car.
Recently had a client make ~880whp on a GTX3584RS through a recirculated full 3″ exhaust which was pretty cool to see 🙂