Tuesday, August 23, 2005

Idle Tuning

Idle tuning is a rather touchy topic, as you can never be really 'right' just by looking at tables and values. Daily drivabilty is what's at stake here, and that's a very subjective manner. Lots of people want that big cammin' sound, I don't know why... Anyway, you gotta start with hardware configuration.

If you have a bigger throttle body (FAST 90, or Nick Williams) you want to multiply your Effective Airflow Area by 48%. (put in 1.48, select the whole row, hit 'multiply')

If your engine displacement has changed (bored, stroked, etc) you need to do some math. HPT wants cylinder displacement in liters, so might as well do everything in metric to start with.

Example 1, stock LS1:
bore= 3.898", stroke= 3.622" so in metric, according to www.onlineconversion.com (great site btw)
bore= 99.0092mm, stroke= 91.9988mm

Cylinder is just that, a 'tube' so to speak, so the volume of it is:
or in our case,
V= Pi*(99.0092mm/2)^2*91.9988mm=708309.6306mm^3
And what do you know, that's the value that's stock in HPT for the 5.7L/346ci motor.

Example 2, 402ci motor:
bore=4.000", stroke= 4.000" thus
bore=101.6mm, stroke= 101.6mm
V= Pi*(101.6mm/2)^2*101.6mm=823703.678mm^3

Go put that value (in liters) into HPT under Engine->General->Cylinder Volume.

Another super important thing to get right when you're setting it up: injectors.
Big myth here is scaling from what you used to have. Forget it, just put in new values for the new injectors and you're done. These are the popular sizes of injectors in default HPT units (lb/hr) stock 99-00 injectors (26.4lb/hr)
26.41431 26.60033 26.78634 26.91036 27.09637 27.28239 27.40640 27.59241 27.71643 27.90244 28.02645 28.21247 28.33648 28.52250 28.64651 28.83252 28.95653
stock 01-02/z06 vette injctors (28.8lb/hr)
28.70852 28.89454 29.08055 29.26657 29.45258 29.57660 29.76261 29.94863 30.13464 30.25866 30.44467 30.63069 30.81670 30.94072 31.12673 31.31275 31.43676
svo 30's at stock GM fuel pressure (34.6lb/hr)
34.64162706 34.85752419 35.07209232 35.2853557 35.49733784 35.70806157 35.91754903 36.12582173 36.33290055 36.5388058 36.74355721 36.94717396 37.14967471 37.3510776 37.55140031 37.75066003 37.9488735
svo 42's at stock GM fuel pressure (48.5lb/hr)
48.49827788 48.80053386 49.10092925 49.39949798 49.69627298 49.9912862 50.28456864 50.57615042 50.86606077 51.15432813 51.4409801 51.72604355 52.00954459 52.29150865 52.57196044 52.85092404 53.12842289
This is all at stock fuel pressure, if you changed that, you gotta adjust accordingly, please use this spreadsheet: DOWNLOAD
Take a Stock VE table (remember to do it on the Primary VE for 01-02 cars and Secondary VE for 98-01), and have the first column (400rpm) go 25-60, second column (800rpm) from 25 to 70, and third column (1200rpm) to 35-70. These are ballpark values, they will differ with your setup, but i find them generally a good starting point, an usually within 15% of what they will end up in once tuned.

These are two tables of idle regions, one is a Futral 228/.575 112+4 Mac Mids M6 car, the other is MTI 236/.588 112+4 SLP LTs A4 car.

Spark in Idle regions:
First you gotta let it idle and see where it idles rpm- and airflow-wise.
Then go to Engine->Spark Control->Spark Advance->Idle Spark Advance->{In Drive, In Park} and you want to set it to about 20-22degs in the idle regions for Park, and 26-28degs for Drive table.
This is an example of such a thing:

Another great helper in getting your setup to idle is to set your TargetIdleRPM.
go to Engine->Idle->IdleRPM->Target Idle RPM table, and this is a good start for any bigger cam):

Of course, bigger cams need more rpms, smaller cams can get away with less, so for example stock/Z06 cam can go as low as 550rpm, while G5X2 wants to be at least at 1050rpm for a truly smooth operation.

Scan, Ready, Go!
Now that we're finally done with preparations, it's almost time to fire it up!
You want to scan for the usual things: rpms, spark advance, MAF, MAP, but also you want LTIT(gear), LTIT(park)(automatics only), Idle Adapt (STIT), IAC count, IAC desired, TPS%, TPS voltage.
Put the car in Accessory Power mode (lights on dashboard on, but not cranking yet), and star scanning with the table I listed above. First, check if your TPS% is at 0% if you're not touching the gas pedal, and 100% when you floor it. You might want to reset your IAC motor, but you'll probably want to do it later once you bring the car up to temperature and start messing with IAC counts, but more on this later.

Assuming that the car is cold, start it up, and start scanning immediately. You also want AC off, and use the live controls to turn off both fans (the increased airflow from the fans will throw off STIT) It might take it a first 20 seconds to figure out what's going on with all the changes we've made, so it might be a bit rough and stumbling around, but it should quickly stabilize and stop hunting. If it doesn't, go back to the settings, and try to up the Target RPMs, that's the easiest fix. In the meantime, watch your STITs gone crazy. Most cammed cars will have the Running Airflow (RAF from now on) tables way off, and STIT will try to adjust for what it should be. You can pretty much eyeball the new values, as long as you know the ECT intervals (notice they're different for 98-00 and 01-02 again!), and just keep track of what values STIT holds at, as the engine warms up and ECTs go up. Or you can be dead on if you just use these spreadsheets:
This contains a config file and two spreadsheets for the different years. The instructions are within the files, so please read them BEFORE you aim/email me. Read them completely, so you know what units to log all the airflow in.

