Twin Turbo LFX Impressions

[Rhino79]

Yes, we may even be in a situation where we could have to reduce these values. The tables we see are just a touch of the complex calculations in the background of an e39.

[Matt @ FSP]

Originally Posted by KMPrenger

So to recap, here is how I see it. Tell me if I'm wrong lol.

Stock tune only allows so much throttle input either up to a certain rpm or MPH. If you take the table, and "max" it outs...it will basically do the same. In other words...it doesn't like it.

So instead, you take the tables and increase those values up from stock, but less than max until you find right where you want to be?

If that is the case, could an LFX owner running a full bolt on N/A but untuned (or perhaps tuned but with maxed out tables) run into this same problem??

Pretty much KM... A STOCK LFx will not have wide open throttle until about 4k RPMs (It flutters in the 55-60% range), then it's fine from 4k to redline. Once you add boost or other modifications, it will start reducing throttle even more because you are over the calculated torque. Then you'll also have the issue upstairs too. So those tables you need to modify just a bit until you achieve the full throttle, these in HPT are called driver demand maps, it's under ETC.

ALL the new Gm calibrations, whether or not V6 or V8 are now based upon calculated torque removing actual throttle position to meet the actual driver demand torque.

Here is the example of the driver demand tables, you have to watch how far you go with these. As you can see the first table below is stock and the second one is a modified SC tune. Before I modified that the throttle would start closing down to 40-50% over 6000 rpms.

[KMPrenger]

Appreciate that info guys.

Pretty easy then to see how the car might fall on its face at launch, or fall on its face on the other end of the strip when you hit say, 4th gear.

I'm not sure I understand why GM would limit throttle input under 4,000K rpms. Is is really all about reliability, or do you just really not want to send 100% throttle until you are up and moving?

I can remember other times in the past where V6 owners at the strip would complain about how it felt like their car just seemed to slow up towards the end of the 1/4 mile. Makes me wonder if things like this were the case, and the tables needed to correct the issues were never altered....maybe nobody every had access to them.

Anyways, glad to see you guys digging in to this on the LFX.

[Matt @ FSP]

Also.. Here is a quick clip from some logs..

** JUst a note, because of how the scanner reads the signal, 84% Accelerator Pedal and Throttle Position is WIDE OPEN throttle.

Notice in the first screenshot, that the Accelerator Pedal Position is 84% (Wide Open), however the Throttle Position is at 59% and the ETC Commanded TPS is at 67% (ETC Commanded is read on a 0-100 scale, that is why it is scaled up a bit from actual TPS). So YOU are commanding full throttle with your right foot, but the ECU is pulling it back from being wide open because of the calculated torque being higher than what the ECU will allow at that pedal position vs. VSS.

Second Screenshot: Notice that the Accelerator Pedal Position is 84% (WOT), Throttle Position is 84% (WOT), and Commanded ETC is 100% (Commanding WOT). Thus now we are at full throttle commanded and actual full throttle mechanically. You'll also take notice a few more items in the log such as ETC Source : Torque (This means the Electronic Throttle Control is being controlled by Torque).

[Matt @ FSP]

Originally Posted by KMPrenger

Appreciate that info guys.

Pretty easy then to see how the car might fall on its face at launch, or fall on its face on the other end of the strip when you hit say, 4th gear.

I'm not sure I understand why GM would limit throttle input under 4,000K rpms. Is is really all about reliability, or do you just really not want to send 100% throttle until you are up and moving?

That is a good question, I do not know GM logics on this one. I was originally thinking someone to do with saving the 6L50E transmission from abuse down-low, but the manual cars have this same affect...

Here is a graphic log showing the the ramp up of throttle position, then full throttle, then ramping it back out. This is stock GM logic on a supercharged LFX. I don't think I have a save of the stock bolt-on one that I did showing the reduced throttle under 4k rpms (But this one did have full all the way through, the SC car removes it upstairs because it goes above the calculated torque vs. vss)

[KMPrenger]

Very cool. So now I can see exactly why in many cases, so much extra torque can be gained in the lower rpms with a tune. I love this stuff.

[GretchenGotGrowl]

Tunes are installed and I have sent some logs to Ryan. Overall, I think we made some good progress on the pull to 40 MPH, but some other issues cropped up. Great first try and I'm sure we'll get everything worked out. May be quicker for me to just take the car back to his shop and let him do it, but right now it is giving me a chance to learn the EFI tool (way different than the old version I used).

[TJ91]

Wow. This is some very cool information. I wonder how much more powerful my car would feel without this limitation. Always hated that lag type feeling
Definitely going to get a tune if this can be tuned out. This is my new reason for a tune lol

Btw great work guys. Wish someone could write an article on the work you guys are all doing together. True car guys

[SC2150]

This is whats needed to sort these out....excellent input from all.

[etmx183]

So any final input on this issue. My LFX really delays WOT until around 4500 RPMs

[JantzenOKC]

Originally Posted by etmx183

So any final input on this issue. My LFX really delays WOT until around 4500 RPMs

+1

Would really like to hear what Ryan has to say about this.