LNF Mod Primer

[wspohn]

This post is just to sum up the results of some interesting discussions about the LNF engines in the GXP and to perhaps act as a primer for newer owners wondering about some of these issues, and how they relate to the claims of advertisers trying to sell them products to enhance performance.

The GM programming is based on torque limiting. There is a table in the program that sets desired power, and the ECM adjusts boost, cam timing, throttle position and ignition timing to hit the targets. It doesn’t matter what you do to the engine in the way of ‘power improvers’, the ECM will always adjust down to the preset power (actually torque) targets. You get 260 BHP and 260 ft-lbs. no matter what you do to the engine.

The programming does not react instantly to changes, but rather learns new inputs over several start/run cycles, so that when you first add a power mod, you may indeed see an increase in output if you put the car on a dyno immediately, but that power will go away as the ECM learns back down to the preset level.

GM offers a second tune, the GMPP upgrade, often called (but not by the factory) the stage 2 tune. This does not eliminate torque management, as that is fundamental to the program. It bumps power and torque significantly to 290 BHP and 340 ft-lbs. This may not be felt the first time you fire up the car, but the learning sequence will take place over several key cycles.

On this tune I defer to Bill Duncan, a GM employee, who explains it thus:

There is a calculated torque model that uses all the inputs pressure, temperature, rpm, throttle position, spark advance, cam timing...etc. If it sees that you have an under performing engine, maybe due to the CR being at the low limit then the program will add power until the original power level is acheived. That is the learn up portion. There is also a learn down portion that if the torque model see there is too much torque, usually due to an add on, it will learn out the torque until the original power is restored. The GMPP Turbo upgrade kit turns off the learn down portion of the torque managing program. Therefore it will not learn out add-ons such as CAI or Exhaust systems. What most people are mistaking as learning out/Learn Down, are the safetys that are still in the software and still active. These are there to help guarentee the system is durable for the 100,000 mile warranty and parts are not damaged. There is still an overboost protection, there is still a program that is calculating what the turbine speed is and will limit boost if you approach the maximum allowable speeds. So as an example if you change the turbo and are getting much higher boost you will engage the overboost protection.

Advertisers do not generally lie about this situation, but they do mislead by advertising the temporary improvements they no doubt record by dyno after installing their product – they just forget to tell you that this improvement is temporary and will go away after awhile. Any mods you buy for the basic factory GM tuned LNF should therefore be done for aesthetic not power considerations. If you like the sound of a free flow exhaust better, that’s great, but don’t be fooled into thinking you are gaining any (permanent) power from doing it. The GMPP tune OTOH would give additional benefits with mods.

To get any improvement in power that would violate factory safety values requires a non-factory tune for the ECM. The disadvantage of this is that it can be used to deny warranty coverage if something goes wrong with the engine – and high output 4 valve VVT engines can be VERY expensive to rebuild, so this is a serious consideration.

After market programming comes in many different flavours, some requiring that you unplug the ECM (be careful, very delicate contacts not intended to be plugged and unplugged often and if you bend/break one a $400 bill), or buy a special tuning unit and software for installation. Some offer a so called ‘stealth’ feature where GM is apparently unable to detect the new program when they plug into your car for service, while others require that you temporarily unload the after market tuning files and restore the GM program if you need to take it in for service.

The feature of all of these after market tunes is that you can at last get some benefit from mods done to the engine. They can’t eliminate the torque management, which is fundamental to the operation of the GM system, but they can ‘fool’ it by replacing the stock values with much higher values such that the system no longer limits torque to any figure realistically attainable by tuning.

With these tunes, and with teh GMPP tune, you can take advantage of mods and actually get some of the power promised by the manufacturers of the parts.

Hope that helps clear up some of the misinformation that keeps appearing regarding these engines.

[Seldom Home]

Thanks for putting it in language that I can understand.

[wspohn]

Information updated.

[I1ULUZ]

Originally Posted by wspohn . To get any improvement in power that would violate factory safety values requires a non-factory tune for the ECM. The disadvantage of this is that it can be used to deny warranty coverage if something goes wrong with the engine – and high output 4 valve VVT engines can be VERY expensive to rebuild, so this is a serious consideration.

$3500 for a complete new crate engine, that includes turbo, injectors, etc... is a really a good deal for those that melt or hole a piston. The engine bay is wide open so swapping one out should be easy. I think less than a Saturday would have the swap done.

[wspohn]

Agree that is a heck of a deal, but that won't be available forever. Plus I'd rather it be GMs $3500 than mine, if it came to that.

We all paid a substantial amount for a warranty, factored into the sticker price of the car. Some don't lightly throw that away....

[LowLife1]

I agree, thanks for posting in a easy to understand style.

