C6 Vette LS9, LS7 and LS3 guys... You're gonna want to see this

[gmtech16450yz]

I wasn't sure how I should tell this story but WTH, I think I'll start with a little quiz! Look at these two log screenshots, specifically the MAF readings. Both of these are at the EXACT SAME SCALES and zoom levels. Both of them are from THE EXACT SAME CAR on the SAME DAY and EXACT SAME TUNE. Only one small hardware change was made, nothing else.

The whole point of this thread is to let you guys know about a potential tuning problem on these cars specifically. Actually, this is a problem that isn't new at all, it happens on just about every engine out there to some degree. I'm sure some of you C6 guys have already dealt with this, and it's actually been said about this particular hardware change already before. But I don't think anyone has ever shown hard proof of the problem like I'm showing in these logs. This is one of those hardware changes that when guys do it they're all saying how amazing it is, but it's really not. It's also a good example of how inaccurate the "butt dyno" can be. (This isn't really about peak power, but this is something that is TOTALLY noticeable in the driveability of a car.)

Here's the screenshots. Let me know what your guesses are, or at least what you see that doesn't look right. Remember, these are scaled exactly the same. What hardware change could cause this?

Edit... It looks like it's a little hard to see the PID names. The MAF is the one in purple in the lower charts. Let me know if it's too hard to see these screen shots and I'll try to make them bigger.

[Rocko350]

Edit: In hindsite a ported throttle body could act this way.

Chris

[sevinn]

I have no idea but I'm subscribing so I may as well guess. Propped open radiator shroud? Ported TB?

[Speedforhire]

It's the famed TB spacer that changes the air flow angle...............just a gimmick!

[gmtech16450yz]

I have no idea but I'm subscribing so I may as well guess. Propped open radiator shroud? Ported TB?

Yay! I was a little afraid when I saw a bunch of views but no responses that I wouldn't get anyone interested in this. Good guesses guys, thanks.

This is why it's good to guess and take a chance on looking dumb. I look dumb all the time, that's how I learn! Your propped open radiator shroud isn't it, but it's the closest so far. Here's a couple more clues... The log on top is from an aftermarket part. The log below is from a stock part. And remember it's the MAF readings that we're looking at. Why do they look like that? Are those jagged lines and spikes supposed to be there? What are those spikes telling us? This isn't about the actual values, it's about the "look" of the data or signals coming from the MAF sensor.

I really should have made the title a little more general, instead of concentrating the thread on Vette tuning. This is something EVERY tuner needs to know and be aware of. This is something that has been a common tuning issue not just in the fuel injection era, but has been an issue with carburetors as well. And it can happen on any type of car, truck or engine too. One of THE most common mods any car guy does can cause this problem.

I know someone will get this. It's one part that was changed from aftermarket back to stock. I'll let you guys guess a little more if you want, otherwise I'll just spill the beans if it's not a fun way for people to learn!

[99z28u_up]

Is it a MAF Sensor with no screen versus a Stock MAF with a screen?

Aftermarket air filter/air filter housing?

[sevinn]

Thanks very much for the info and raising the questions. This makes me think it has to be either a new filter in the stock unit or aftermarket filter and housing all together.

I'll sit here with my popcorn and wait for the answer now .

[ProTools4]

Ok I'll play...My stupid guess,

Intake Pipe / MAF ID is so big and also so close to the throttle there is a double whammy effect

and the maf is reporting three different phenomenon at once that happen after Air speed stalls ...aka lack of velocity..:
-air reflection / bounce / backwash / reversion off the throttle plate
-air intake tube size and resonance
-individual runner pulses not fully equalized by the plenum


The MAF reads air volume derived from temperature delta then delivered in the form of a Frequency
if the air is sea sawing back and forth like a DJ scratching a record this could happen.

I have seen ultra restrictive exhaust systems with baffled mufflers do weird things to the maf with bigger cams.
who would put a 106 LSA cam in a 2x 2.25" piped exhaust w/ flowmasters.... honestly?

[OldFartC6]

All ears

[gmtech16450yz]

All ears

Lol! You guys are funny.


All EXCELLENT guesses! A couple of you pretty much got it. Here's the one single change between those two logs...

First log is with an Attack Blue filter.

Second log is with the stock LS9 Donaldson filter.


No other changes, stock airbox. I have to say there is one other factor, but it simply made the problem show up worse. This particular car is a Saturn Sky Redline with an LSA running an LS9 air cleaner and MAF setup. Don't dwell on that though, this problem will also happen on the Vette's, especially if you take the hood thingy off the top of the air cleaner assembly.

It's all about smooth airflow across the MAF. The Attack Blue filter is just like a K&N, it's only really got one layer between the outside air and the filtered air. Take an air nozzle and blow it over a K&N filter and you'll feel all of that turbulence and bursts of air right through the filter. Take a Donaldson filter and do the same thing and you won't feel any of those "bursts" of air. A filter like the Donaldson does and EXCELLENT job of "filtering" the turbulence coming into the air cleaner. That's why C6 guys get surging when they use these Attack Blue or K&N style filters and they remove the deflector above the filter housing. The outside air gets blown into the filter and without the stock style filter to "clean up" that airflow, you get surging.

