KoreaJon

Hello Everyone,

I've recently been doing incremental changes to my tune using HP Tuners. I also installed a WB O2 sensor, but I have a few questions.

Is my O2 sensor showing the ~actual~ air / fuel ratio? I'm not sure if there's some interpolation that I have to do, or if its showing the actual ratio.

During the run (log file attached) I did a couple of 0-60 mph and 0-100 mph runs; (starting at the 12:57 point in the timeline)given my mods, what are your thoughts regarding the performance?

I've also noticed some "burbling" during coast-down from speed. What I mean is that under certain conditions, when I let off of the throttle, I get that gentle "popping / burbling" in the exhaust pipe. I'm thinking that this is a rich condition where the un-burned fuel is actually burning in the headers. Not only is this (probably hurting performance, but I'm sure that its no good for the fuel economy, as well.)

I've got a '98 Coupe, LS1

My pertinent mods are:
LS6 intake
Kooks 1 3/4 LT headers, X pipe, and axle-back
3400 stall TQ converter
My tires are Sumitomo HTR's (I know, I know....they're cheap, which is great because my 9 yr old son LOVES burnouts and donuts!)

I'm curious to hear comments / suggestions regarding my questions and my tune file.


Thanks in advance!
KoreaJon

enoniam

I can't open your file here at work, but regarding the WB O2 it would probably help to know which one you have.

There's several that are pre-populated by HPTuners with the equations needed to go from the analog output signal of the WB to AFR. Mine isn't one of them but it turns out there's a couple with the same equation as needed for mine which is basically AFR=10+(2xWB signal volts).

Yours may be the same or it may be something else - your WB documentation should tell you or you should be able to find it on the company's web site.

KoreaJon

Hello,

Thanks for the reply. I have the LC-1 and set it up using the parameters on their web site. I'm just uncertain whether I got everything set up correctly, and if what I'm seeing charted is actually the air / fuel ration, or if I have to apply some other "correction factor."

Thanks again,
KoreaJon

tblu92

The burble you are hearing when lifting is caused by the DFCO setting in your stock tune
"deceleration fuel cut-off" It basically shuts off the fuel on hard decels and the AFR's can momentarily spike to 16-22:1 No big deal--this is STOCK ---On some large cammed engines or heavily modded ones some tuners will turn the DFCO off--and you won't hear any of that sound--
ALSO---while in lower gears and tuning the AFR's with a wideband--you have to simulate a dyno run for the AFR's to be accurate---On a dyno they check AFR's ONLY when the trans is 1:1 or in 3rd gear--same goes for on the street--You will not get a true AFR in 1st or 2nd gear as the engine is not under full load --being underdriven
It will always be RICHER in the lower gears---The true test is in 3rd--It can become dangerous however as in a C5 in 3rd you are over 100MPH---but you can get a fairly
acuurate measure even if you only check it in 3rd for 4-6 seconds---like from 4000 to 5000 RPM's---
Tuning for the street I always use about a 12.45 AFR in 3rd
Street hot rod non daily driver maybe 12.5-12.7
race dedicated car maybe 12.8--13.0 ( with race gas)

enoniam

Why would you have to be in 3rd for the AFR to be accurate? The PCM doesn't do anything differently based upon what forward gear you are in. As long as you can maintain traction at full throttle you should be able to get decent tuning data in lower gears.

Dyno operators usually run in the 1:1 transmission gear because it generally has the least transmission loss (giving the best power and torque numbers) and you won't fly through the range as quickly so you get better measurements.

