ACIS- dyno plots

[ashley]

Just ran my new engine in today (stock rev3 NA, decat, Mongoose exhaust and carbon dynamics airfilter), and managed to get a direct comparison of the engine running with ACIS active, and with it disconnected:



Worth noting this was on a hub dyno, and my rear pads were dragging (now sorted)

Interesting to see the 'dulling' effect you get at 5.5-5.75k rpm when the system activates- a significant drop in torque, and the hp flat lines.

Leaves me wondering if I'd get better response with the system activating higher up in the rev range, or maybe not even activating at all....

Just thought I'd share, it's got me thinking anyway!

[ashley]

Is my understanding correct?

The butterflies in the inlet manifold, in their default position are open- so larger volume.

At low rpm the butterflies are held closed, so decreasing the inlet manifold volume and giving better mid range torque.

At 5.5k rpm the butterflies open, increasing the inlet manifold volume and giving better top end response.


I'm struggling to reconcile the dyno plots I have with the common experience that people feel an increase in power at 5.5k rpm

I wish I had done a third plot with the butterflies held closed above 5.5k...

[phipck]

from my reading it was the reverse,

low rpm = open for longer/larger inlet keeping low torque and hp then at high rpm = closed for short inlet length and more efficient pressure and flow giving better higher end torque and hp.

simular intentions to create efficiency at low and high revs to vtec but clearly a much less capable and effective solution.

[ashley]

So on my dyno run with a leaking vacuum pipe the butterflies would have been closed the whole time?

I'm confused- when I assembled the manifold the default position for the buterflies was open, and sucking on the pipe closed them...
So surely if the pipe was leaking the butterflies would have been open the whole time? I think I'm just confusing myself!! More reading to be done I think...


Whatever the case- I still don't understand why you feel like you get more power at 5.5k, the plots just don't seem to back it up!

[phipck]

the default possition is open, in a previous post you said at low rpm they would be closed and open up at a set rpm, it is in fact the other way round. open as defualt and close when activated at higher rpm

you are right, if the vac pipe leaks then the butterflies would be open at low rpm as standard, but not close at 4-5k rpm as they should under vac suction, preventing you from benifiting from the shorter inlet at higher rpm.

theres a few akward examples online along side confusing discriptions where people are trying to simplify the explination.... good old internet at its best!

[ashley]

....but the difference between my plots was in the mid-range...ie the leaking pipe was causing a difference under 5.5k rpm, not a difference above....hence my confusion!

[phipck]

it is indeed interesting. the point it all starts to vary is at about 3.3K, i always read that acis cut in at 4.2k so clearly something else is happening or not?

it could be your the combination of breathing mods you have taking some effect, but im unsure

[ashley]

Reading the BGB it states that there should be a vacuum to the ACIS up until 5.4k rpm, which suggests the butterflies are held closed by the system until then, and open at 5.4k rpm.

And that's pretty much the effect you can see on my dyno plots...when the system had a leak, there is no ACIS under 5.4k rpm- and so lower torque. Once the pipe was replaced, there was a vacuum under 5.4k rpm- and so the system worked, and the torque levels rose.

ACIS is active under 5.4k rpm...not over.

That's my understanding from the BGB anyhow

[Super_red]

Yeah normally variable induction systems offer a closed butterfly at lower RPM's forcing each runner into an individual long runner, then at higher RPM's they open linking all 4 runners together half way down, this makes the plenum and the first half of all 4 runners (plus the second plenum) into one big plenum, the second half of the inlet runners is then a shorter runner to each cylinder. A large plenum and shorter runners are better for high end power alhtough a large plenum can be beneficial in the mid range on long duration cams.

[jimGTS]

id have thought its like tvis for the turbo

held closed low rpm, open for full flow at high rpm

doesnt make sense to restrict flow at high rpm!!


by default if you unplug the tvis stays open all the time, purely as a safety feature incase the line broke or whatever.

id imagine exact same thing for the acis.

[T.F.S.]

id have thought its like tvis for the turbo

held closed low rpm, open for full flow at high rpm

doesnt make sense to restrict flow at high rpm!!

this.

[ashley]

Sweet- as expected then. It's interesting to see the detrimental effect on power of opening the butterflies at 5.5k rpm though isn't it? Wish I'd had the chance to do a pull with the butterflies held closed all the way to the top end, there may be a bit more to be had for another 500rpm or so, and every little counts with an NA

[ryan]

Sweet- as expected then. It's interesting to see the detrimental effect on power of opening the butterflies at 5.5k rpm though isn't it? Wish I'd had the chance to do a pull with the butterflies held closed all the way to the top end, there may be a bit more to be had for another 500rpm or so, and every little counts with an NA

Im sure Toyota wouldve optimised the system during engine development (alibet with economy/emission restrictions in mind), so i'd be suprised if you made any more advances to be honest. Theres a definite kick though in the range youre talking about

[ashley]

I'm sure you're right, which is why I was surprised when I looked carefully at the dyno plots