https://ls1tech.com/forums/generation-iv-internal-engine/530111-tuners-inside-loaded-vs-unloaded-wot-f-ratios-long.html

This was posted in the wrong section by myself accidentally so until the mods have a chance to move it for me take a look. Any input is greatly appreciated!

Discussion that myself and a friend had on this issue.

Me:
"Well if your clutch is slipping you'll find that you'll end up richer then you would normally be as the motor is not loaded as much. Get that clutch in and give me a yell, i'll put my wide band 02 sensor on it and tell ya exactly where it's at!"

Him:
"......the computer is dumping fuel in according to the amount of air going through the MAF so the amount of load on the engine doesn't matter for fueling on my setup "

Me:

"......In either event the amount of air drawn into the motor will not change weather it's loaded or unloaded which is all the maf measures based off of how cool the wire element gets in the maf reporting a frequency to the computer. But what will change is the force against the piston on the power stroke which will cause differences in the burn characteristics according to my understanding of the fuel injected ICE motors. This in turn will cuase differences in air fuel ratios.

For instance, the dyno jets typically use 3000lbs of resistance to get a measure of hp. But when you have a heavier then 3000lbs car, like an fbody, the wide band readings taken from a dynojet are often richer then what's seen on the street/track/real world under the fool load of the car! "

Basically i'm looking for actual descriptions of what's going on in the internal combustion engine (ICE) in loaded and unloaded situations that causes the difference in wot air fuel ratios. If this is a myth then don't be afraid to pipe up and say so.

 

That's an easy one.

Air fuel ratios will change according to manifold absolute pressure (MAP).

Raod testing with my LM-1 shows fuel ratios will change between 2nd gear
and 3rd gear during wide open operation (TH-350 transmission).

Ask him to rev his motor to 6000 RPM in neutral and check the air flow and
fuel ratio. Also look at the injector activity while scanning.

Repeat the scan under load on the highway.

As for the dyno AFR against track AFR, it will be close but consider wind resistance,
different load conditions (time to RPM) as the engine will work harder in real
world applications.

 

I'm not really sure how opening the throttle all the way while under load vs. not under load will do anything different to air demand in the motor so i'm going to have to disagree with this politely

The response I recieved in speedtalk is more along the lines of what I was thinking and what I think is accurate. That is the wot a/f ratios are generally leaner under load as the heat available for combustion is greater then that of a shorter dyno run, slipping clutch run, or burst through the lower non-1to1 gears which in turn will more completely burn the a/f mixture.

 

One thing that goes on is, unloaded you have a large
rate of change in RPM and loaded, much slower. The
MAF is a slow instrument and always tells you
"yesterday's news". So unloaded with a large RPM
rate of change, will be working from old (short)
airflow data and your airflow-based fuel calcs will
likewise be a bit short.

That's my theory.

 

Less fuel is required to keep an unloaded motor turning than while loaded.

It's the fuel demand that is the key point, and would be something you could
show your friend while scanning.

 

Under WOT the calibration is set to deliver a predetermined amount of fuel based on RPM. WOT is determined by TPS (typically 100%) and MAP (~13Kpa) while PE (EQ) is based on RPM. When the clutch slips, the environment for which the PCM was calibrated has now been modified ie. the particular MAP which should have been higher, but now isn't since the clutch has reduced the load. The PCM will see a potentially small difference in MAP readings, but not enough to modify the commanded AFR which will cause the PCM to continue dumping the predetermined amount of fuel which in this case will be too much. Until the TPS or MAP fall below their respective WOT threshold, the PCM will remain in WOT mode.

 

This is an excellent thread guys!!!

I think fuel injection complicates this discussion some as you the user set the maf/ve/pe tables according to what the wide band indicates and what you, the tuner desire. Now, as pointed out above, if the motor is unloaded (slipping clutch, lower gear, spinning tires, etc. etc.) the calibration will in fact be off or atleast the wot range of the maf/ve/pe tables will be off if these tables were previously calibrated while loaded conditions were put on the motor. Now consider it in the sense of a carb which essentially a/f changes are made by jet changes with no map or maf sensor commanding injector pulsewidth. Since the jets only are acted upon by a vacuum upon the jets and they see the same phenomenon as a fuel injected motor when partially loaded vs. fully loaded I think the combustion effects are souly the cause of the leaner when fully loaded condition.

 

Jimmy, if this was true though then an unloaded conditions would be even leaner as you'll be working your way up the rpms very fast (with the maf/map/ve table trailing) and generally speaking within a reasonable range (3000-6800 or so) the fuel requirments of the motor will increase with rpms so if fuel was slow to match the very fast revs of the motor it would be even leaner!