[Kappster]

HUH?
Since supposebly the 2.4 has the same drivetrain set-up I wonder why GM sets the torque controllers so low for it.

[wspohn]

The 2.4 isn't a turbo engine so boost isn't controlled, right?

Without turbo, the NA engine produces whatever it is capable of, depending on the usual things - compression, ignition, cam timing....

[DEJON-Dave]

Tunes & Torque
The Trifecta tunes we sell are able to increase boost and torque to whatever the customer wants and the turbo is capable of, effectively eliminating learn down and limp mode. You can get whatever power your mods are capable of. The real limit is the small factory turbo which cannot deliver enough air to maintain high boost levels at higher rpms where the engine can intake more. So with the factory turbo you can get very high torque at low rpms but it cannot hold it across the rpm range.

With LARGER TURBOS and their different wastegate actuators, we are able to get higher boost levels and hold them till redline. The Trifecta tune again can give you whatever you want and the turbo is capable of. We can (DEJON Tune)supply a modified factory tune (for factory sensors) that will do about 23psi and is limited by the factory tune's limp mode. We can supply a modified GMP2 tune (for cars with the upgrade) that will do about 26psi and is limited again by limp mode.

[snaponbob]

Dave, thanks for jumping in with that info. Would you happen to know how the Cobalt/HHR crowd is achieving and maintaining higher boost levels? That is what started all the hoopla in the Kappa community.

[DEJON-Dave]

Originally Posted by snaponbob Dave, thanks for jumping in with that info. Would you happen to know how the Cobalt/HHR crowd is achieving and maintaining higher boost levels? That is what started all the hoopla in the Kappa community.

Trifecta's tune which I can sell for Sol & Sky but not for Cobalt SS because he has an exclusive agreement with another vendor. I run the Cruise switched version on my car with the 16g kit and switch between 20psi (stock Mode) and 25psi (Power Mode). I can run higher, but am satisfied with 25psi. I can also increase it myself with HP Tuners if I want.

[mkriebs]

The Trifecta tune is black magic compared to HPTuners (til we get an unlocked ecm... **AHEM**).

As for the reference to the Cobalt HHR community, the only way we (yeah, I own a Balt) are getting RELIABLE higher boost is through Trifecta. Many people are running wastegate line restrictors, and the ECM reacts by closing the throttle to limit the boost. It works to a point, but hasn't proven to be very reliable.

Also, very well written Wspohn The only benefit to aftermarket parts on the stock tune is maybe a bit faster of a spool from the turbo, resulting in a little more responsiveness. Sadly.

[snaponbob]

Originally Posted by mkriebs The Trifecta tune is black magic compared to HPTuners (til we get an unlocked ecm... **AHEM**). As for the reference to the Cobalt HHR community, the only way we (yeah, I own a Balt) are getting RELIABLE higher boost is through Trifecta. Many people are running wastegate line restrictors, and the ECM reacts by closing the throttle to limit the boost. It works to a point, but hasn't proven to be very reliable. Also, very well written Wspohn The only benefit to aftermarket parts on the stock tune is maybe a bit faster of a spool from the turbo, resulting in a little more responsiveness. Sadly.

Please specify what you mean "unreliable" in reference to wastegate line restrictors? Also, hopefully you are not including a downpipe as an aftermarket part that has little benefit, because it absolutely does have a significant positive effect as does a low restriction exhaust vs. stock.

[DEJON-Dave]

[quote=mkriebs;904713]The Trifecta tune is black magic compared to HPTuners (til we get an unlocked ecm... **AHEM**).

I think "Black Magic" is a misnomer. Vince is a former Microsoft programmer who probably understands the code better than HPTuners (and I sell both so I'm not biased). He can lock his tune so that HPT cannot download it, which is something Lyndon Wester wishes he could do, truly eliminate limp mode which is something HPT still does not fully allow and has written a dual tune that the driver can switch between. I think that's far more advanced, not "black magic"

[mkriebs]

[quote=DEJON-Dave;904761]

Originally Posted by mkriebs The Trifecta tune is black magic compared to HPTuners (til we get an unlocked ecm... **AHEM**). I think "Black Magic" is a misnomer. Vince is a former Microsoft programmer who probably understands the code better than HPTuners (and I sell both so I'm not biased). He can lock his tune so that HPT cannot download it, which is something Lyndon Wester wishes he could do, truly eliminate limp mode which is something HPT still does not fully allow and has written a dual tune that the driver can switch between. I think that's far more advanced, not "black magic"

Sorry if I cam across as bashing it. I LOVE what Vince is doing, don't get me wrong. His ability is obviously awesome, and I know he is capable of more. But I meant black magic as opposes to HPT, because he can do so much more awesome stuff. It was a compliment for sure.