TVIS?

[D.Wars]

i know that, but I found it weird that when I kept the revs just a little above 4k rpm and the t-vis all open, i could keep the car in the drift.

But 200 rpm's less and the t-vis 'closed' (16v/12v was easier to explane ) the car just lost power and rev's. So there has to be a significant diffrence in power at that rpm range with the t-vis on and with the t-vis off.

And I dont mind if the car is a bit slower at low revs. I'm using my car mostly in midrange and high revs.

[The Doctor]

Dennis, your going to fast there...

Don't forget that in 3rd gear, you'll have less power at the rear wheels.

I didn't change a single thing to my engine, but i did fitted a taller diff, and now it's just rubbish to drive, it's just slow

[jamiemirror]

D.Wars, TVIS removal leads to ITB solutions

[D.Wars]

that's another idea

[banpei]

AFAIK the tvis opens at 4400-4500 rpm, but that might differ per ECU. But as said before: removing the tvis doesn't help too much. The ECU will still inject the same amount of fuel, so removing it would require remapping your ECU. But then you'd better go for the ITB.

[JMR_AW11]

On the UK 4A-GE ECU for both AE86 and AW11 MR2, Toyota employ a little trick in the ECU program code to add some kick to the TVIS.

When the rpm exceeds the TVIS threshold the ECU starts a little delay counter. This counter adds a delay to allow the TVIS flaps to open, once the counter finishes the ECU suddenly adds 3 degrees of ignition advance to the timing!

This was maybe a marketing ploy to help sell the benefits of TVIS. i.e. some of the kick is really the sudden ignition timing change!

if you remove the TVIS mechanicals you will still get the 3 degree step in timing at the TVIS rpm.

It is actually quite annoying as this means the engine is starved of optimum ignition timing below the TVIS point (by maybe 3 degrees!)

Just to get that kick...

[banpei]

Just a stupid side-thought... During the late 70s and early 80s turbo was a huge buzzword... Perhaps someone loved that kick enough to build something like that in the ECU?

[jondee86]

The TVIS system increases the intake air velocity at low rpm's to
promote fuel vapourisation and cylinder turbulance. This gives
improved combustion, more torque and better low rpm acceleration.

After 4200 rpm the TVIS butterflys are open and the throttle area is
doubled for greater airflow at high rpm. But as can be seen from the
graphs, torque drops off at high rpm in a standard engine, meaning
that revving past 7000 rpm offers no performance advantage.. only fun

For normal street driving the TVIS makes the car pull stronger out of
corners and generally nicer to drive. Disconnect the vacuum hose to
keep the TVIS permanently open and compare, before you decide to
remove the butterflys.

Cheers... jondee86

[Ivan141]

Quote:torque drops off at high rpm in a standard engine, meaning
that revving past 7000 rpm offers no performance advantage.. only fun

It might have performance advantages when you want to hit your powerband on an upshift.

[jondee86]

Quote:It might have performance advantages when you want to hit your
powerband on an upshift.

Sure... especially from 3rd to 4th !! And having a few extra revs
to play with means you can often hold a gear between two corners,
rather than upshift then downshift.

Cheers... jondee86