So you can see that this isn't just about the particular setup in a C6 Vette. "Cold air intakes" that draw air in from the front of the car and through a free flowing air filter will have these same issues. I've fixed issues with MAF turbulence before with screens like one of you guys mentioned, but that wouldn't have worked in this situation. The C6 air cleaner is so short that there's really no place you could put a screen in front of the MAF. And anyway, a screen wouldn't fix an air buffeting problem like this. The 100% fix is to use the stock air filter. Contrary to what some guys think, the stock Donaldson filter works awesome as far as flow. Unless you're over 1000whp I don't think going to a K&N style filter is going to get you ANY power, and as you can see it quite possibly will give you a surge you can't tune away.

Thanks for playing guys! I hope somebody learned something. The other lesson here is to zoom in on your scales and look closely at inputs sometimes. If you noticed, I changed my MAF scale in the scanner to only read low airflows so that the resolution would be higher and make this easier to see. You can still see it with the MAF scale wide enough to see full load airflow, it's just not as noticeable. Still pretty amazing that a simple air filter change could cause this much of a surge and driveability problem. On this particular car, since the outside airflow into the area the air cleaner is in is fairly wide open, it made the problem worse. I've heard people talking before about surging with the Attack Blue LS9/LS7/LS3 air filter so I know it happens on the C6's also.

[Speedforhire]

I'm going to be the devil's advocate and say I disagree somewhat. The first log is idling at 734 and the second one at 949. That difference will cause a variance. The high flow filters are designed to increase power on the top end so this low rpm surging would be normal.

I also would like to know how this log was obtained. I see a lot of tuners making the common mistake of running the cars with the hood open which will cause abnormal air flow around the filter. All tuning should be done with the hood closed or laying flat.

..............but heh; what do I know. I'm just a hillbilly from Arkansas.

[gmtech16450yz]

I'm going to be the devil's advocate and say I disagree somewhat. The first log is idling at 734 and the second one at 949. That difference will cause a variance. The high flow filters are designed to increase power on the top end so this low rpm surging would be normal.

I also would like to know how this log was obtained. I see a lot of tuners making the common mistake of running the cars with the hood open which will cause abnormal air flow around the filter. All tuning should be done with the hood closed or laying flat.

..............but heh; what do I know. I'm just a hillbilly from Arkansas.

Don't look at the values, look at the signal traces. And don't just look at where the cursor line is, look at the WHOLE log. Does the trace from the MAF in the first log look anything like the one in the second log?

These logs were done while driving, if you look at the speed it's at 15.5 mph where the cursor lines are. I don't agree with the "surging is normal" part. Unless it's got a huge cam, which this doesn't, there shouldn't be ANY surging at low speeds or rpm's if it's tuned properly. That's part of the reason why I posted this. On these modern engines it should be no problem having perfectly smooth as stock driveability even at twice the stock power levels. So many guys think these things are normal because of the power mods and bolt on's we all do on these engines. Again, unless we're talking huge cams, you shouldn't lose driveability while gaining power. Surging isn't normal, it means something's wrong.

[Speedforhire]

Well, I stated that I disagree somewhat, not totally. However, your parameters are not the same even though your cruise speed is. Too much variance.

But Heh, it's nice to know that you are one of the very few guys that actually tunes a car correctly.

Let's have a beer sometime and compare notes.

[ingsteve]

LS2 m6, g5x1 114,k&n, fast 102, 1-3/4
I used The velocity ring 102/92 and i removed 80% of surging, same tune....
I have a similar profile of the maf under wot but with less spykes...this can be the air filter as you are saying don't know at idle if i can get the situation better with a different filter...i do have some limited bucking under 950rpm without accelerating...

[Pekka_Perkeles]

Unstable MAF, yes.

http://www.hptuners.com/forum/showth...S3-A6-Corvette

Owner sold the car shortly after my last post.

[gmtech16450yz]

Unstable MAF, yes.

http://www.hptuners.com/forum/showth...S3-A6-Corvette

Owner sold the car shortly after my last post.

Awesome! Thanks for posting!

I read that whole thread, when it was going in the direction of a "bad" or "weak" MAF, I was thinking "That's not gonna fix it"! Definitely not a MAF problem with mine, and you found out it wasn't the problem with that one either.

Yep, that's EXACTLY what I've seen in the past and exactly what I saw on this particular intake with the Attack Blue filter. Cool to see somebody else echo what I was trying to say. These posts were right on the money, I figured they deserved to be copied and pasted here...