 

[Quote]
For instance, the dyno jets typically use 3000lbs of resistance to get a measure of hp. But when you have a heavier then 3000lbs car, like an fbody, the wide band readings taken from a dynojet are often richer then what's seen on the street/track/real world under the fool load of the car! "
[Quote]

That doesn't hold much water. I don't know how you equate spinning a roller equal weight of the vehicle to pushing the car down the track. In my limited experience lighter and heavier vehicles exhibit about the same air/fuel change from the track to the dyno. The difference is the more powerful cars that spin the rollers up very fast, not vehicle weight.

The wide band in my car reads the same as the one connected to my Dynojet when on the dyno, and shows every little difference on the track. I have several customers with wide bands in thier cars also, both heavy and light vehicles, and both change about the same. Both MAF & speed density. I have run my car both ways, very little difference when tuned correctly.

The "10.5 shootout" cars around here making well over 1000 rwhp na change much more when run at the track NA. I can't measure their power on the spray, my dyno flat lines at 1250 rwhp, so can only see their air/fuel when they spray them. Those cars will indicate a good bit leaner at the track. Like from 10.8 on the dyno to 11.5 a/f or so at the track. They aren't that heavy, but spin the rollers up much easier and faster. Doesn't appear to be any corrolation to vehicle weight. Lots of cars of all variations have gone across this old Dynojet in ten years.

 

Ed, I see your examples, but others have indicated the same thing as I have. Further, if you have 3000 lbs of resistance via a dynojet and you're moving a 3500pound vehicle on the street (with traction and no tire spin) I don't see how there isn't more load on the motor???

Hmm, actually I think i'm starting to see you point about correlation between 3000lbs of resistence via a dyno jet and 3500pound vehicle not necessarily indicating more load on the motor. I guess i'd understand a little better if someone would indicate or I did some more research on how a dyno jet actually loades the tires with resistance.

 

I'm afraid Adrenaline_z is correct on this one. Fuel demand by the engine (not the computer system) increases with load.

On cars tuned close to the edge this becomes quite obvious. For a conservative/rich tune (like stock), you probably will not notice it unless you are doing a very specific testing to show it.

 

Keep in mind the gearing between dyno and street. How many times do you stay fully loaded through your high gear on the street?
During those times most people would be going extremely fast with wind drag adding a significant amount of load to the engine. Fuel demand will absolutely be increased.

 

I'm not disagreeing that a fully loaded or more heavily motor needs more fuel, i'm agreeing 100% with it. In that sense me and adrenaline are exactly on the same page

Also, good point on the wind resistance, that's something I did not think about. Obviously not too much wind resistance on the dynoe, ha, unless ofcourse the calibration in the dyno accounts for that some how.

 

And fuel demand by the engine decreases with decreasing load. Therefore, when the PCM continues to send the same amount of fuel the mixture goes rich due to the engine seeing less load.

 

The Dynojet is a set of heavy rollers, it is simply inertia. The people that tell you that spinning up a set of rollers of equal weight to the vehicle is the same work as accelerating that vehicle down the race track have been playing with themselves too much. A dyno pull from idle to red line takes much less time than a 1/4 mile pass. As I said, the power output has much more to do with how much the indicated air/fuel ratio changes from the Dynojet to the track.

 

Holy ****, that made me laugh out loud.

 

Is your MAP different under WOT in 2nd vs 3rd?

 

I am curious about your opinion on whether the engine is "more" loaded during the first 60' at the strip or the last 60'? If we need a specific car, assume the car is a low 11 second f-body.

How can this extra load be measured? Is there anything in the common scan tools that would help determine how much more fuel is needed? Is the cylinder pressure actually greater?

The part I am confused about is the fact that if the engine ingests 130 grams of air per second in 1st gear and I want 13:1 AFR, then I need 10 grams of fuel per second. Is that correct? So, why wouldn't it be true if the engine uses 130 grams of air per second in 3rd gear, that I would still need 10 grams of fuel per second to achieve 13:1? Why would I need more fuel?

I ask because the tables in EFILive and HPTuners don't have a 'gear' function offset. Assume I am running SD, so my fueling is determined by the ideal gas law, and my primary means of modifying that is through the VE table. Isn't 100kPa at 6000 RPM's equal to 100kPa at 6000 RPM's regardless of the gear?

Just confused. Thanks.

 

I'd say that it is most loaded in the 1st gear launch (first 60') then the last part of the track. Once the car is moving the highest gear the car sees will be the most load on the motor.

It would seem to me the cylinder pressure is in fact greater cause the forces fighting against the piston while traveling down on the power stroke are greater but it's kind of hard to quantify.

I think it wise to tune the car in top gear as it will allow the car to run a little richer in the lower gears and according to Mr. Lingefelters book a motor will drop hp much much faster when too lean vs. too rich.

 

Interesting. Why do you think we see cars running lean on the big end then?