I agree speeds in 3rd gear can get quite high. My C5 saw 150 on the dyno in 3rd.

tblu92

Reason like I said---When a trans is underdriven the engine is NOT under the max load and the max airflow is not achieved---This goes for both manual and auto trans---
Using a data logger you can verify this-- A C5 in 1st or 2nd gear usually will max out about .58 grams per cylinder--But as soon as you hit 3rd it will move up to about .68 to about .74---showing that even though the RPM's may be lower the airflow is increased when the engine is under full load---In 4th gear at WOT it would be even higher as the trans is overdriven--But who wants to check AFR's on the street at 140 MPH ??
This is not an opinion this is factual engine dynamics of dyno or street tuning AFR's
PS: Even on my '67 Chevelle with a carb my AFR's in 1st will be about 12.4---In 2nd gear about 12.5 and in 3rd at 1:1 I have it set at a safe 12.7----
If you set the AFR's at 12.7 in 1st or 2nd--When you are in 1:1 (usually 3rd) you will be very lean and risk engine damage or melting a spark pulg tip----

enoniam

I'm still having a hard time swallowing your "fact" that airflow goes up at WOT with more resistance to acceleration on the motor. My belief is that engine "load" is based upon amount of vacuum (or boost if boosted) in the intake manifold and that together with engine RPM are the controlling variables that dictate what the airflow per cylinder intake stroke is. Those two variables alone are the pointers into the PCM Volumetric Efficiency tables and I don't know of anyone who has developed an input to "adjust" the VE based upon gear.

I'm also pretty sure my C5 doesn't show higher grams/cyl right after hitting 3rd at WOT than it did before hitting the 2-3 shift point.

I ran my car up to 110 on New Years Day, with HPTuners data logging, including grams/cyl. I'll report back after I get a chance to review that log.

enoniam

Using a data logger I've debunked this.

WOT, last 1st gear data point 0.79g/cyl.
first 2nd gear data point 0.90

last 2nd gear data point 0.80
first 3rd gear data point 0.88

Essentially the same 1-2 and 2-3. Gear doesn't matter. Increase after shift indicates engine in higher torque range after shift as one would expect.

tblu92

You don't have to take my word for it---Just go to any dyno shop and they will all tell you the same thing as I said
ALSO My data logs show spikes below 2000 all the way up to 1.04 grams--- then they settle down to about .68-.76 up to 4000---The spikes at low RPM's are simply false readings due to burst air speed from fast acceleration and not accurate at all---From 4000 on up mine are all .88-.92
That's why the MAF table is used solely only during steady airflow rates below 4000 RPM
During "rapid changes in airflow" the fueling is set by a combination of values in your tune--mainly the VE coefficient table AND the MAF table- to level out the spikes from the MAF----

enoniam

At least we agree on something!

More BS. I've had my 5.3 chevy truck dyno'd by at least 3 different shops and I've never heard this EVEN THOUGH IT WAS DYNO'D IN 2ND GEAR BY ALL OF THEM. This was done at MY request since I know that 2wd Avalanche driveshafts tend to explode around 130mph, which the truck would hit in 3rd gear. Never heard from any of the shops that AFR readings would be off unless run in 3rd.

2 things here - first it seems your car sees peak torque above 4000 rpm since the grams/cylinder intake stroke are higher there. Second, you need to be logging dynamic airflow / stroke not MAF airflow / stroke so you won't be logging those spikes you speak of, for the vary reasons you stated.

Joshboody

Tblue is right with load greater is taller gears... think of it in terms of piston acceleration. You'll be on stroke longer in higher gear allowing more time to fill cyl. Ultimately should have diff set points for each gear... very important with FI. And timing also important... tune in 3rd then run Texas mile, watch out.

enoniam

Umm, I hate to break it to you put time on a stroke/time to cylinder fill is directly correlated to engine rpm. Only thing gearing has to do with it is how much it will be changing from stroke to stroke. Depending upon whether or not the dyno is only centrifugally mass controlled or whether it can be braked even then the engine speed can be maintained regardless of gearing.

Joshboody

RPM is instantaneous speed. IVO vs IVC will be 2 different rpm readings if accelerating. This is load... highest would be no acceleration which you can accomplish on a dyno and best way to tune.

enoniam

First off, I am not saying that 3rd gear on a dyno isn't the best way to tune. What I am saying is that tuning otherwise isn't as handicapped as has been proclaimed on this thread.

