TVIS or not to TVIS...

[Hydra]

From what I understand, the cams for a turbo engine need to have minimal overlap for fairly obvious reasons. I can see the benefit of TVIS on a standard 1G-GTE, but one with a bigger turbo and perhaps better cams would possibly see some benefits from the increased flow and lesser turbulence.

But hey, i've not tried this out yet

[Hydra]

"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."

From Bills site

http://www.billzilla.org/4agmods.htm#150hp

[JustCallMeOrlando]

Hehe, thats the bit I read on Bills site.

Forgive my ignorance, but given that an aftermarket ECU can't change the airflow, why would it remove the need for TVIS? You might be able to smooth out the curve a little bit, but nothing drastically. I look at it this way. When I build my next 1G, it's going to have a bigger turbo than factory. I'm looking for above the 225rwkw+ mark. It will most likely have NA cams.

Ultimately, it's going to make more power, because I'm shoving more, and cooler air into the engine. Ultimately, the bottle neck is going to be the head, so I have no real qualms about leaving the TVIS setup intact (although I'm keen to even out the flow a bit).

My question is, have I drastically altered the need for some low-end assistance? If so, I can't see how. While still making a lot of power, I can't see how it's been removed that far from stock in a way that TVIS is going to lose its effectiveness.

[JustCallMeOrlando]

Oh, and apologies if I seem like I'm going over and over stuff, I'm doing a brain dump of the way I'm thinking about so it can be critiqued

[Ben Wilson]

It depends on weather you're interested in top end or bottom end.

Removing the T-VIS and porting the plates back may well increase top end power, but you will lose bottom end because of it.

[JustCallMeOrlando]

How will it increase top end if the manifold already greatly outflows the head, excluding any perceived advantage from reduction of turbulence?

[Hydra]

In that respect, removing TVIS on the 1G-GTE is a bad idea It isn't exactly the best motor for torque. In that same respect however, you can just keep the revs high at all times

JCMF, maybe you could have one TVIS plate functional, and another gutted and plugged, and do a bit of testing for us

[JustCallMeOrlando]

Haha, nah. I'm building it once, and once only. I'm over replacing shit haha.

[Lambolica]

Also if you run a ported head and hi lift cams the air is going to move faster at lower revs.. this is where TVIS would be a restiction.

I think Stock head = TVIS

[JustCallMeOrlando]

How bout if someone was just planning to say...run NA cams and tidy up the casting marks on the head and give it a general tidy up?

[Ben Wilson]

How will it increase top end if the manifold already greatly outflows the head, excluding any perceived advantage from reduction of turbulence?

Ignoring the turbulance (which I believe can't be discounted), and restriction will still have an effect. Flow testing the manifold and the head don't show how they flow together. I believe that if you bolted them together, you will find an improvement by getting rid of the T-VIS.

[Lambolica]

You would achieve better flow at the bottom end obviously, but no where near enough to justify removing the TVIS plate IMHO.
If the head was ported out as far as it could go and you were running uber Cams then it would be a concideration depending on the use of the engine.

The is a graph that I'm trying to find that shows the relation of air flow vs area.
the curve isn't linear but there is a point where the area of the open port in the TVIS plate at a certain air velocity = that of both ports being open with higher head flow.

I am having trouble putting this into words but there is a point where standard head flow and active TVIS open port air velocity = the velocity of both ports open at same engine speed with higher head flow, but the head flow is far higher than can be achieved by the head.

[Lambolica]

Turbulance is somthing I need to look into. but in short yes it does play a significant part.

on a stock 1G head probably not but on a highly ported head

[Fattony]

Personally i would not bother with the TVIS in a 1g just because the reason why there is an unequal level of flow through the runners is the fact that the 1g runners are divided into 2 parts giving you 12 parts to the 1g intake, the ends on either side of the manifold lack a butterfly, as those 2 runners always remain open, hence this is what gives you a 10cfm difference between using the 1g TVIS and not using it, so apart from addind a static butterfly there aint no other way of leveling the flow by removing the system completly. I would do this by removing butterflies not by taking the whole plate of the motor itself as you then shorten your intake runners by about an inch and genrelly arse up intake valve backpressure and it gives you the effect of shifting your powerband up by about 300-500rpm or so.

[Hydra]

From what i've seen when people have removed TVIS, they have removed the shaft and butterfies completely, then sealed the holes. I know in NA applications it is commonplace to use epoxy to reshape the intake ports (even though this often ends up worse off...) so I would imagine that a well done epoxy job on those shaft holes would achieve some nice results - also keeping that 1" of runner length there.

I guess the alternative is to make a custom intake plenum and runners

EDIT: removed retarded mistakes