"Asymmetric" inlet cam for TVIS

[AdrianS]

Given the way the TVIS works, has anyone made an inlet cam with a more radical duration on the valve that is closed off by the TVIS butterfly ?
It seems to me that you could run more overlap without losing bottom end, relying on the port being blocked off at low RPM. You could also (maybe) get more swirl / better mixing at high RPM due to one inlet opening earlier.
Has it been done ? If not, why not ?

[trdee]

All inlet valves are always in operation whether t-vis is activated or not. t-vis just increases the velocity into each cylinder port at low rpms where there isnt enough air flow compared to the volume of the port/runners.

[AdrianS]

All inlet valves are always in operation whether t-vis is activated or not. t-vis just increases the velocity into each cylinder port at low rpms where there isnt enough air flow compared to the volume of the port/runners.

I know all valves are in operation at all times, but I had missed the fact that the 2 inlet runners appear to be joined near the head (after the TVIS butterflies), which ruins my idea.

If the runners remained separate all the way to the head, as they appear to do from the outside, my theory should hold.

[MWP]

Heh, that is quite an interesting idea though.

[oldcorollas]

I know all valves are in operation at all times, but I had missed the fact that the 2 inlet runners appear to be joined near the head (after the TVIS butterflies), which ruins my idea.

there used to be "port dividers" available as inserts for early 4AG heads, which did completely seperate the flow for each runner

[trdee]

So then the engine will be running as an 8 valve until t-vis opens up? Wouldnt you have issues with cylinder filling and whatnot? **



**i am not a mechanical engineer

edit, no it would be running as a 12 valve, as both exhaust valves would still be opening. still, it's a bit strange to me to do such a thing. Unless you're just doing it cos you want vtakkkk yoooo style switchover?

[oldcorollas]

**i am not a mechanical engineer

perhaps restrict comments to things you know about then heh heh

[trdee]

lol. i was hoping for some clarification to my question what would it do to the breathing characteristics of the engine seeing as all the airflow will be coming from one valve now rather than both?

[oldcorollas]

that one valve will have higher velocity.
remember that ports rarely max out velocity by redline (usually too big) so at a couple thousand revs, you have really crap port velocity = not such great filling.
by blocking off one completely (or partially) you have better velocity of the gas and probably better filling than if both runners were open.

the problem will come, when you start opening the TVIS, so you have a long duration valve which allows some reversion...

also need to think about if you want to promote swirl over tumble etc etc, and if having one valve closed longer will actually be of benefit. either way, you will compromise top end, but maybe not bottom end so much with the TVIS and the runners completely divided...

[AdrianS]

It's just a thought experiment, but seem do-able; fit port dividers, take a high-lift+duration cam, and re-profile every 2nd lobe to reduce overlap. Fit as big valves as possible, since only one is flowing gas at low rpm.
All you need then is an ecu that can handle the TVIS (megasquirt ?) and many many hours of dyno time to tune it all. As oldcorallas says, the TVIS changeover point could be nasty.
Realistically, not worth the time and money, but I'd love to see it done; a nice, torquey, economical motor below 5k, with a good top end, and a lot less complicated than VVT / VTEC.

[trdee]

that one valve will have higher velocity.
remember that ports rarely max out velocity by redline (usually too big) so at a couple thousand revs, you have really crap port velocity = not such great filling.
by blocking off one completely (or partially) you have better velocity of the gas and probably better filling than if both runners were open.

the problem will come, when you start opening the TVIS, so you have a long duration valve which allows some reversion...

also need to think about if you want to promote swirl over tumble etc etc, and if having one valve closed longer will actually be of benefit. either way, you will compromise top end, but maybe not bottom end so much with the TVIS and the runners completely divided...

Cheers for that, didnt even think about reversion hey.Well at least now I have time to learn more about this shit since I dont need to study anymore

[oldeskewltoy]

There ARE cams with slightly different durations for each lobe, they are called Tri-Flow cams - http://forums.club4ag.com/zerothread?id=33916

I've asked, and not yet been told if Colts Tri-flow cams favor the non TVIS port.


Now... there is WAAAAY more to a TVIS head then just a TVIS plate! If you do any port work you'll immeditately notice 2 things... 1 the injectors are slighty offset(favoring the non TVIS plate port, and secondly, the ports themselves are NOT symetrical, the TVIS butterfly port is slight offset.

there used to be "port dividers" available as inserts for early 4AG heads, which did completely seperate the flow for each runner

Kai Power - not sure how completely separate the flow was... its main purpose was to narrow the ports some, to increase velocity

[amichie]

Do you have a link with more info about these port reducers? I have been wanting to make something like this for my 7MGE for a while now.

Many thnaks.

[oldeskewltoy]

Do you have a link with more info about these port reducers? I have been wanting to make something like this for my 7MGE for a while now.

Many thnaks.

http://kaipower.web.fc2.com/

[oldcorollas]

thanks for that
i thought they did go all the way.. can see the notch for the normal port divider (that you grind down for better match)
http://kaipower.web.fc2.com/price-parts/spl-p.html
pics added as attachments