Displacement on Demand - Highway Use

[Penguin]

Congrats Penguin!

Try lowering the 4-th gear numbers on the "DOD Vacuum Table Disable Vac" table at the RPM where you would like it to hold V4 mode a little more.

That is what I was thinking too, with the new charts the V8/V4 is just as smooth as ever so should be some left. Pedal position bumped to 15% as well from 6%. On the shifting after doing some reading I understand actually need to bump shift pressures up a bit to firm my 1>2 shift up but I will wait on that until I install my corvette servo (on the way).

Never bought the truck for mileage of course, but doesn't hurt to learn a bit. Eventual plan is L92/6speed once the prices drop a bit (might even trade in once 6 speeds come across the board and then its just a matter of swapping in a crate LS3).

[LazMan]

I am writing a "ridiculous V4 time" tune for my Monte Carlo now. The opposite of the tune I posted earlier (ridiculous V8 time) ... I'm testing using values of 0.01 at some points to keep it in V4 mode as much as possible, no harm done (and it does get out of V4 mode when you give it a lot of pedal).

Ive set my enable pedal position to 9.5 ... never liked more than 10% ... but on a truck with tons of wind resistance, I can see where going a bit higher than that could be useful.

[Penguin]

I am writing a "ridiculous V4 time" tune for my Monte Carlo now. The opposite of the tune I posted earlier (ridiculous V8 time) ... I'm testing using values of 0.01 at some points to keep it in V4 mode as much as possible, no harm done (and it does get out of V4 mode when you give it a lot of pedal).

Sounds interesting. I made a few minor changes right at the speed that I want, we'll see what happens. I do wonder what would happen if you allow it to lug too much in V4 mode? Any thoughts?? Also added vac info for next couple scans, so can see exactly where its running.

[Russ K]

You make the engine stay in V4 mode under high loads, but the TPS% will be high enough to enter PE! Also the engine will actually vibrate the vehicle when in V4 mode under high loads, and your not really improving the fuel mileage anymore.

Russ Kemp

[Penguin]

You make the engine stay in V4 mode under high loads, but the TPS% will be high enough to enter PE! Also the engine will actually vibrate the vehicle when in V4 mode under high loads, and your not really improving the fuel mileage anymore.
Russ Kemp

That would be a pretty extreme case though, correct?

[LazMan]

From my experimenting, Russ is absolutely correct. Extreme V4 mode requires either relaxed TCC numbers or putting up with lots-a-shaking. ... and the fuel MPG is not better, in fact it gets worse.

Still, its been interesting to get a feel for both ends of the V4 spectrum.

[BAD LS1]

I tried these V4 settings on my 06' MC-SS and it deff keeps it in V4 longer, tends to lung now when it slips into V8 on a hill.

My issue is that i cant tweak DOD specific timing like the 07's. I could not find a spark table specifically for this like i saw in that 07' file above.

The thing runs about .45g/cyl when crusing in V4, ive got the timing set to like 38 right in that range on the regular spark table, still reads a flat 27* in V4.

I got the DFCO activating regularly and leaned out the o2' signals to .350 and it all seemed to help it get about 28-35 mpg in V4 on instant economy @ 65 mph and about 28-24 @ 70

[LazMan]

Yep. I gave up on such extreme DOD. Wasteful. Just makes the engine lug.

The O2's are ignored by the LS4 computer when they are below 450. I set them in the hopes this will be fixed one day.

Log your "IAT advance" and "ECT advance" and see if they aren't negative. If so, then they are pulling timing for you when you are trying to cruise.

Ive gotten better MPG by playing around with the torque converter lockup lots more lockup in V8 (the max) and a little more in V4 (the min and somewhere in between) and am not working to make things smoother.

Less lock-up gives you more V4 time without lugging. Too little lock-up means waste of fuel too though because the RPM are always around 2200rpm no matter what the speed. Too much and it BUCKS like a bronco and wastes fuel because V4 needs a looser converter. I'm looking for a happy medium.

I also shift sooner from 1 to 2, from 2 to 3, and from 3 to 4 than stock at the lightest of throttles.

Got my @80MPG from 20-22 when I was forcing V4 mode and lugging the engine to 25-27MPG, and all over the lower area, and all this with MORE V8 mode than stock! I'll post the tune if you want, and what things to look for. I've still got a little bit of buck left sometimes but its VERY light, and seems like this is pretty close to as good as it gets for this car.

[Penguin]

Just an update, I dropped the vac chart cells just a bit right in the range where it sits at 120hm/hr...def stays on more, but now I can feel it engaging and dis-engaging. Don't like that so going back (its not rough or anything, just don't like it).