Now to address the 2 different rpm readings if accelerating. I don't know my C5's cam specs, but I do know them for my truck. At 0.050 intake duration is 212 degrees. At 4000 rpm the 0.050 IVO to IVC time is less than 9 ms. Let's just say for simplicity that the average opening time over the typical dyno rpm range is 10 ms. If one were to do a dyno pull lasting 15 seconds over a 3000 rpm engine speed range, the average rpm change between the IVO and IVC is 2 rpm. The engineer in me says my first point above notwithstanding, 2 rpm isn't too bad. I guess you can claim otherwise.

Joshboody

If I tried to get into the math, my head would break. I’m not sure of the actual AFR differences, which could be calculated in time per stroke… very small variation yes. In my past tuning the effects are seen more in timing.
Really fueling should adjust since your MAF or MAP would also change based on load.

I was more commenting that there are load differences between gears and lower acceleration is best for tuning.

OP, took a brief view and seems your WB is reading lean relative to NBs… ie you are richer than logs show. Also your WOT trims are high… I still haven’t figured how cell 22 determines trims. Some say cell when you go WOT, others say based on cell 15 but haven’t seen correlation to either one when viewing logs.

enoniam

I think one of the biggest limitations to tuning when accelerating at WOT in 2nd gear is the rpm change between logger data points. With the number of parameters I'm normally logging via HPTuners I'm seeing about a 10th of a second between data points.

I also don't think that the data being sent though the OBD II interface to the data logger is taken at the exact same moment for each logger data point. If you can load the engine to the point that it's at a steady rpm then for the most part these timing effects don't matter.

That said, I primarily do my tuning on the street and use dyno sessions primarily to measure the results.

tblu92

A dyno shop that logs AFR's in 2nd gear or any gear underdriven is laughable in Calif---They are not true HP/TQ readings---If you set the WOT AFR at 12.9 in 2nd gear---in 3rd under a full load it will be lean-maybe even damage lean-- You need to research the use of the VE table and where the MAF is signed off as the only data used in fueling
The VE table is MAP/BARO based by RPM---The MAF table is strictly airflow based--If you data log the MAF table in 2nd gear it may only reach 7500 HZ--but under a full load in 3rd it can hit 9000 HZ
You can tune how you please I really don't care---But be careful--the way you suggest of tuning AFR's is 2nd gear can damage your engine if you are already on the edge of lean---

enoniam

Gee whiz, have the California liberals tried to rewrite laws of Physics? LMAO

No **** Sherlock. We both understand that much.

Why do you keep telling me what will happen if I log something when I already have and know that what happens isn't what you think it is? And then when I tell you what I'm seeing in my logs you turn to something else to try to educate me when it seems that I'm not in need of your education? My truck MAF is usually higher in 2nd than 3rd because my supercharged and un-intercooled but water/meth injected airflow keeps climbing in temperature which doesn't help with pulling preboost airflow through the MAF. In my NA vette the MAF is essentially the same for the same rpm whether in 2nd or 3rd.

So now I'm going to tell you something. If you are seeing less airflow in 2nd than in 3rd then you aren't making as much power in 2nd as you are in 3rd. Either you are always seeing a REALLY GOOD ram air effect (which you won't be seeing on a dyno any different between gears) or somehow you are doing a poor job of tuning for 2nd gear performance. How you manage to do that trick I don't know.

MVP'S ZO6

Would you mind posting some data logs supporting the portion of your statement in bold?

BLOWNBLUEZ06

Richer in lower gears as in Richer in 1st than 2nd and richer in 2nd than 3rd? If that's what you're saying, it's absolutely not true. Not on an auto. Not on a manual car. Less load will show up leaner. More load will show up richer. Counter-intuitive? Maybe. True? Absolutely. I know you've been posting here for a long time. Not sure of your relative experience, but regardless, it's bass ackwards.