Announcement

Collapse
No announcement yet.

Should you make EFI super-lean at cruise?

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • #31

    Re: Should you make EFI super-lean at cruise?

    The 4-6-8 failed due to lack of computer power. The 4-6-8 shut the valves off by lifting the fulcrum of the rocker arm. The modern DOD uses oil pressure to collapse the lifters. Both intake and exhaust valves are turned off, so the cylinder becomes an air spring. Neither system cycles which cylinders are "off" either the set of4 is off while in 4 cylinder mode, or they are on. Doesn't alternate or anything like that and its the same 4 cylinders every time.
    Last edited by TheSilverBuick; April 15th, 2012, 11:17 AM.
    Escaped on a technicality.

    Comment


    • #32

      Re: Should you make EFI super-lean at cruise?

      Here's something to think about, on my '99 Z28 at 65mph doing 2200rpm with 6% TPS opening, my injector duty cycle is only 7%, which means for the majority of the combustion cycle the injector is closed....... and at idle the duty cycle is 2%..........

      Comment


      • #33

        Re: Should you make EFI super-lean at cruise?

        Here's something to think about, on my '99 Z28 at 65mph doing 2200rpm with 6% TPS opening, my injector duty cycle is only 7%, which means for the majority of the combustion cycle the injector is closed....... and at idle the duty cycle is 2%..........
        Those are numbers I'm looking at working with on the Sequential injection. It could be internet myth on any savings. Never heard of real proof, just theories.

        My car, I cruise around 18%** TPS, duty cycle at 8%, and 2.5% at idle. Of course my engine is 25% larger. The intake valve timing on the cam in my Buick is open 6% of the 720* of crank rotation after the exhaust valve closes. So I'm going to bump the fuel pressure up to see if I can get the duty cycle down below 6% and try and phase it right. It's academic at this point, and might not net a thing.


        **My throttle body is progressive, the secondaries don't start opening until around 75%, so the true % open is less than 18%.
        Escaped on a technicality.

        Comment


        • #34

          Re: Should you make EFI super-lean at cruise?

          Here's something to think about, on my '99 Z28 at 65mph doing 2200rpm with 6% TPS opening, my injector duty cycle is only 7%, which means for the majority of the combustion cycle the injector is closed....... and at idle the duty cycle is 2%..........
          Something else I found out while chatting with a pal who used to be a GM engineer when your car's EFI controller was being developed, there IS "per cylinder" fuel adjustments that are locked into the LS engine computer. He told me that HPT and EFI Live don't let you access those maps - can you confirm this? Also is there maybe a way you can use your HPT to monitor individual injector pulsewidth or dutycycle to see the differences? He told me this has been in place as far back as late TPI and early LT1 engines, any that had a front mounted throttle body... pretty cool stuff.
          Proudly using www.DIYAutotune.com custom EFI components!

          Comment


          • #35

            Re: Should you make EFI super-lean at cruise?

            Something else I found out while chatting with a pal who used to be a GM engineer when your car's EFI controller was being developed, there IS "per cylinder" fuel adjustments that are locked into the LS engine computer. He told me that HPT and EFI Live don't let you access those maps - can you confirm this? Also is there maybe a way you can use your HPT to monitor individual injector pulsewidth or dutycycle to see the differences? He told me this has been in place as far back as late TPI and early LT1 engines, any that had a front mounted throttle body... pretty cool stuff.
            Definitely cool stuff!!!, I will have to check, there is a lot of stuff you can watch, like when I was looking at misfire data, I was able to do it for each cylinder, that how I know every time 5 and 6 rapped up about 30 misfires that's when the lockup would disengage.......I'll look through it tonight and see.........
            Last edited by TC; April 15th, 2012, 06:58 PM.

            Comment


            • #36

              Re: Should you make EFI super-lean at cruise?

              It would seem to me your not going to find much trying to kill cylinders unless you can kill friction losses with it. You have to make X power to Go Y MPH with the same friction and losses involved.
              2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
              First to run in the .90s .80s and .70's in SBN/A
              2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
              2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

              Comment


              • #37

                Re: Should you make EFI super-lean at cruise?

                It would seem to me your not going to find much trying to kill cylinders unless you can kill friction losses with it. You have to make X power to Go Y MPH with the same friction and losses involved.
                I'm looking at the possibility I have to add more fuel than needed just to support combustion (light off a lean mixture), not necessarily for HP creation. Too much air in the giant cylinders, so double up the fuel in half the cylinders, and lean out from there. Small block guys wouldn't understand too much air j/k!
                Escaped on a technicality.

                Comment


                • #38

                  Re: Should you make EFI super-lean at cruise?

                  shared journal counterbalance..

                  how the heck can anything shut off.

