TVIS....Bonus or Hinderance?

[no_8wire]

What is the benifit of the tvis system on a 4age as opposed to a non tvis?

are the non tvis/tvis better?

[Lloyd]

Depends what you want it for. TVIS system basically allows for better air speed at lower revs which increases torque. Butterflys open up and give more air to the engine up top.

Should be heaps of info if you search on here for it. Even more on Google I would think...

[no_8wire]

so there are power/torque differences?
and fuel eco?

[Pelo]

If you completely removed the TVIS plate/valves from a bluetop 4age, in theory it would have better top end but worse bottom end power... the valves look like they make quite a restriction before the ports... hmmmmmm

[no_8wire]

why would it have worse bottom end? I would have thought the more air going to the engine the better?

[Truenotch]

Nah at low revs if theres too much air and fuel going in then the motor will struggle or drown. It has to be doing enough revs to burn off all the petrol, otherwise it just gets shoved out the exhaust.

[vvega]

its all about port velocity
but i didnt say that

v

[Malcolm]

that's right, higher port velocity improves cylinder filling, especially at low rpm. also improves fuel atomisation. theoretically it's a pretty good system, not sure just how much restriction it causes when the plates are open, there would definitely be turbulence introduced, but I wouldn't want to speculate on how much of an effect it would have.
Also, when you increase the amount of air the engine flows, the tvis can cause a restriction by staying closed for too high in the rev range, some people have adapted v-tec controllers or just simple rev switches to open the tvis sooner to combat this.
Personally, I have removed the tvis from my gt4 engine and ported the manifold and spacer plate out to provide a smooth transition from 2 runners to the single port, but this is an engine intended more for race use.

I think you would be best just leaving it connected unless you do some reasonable mods to the engine (ie higher lift/longer duration cams, turbo conversion or similar)

[Ebola_One]

Personally, I have removed the tvis from my gt4 engine and ported the manifold and spacer plate out to provide a smooth transition from 2 runners to the single port, but this is an engine intended more for race use.

Eh? 3SG series engines have/had TVIS? First I've heard of it?!
I know some of the GT4's had Twin Scrol turbos, but that's completely different.

[Malcolm]

first generation (85-89)3sge's had tvis
first generation (86-89)3sgte's had tvis
second generation (89-93) 3sgte's had tvis

Trust me, I have had several 3sgte's apart and they most certainly have T-VIS. I will get a picture of mine all ported all to show

[Malcolm]

the t-vis spacer (which used to have plates in it) is from an st185 gt-four (2nd gen 3sgte), intake manifold is from st162 celica (first gen 3sge)

Seriously, before you suggest someone has no idea what they're talking about (no, I don't often confuse intake manifolds with twin entry turbos), do just a tiny bit of research

[Dell'Orto]

Eh? 3SG series engines have/had TVIS? First I've heard of it?!
I know some of the GT4's had Twin Scrol turbos, but that's completely different.

Yes, they most definately do...learn something new every day dont ya

[CozmoNz]

Toyota Cynos b / Sera engine
(5efhe), has acis, a type of tvis

toyota camry v6 engine
tvis

wow look, you learnt something else >.>

[Malcolm]

actually several Toyota engines have ACIS, gen 2 & 3 3sge's, 1MZ-FE, possibly more

[spencer]

Isnt acis a system with two different length inlet runners giving you two different rev ranges of helmholtz tuning? theres a newer ACIS-IV which has 3 stages. Its a different concept to TVIS, also 1gge had tvis

[vvega]

correct please go to the head of the class


v

[RedMist]

It's all about velocity.
Toyota were into the 80's craze of making ports radically big. This meant that the velocity of the fuel air mix was low (the ports flowed too much air) and the fuel fell out of the air / fuel mix. TVIS was introduced to increase velocity at low RPM and hence keep the fuel in the mix. It works, however it's not a nice solution as the air is disturbed around the TVIS butterflys. If you can get one you want a small port head, which increases velocity natively.
My race engine has ports reduced using a form of Bog to even smaller than that of the smallport. It comes on very strong at 5.5k and looses all puff by 8k. 173bhp at the wheels in a NA engine isn't too bad.

Don't ever remove the TVIS butterflys. You may get a small top end gain but you'll drastically loose out on mid range. Butt dyno will tell you it's far more powerful, true dyno and lap times will tell you it's DRAMATICALLY slower!

[RedMist]

Think of it like using a garden hose flowing water with varied pressure, to wash your car. At small flow rates (low RPM) you stick your thumb over the end (TVIS closed) in order to maintain velocity and keep the water hitting the car. Large flow rates you don't need to stick your thumb across the end. Its a very clever solution however with TVIS your thumb is never completely removed from the end and you tend to restrict some flow, and disturb the remainder of that flow.

By porting the head (something I would NEVER do on a BIG port) your increasing the diameter of the pipe without increasing the amount of water it flows. It's very much like using a fire hose instead of a garden hose but still using the garden hose outlet set at the same tap opening. You end up with a pathetic trickle out of the end. Sticking your thumb over the end helps, but only a bit, you still can't wash the car.

I run a bloody small diameter hosepipe, rips the paint off my car, however it's so small I can't get large volumes of water through it (runs out of puff at about 8k)

So what you are aiming for is the most water flowing through the pipe as possible while making that water flow as fast as possible. A large pipe will flow tonnes of water but the velocity will be low. A small pipe will have high velocity but will flow considerably less water. Its a trade off that Toyota almost got right with the smallport however there are rally / race engineers still reducing the size of even the smallport with much success. My ports are approximately 10mm in width smaller than that of the smallport, and were developed by a TWR engineer.

GEDDIT?

[pc]

This thread seems to cover TVIS quite well, thanks to RedMist

How do I vote to have put it in the FAQ section?

[MilfHunter]

The ports on the GTE's are smaller than the GE's (presumably to aid low end torque)?
GTE


GE


I'm using a GTE head on a GE gen1, low torque/midrange is way better.
With a gen2 header and the same cams etc, had to increase injectors to 305cc from stock 246cc.

T-VIS works, but is prone to losing flaps and destroying valves/pistons/heads.
flap screws need to be peened or they come loose


Later gens have even smaller ports and the ACIS system [/img]