PE curve trend?

[Scooter70]

What should a properly tuned PE table look like? I've read something like you want to be at XX.X at peak torque, XX.X at peak hp, then go a little richer on the upper end to keep it safe. What are the XX.Xs? Anyone care to share their PE table so that we can see what the curve looks like?

(I seem to remember that someone compared the PE tables of the LS1 F-car, LS1 Vette, LS6 Vette, truck, and maybe the Holden and they were all pretty different. I can't seem to find that thread.)

Thanks in advance.
-Matt

[Bill@HPTuners]

properly tuned huh...well properly tuned on say a fbody with LT headers, !cats, catback would probably have 1.13 at all cells up till 4000 rpms then 1.15 at 4000 and 4400 and 1.13 up to 6000 where it would probably be 1.15 again...now that would be with full VE tuning, COT deleted blah blah blah.

[redhardsupra]

i do it the other way. start leaner, end up richer. kinda like with timing, you can have a lot of timing down low, but not as much up top. there is simply less load down low, so it takes a lot more timing/lean condition to blow things up. conversly, on the high rpm end of things, there is so much more compression/load on the mixture, that you simply don't need that much timing, as the molecules bump into each other easier, causing a quick and complete combustion.

the real problem is that afr/timing are very intertwined, so you can't really discuss one without the other. some cars like more aggressive timing, others like leaner mixtures. you just gotta try a few combos and see which one yields best times. if you don't wanna deal with it too much, go for a nice 'middle of the road' combination, i find that 26degs/12.6afr works pretty well for just about everyone.

this saturday i'm going to the dragstrip to verify some more theories about timing/afr combination and their effects, so i should be able to post more on this later.

[Scooter70]

Thanks Supra-man. I'm also headed to the strip on Saturday, so that's why I posted the question in the first place. My SD tune is decent enough and I have an MAF curve for my setup (thanks to your spreadsheet) so I wanted to make sure that the PE table was in line before making passes. Right now the stock table is 1.25 across the board so I wanted to know if I could change it up and get a little more out of it.

14.7/12.6=1.17

I'm not setting any ET records so 1.17 across the board should get me started, right? I'll log some runs and watch WOT O2 readings to see where they sit. My goal is a 12 second timeslip. I'll post results later this weekend.

-Matt

[redhardsupra]

you might wanna bump up the precision on your math. grab the stoich from your bin (they differ a bit from year to year, i don't know why) and get your numbers exact. my setup is set to 14.62/1.16=12.6

[Scooter70]

I just started looking over my dragstrip logs. On a couple of runs, bank 1 O2 was ~877mV and bank 2 was ~920mV at WOT. Why is there that much difference between the two? Is that "normal" since narrow band sensors aren't that accurate down around 12.6:1?

All in all, I was happy with the day. I didn't get the 12 second timeslip that I wanted, but it will come with some practice launching. My best run was a 13.2 @ 108 (2.2x 60'). Looking thru my logs, it looks like my 0-60 time was around 4.8 seconds. Not bad considering how much wheelspin I was getting.

[redhardsupra]

hmm...that seems to be a slightly 'off' time, i got a [email protected] (2.0x 60ft) in my heavy (road racing parts) formula, on a much smaller cam and a completely off tune. is your car extra heavy, or the tune is just off? what kind of timing do you get? any knock? post your logs, especially if you have actual logs of the quarter mile runs.

[Scooter70]

I'll post an Excel sheet with 6 runs when I get home. I couldn't launch the car and get it to hook to save my life. 2.2-2.4 60' times with heavy wheelspin thru first gear. If I launched at a lower rpm, it would just bog. The mph shows that the car is making power but the ET shows that I don't know how to drive it.

The car should weigh ~3300 with me in it. I haven't put it on a scale, so it's just a guesstimate. My setup is: TR224-112, stock LS1 heads, '99 F-car manifolds thru 2.5" chambered exhaust (no cats). Opening up the dumps gained a couple of mph but didn't do much for ET.

-Matt

[Scooter70]

Excel sheet with six drag strip runs. The first sheet has 3 runs with full exhaust. The second sheet is with the exhaust dumps open.

Here's my current .bin. If you see anything interesting, I'm open to suggestions/comments.

