TVIS...."shit" or "the shit"??

[kingcorolla]

now with TVIS...
ive herd many people say its all bulshit and just restricts airflow and should be biffed..
and the other half say ure stupid for taking it off because it increases midrange torque..
I know that was toyota's intent for making it but did toyota balls-up on this one??
or does it significantly improve power/torque??

opinions please.


reason for question is explained in my signiture..
I
I
V

[Ae92typeX]

They put it in a lot of engines so I doubt they balled it up.
if you take it out you will loose torque and unless you are doing big mods I personally dont think it restricts much.

[Jools]

I have TVIS on my 3S and its pulling 184kw+ at the wheels, so cant be that bad

My car has plenty of response down low still so im reluctant to remove it. Never tried it off

[badidas]

yeh im with everyone else on this one
the only reason people prefer the non tvis engine is its got more power due to a different head design
oh and with ur rebuild try a type 41 ecu (?) aparently the fxgt/mr2 ones are carp type 41 is from a carina/corona something


good luck

[Inane]

wtf is TVIS?

[EVLGTZ]

TVIS (Toyota Variable Intake System) is a set of four butterflies located in the inlet system next to the head. These butterflies are shut below approximately 4500 RPM, effectively blocking airflow to one valve per cylinder, increasing the air speed and thus improving mid range torque. They are opened by the ECU via a small plastic vacuum tank and solenoid triggered diaphragm actuator located under the inlet manifold and open above this speed. The effect is similar to a second throat opening on a carburettor.

Also, from Club 4AG...

There have been many arguments on the issue of TVIS on early model 16 valve 4A-GE. Now, this is a highly effective method of making usable torque curves while retaining higher volume flow at high operating range. In most near normal applications, generally meaning light bolt-on tuning, the TVIS continues to function very well. Thus keeping it is a very good idea. However, heavier modifications including ECU, Carburetion, highly aggressive valve train/cam and internal work all present effects which create difficulty in controlling these items. For example, the triggers for the TVIS will be eliminated for carbureted applications, and it's variable induction, even if it was operational presents more complex challenge to jetting your carburetors. Heavily modified engine which greatly alters maximum rev range and shifts the power band in either direction will present similar challenges to an ECU programmer as well. In those cases it is easier to remove the TVIS and use the capabilities of the ECU tuning or carburetor jets to match your desired torque range. In short, for most basic performance upgrades, the TVIS should be kept and maintained to give nicer overall torque curve which does NOT inhibit power in any significant way.

So im summary, keep it in there unless you've got an aftermarket ecu and can tune for the effects of taking it out.

[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!

[EVLGTZ]

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!

haha yeah, that always cracks me up when someone says it feels faster and ya have to explain that instead of going from normal low revs to normal high revs speed that they are actually going from a slower low revs speed to normal high revs speed hence feeling the difference.

[kingcorolla]

..makes sense.
jus wanted opinions.

[Leon]

I had a workshop give me back my AW11 with the t-vis disconnected (accidentally). It had no power at all down the bottom end, then exactly the same power as usual at the top end.

It drove like complete arse, and they were immediately given the car back for them to sort out. Definitely don't drop the t-vis unless you're doing some pretty serious stuff to the rest of the motor.

[Drifter4ag]

this is very interesting . .. one of these tvis posts comes up a few times a year and every time is is different
last time everyone was saying that tvis was crap and you should take it out on stock engine. Oh well
TVIS is mean and i wouldnt remove it its great on turbo motors esp for massive low down torques you can really feel the powa

[NA Drifter]

yeh, i'll keep it... why take it out.. they are there for a reason. Toyota doesn't waste their money on an engine parts that no need to be there. I even stay with the factory airbox with abit of mod to it than a pod filter. The surface area of the filters on the factory AE86/AW11 are much bigger than the pod filter.

[GOLDAE86]

Yeah i took my T-VIS out just to see what the difference would be, and all that happened was that i lost most of my bottom end torque and had no difference up top. I have been meaning to put it back in but i keep working on my race car instead of my road car.

[kingcorolla]

so say i keep the tvis, and do some porting on my head, would that bugger the extra velocity the tvis is creating? or just slightly increase air speed due to bigger tunnel for air 2 flow?

[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?

[kingcorolla]

nice way of puttin it dude.
seems logical NOT to port my BIGPORT head.

can anyone 2nd this comment?

[Al]

Well RedMist's knowledge of the 4age engine doesnt need backing up. He knows his shit and hes built engines before.

Al

[RedMist]

Al cheers for the vote of confidence but I, like everyone else on this list, are still learning and I've been proven wrong before. I done a shyte load of research and development on the 4age in the course of attempting to stretch a dollar to make an overweight race car compeditive, but it still makes me no expert. Questioning someones "theroies" in any forum is well advised.
I actually looked at the TVIS mechanism to increase low flow velocity in one of my other race engines. However just looking at the device you realize how much flow restriction there is in the two port design. Couldn't find a smallport and ended up with a Blacktop (which I killed and wasn't compeditive anyway!). We also looked at the flow charistics of the bigport head (ex Atlantic) flow was incredible, but the velocity was shyte and the engine only realy woke up from 8-10k RPM.

What am I trying to say? Buggered if I know its 2am.

[NZ_AE86]

mmmmm 8-10K rpm and beyond!

[Mr Revhead]

hehe yeah redmist knows his stuff, but i think he should sleep more
his description above is very well put, i must remember that next time im asked how to remove tvis!