I too am seeing pretty drastic timing changes as well when going into V4 mode (from 30 down to 24 or so). Could bump up the timing on the DOD (low) charts or perhaps try premium to see if that helps (no KR but it might use the DOD high chart to advance timing) but that might cost more in the end (would have to crunch the numbers). Also, looks like my 120km/hr cruise in v4 is a pipe dream, you can watch the MAP and the throttle control rising as soon as it engages, then hits about 85kpa and kicks out so the load is just too much I think. 115km/hr is pretty good but kinda slow. Freeing the TCC up might help, but don't want this to get out of control....

[LazMan]

Oh, you can go nuts with this. I had.

[rob82]

So has anybody got to the bottom of the maximum reliable rpm for the DOD lifters? Would they cope 6400rpm occasionally?

[domestic rice]

Laz and GTX,

What method are you guys using to "bump" the timing up? I dont want to just copy and paste your logs, but do want to up my timing a little in hopes of a few hp and mpg. Did you guys just do an across the board increase or just at cruising speeds or what?

[LazMan]

I completely re-wrote my part-throttle timing tables, with the end of making the transition less feelable while getting better mpg than stock. My procedure was (roughly):

1. With DOD disabled, increase non-wot timing.
2. Drive around.
3. Adjust timing if knock.
4. Copy spark tables to DOD spark tables.
5. Enable DOD and drive around.
6. Adjust DOD timing if knock.

Over the year I've owned the car I've learned quite a bit from the experience of dealing with DOD (as well as from Russ and a few others here) ... The trucks (avalanche for example) are a different animal than the cars (Monte SS for example) because of weight, gearing, and wind resistance.

I'd try a 4degree bump past 24g/cyl, smoothed in, at part throttles, and use the procedure above to make sure it takes.

[domestic rice]

I completely re-wrote my part-throttle timing tables, with the end of making the transition less feelable while getting better mpg than stock. My procedure was (roughly):

1. With DOD disabled, increase non-wot timing.
2. Drive around.
3. Adjust timing if knock.
4. Copy spark tables to DOD spark tables.
5. Enable DOD and drive around.
6. Adjust DOD timing if knock.

Over the year I've owned the car I've learned quite a bit from the experience of dealing with DOD (as well as from Russ and a few others here) ... The trucks (avalanche for example) are a different animal than the cars (Monte SS for example) because of weight, gearing, and wind resistance.

I'd try a 4degree bump past 24g/cyl, smoothed in, at part throttles, and use the procedure above to make sure it takes.

why from 24g and up? any problem with doing a 4deg increase across the whole graph? Maybe even hit the smooth a time or 2?

whats the purpose of disabling the DOD, cant you just adjust both as you go?

[domestic rice]

I was just comparing the 2 tables (high oct. spark vs. the high oct. DOD) and if I was to copy and paste the data from the main to the DOD I would lose several degrees of timing throughout the whole range. My DOD timing is anywhere from 2-13 deg. higher than the normal high oct spark. Is this not so on your car?

[Zim]

I completely disabled my DOD, found i get better performance and better milage if i keep my foot out of it....

[SilverG]

whats the purpose of disabling the DOD, cant you just adjust both as you go?

Because when logging KR you cannot filter the histogram by DOD. So first, you turn off DOD and remove all KR by copy/paste special/subtract. Then when you turn it back on any KR you see must be while DOD is active. At least that is the hope.

When I had DOD off my mileage dropped to 18-19 from 20-21 with it on. I think the biggest difference is coasting to a stop. With DOD the MPG numbers aren’t as high but there is very little drag. With DOD off, DFCO kicks in and starts slowing me down right away. The best mileage is when your foot is on neither pedal and you are moving.

[domestic rice]

Because when logging KR you cannot filter the histogram by DOD. So first, you turn off DOD and remove all KR by copy/paste special/subtract. Then when you turn it back on any KR you see must be while DOD is active. At least that is the hope.

When I had DOD off my mileage dropped to 18-19 from 20-21 with it on. I think the biggest difference is coasting to a stop. With DOD the MPG numbers aren’t as high but there is very little drag. With DOD off, DFCO kicks in and starts slowing me down right away. The best mileage is when your foot is on neither pedal and you are moving.

Do you have your tune handy? I have a 07 LTZ and im getting 12-14 mpg. I look at yours and want to know what is so different to give you so much better mpg.

and thanks for the DOD info, makes sense!

[SilverG]

I don't have my current one here at work (new Vista machine). I will try to remember to send it to you tonight.