PorKen

After comparing a bunch of past WOT run logs to the newest, accounting for air temp and pressure, I can see the effect of the retard in the MAF graph. (Normally, most tuning changes are so slight, compared to the amount of airflow, that it's difficult to see a pattern.)

It looks similar to the graphs from my last dyno run. No change around 4100, the pivot point, and a near equal swap for airflow between the TQ peak at 2700, to the HP peak at 5700.

After 5700, however, with this last bit of retard (-12°), airflow keeps increasing, until redline, instead of leveling off. Airflow >6000 at ~54F/12C (May) is about equal to what it was at -8°, tested at ~42F/6C + higher air pressure (Dec).

Guesstimating with SAE temp correction at 1.5% per 10F, then the additional -4° has added another ~5 rwhp SAE. (Maybe more because of higher ignition advance, but the dyno is a cruel mistress, so I'm not so sure.)

PorKen

With this much retard, starting is a bit 'clumsy' when it is warm, and the idle is still a little bumpy. I will have to work on the fueling/ignition a bit more.

I also re-enabled the injector cutoff. The after burning fuel was overheating the WBO2. (Stupid LC-1 'Error 8'.) And, come to find, it doesn't need to be disabled, as there is very little engine braking with high cam retard.


BTW, it may not be clear to people that don't mess with fueling maps frequently (I forget this too) that many of the changes while 'tuning' don't mean there is an actual need for greater or less fuel, it just means the MAF vs. RPM relationship in the table has changed, so the fueling calculations are wrong. (The small maps in these early computers exaggerate the errors.) A small change of airflow to a different engine speed makes the LH look towards the wrong part of the table, so you have to compensate for it, either by reprogramming the entire table (often impractical), or covering it up with an external addition, like the WOT table.

The maps/tables are set up at the factory for a specific engine configuration, under certain atmospheric conditions. The WOT and temperature additions help mask the errors, but don't actually fix them. Mostly, it's up to the O2 sensor loop to keep the mixture stable, when possible.

Speedtoys

Went to Bill ***** today..to see where the cams were, since some bonehead did a TB in the past, and put the HB on backwards...

So we got the HB turned around, and go to cams.

Right side was +3, left was +2.

Theyre now both 0 (set warm, not hot, but not cold).

Runs smoother
Exhaust IS quieter
MORE power up top
Throttle response better.

PorKen

Yet more WOT run logs... (My apologies, if this is tedious.)

A brief temperature drop, along with higher air pressure, gave me a set of runs with much closer atmo to my comparative December logs. Air temperature has a smaller effect than air pressure. Air pressure makes a big difference in MAF readings!

At the S3 stock torque peak, 2700 rpm, airflow hardly changes, no matter the cam setting. (Intake harmonics.) 3500-4000 swaps with 5500-6000. 6000-6700 MAF airflow is higher, and keeps climbing, vs. leveling off though. This should mean higher HP near redline.


Comparing times for the runs, in 3rd from 1700-6700 rpm, acceleration is markedly slower up to ~5000, above that is the same or better. (Consider the air drag at 6500 rpm in 3rd...)


So...do I go for max HP numbers at redline, or best acceleration at 'reasonable' rpms?


Tidbit: with a No-Lift-Shift, smooth gear changes, for me, still take >0.5 seconds from power off, to power on.

mark kibort

so, if that is a real question, you always go for max HP or max area under the curve up top. remembrer, if you are racing, you are in the 4500rpm to 6500rpm range , every shift. if you are not, in that range, you are not racing and it doesnt matter anyway. flappy , and low end torque are strictly for "feel"
However, on the street, i like that feel because i dont "race " the car on the street.

Speedtoys

Learn to calculate Density Altitude...that's what you're REALLY talking about.


DA is performance. Both temp and pressure work together.

mark kibort

Yep, DA!!! you got it

your avitar just got me in trouble!

Speedtoys

Yup..DA is when im landing on a 9,934' high airport, but the plane thinks I'm closer to 15,000' high.

FUN landings.


Just so ya know:

http://wahiduddin.net/calc/calc_da.htm

mark kibort

6000ft. 20% loss +/- whatever!

dcrasta

Dramatic effect on N/A engines. This is why Budds Creek is such a fast track (65feet above sea level baby!)

Bwaaaaaa!Bwaaaaaaaaaaa!

Speedtoys

Rule 'O Thumb in the air is 3.5% loss per 1000' of increased DA.

PorKen

That's cool. RECALCULATING...

(I like this link better - http://wahiduddin.net/calc/calc_hp_dp.htm)

What's nice is that my test track is at the airport, so I can get all the old data.

Dec 26, 30', 42F, 30.34, 35F = 0.928 SAE, -1428 DA
Apr 02, 30', 56F, 29.98, 38F = 0.958 SAE, -129 DA


If I'm flowing the same, or more, air at 3% worse SAE...that could be +9 rwhp...322 SAE.

PorKen

Since I am a street drivin' track poser, if it does dyno close to 320 rwhp sae, then I'll likely keep it. Low end power is not noticeably diminished, and I am pretty sure it will get better MPG with lots of retard. (Even with all the WOT runs, I'm getting 14 mpg. Previously, it would be more like 12.)

I may dial it back to -10°, though, for an easier adjustment, and move the HP peak back down a little.


The real test will be to see how it feels on my auto, which is also 500 lbs (227 kg) heavier.

mark kibort

you have to trade off the loss in power vs the loss in aero. NOW, this requires some additional thinking too because its effects are up by the square of speed. so, slow tracks, its about power loss, fast tracks, its about aero benefits. the nice thing is that on the track, its all relative, unless you have absolute boost control on a turbo.



Yup, thats where i got my 20% for 6000ft. did an interesting test with the holbert car at 6500ft (60-100mph) and then doing it at sea level. coorelated with the DA figures.

power output vs MPG are totally differnet tests , and it would be curious to find out how retard helps part throttle gas efficiency.

heck, if we could only have a switch to go full lean on cruise, open loop and have a *** for richness. get that thing about 17--18:1 and I bet we get near 26mpg ! love to do that for the chevy tahoe on long trips. heck, the earth is going to burn in the sun someday, so a little extra NOX wont matter, will it??

PorKen

Having sorted out the WOT fueling, I looked to why hot starts were difficult. One thing I did was unplug the O2 sensor. Turns out it needs quite a bit less fuel (injector time) at part throttle. IE. at -12°, it swapped from low to high, needing much more fuel at WOT and much less at idle/cruise.

Starts normally, now. Hopefully, this means it's more efficient, for better MPG (not just rearranging the airflow/RPM relationship).

You could do this with a WBO2 using the analog outputs. Program one output for 14.7, the other for 18. Use a relay triggered by the cruise control to switch between.

Your Tahoe may have 'lean cruise' programming that's not enabled. Some GM ECUs had this feature for Australia, or something. Search 'lean cruise' on the internets.