Tuesday, September 26, 2006

Tuning Methodology

Someone brought it up on the forums, and it's a good thing, so I'm reposting it for the sake of completeness on my site.

1. Try to keep tuning sessions as close to repeatable as possible, same gas, same route, same time (like driving to/from work) work great. This way you get approximately the same amount of samples in the same temperature range. If the weather is particularly extreme (super hot, extra humid) take a note of it, expect your values to skew one way.

2. Long steady inputs--I can't stress this enough, this is #1 reason why most people never get their numbers straight. If you get on the throttle--hold it. If you get off throttle, don't half-ass, lift completely--this way it's easy to filter unwanted (transients/not steady airflow) cells. In HPTuners, there's now way to ask for a derivative of anything, so there's no way to know if you're accelerating or decelerating. EFILive has 'filter out if value changed more than X %' capability

3. Warm up the WHOLE car, don't just look at the coolant temperature. Fuel warms up too. If you don't believe me, go scan for a while, and then go fill up with new fuel, and continue scanning, I promise you your trims are gonna go nuts. Fuel temperature affects atomization, which affects how complete is the burn, which affects the resulting AFR. The rule of thumb here is 15 minutes of normal driving before you log for VE.

4. No lugging it in tall gears (5-6th). Laziness gets the best of you, and you end up tooling around at 1500rpm in 6th, give it more gas, it knocks. While it's not a real dangerous knock, but it will show up in your logs, and you might end up pulling timing where you really didn't need it. Avoid doing it in general, not just for tuning, if you need to accelerate, downshift.

5. Be creative -- use the environment. Hills are GREAT for getting the more extreme cells. how else you're gonna get these 20kPa at 4000rpm cells without decelerating? (you can always use a real dyno, like Dyno Dynamics)

6. Be observant, learn the ways of your car. There are things that are particular to every car, and the most seasoned tuner won't notice them, simply because they don't have the milage on your car you do. Use it to your advantage. My car, for example, has random knock 1600-2000 rpm; it's just tight suspension on lousy roads, making things rattle and set of knock sensors. If you give it more throttle and it binds up, then there's no knock, but driving gently makes it rattle. Pure 100octane and lame timing won't cure it either.

7. Organize, label, and take notes on your logs. Temp/pressure/humidity/terrain often explain a lot of goofyness in the logs. once I was chasing what I thought was an intake leak, but it turned out to be that the guy lived in some serious hills. During a 20 minute commute between work and home, his WOT MAP would drop from 100kPa to 93kPa max. I didn't know that, he didn't tell me. It took us a while to sort it out.

8. Tuning is science--don't ever forget about that. Repeatability, changing one thing at the time, taking notes, not falling into routine or assumptions, all these boring things psychotic science teachers tried to drill into your heads in high school--they weren't cool, but they were right, so deal with it.

9. Keep your hardware fresh and clean. If you see AFR scatter more than usual, check your filters. If you see MAP not getting up to where it used to be in the same conditions as before--your cat might be clogged up. If you installed headers and you're tuning for them and it's starting to converge on some new numbers but then out of nowhere they go crazy on you--retorque header bolts, something might have gotten loose after few heat cycles, etc.

Saturday, September 23, 2006

LS2 VE tuning spreadsheet

I've started reading LS2/GTO/Vette boards, and a lot of people seem to have a problem with tuning their VE, simply because it's different than what they're used to with LS1.
The funny part is that the form we see in LS2's is not functionally any different from the old form. It's just different numbers, but the shape of the 3d surface is the same. Now that my Speed Density paper is out, we know that the factor is exactly R/CylinderVolume. However, because it is a linear factor, mutiplying the VE table by AFR%Error should be the same, no matter what factor is there. So viewing the table in the traditional VE is more for information than actual functionality.

Theo ne new thing I'm trying with this spreadsheet is to see how people use them:
Do you want everything on one tab?
Do you want step by step on different tabs?
Do you want everything on one tab, with multiple copies of the setup, so you can keep track of progress?

Leave comments, send email/IMs or whatever, I just wanna know how I should make them for the future.



How Speed Density works

This is the most important work I've ever done, or at least it feels like it. It takes you from sensor data through calculating pulse widths, and all the forms of VE and their particular meaning.

I feel particularly proud, because it all makes sense so far with everything else we've been discovering how these cars run, how the PCM operates and explains a lot of peculiarities of the model GM decided to employ.

The understanding of concepts helped me tremendously. Some things you take for granted, others you just kinda understand, but this puts it all in black and white, solid, precise numbers that show you what and how you wanna run in your car.

I tried to make it as universal as possible, but because of the GM-particular VE form (that I refer to as GMVE) a lot of the paper deals with that. However, the rest is just about universal. Some of the language like ECT (coolant temp) or IAT (aircharge temp) might not be universal, but I tried to explain what they all mean at least at one point, so you can change IAT to AIT if that's what you're used to.

The cool part is that I have gotten some data that confirms the formulas. I've logged all the sensor data necessary, and tried to calculate data normally we'd obtain through PIDs. Cylinder Airmass seems to be very close, with less than 2% error through the whole range of values. Other values dont seem to be that far off either. Considering how many filters there are on anything airflow related, I consider this to be a very good result completely backing up my work.

Due to the fact I needed a lot of math formulas displayed nicely, I had to put it in a Word document, and not a webpage. If you know a way to easily convert it over to a webpage, please let me know, until then, it's just a paper.

I also include a spreadsheet with stock 2004 Z06 values, and convert them to other forms using my math, side by side with the originals.

I hope you guys like it, cause this was a shitload of work.

Saturday, September 09, 2006

Cylinder Volume Spreadsheet

This is so simple I'm embarrassed to post it. At the same time, I've seen it messed up too many times to be unaddressed.

Cylinder Volume= Pi * radius^2 * height
Cylinder Volume= Pi * (bore/2)^2 * stroke

To justify releasing it, I integrated a trick where if you so far have tuned your VE but haven't changed your Cylinder Volume, I also give you a number to multiply your entire VE by. This way you don't have to retune the whole VE again.

Also, the inputs are in inches (unfortunatelly popular with the LSx crowd) but it gives you output in Liters, which are the units to be used in HPT's Cylinder Volume field.



Wednesday, September 06, 2006

Rated fuel pressure on SVO 42s is...

Rated fuel pressure on SVO 42s is 43.5psi (3bar). End of argument.

Here's a proof:

So apparently my empirical experiments year and a half ago were right 3bar it is.
and now we know better...

I got another one from another friend, so here's more examples on a typical flow spread