Info on the benfit of removing the T-VIS from the bigport intake in boosted 4age's

[_gear2]

Frustratingly there seems to be a large amount of conflicting information regarding using the T-VIS plate in boosted applications on the 4age.

It seems a number of people want to eliminate the T-VIS system in boosted applications, often following this method of removing the butterflies
http://www.toymods.org.au/forums/faq...4ag-t-vis.html

But I cant seem to find the reason why, beyond 'shit yer bro runs heaps betta'
Is it because having the t-vis restricts the air flow? (In the case of a turbo) I would of though having the TVIS would help it spool up earlier? and as noted in the following link help with down low torque. (thought he only did his tests with a N/A engine. Is it different for boosted applications is this low done torque benefit not really noticable?)
To TVIS or not to TVIS.

I found this point on Bill Sherwoods site
’Note that with cams larger than about the 260° mark you will actually benefit from removing the TVIS, if fitted. The TVIS, when used with cams smaller than about that duration, will give you more low end ( < 4,400rpm) power, but this effect disappears with the bigger cams.’

But what is the actually benefit?
Can anyone give a solid answer? I seem to have to sort through so much misinformation and simply don't know what is correct.
Thanks

[_gear2]

Can anyone give an answer?

[white_sandshoe]

http://www.performanceforums.com/for...-67252137.html

Have a read of the second post in this thread... There is a bit of theory for you, which may be enough to calculate an answer, but i've been up all night looking after a new-born, so i'm in no mental state to figure that one out myself right now, sorry.

[Hiro]

If you want a factory-backed answer, Toyota removed the TVIS butterflies in the bigport 4AGZEs, but that is a supercharged application so low-down torque isn't as much a problem as in a turbo'd car.....

[trdee]

if i could be bothered, i would connect the vsv setup to an output on the adaptronic and do two runs on the dyno. one with tvis open and one closed, and then set the switch point to where the two torque curves intersect. i am sure that on a turbo setup you would indeed see low end gains, but where and how much depends on the response of the turbo, whether you have done any work to the top end etc etc.

most people put it in the too hard basket and piss it off, again, i could do it but i cant be bothered and my next engine will either have a smallport or 20v head anyway...

[Moppitt]

if i could be bothered, i would connect the vsv setup to an output on the adaptronic and do two runs on the dyno. one with tvis open and one closed, and then set the switch point to where the two torque curves intersect. i am sure that on a turbo setup you would indeed see low end gains, but where and how much depends on the response of the turbo, whether you have done any work to the top end etc etc.

People who care, do this ^^

most people put it in the too hard basket and piss it off...

People who don't care, do this ^^

I haven't seen anyone who did back to back dyno runs with tvis fitted and active versus tvis completely removed on a turbo set up. That would be the ultimate test (for that particular set up).

[Ken_T]

I think the thing with turbo motors is your already seeing boost at 2k and hitting full boost at like 3.5-4k when tvis would be switching at 4400 on stock motor.

The whole point of tvis is to try and increase air velocity through the port by reducing the cross sectional area in part of the port and also partly creating a swirl in the port(iirc 4a were a 4 port head, not 8 like ca18). By turboing it you've already created a larger pressure differential which will increase air velocity upto a point.

On the other hand, ca18 is factory turbo but has butterflies in the intake. Has this weird 8 port head so, iirc, the ca does reduce the cross sectional area of the port from the plenum all the way to valve. There's a vsv to control it too but I pulled it years ago so it I'm pretty sure it's only vacuum actuated.

Which just got me thinking for off boost driving it'd be better to leave the butteflies in. On boost they'd probably be a small restriction.