PDA

View Full Version : TVIS questions



UtahSleeper
07-08-2012, 06:43 PM
So, I have a st165 and I have everything connected properly, except the TVIS. Previous owners pretty much left it not connected(vacuum hoses and such). I am considering hooking it up properly, but I have a few questions to see if its worth the hassle of trying to fit my giant arms back there for detail shit lol.

1. If TVIS is disconnected, what is its default position, open or closed?

2. Is there any major draw backs to leaving it non - operational?

Right now I just want to try and get the car running and see where the motor sits as well as the rest of the car. No plans for racing or anything special for awhile, so thats why I am considering not messing with the TVIS.

Thanks for any input.

joe's gt
07-08-2012, 09:52 PM
Just going off memory here, but TVIS is very beneficial for low end torque. It is in a normally closed position and closes off intake runner ports so air is only drawn through one section of the intake runner for each of the four cylinders, thus decreasing volume, and increasing flow velocity (which in turn increases flow rate) into the head and cylinders at low rpm. At about 4200 rpm it is suppose to open and allow full air flow through the intake runners because there should be enough airflow from the turbo now to take advantage of the excess volume without sacrificing velocity. From my understanding, on a relatively stock engine, it is a noticeable difference having it hooked up. However, most believe for cars with breather mods and bigger turbos, the airflow limitations it causes makes eliminating it beneficial. I don't necessarily agree with that though. I think it could be beneficial on even modified cars, just lowering the rpm opening point would be the key in that scenario.

CollapsedNut
07-09-2012, 03:22 AM
Its open if no vac lines are hooked up, it uses vac to keep it closed.

joe's gt
07-09-2012, 04:59 AM
Its open if no vac lines are hooked up, it uses vac to keep it closed.

^^ haha. I guess I forgot to mention the most important piece of info. Yeah its normally closed, but only if its hooked up. So I personally would hook it up ASAP! Let us know if you can feel the difference with the butt dyno!

alltracman78
07-27-2012, 03:30 PM
^Even when it's hooked up it's normally open. It's only held closed by the VSV when the engine is between 0-~3800 RPMs. All other times [including start IIRC] it's open. :)



and increasing flow velocity (which in turn increases flow rate) into the head and cylinders at low rpm.
The increased velocity isn't to increase flow, it's to improve mixing. :)
The cylinder can pull [and the turbo can push] more air in with both runners open, but the faster the speed of the air is going into the chamber the more turbulent it's going to be, so the better the air:fuel will mix, which gives you more power. At higher RPMs the single runner can't provide enough air, and the amount of air available [or lack therof] becomes more important than the turbulence in the chamber.
Generally when you make something smaller to increase velocity you're sacrificing how much you can flow. A hose nozzle is a good example of this. With the nozzle you have a much higher velocity, but it won't flow as much water as the open hose can.