So let's say your car warmed up and it's idling decently. Save your log, turn off your car, put the data in the spreadsheet, alter your RAF tables with the new results, and flash your PCM with your new configuration.

Note: Automatics will want to do the whole 'cold startup' procedure twice, once in park, once in drive (either go drive with a lot of stop'n'go traffic, or just sit in your driveway in Drive and your foot on the brake). Then use the data from the right result table and paste it into your config.

Another note: if you do this config in the middle of the summer where your starting ECT is ~80F, don't expect it to work well on a cold startup in the middle of winter when ECT is closer to 4F. You might wanna do it again then and complement your new table with some values for few more intervals.

Once the car is warmed up, start it up again, and watch your IAC counts. You want them to be less than 70, and if you can, less than 50.
Idle settings are pretty much done. Now just tune your VE in the idle range (running around the block few times is perfect for it), and your idle should keep getting better and better.

If you see STITs still posting significant numbers (more than 1g/sec), you might want to redo your RAF configuration. Since you're dealing with rather peaceful data (no crazy swings or transitory conditions), you should be able to get it near perfect in 2-3 rides/cold startups (depending which RAF you're tuning) even on the most radical of setups. I was able to keep my STITs under 0.2g/sec.

If that doesn't help it, raise that Target Idle RPM another 100rpm, and redo your RAF again.

If the spark advance hunts around a lot, it means your Over/Under Speed timing tables (Engine->Spark Control->Spark Advance->Idle Adaptive Spark Control) need to be adjusted to slightly less radical numbers. The way I like to do it, I use the live controls in the scanner to find a RPM that allows the RPM to vary <>

Knowing is half the battle, and now you know, but keep in mind all this might as well be a big pile of horsepoop ;)

Monday, August 15, 2005

Road racing an automatic

Road racing an automatic is historically speaking a big no-no. No engine braking, no blips, uncontrolled shifts, not being able to hold at certain rpm for arbitrary periods of time, they're all good reasons to declare an automatic an ill choice.

But this is 21st century, and even GM's crappy transmissions are a subject of being electronically controlled. There are tables controlling when to up- or down-shift, depending on Throttle Position Sensor (TPS) and speed. There are also separate tables for cruise and overheating conditions, which are are a nice touch, albait useless for the purspose of road racing. Now though, with the help from HPTuners or EFILive packages, we can adjust it any way we want. Let's take a look at what we can do with them.

Normally they look something like this:
1->2 10 10 11 12 13 15 17 19 21 24 27 29 32 33 35 37 37
2->3 20 21 23 25 27 29 31 34 37 41 45 51 59 66 74 75 75
3->4 37 37 37 37 44 52 69 83 99 108 112 117 117 117 117 117 117
2->1 9 9 9 11 12 14 16 18 20 22 24 27 29 31 32 34 34
3->2 17 18 19 21 23 25 27 30 32 35 39 44 51 59 67 72 72
4->3 32 32 34 36 37 45 61 75 89 99 106 110 111 111 112 112 112

This is what I figured out by simple trial and error at the track:
1->2 15 15 15 15....
2->3 67 67 67 67....
3->4 115 115 115 115....
2->1 15 15 15 15....
3->2 65 65 65 65....
4->3 115 115 115 115....

What we basically did, we eliminated partial throttle! If you think about it for a second, at the track, we want to very rarely shift early, you want to shift when you 'run out of revs.' This simulates it, as we set WOT shifts to partial shifts. The important part of it is the first column, which is for 0% TPS. That means, that even if I take my foot of the gas completely, the transmission will not suprise me with an upshift.

Another interesting things you might notice, that while the stock table ends with a 75mph shift, the racing table ends with a 65mph. Why is that? Because at the track, the trans fluid gets so overheated (yes, even with B&M 24000GVM trans cooler!) that it turns into 'water.' It seems to lose so much viscosity, that the shifts that were normally intended to initialize at 6000rpm, now would start at 6200-6300 and would not complete sometimes until my revlimiter at 6600rpm. Thus, I lowered the speed/rpms at which I wanted it to start shifting, and everything was fine again. It was suprising however how much this can change at the track, and never on the street.

So what was the result of all these experiments and strange changes? It worked great! I went to the Autobahn Country Club in Joliet, IL for a track day on the 'North Loop', and the car was more fun than ever. Granted, the long automatic gears aren't the greatest for roadracing, but it would feel good. There is a sequence of T3-T4-T5 which by the end of the second session I figured out how to take without any braking whatsoever. All these corners are about 50-60mph, and with the transmission in 'track only' mode, I'd plow through all of them holding ~5000rpm, letting off throttle completely in some moments, and feathering it in others. Laying into it completely coming out of T5 and setting up for T6 was extra fun, as I'd rocket out of there at the top of second gear which feels very powerful in my car (right about peak hp and before torque starts to drop off).

The gear spaceing was actually not bad considering how the track was laid out. Most turns were 50-60mph turns, with T1 being about 75mph (I tried it out at 80mph few times, but brakes just weren't up for it going into T2 and I'd overshoot the turn in point) and T2 being ~40mph. If fit the car well coming out of these corners hard, charging up the top of second gear. The 3 straights were fun two, two of them topping out about 85-90mph, and the main one was about 105-110mph (depending how chickenshit I'd go through 'the kink' T1. So I'd come out on power, and utilize the powerband fully. I wish I had another gear between 2 and 3, something like Supra gears were (60-90-125mph) as that would put me at the peak power at all times. But, I still claim it's the most fun thing you can do with your pants on.