camcojb

OK, I got the stock motor tuned well with the twin turbo kit and 8 psi of boost. But I have a 402 turbo-specific engine sitting here so I installed it this weekend.

I am using the HPTuners Pro system and I have the 15000HZ patch in. As soon as I go WOT the HZ jump to 12700-13000 or so. The car doesn't shut off but acts like it has a rev limiter on it. The rpms in this case were about 4800 but it won't accelerate, just barely speeds up.

A/F is not completed yet, but at WOT was 12:1 or so. Boost was only hitting 9 psi as the engine won't accelerate at all.

With the 15000HZ patch you still have nothing past 12200 hz to tune with. Seems like too much of a coincidence that this is exactly where I am having problems.

Has anyone here tuned an LS2 with a maf past 12500 HZ or so? Is it possible that since I am exceeding the maf table it is limiting the engine?

Jody

SMOKINV8

iTrader: (6)

You may be hitting the max MAF value in the PCM. Does anybody know if the table maxes out at 512g/sec on the gen IV PCM?

camcojb

With the patch the max is 15000HZ and I saw a max of about 13000 on the log. It did hit 469 g/sec so it it close to the 512 g/sec max.

Jody

RedHardSupra

iTrader: (1)

i've seen a base sts system (5psi) max out 512g/sec below 5000rpm, so i'd say you're gonna max it out even faster. either way, it's useless. for FI go 2 or 3 bar SD

camcojb

Great idea, except nobody does sd for LS2's yet.

Jody

GuitsBoy

iTrader: (4)

Hate to say it, but how about porting out the MAF to get the Hz down to a more readily acceptable level? My ported MAF table is about 140% scaled from stock. That means the freq. is only abouyt 60% for any given airflow. Just an idea to throw out there.

RedHardSupra

iTrader: (1)

how does this prevent hitting the upper limit of airflow?

you're shifting values on the MafFreq axis, not the AirFlow axis. if you can put more air in, that is just gonna cool the hot element of the MAF easier, forcing the MAF to command bliping it with voltage more frequently.

that's the ultimate download of MAF setup on our PCM's, not the size, not the frequency range, not MAF itself really, but just the number that is used to describe MAF's capacity in the PCM.

it doens't matter at what rpm you hit the limit either, we have this artificial ceiling, and MAF's are only useful when you make power less than what you can get out of 512g/sec of airflow.

GuitsBoy

iTrader: (4)

So the limit is the 512 g/s? I though the limit he was running into was the frequency (at 13500 or 15000).

But in theory, enlarging the cross section will decrease velocity for the same volume, this slower moving air will not cool the hot wire as quickly as a faster velocity would. This of course is why porting a MAF leans out a cam, and boosts timing as the motor sees a lower engine load. Im sure this is obvious to you, but its not what you stated above. Of course if you scale the MAF table and it hit the 512 ceiling it does no good.

RedHardSupra

iTrader: (1)

yes, the PCM's MAF airflow limit is the ceilling, as it effectively locks us to a certain number of hp we can account for! it's like in WRC(i think Nascar use it for some tracks too) when they use air restrictor plates to limit how much power you can make. they do it mechanically, our PCM does it to us electronically.

i'm not quite sure what does extending the range of frequencies does (do you get more cells or just a higher number?) if you get more cells, then it would be smoother at least, as you'd have more precision stemming from less need to interpolate, or at least interpolate between numbers that are closer together.

camcojb

I haven't hit 15000 HZ or 512 g/sec yet. I hit 13000 HZ or so and it acts like a rev limiter; I've seen 470 g/sec at 4800 rpms, so I will likely peg that once I figure this other deal out.

Thinking of putting the GTO back to stock and selling off the car and mods. Keep the 402 LS2 for my 67 Chevelle. Never figured I'd be so limited with power on this thing.

Jody

RedHardSupra

iTrader: (1)

470g/sec ain't much, i've seen NA 347's flow more than that. so i'd say you have a leak or you're making like 2psi max (which would be a result of a leak).
you got any logs/bins you could send me?

camcojb

The most I saw with the stock LS2 and 8 psi of boost was 390 or so, and that was at the top of third gear. So seeing this much more on the initial wot at a much lower rpm says it may peg, but at least it's much higher than the stock motor at 8 psi.

No logs to show yet, gonna look at a few more things.

Jody

Project GatTagO

iTrader: (7)

Now your talking!

Andrew

camcojb

Hey dude, what it be! Hope all is well.

Jody

camcojb

Dropped the boost as low as it would go (8 psi) and it seemed fine, though my maf lb/min maxes at 61.04 and stays there throughout the run. That equates to 462.42 g/sec, but it appears maxed to me as it doesn't wiggle one bit during the run even though the rpms climb.

If I go to any more boost the car breaks up and does the "limiter" thing. I can't meet the max 512 g/sec because the maf lb/min locks up at 61.04, but I'm sure something in here is the issue. With the extra boost (1-2 psi) it breaks up, lb/min still stops at 61.04. But the bank 1 O2 goes lean off/on, the HZ have spikes down to almost 0 from a high of nearly 15000.

Does this sound like a maxed maf issue? Is there a way to fix it with an extender? Is the max of 61.04 on the maf lb/min a symptom of a maxed something, or just as high as it can read?

Jody

camcojb

OK, raised the maf HZ fail to 16384 and that helped. Short of finding a way to extend the maf readings 10 psi is at the limit with this 402. When I go to 11.5 psi it maxes the g/cyl and the MAF HZ.

Kind of a bummer having a motor that can run 18 psi or more and be limited by tuning to 10 psi (and probably should be dropped to 8 or 9 as 10 hits too close to the limits). When I built this engine I knew HPTuners was going to have the LS2 tuning. I did not know they wouldn't have 2 bar speed density with it though. Not blaming them at all, Chris and Keith have been great. I didn't ask the right questions!

Jody

camcojb

Okay, caught a bit of dry weather so I went out to see if the changes made a difference. Now I can go 12 psi without issue. I was lean, so I changed my PE table where it was pegging the maf and took a shot as far as how much richer to go. First try hit 12.0 A/F in top gear at wot.

This is on the 8:1 402 so 12 psi is not pushing it at all. I can say though that even with the 285 dr's a downshift to second at 50 mph (auto trans) will spin the dr's; first time I did it the car went sideways. It's never done that before with the drag radials.

The changes that worked were setting the maf fail point to 16384 which is as high as it can go, plus shutting off the high maf dtc's. The 15000 HZ patch stops reading beyond that and so you adjust your PE tables from the point you max the maf and set the A/F that way with a wideband. Biggest issue is you'll probably need a different tune for different boosts, but once you set them all you're set. My thoughts are this will work fine until HPTuners can do a SD 2 bar setup for the LS2's. And I don't change the boost very often. I'll find a level that keeps me happy and stick with it.

I am going to swap springs in the boost actuators to try 14 psi just to see how it reacts. Thanks again for all the help guys.

Jody

gametech

iTrader: (1)

As a work-around for the 512g/s limit, could you port the maf as suggested earlier, but then fiddle with the injector flow rate tables instead of the maf tables in order to trick the computer into proper fueling? This way the computer would believe there is less airflow than the 512 cap, but the injector scaling would allow you to fuel it properly for the real airflow. I haven't looked at the ls2 pcm yet, so I may be off-base.