-Matt

[Scooter70]

I'm bringing this thread back from the dead to see if anybody has any new comments. It's been 2.5 years. There must be some agreement on what a PE curve should look like by now.

On a side note, I ran a 12.90 a few months after I posted this thread. I haven't been back to the drag strip with that car since but I know that there's more in the tune if I had time to work on it.

Right now, I'm playing with my DD LS2 GTO so that's what made me bring the thread back. Would the values of XX.X be different for an LS2 with the added displacement and/or compression?

[5_Liter_Eater]

I don't know that there is a magic bullet PE curve. The best way to do it that I can think of is to do a dyno pull at say 12.6:1 flatlined. Then one at 13:1. Lay the dyno graphs on top of each other and wherever the HP and/or torque numbers are higher, use that AFR for that range.

[PurplePiss]

I know where he is coming from. There seems to be a lack of information on the LS2. Everyone out there will tell you what an LS1 or LS6 likes. 24-26* 12.9-13.1 AFR. Then you ask about the LS2 and people say it depends. Is it because of the higher compression ratio?

I've been trying to dump logs, create excel spreadsheet to help compare tune results and haven't come up with anything conclusive. I do not think the calculated torque PID in HPT is worth anything, not even to spot a trend. It doesn't seem to correlate to faster track times. I have 2 tunes, one reads 350 ft lbs and another reads 410 ft lbs and both run the same time and mph.

I'm thinking about creating a histogram to just plot lb of air moved per rpm/load. Comments on that? Can someone setup a histogram like that?

If I run "Diablo 93" timing, I get knock. Expecially tip in knock. Could mine have too much compression?

Also, my car is basically stock except for my cat back and omega IAT. What would cause my maf % error to be -4 to -8 from 8000 hz to 10000 hz? Shouldn't mods make a car leaner?

[5_Liter_Eater]

You could plot dynamic airflow (g/s) or dynamic cylinder air (g/cyl) against the VE table so you could see how much air you're moving but you'd have to open two logs at once to see which one was higher in what range and then correlate that to what is different in what range. There wouldn't be a super easy way to show the deltas in airflow at each point between two logs.

It would really be best to do it on a dyno. Start off with a base run, lean out the AFR by 1/2 a point or so via the PE and see if it helped or hurt all throughout the RPM range. Keep it where it made power, roll it back where it lost power. Then try richening it up by ~1/2 point or so. Keep it where it made power and roll it back where it lost. Now you should have an "ideal" AFR and can then play with the timing which may throw your ideal AFR off.

[PurplePiss]

I was using this spreadsheet I created to compare torque and timing results. It uses rounding and conditional formatting. I think it could be used to compare airflow, which may ultimately be a better way to figure out what makes the most torque.

Can someone help setup a histogram to show how much air your moving per load/rpm?

Rename from .bin to .xls. (Can we get the xls size limit upped)?

[PurplePiss]

Would this histogram be good to use to compare scans?

[eficalibrator]

You will find that the torque (power) gains from a change in AFR in the region from 12.6-13.2 are relatively small. Timing has a much more profound effect, provided you are not getting into knock. As Marcin said before, the two are related. Richening the mixture below ~13.0AFR has the net effect of slowing burn rate, which requires an advance in timing to maintain the same torque, but also ALLOWS for a little further advance before getting knock.

I usually set PE flat as long as MAF measurement isn't pegged and the injectors continue to flow as modeled (not losing flow rate due to an increase in manifold pressure without a boost reference regulator) for most street performance applications. With this flat target AFR, it's easy to see if my airpath and fuel modeling are correct and I can still add/remove timing as necessary to make torque or avoid knock with a more or less constant safety margin.

In the OEM world, we use PE as a cooling agent to control steady state exhaust component temperatures (in addition to COT logic), so this tends to drive some of the "crazy" OEM curves you see where more cooling is needed at some points vs others.

[EC_Tune]

Exhaust systems will change the AFR requirements as well. I had a head/cam car on the dyno and it would barely break 400 ft/lbs peak at 13.0 until I leaned it out to 13.3 then it jumped into the 410 ft/lbs range. Top end only moved by 1-2 HP though.

BTW: I added a couple degrees of timing to my "street tune" and it did nothing, took out two degrees and it fell off.

Dyno's and dragstrips are the most reliable methods of finding what your engine *truely wants* : as long as you do your part at the diggs.