Brettus

iTrader: (2)

With Hymee's pro tuner I am able to adjust these parameters .
Have been messing around with this for a few weeks now and come up with some interesting findings .
Firstly
Stock Aux port opening : 6100 rpm
Stock Vdi opening : 7250 rpm

I looked at the mass airflow on an N/A car that these were opening and came up with these numbers as a starting point for my turbo setup

Aux port : 4100 rpm
VDI : 6000 rpm

What I expected to happen :
I thought that having that extra port size from an earlier rpm would give me more power from 4100 through to the stock opening rpm . It should also get rid of the lean spike at 6500 (straight after the port opens)

What actually did happen :
Yes the lean spike at 6500 is gone and i get a less prominent one now at 4500.
I made way less power on the same boost settings . If mass air flow is a rough approximation of hp i lost a minimum of 30hp through that range .
My butt dyno confirms this - the violent acceleration i had in the 4000-5000 range was tamed markedly.

previously I was having to run lower boost in that range to prevent wheelspin I have now bumped up the boost low down to get back what I lost .

I'll put up a maf chart later to show what i'm on about (when I get my laptop back from repair)

If anyone can explain this i'd love to know why i got these results - It has me somewhat confused .

Kane

iTrader: (1)

Whenever you add in the extra ports - there is always a dip in power - even NA.

You just moved it down some. Remember; air velocity might be different even if air mass is the same.

Think of opening the size of a water hose when the water is moving at 1 knot vs 10 knots... the flow change will happen a lot faster if it is moving at 10 knots - even if the two hoses are both flowing the same mass per minute of water.

Brettus

iTrader: (2)

I would have expected the dip to last about the same as it does higher up the rev range . It actually lasted all the way to the old opening position .
I could hardly believe my eyes when i looked at the maf chart .

Kane

iTrader: (1)

Velocity me thinks....

You just add so much surface area to the motors intake. I notice with my SSV and APV stuck open - it takes a bit more to get my car moving.

olddragger

iTrader: (3)

velocity does influence volume. playing catch up.
OD

Brettus

iTrader: (2)

yes - so it seems .
Interestingly , when i upped he boost i still didn't get to where i was before .

dannobre

iTrader: (3)

You are going to get a lot of reversion in the intake manifold from the VDI being open that soon...or at all. I would try leaving it closed on a turbo car and see what happens. I have my APV open all the time as well.....

Brettus

iTrader: (2)

reversion ? So far i cannot detect any differences from having the vdi opening earlier .

Having the APV staged rather than open all the time has to be a better solution for low rpm runnng ....

Kane

iTrader: (1)

Remember - the motor's power curve is based on air velocity into the chamber. The velocity is determined by the pressure differential of the motor. Air will only move as fast as the DIFFERENCE in IM and chamber vacuum.

So if you open the ports too early; you are in essence reducing the differential and hence airflow into the chamber. You can make that up with more boost - or you can keep the excess valves closed longer. Basically; you trade top end for bottom end (simply speaking).

So - if you left them closed all the time your top end would suffer but your bottom end would be better. And vice versa. The question on tuning them is to determine the moment when the intake becomes the restriction - and open them at that time.

Ready.... go.

Brettus

iTrader: (2)

That's why i thought opening them at the same maf as on an n/a engine would be the right rpm to do it at as velocity should be the same ....

Kane

iTrader: (1)

No - cause the pressure differential is different.

With your boosted motor - you have two issues; pressure and engine speed. The faster a motor spins the more air velocity it will generate - and boost causes more air velocity as well.... but with a lower engine speed - so kind of a catch 22.

I would run two MAF pulls - one with everything closed and one with everything open and see where they intersect.... that would be my target for additional ports - and then work from there.

Brettus

iTrader: (2)

Another good reason to open them at where i have them is so that they stay open when running through the gears - keeping the afr's more stable ..... perhaps ?

Kane

iTrader: (1)

It does simplify things.

MazdaManiac

iTrader: (3)

I keep the VDI closed, open the SSV in the usual place and open the APV later.

BTW - its the opening of the APV that makes most motors knock (because of the sudden change in load and AFR), so I figured getting that sudden change a bit further up the RPM band than the torque peak would be a good idea.

Brettus

iTrader: (2)

Interesting - I figured opening it before the torque peak would have the same effect (on knock) .

MazdaManiac

iTrader: (3)

Except you run into the same problem you found in opening the ports early.
On the 3071, it is less of a problem (because of the increased flow capacity), but it is still better to keep the pressure up in the turbo's efficiency band, rather than falling to a lower pressure at an equivalent flow.

Brettus

iTrader: (2)

I think in that case (for my turbo) it could be a good thing as i will up the boost earlier on in the rev range thereby increasing the efficiency at that point .
The only reason i dropped the boost was because I had too much power in the 4000-5000 rpm range - now i can run that boost and more to get back to where i was ...

MazdaManiac

iTrader: (3)

I'm not really sure how that is possible, but I guess I'm running bigger tires than you.

Brettus

iTrader: (2)

/\ yes - i'm still on 235/40s

MazdaManiac

iTrader: (3)

I've got an extra 3" or rubber on the ground.
I'm also fairly smooth with my throttle inputs and I've recalibrated the throttle response to better suit FI.

ChrisRX8PR

iTrader: (1)

Here is my take on your situation. The turbo now has to fill 6 ports worth of air instead of 4 which means that if you can't spin it fast enough at that rpm(I doubt you can't, this would be with a much larger turbo) you will build boost slower. Also, the APV ports are not very efficient in that range because they allow air to escape the chamber before the rotor closes over them effectively reducing the amount of air that gets compressed and ignited, resulting in a loss of power. These ports are meant to be effective at higher engine rpm where the air has no time to run back out before the rotor edge passes over the port.

I would say that on a turbo car the trigger to open up the APV ports should be based on boost and not rpm, even if it looses a little bit of power from opening earlier. That way the lean spike issue goes away(which could break an engine under enough boost) because if you open them at say, 7psi of boost, then when you tune all there is to do is have the required fuel come on at 7psi and this would take care of the dip. I experimented with this using an electromechanical actuator for the APV I made on my own and it worked good. And when you aren't in on the throttle it doesn't open, just like the stock car. Regardless, in the end I ended up just leaving the APV open at all times because the power difference it made before boost came on wasn't all that huge to justify the complexity of a separate APV actuator. Now if the Int-X where able to open and close it then it would be worth it. Even with all ports open the engine idles fine under 900rpm and has no problem moving the car from a stop or while cruising.



Chris

olddragger

iTrader: (3)

i wonder what happens on a s/c engine when keeping the apv open? I know boost is boost but would the changes be any differant? We are looking at opening the ssv a little earier as there may be a little boost building going on.
OD

MazdaManiac

iTrader: (3)

It still amazes me how people just can't wrap their heads around the idea of flow and still think in terms of "boost" pressure.

The IM was designed to flow air up to 102% of engine Ve at 1 BAR.
As soon as you exceed 1 BAR, you are no longer at the mercy of pressure.

Its not filling a glass with cola.

Brettus

iTrader: (2)

Here is a chart illustrating what I was talking about .

MazdaManiac

iTrader: (3)

Uh, I say go with blue?