JDMC5

iTrader: (3)

yes, timing's role in gas mileage is maximizing power at part throttle. Thats actually how you tune part throttle timing on a dyno. Your basically getting the most cylinder pressure out of the a/f mixture, I.E. the most torque, to keep the vehicle moving at the lowest possible throttle position. Otherwise you would have to introduce more a/f to get more power and in turn use more gas.

LS1 Racing

iTrader: (15)

So, it definitely is possible to drop down to 87 Octane, even in a high compression motor like the LS4, and not lose fuel economy.

Now it's just a matter of how much HP loss we'll see. And I'm wondering if the usual mods will help off-set the loss of HP. In other words, with the mods in my sig and an 87 octane tune, could I perhaps expect near-stock performance, instead of being down HP?

JDMC5

iTrader: (3)

yeah you should have at least stock power levels with your mods, probably more.

BTW, don't forget the DOD timing tables.

06MonteSS

you'll have better performance than stock, even with the 87 octane gas...

EmersonHart13

iTrader: (3)

Lew rocks, it is too bad that Diablo hasn't given you TCM yet... These cars will be so wicked once you get your hands into there!

LS1 Racing

iTrader: (15)

Sweet! Sign me up!

We'll fillup with 87 in the next week or so, and I'll get a log.

Lew, is there anything additional that you'll need to be logged for this project?

JDMC5

iTrader: (3)

well not to step on any toes but, he shouldn't even need any logs. Diablo doesn't have any TCM tables???

06MonteSS

hahaha.. don't need logs for any tcm/tranny stuff... but there ARE a lot of parameters to log for the engine side of the tune man... fuel trims, timing, knock retard, rpms, intake air temp, etc etc etc... just to name a few... hahaha...

LS1_Racing - just log the usual that I need....

air fuel ratio (Equivalence Ratio)
commanded throttle position
engine speed (RPM)
intake air temp
long term fuel trim bank 1
MAF Sensor Mass Airflow
spark advance
total knock spark retard


.

JDMC5

iTrader: (3)

ok I'm confused, I thought you were just turning an already tuned 93 octane tune into a 87 octane tune, which in that case would only require the reduction in timing.

LS1 Racing

iTrader: (15)

Looks like I'll be doing the log today. My wife mistakenly put 87 in it when she filled up yesterday. Apparently, she got used to driving our Saturn for the last month while the Impala was getting the trans work done. So, we'll top it off again with 87 and run a log.

Lew, do you need me to flash back to a stock tune with no DoD for the log?

06MonteSS

LS1 - nah, no need to flash back to stock... the 91 octane tune you have in the car now uses the stock timing table already... so that's why I want a new data log with that tune in the car, to see what the timing is doing, KR levels, where KR occurs, how much, etc etc...

JDMC - correct, well, kind of.. he's using the 91 octane tune, not the diablo/93 octane tune.. and the 91 octane tune, uses the stock timing table... but I still want a data log to see any KR levels.. I could just reduce the timing by -2* or whatever, but that doesn't mean it's going to be enough depending on how his car's running... and I don't want to just do a blanket change of the timing table.. I'm going to pinpoint the problem areas by rpm, g/cyl, etc... so yes, I do want a data log - and that will give me all the info I need...

LS1 Racing

iTrader: (15)

Thanks, Lew. I'll get that log to you tonight.

JDMC5

iTrader: (3)

just remember that timing advance to the point of kr doesn't always mean MBT. If you do that his timing might be a little over advanced. Not saying your going to notice it in mileage, maybe, maybe not. Just stating the facts.

LS1 Racing

iTrader: (15)

Did my log last night and sent it to Lew.

Surprisingly, when running 87 octane fuel with Lew's 91 octane tune, I still get less KR than I used to get with 91 octane fuel and the stock tune.

JDMC5

iTrader: (3)

not that it matters but where do you see the KR when you see it? I would expect you are seeing it during throttle changes and WOT.

If the timing tables are the same then it's a matter of fueling, I'm sure with his tune your getting more precise metering of the fuel warding off KR.

LS1 Racing

iTrader: (15)

Didn't see any at WOT, but when cruising at 2000 RPMs or so in 4th, I would see it at TCC lockup. Also, I see it under moderate load (slight hills) at 1500-1600 RPMs in 4th, but that was not logged.

I attached the log, if anyone is interested. I had to upload as a .tun file so I could ger around the limitations of the site. When you download it, you'll need to change the file extension to .log. To view the log, you'll need DataViewer, which is a free download from the DiabloSport website.

nmp0098

Why Total Knock Retard and not just Knock Retard? I find that looking at Burst Knock too just makes it harder to see any real knock.

Edit: Unless Diablo uses different PID names than the Tech II and HP Tuners, that is...

06MonteSS

on the newer vehicles, "knock retard" would show the max allowable retard setting for a particular area...

"total knock spark retard" shows you the actual retard value of how much timing is actually getting pulled at that point of KR...

so... I want to see what is actually happening and the actual amount of timing being pulled at the point of KR... don't care what the max is that it would allow...

and yeah, don't really need to see burst knock.. that won't tell ya anything about actual/real knock happening...


yep, I know all about that man... have done this a few times before

and I'm not advancing it anyway... I'm looking for any areas where it may need to be reduced, if he's getting excessive KR (more than 2*) anywhere when using the 87 octane gas...

nmp0098

Maybe this is a naming thing, but there are two Knock Retard PIDs, one called Knock Retard (in a Tech II and HP Tuners) and one called Total Knock Retard (in a Tech II and HP Tuners). The one called Knock Retard behaves as you describe above, while the one called Total Knock Retard includes Burst Knock as well. You can find Burst Knock Retard by subtracting Knock Retard from Total Knock Retard.

LS1 Racing

iTrader: (15)

Update on our progress:

We're on the second iteration of the 87 octane tune, and we're fighting our way through some heavy KR issues at crusing speeds under moderate load (up hills and stuff). There was a huge improvement from the first tune to the second, but there's still some pretty ugly stuff under load.

Lew will probably be taking another stab at this on Sunday, and I'll update again when there's more info.