Friday, March 02, 2007

LS2 airflow uncorked?

I'm not sure if anyone noticed this before, but when you're tuning LS2's with the new funky GMVE units, they go up, reshape, but ultimately reach an early upper bound of about 2500. I always wondered about this, as it made no sense, most LS2's VE table and the resulting airflow would not reflect the real torque and horsepower gains.

Today, completely by accident I find a table called Maximum VE, sitting right there under Airflow->Dynamic Airflow. In EFILive, the symbol is {B2030}.

I open it up, and low and behold, it maxes out about 2500, with a peak at 4400-4800RPM, just like most LS2's peak torque. I quickly punch in some numbers into a spreadsheet, to see what kind of Dynamic Cylinder Torque am I going to see. Again, everything agrees with near stock LS2 numbers, around 0.85g/cyl airmass at peak.

This little spreadsheet also shows how much airflow you'd see with these airmass numbers at given RPM.

So I grabbed some recent logs from a well flowing, healthy, well tuned big cam LS2, and started charting max Dynamic Cylinder Air vs RPM. To make this task easier, I try to find a table that's already preconfigured for the same RPM intervals, as the VE Maximum table. Not only I found the VE Maximum table, but I also found few other tables that seem to pertain to the same problem: Maximum Airflow vs RPM, Maximum Airflow vs IGNV, and Maximum Airflow Delta vs TPS. They're all set up to deal with stockish power, 280g/sec (37lb/min) airflow, and small MAP and Airflow deltas. On the editor side of things, you can find them under Engine Diagnostics->General->Diagnostic Tests. In EFILive, the symbols are {C0803} to {C0806}

I quickly eyeballed what the numbers mean, and what they should be set to more realistically, and came up with this:

So this should work for most NA LS2's. I hope this is the limit, because it would explain a lot of issues I've been having tuning a large cam LS2, and the more airmass we'd get, the more timing would get pulled without a reason. Hopefully this is yet another Torque Managment issue, this time trying to save the engine from too much torque by pulling timing when hitting airmass/airflow limits. With this

The problem is that I still don't have a local access to a damn LS2! Anyone around Monterey wants to be my lab rat and get their car tuned in the meantime?

Anyway, I need you LS2 folks who have already braved the weird VE table and are running abyssmal timing to prevent it from Knock Retard, this might be your solution. I need you to change these limits that I posted pictures for above, and watch what happens to your Dynamic Airflow and Dynamic Cylinder Airflow. I'm predicting it's going to go up a significant amount. This means it might need a retune. Suddenly you'll be using deeper regions of timing tables, so please alter them accordingly.

Of course, this is all liability free, you're ready to blow up your engine, yadda yadda yadda, can't sue me stuff...

Please report back with your results, they're absolutely crucial as I don't have direct access to a LS2. The best way to do this would be to have a before and after pairs of logs and tunes, with the only change in between being the changes I recommended above. Remember that because you're going to 'uncork' your LS2 vehicle, you will probably experience lean conditions so please proceed carefully, set your PE ratios on the rich side with a healthy amount of safe margin.

The great thing about all this is that you will possibly be able to get more timing out of it, and get even more torque. So far I've had to cut down the timing on the big cam LS2 I've been helping with lately to below 20* to get rid of most, but not all knock. Without limits, the preemptive KR should disappar, airmass and airflow should skyrocket, timing would not have to be severly limited to push the airmass under the 'safe' limits.

This should really help. Airflow numbers should be realistic, torque should improve, and we'll all support the economy by buying new tires and clutches.

Got airflow?


At 9:12 AM, March 03, 2007, Blogger Glenn said...

would you mind posting your spreadsheet?

At 10:56 AM, March 05, 2007, Anonymous Gib said...

So, my tables should have the same numbers as those above, regardless of what my mods are? You say that should work for all NA LS2s...I'm just a bit confused....

At 12:36 PM, March 05, 2007, Blogger Marcin said...

since I assume these are the limit tables, just up them to the limits that would make sense for your application. the numbers i posted should work well for any stock cube NA applications.

At 1:42 AM, March 07, 2007, Anonymous Anonymous said...

Max VE in EFILive V2 is 500%. Would I still put your "400=1891, 800=1971..." in Max VE?

At 2:00 AM, March 07, 2007, Blogger Marcin said...

no, % and the 1891... numbers are two completely different units. in EFILive you have the option of displaying your VE table in 4 forms. if you're seeing %, that means you're viewing is at the traditional VE (theoretical flow), so change it to the native (g*kPa/K) units so you can be on the same page. LS2's GMVE units are actually much better, even if they're not as easily grasped as the traditional VE.

At 9:57 AM, November 10, 2007, Anonymous Steve said...

What would you recommend for forced induction applications? The same mods to the tables, or different mods? I'm running a twin turbo '05 GTO here.


At 10:29 AM, November 10, 2007, Blogger Marcin said...

turbo applications make it totally different, it depends on so many variables that i wouldn't brave guessing any numbers. this one you'll have to figure out empirically.

At 3:00 AM, June 03, 2009, Anonymous Jay said...

I made all the changes except for VE maximum Table and was wondering what numbers i should have in there.


At 4:01 PM, July 05, 2009, Anonymous MrDrezzUp said...

Has this been tested? Are you still looking for a test candidate? I have a LS2 with 500+ RWHP NA that can be tested on.

At 4:04 PM, July 05, 2009, Blogger Marcin said...

I've tested it on few E40 GTO's, and it didn't seem to make any difference.


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