                  I could see a diesel trying it..but gas mistakes. that is milliseconds versus seconds of something slower burning.

                  throwing in some boxer tricks.. I have run on two...could do it all day.
                  I ran misfire my first couple of years (back when I did not understand the boxer, I thought they all just "thumped" along)..

                  big inertia, self balance..go from there.
                  else, I'd be playing with injection dieselgeek has been using..individual cylinders mastered.

                  the vette does something smart enough. I'd stick with that stuff.

                  when it does seem good, real lean..there is other reactions. I could guess engines gain eyeballs sucking in strange things for many yards around.
                  Last edited by boxer3main; April 15th, 2012, 08:53 PM.
                  3...2....1....What happened!?!!

                  Comment


                  • #39

                    Re: Should you make EFI super-lean at cruise?

                    Yes I remember when a 455 was a big block. Now they're small blocks.
                    Drag Week 2012 - Winner Street Race Big Block Naturally Aspirated - Big hat no horses Drag Week 2013 - Watching the live feed Drag Week 2014 - Maybe I'll go faster with a 1000 fewer pounds?

                    Comment


                    • #40

                      Re: Should you make EFI super-lean at cruise?

                      Yes I remember when a 455 was a big block. Now they're small blocks.
                      Dang you Bill!
                      Escaped on a technicality.

                      Comment


                      • #41

                        Re: Should you make EFI super-lean at cruise?

                        Correct me if I'm wrong but an engine is most efficient making about 75-80% of its power as the throttle is more open filling the cylinders more and raising the effective compression ratio. This would mean 4 cylinders would be more efficient at cruise than 8 because the cylinders under power are operating at a higher effective CR. It would follow that your engine would be even more efficient on 2 cyls. at cruise as you would be close to that 75-80% but the engine would probably be objectionable from a smoothness standpoint.

                        Comment


                        • #42

                          Re: Should you make EFI super-lean at cruise?

                          It would seem to me your not going to find much trying to kill cylinders unless you can kill friction losses with it. You have to make X power to Go Y MPH with the same friction and losses involved.
                          that's kind of what I was wondering - how to bleed pressure in your unused cylinders. Since you aren't firing BTDC on those holes, wouldn't you lose some of your friction / pumping losses?

                          I wouldn't want the intake open, but the Exhaust might be a candidate. That would require something besides a cam / spring setup for valve actuation though. As long as I'm daydreaming, a servo based valve actuator would be a total hoot. Programming up a new "cam lobe" with the laptop.. I guess it wouldn't really be necessary.

                          BMW did a study a while back about running WFO and short shifting to get improved economy, I'm not sure what they ever did with the data. I tried to emulate it with the Mustang, didn't see any significant change from normal driving.
                          Last edited by Beagle; April 16th, 2012, 06:56 AM.
                          .

                          Comment


                          • #43

                            Re: Should you make EFI super-lean at cruise?

                            Don't forget pumping losses (and as Oldmachinist stated - throttling losses) and associated heat, unless you can control the valve actuation to the "dead" cylinders to bleed off pressure - the "DOD" idea doesn't work too well.
                            There's always something new to learn.

                            Comment


                            • #44

                              Re: Should you make EFI super-lean at cruise?

                              Don't forget pumping losses (and as Oldmachinist stated - throttling losses) and associated heat, unless you can control the valve actuation to the "dead" cylinders to bleed off pressure - the "DOD" idea doesn't work too well.
                              Going back to post #24.
                              Pumping losses are still big with the valves going, especially with big displacement.

                              This is the angle I'm shooting for. I've gone as lean as I can to support combustion in the cylinders, so if I cut half the cylinders out of fuel, it forces the remaining four to work harder and thus require more fuel, and dropping the AFR's, which opens the possibility of using less fuel over all. Basically the limiting factor in reducing fuel into my engine is to support combustion because running the cylinders even leaner will result in mis-fires, now if I take all the fuel currently being used but distribute it to only 4 cylinders, effectively doubling the fuel in the cylinders that are getting fuel (for cruising), my AFR's at that point can then be leaned out some amount again because those 4 cylinders will likely be running at 13-something to 1 AFR's. If I can cruise highway speeds, on something leaner than 13-something to 1 AFR then it could net some gains. Shutting the valves off is definitely the most ideal and would likely net big gains, 25%?, where as this will likely be 5%(?) or so. So definitely splitting hairs at this point, and I think is really only practical on large engines that have so much volume per cylinder there is a higher minimum fuel requirement per cylinder just to support combustion, not to contribute HP. Remember, four of my cylinders is 3.8L, or 231cid, more than adequate to support highway cruising, and yeah the pumping losses are going to eat at least 75%+ of the gains according to my gut feeling.
                              Escaped on a technicality.

                              Comment

                              Working...
                              X