EFI University

[mrx]

Hallo,

while tuning my engine today i saw something which raised a question.
At WOT under boost (1,2bar pos. pressure) i see a steady Tq Drop after 5500rpm towards redline at 8000rpm.

The Tq falls almost 60Nm in that area. (boost drops also -0.1bar but still, 60Nm is too much)

From my inj. PW and Lambda i can say that VE is not falling of. In fact at 7300rpm i have maximum VE.

First i thought about a restrictive turbine as i have a rather small one on that engine .48ar T3 on a B16A1 engine.

But if the exhaust pressure would be too high (could not measure actualy) the VE should also drop - or not?

So in thought maybe my ignition advance vs. rpm could be too low.
The engine has an 8.5:1 CR and at the above mentioned boost level i run 22°BTDC @ 5,5k up to 28.4°BTDC @ 8k

Do you think that he maybe need's more timing?

Fuel by the way is ROZ98

[stevesingo]

Friction or other parasitic losses within the engine?

Losses from car dyno interface, unless it is an engine dyno?

[Turboivo]

IMHO max VE should be around max Torque rpms. I guess you tune on dyno. Can't you find the best spark advance by power/torque lines overlay after every run?

[Johnny_9]

Is the torque curve (after the drop) jagged? If so too much timing.

[mrx]

In fact it's realy a bit jagged.
I took a closer look on the ignition values and saw a raise in Spark Advance when the jegging begins. I will try to reduce ignition angle in that part and see if it helps.

Unfortunatly haven't seen it during the dyno session yesterday

But in the past i've also seen some jagged tq figures from too low timing.
Couldn't explain that to myself why 4-5deg more timing helped and also didn't felt compfortable with the absolute values but it helped.

Does someone have an explanation for that?

This was also on NA as well as on Turbo car's.

[Johnny_9]

Be interested to see the topography of your torque curve and related ignition map.

The theory: as combustion approaches detonation, the combustion pressure rise becomes unstable/irregular; detonation burn speed/ is 100X faster normal burn

[fire]

What fuel pump do you have?
This is tipical when your fuel pump is to weak.

[mrx]

[sohc_mshue]

I see this often on cars that have a fuel flow issue. Pressure drops as rpms increase. Even though your VE may be dropping there is still a greater demand for fuel flow in high rpms because you are turning more engine cycles in a shorter time. If the pump cannot keep up or there is a restriction somewhere then pressure will drop rather than holding flat and cause you to need a higher pulsewidth at high rpms than at peak torque.
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efi101/102 graduate

[Turboivo]

[Roberto Arano]

monitor the rail pressure throughout the entire pull (with respect to accurate VE calcs)
_________________
www.circuitse7en.net
http://stores.ebay.com/Circuit-Se7en

[Johnny_9]

Moral - Fuel Pressure is an vital variable to log, when calculating VE.