TVIS?

[Mux213]

Alimonos,

Very simple. We have 'big port' engines. Its all about flow. With N/A cars big ports and low RPM means bad airflow means bad power. The TVIS simply closes off part of the port making it in effect a very small port engine. This increases airflow (amongst others the speed of the air) making it possible to suck more air/fuel mixture into your engine, giving you more HP in the lowend.

So if you simply remove the TVIS all you do is get bad airflow on low RPM and a tiny little increase of airflow in the high RPMS (where the TVIS butterflies become an obstruction).

Different Cams do not solve this issue, they just give you more HP over the range making this situation less noticeable.

The newer 4AG engines are small port engines, meaning the ports are smaller to begin with giving a more ideal size for the whole RPM range. Thus the newer engines no longer need TVIS. But I recon that big port engines can theoretically produce more HP in the high end then the smallport engines can.

Denmarks remark about the turbo are also dead on. Because now air is not sucked into the engine but pushed into the engine, the bigger the ports the more fuel/air can get in there, the more HP you get Only downside, at very low RPM you have low boost and you could end up with very little power for the first 1500 rpm.

Atleast, this is how I understand the theory anyways I'm by no means an expert

*edit* for rotary fans, the TVIS system is nearly the same principle as the 6 port system on our 13Bs