I thought I'd put up my latest dyno chart comparing the power and torque curves of my old single scroll turbine housing setup vs my new twin scroll turbine housing setup with some comments around the actual perceived differences in drive ability of the car.
The turbo is a Garrett GTX3076R. The single scroll turbine housing was a 0.82 A/R size and the twin scroll is a 0.83 A/R. The motor is a 2.3 stroked 4G63 on E85 with a 3" exhaust.
In both instances, fuel, timing etc have not been changed. The only changes were the turbine housings and the exhaust manifold. The same dump pipe was kept but modified to accommodate the new geometry of the twin scroll manifold. The boost map was altered slightly to suit the new characteristics of the setup but in both instances max boost was set at 26psi.
The twin scroll exhaust manifold was completely brand new - I did not have the exhaust manifold from the single scroll setup modified to suit the twin scroll. The new twin scroll manifold was designed and built so that the cylinders would fire into the merge collector in paired pulses and the runner pairs are completely separated all the way to the turbo. The manifold uses two external 44mm waste-gates (1x each runner pair) that are also completely separate and each have their own screamer pipe. The single scroll manifold used one 44m external waste-gate with screamer pipe.
It's quite evident from the dyno chart that the power and torque response has improved by upto 600rpm, with a new peak torque of 570Nm at 3647rpm vs the previous peak torque of 550Nm at 4422rpm. Power output is the same but this was expected.
The change in torque delivery has noticeably transformed how the car performs on the track. Where I used to keep the car in 3rd gear around the tighter corners and it would exhibit slight turbo lag upon exit, it now "slingshots" out of the same corners in the same gear with absolutely no lag. Throttle response on each gear change has also noticeably improved and the overall performance of the car feels much better.
It was not a cheap exercise to do the change from a single to twin scroll. The cost of the new turbine housing + the cost of purchasing the additional waste-gate needed to be considered. The time and cost behind the design and fabrication of the new exhaust manifold was also substantial, however very necessary as a poorly designed and made setup would not have enabled the full potential of the change and resulted in it being a waste of time and $$$$.
However for my application and setup I feel this modification was very worthwhile - whilst the single scroll setup performed well, the twin scroll has made the performance characteristics of the car more suitable for what I want to do with it.
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