"I have heard people complain of surging from just about every type of aftermarket unit out there. Even running the stock LS3/7 air intake and adding a Vette-Air scoop can cause turbulence (I had bad surging, and CEL, with this MOD and it took a lot of time to correct the problem by fabricating a diffuser to prevent the incoming air from being forced directly into the mouth of the air breather. I found that using the Attack Blue filter in the stock housing did not straighten the airflow nearly as well as the OEM Donaldson PowerCore element). GM has experienced customers complaining about surging (and CEL) on completely stock cars. The TBS instructs the tech to not mess with trying to diagnose the problem if the car has any type of aftermarket air breather modifications. If the car has no air breather MODs, then the tech is instructed to make sure there is no air leaks between the shroud and the bumper beam and even instructs the tech to tape over the holes in the bumper beam to prevent air intrusion directly to the mouth of the air cleaner housing."

Another post on CF:

"As only part of my engineering background dealt with air control I think I remember the part about turbulence in a closed system being a function of shape and directional speed of airflow. 70 MPH is about 1500 RPM and only requires about 165 CFM on a LS3. That's roughly 4 CFM per square inch of filter face area. The stock LS3 filter is about 3-4" thick with around 100 passages per square inch, which gives plenty of time to difuse turbulence on direct inlet airflow at most any speed and create nearly linear airflow which is then directed by the housing shape prior to passing the MAF.

The surging happens when that airflow is not evenly distributed and/or perpendicular to the face of the filter. Pre-filter turbulence causes differential pressures post-filter in the same manner as putting your hand out the window to experience the buffeting effect. GM resolves the problem by eliminating direct turbulent sources. Vararam takes in air and straightens it slightly, then dumps it into an expansion chamber prior to the filter to slow the speed, which effectively kills the turbulence. A propped shroud works kinda OK at low vehicle speeds opened wide and higher speeds with a narrower opening to reduce turbulence."

[Jabbott]

I think the RPM makes all the difference. First off you are looking at the MAF in low speed air. The car is looking at the MAF, but it is operating in the VE side of the calibration. The 6.2 sucks at idle and low speeds anyways because of the size of the intake port on the head is so big. The filter doesn't have too much effect on this except maybe to magnify the issue even more. So right way to fix it is to get the fueling dead on and then get the timing stable and all the surging will go away.

[gmtech16450yz]

Well this isn't exactly an issue, well at least not all of it. First off you have to look at the other values. You are looking at a MAF, but the MAF is not in play for the most part at that RPM. The factory does not bring the High speed air into effect until 4000 RPM. The reason for that is because the air speed through the MAF is too slow and you get allot of turbulence in the MAF. So to be fair the Attack Blue will not cause an issue like you are talking about. The Donaldson though does a great job straightening the air flow. I have used the Attack Blue and Green on all of the Corvettes and really don't have issues like what you are describing. If you log the car during the surge you can see the MAP moving around a bit and it is making the timing jump around which is your surge. It is the constant removal and addition of torque, the same thing when fuel is causing is by MAF turbulance when the High Speed air is being started too early. I did allot of testing when I designed our airbox and it caused allot of turbulence during testing. I had to redesign the sides of the box and how it ramped air towards the MAF and also using a honey comb in the box.
The LS3 is the worst by all accounts, the heads are too big and no air speed through the intake ports a low RPM's, that makes all the little problems big problems. So if your LS9 is surging, you need to raise your high speed air and use the VE to fix the surging, also need to stabilize the timing in those areas.

Ummmm yeah, no.

Are you a 'Vette guy? It seems like the Vette guys always want to challenge things like this instead of acknowledging the obvious.


Does this steady cruise MAF trace... (Purple line that looks like an 8.6 magnitude earthquake.)





Look like this steady cruise MAF trace?







Or does this idle MAF trace...






Look like this idle MAF trace?








Sorry if you don't see it or get it. That doesn't mean it's not there. And it most certainly WILL cause surging, even with the dynamic settings stock. (The dynamic WAS stock at the time of these logs. I could do a blind back to back test between the stock filter and the Attack Blue and even my wife and son could tell you which one was which. You can set dynamic to 6000 rpm and I guarantee you if you have MAF issues even at 2000 rpm, you're gonna feel them.

I apologize for being a little snotty here, but this wasn't a thread asking for help diagnosing my issue. It was a thread stating what the issue was and how it was fixed. Anyone local to me that wants to see how a simple filter change can make a car surge, I'd be more than happy to show them.

[Pekka_Perkeles]

I think the RPM makes all the difference. First off you are looking at the MAF in low speed air. The car is looking at the MAF, but it is operating in the VE side of the calibration. The 6.2 sucks at idle and low speeds anyways because of the size of the intake port on the head is so big. The filter doesn't have too much effect on this except maybe to magnify the issue even more. So right way to fix it is to get the fueling dead on and then get the timing stable and all the surging will go away.

In my thread posted earlier, forcing the engine to "VE only" cured the issue.

And when activating MAF, the surging was there again. All this with stock engine.

Funny, ain't it...

[ingsteve]

are you sure you don't have ground problems?
original radio?
it is fluctuating too much