Intake valve lift at BDC

[digger]

IMO if there isnt a little bit of reversion prior to IVC then youre closing the valve too early

I suspect there is no easy way of testing this?

my opinion is formed from sims in ENGMOD4T which is a virtual dyno. it comes from the observtation that if you close the inlet valve a bit earlier it doesnt just affect the IVC, it also affects the duration and centrelines so the fill at every degree from IVO to IVC changes and usually detrminantally so you end up needing a little bit of reversion to set the valve down gently and maximise trapped mass

[steve cowan]

IMO if there isnt a little bit of reversion prior to IVC then youre closing the valve too early

I suspect there is no easy way of testing this?

my opinion is formed from sims in ENGMOD4T which is a virtual dyno. it comes from the observtation that if you close the inlet valve a bit earlier it doesnt just affect the IVC, it also affects the duration and centrelines so the fill at every degree from IVO to IVC changes and usually detrminantally so you end up needing a little bit of reversion to set the valve down gently and maximise trapped mass

Thank you for your response, very interesting how a early intake closing can effect the entire fill cycle

[swampbuggy]

Hello Steve, the Dyno ? , not easy but ? What is Marcose Ambrose up to now days ? Cheers, Mark H. sunny central Florida.

[steve cowan]

Hello Steve, the Dyno ? , not easy but ? What is Marcose Ambrose up to now days ? Cheers, Mark H. sunny central Florida.

mark,
i am sure Ambrose has retired back to his home town,he done a short stint back in the Australian supercars but did not hang around long.
i have zero experience with dyno but i did think off that,the problem i see is in cam timing changes as in a SBC you change all events by retarding/advancing so how do you optimize IO,EXOP,EXCL before testing INCL?? its a rabbit hole at best.
for people trying to learn like myself i have to try and follow trends from people who pick lobes frequently or at least look at application,rpm ,valve size etc as has been previously mentioned,this is a good thread its just i am out of my depth

[MadBill]

IMO if there isnt a little bit of reversion prior to IVC then youre closing the valve too early

I suspect there is no easy way of testing this?

My ancient version of Dynomation certainly shows this. With IVC optimized for power at the studied RPM, cylinder pressure exceeds port pressure well before IVC and some reverse flow is seen at or nearly up to said RPM

[Stan Weiss]

How does greater valve seat angles which reduces effective curtain area at lower lifts come into play?

I believe that this has been talked about before but can not find it.

Stan

Bill,
If you measure the flow / pressure in the port and now have that same flow throw a 50 or 55 degree seat @ .100" valve lift, How has the localized depression changed verses the port?

Stan

[steve cowan]

IMO if there isnt a little bit of reversion prior to IVC then youre closing the valve too early

I suspect there is no easy way of testing this?

My ancient version of Dynomation certainly shows this. With IVC optimized for power at the studied RPM, cylinder pressure exceeds port pressure well before IVC and some reverse flow is seen at or nearly up to said RPM

thanks Bill,
i have engine pro sim so i will look at that and try and make some sense of it.
i was just reading what Bob Hoff put up on the other thread about cam lobes with opposite ramps which adds a new mix in the equation