Truth about turbo positioning

[VitViper]

Originally Posted by jsimon7777

Where is the power cost? In that 700-800 rpm or above? Why?

The whole time during spool up, so in the 700-800 range -- the sooner you want to bring the turbo in the more aggressive you have to be with injection timing & ignition timing. Super late injection timing actually leaned the motor out significantly and I had to add some fuel volume compensation logic in there.

The power loss varied from levels of 'nuisance' to 'terrible', depending on how I chose to run the settings. Initially you'd start to feel very slight hesitations as you got more aggressive with the settings, to downright falling on it's face before the turbo hit target boost.

There was a power gain once the turbo hit the boost target -- which it is doing 200-300 rpm sooner than normal.

So look at it this way. Normally my turbo makes full boost at say 4500 rpm in 3rd gear. I do a pull from 2k rpm it will start coming in sooner and make 1.5-2.5psi more and and roughly around 4200 rpm it's at peak boost. below roughly 3600 rpm it's nothing but losses, that you can feel. 4200 to 4500 rpm would show a slight gain.

Pretty pointless really as no one is doing these kinds of pulls... and a 5862 isn't exactly super easy to move at low rpm's with this motor anyway.

From my test on my car, I would say the injection timing had minimal effect on spool -- the ignition retard had a huge effect, as expected. However, if you pull timing, you lose power. Small amounts of timing retarded (depending on fuel, 5-10*) have basically no impact on turbo spool, so by the time you've pulled enough timing to spin the turbo up you've lost a lot of power and are actually accelerating quite slow...

Transient response between shifts stayed the same (7500 rpm shifts) regardless of what I did.

I would say my rolling anti-lag is much more useful if you want to do a roll on hit at like 4500 rpm and have the turbo already 'on'.

Originally Posted by johan

This is the joke....

The joke is on everyone.

OEMs do this so they can claim their turbo engine has xyz torque from 1800rpm - 6000rpm. Doesn't matter that it destroys transient response.... because numbers win for marketing.

You can feel it on the OEM's -- you'll get some shuffling and light hesitation sporadically. The cars don't feel "smooth" when you drive them.

Granted the test on my car may be kind of the extreme -- I'm using a way larger turbo than the OEM's do. With a tiny donut turbo you may be able to use the injection timing & timing retard for a short period of time (in the milliseconds) to help spool up. But this still really goes back to boost control IMO...

Remember your Acura RDX? I've got quite a few customers with those now... the OEM programming loves to run negative timing during spool up events... once you eliminate that everyone's reported how much better the car drives and feels. LoL.

[EAGLE5]

Thanks. That's clear. What would an extra injection of DI fuel, timed to burn while exiting the cylinder, do?

[VitViper]

Originally Posted by jsimon7777

Thanks. That's clear. What would an extra injection of DI fuel, timed to burn while exiting the cylinder, do?

The idea is to burn it as late as possible to create heat -- boom, better turbo spool. I don't think just moving the injection event alone will do it -- it has to be combined with an appropriate response from the ignition event as well.

The problem is it feels like crap when you do this and I find it hard to believe anyone could argue there is zero power loss when retarding the ignition timing event.

[Anthony7515]

[ame="https://www.youtube.com/watch?v=rnfITOnrV48&spfreload=10"]Subaru brz turbo 3rd to 4th gear pull. - YouTube[/ame]