Hey..is the factory setting for the tvis valves (4200rpm) tied in with cam duration?, as in the optimal point for it to open? reason I ask is, the guy who just did my car said that 4200 rpm was the point that the torque started to drop off, and opening the valves there kept the torque curve going..now he didn't know that that is the point that they open on a factory ecu, I told him to open them at about 3700 rpm, but play round with it a bit.. my theory was that since I am running a bigger turbo, more boost, better intercooling, etc you would benefit from allowing this increased flow into the engine sooner...if the switching point is the same though, that would mean that you wouldn't benefit from changing the opening time unless you changed cams?, or what?...maybe I am way off base, or maybe that is just really obvious?
best rpm for t-vis?
- Thread starter ruffneck
- Start date
Ricky B has dyno graphs to prove that.
3600 is a good point.
3600 is a good point.
The difference that a properly controlled TVIS can make is quite measurable on a dyno. Here is the difference between a pull with the TVIS kept closed (blue) vs. one with the TVIS kept open (red) on a 300rwhp setup:
As you can see, the TVIS adds up to 10% more torque at 3K and spools the turbo 100 RPMs faster in 3rd gear. That's nothing to be throwing away without some guarantee of a suitable payoff up top.
The main issues: the stock ECU controls the TVIS very poorly. Often it will keep the TVIS open if it detects any knock and thus suspects your fuel does not have a sufficiently high octane rating. As you modify the engine and improve VE, the point at which the TVIS should open decreases. The stock ECU keeps it at around 4200 which is way too late for anything except a stock setup. As you can see in the dyno pulls above, the ideal crossover point for this car was around 3700, which is where the EMS used to control this setup was programmed to open the TVIS as a result of doing these tests.
My own observation tuning cars with and without TVIS setups is that it always makes a noticeable difference at the low end when it is properly controlled. The reason it has such a bad rap is probably because the stock ECU does such a lousy job of controlling it.