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Thread: Add Highway mode to LT1

  1. #61
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    Quote Originally Posted by Fast355 View Post
    Burst knock retard does not show up as actual knock retard.

    You won't get more than about 40° advance into a distributor that has the base timing at 0.

    The aluminum head L98 Corvettes ran up to 48° in their timing maps. They had horrible quench as well.
    The L98 corvette table maxes at 46* with a programmed limit of 41.84* to override the table. Stock the distributor is set to 6* advance and the computer is designed to account for this. Now lets go so far as to say the computer is not factoring it out and the hard limit is not actually there, Highest you will see is 52* at 2000-7000rpm with a MAP of 40. The only way to get to this point is with the throttle plate closed so coasting/ decelerating. For Loaded situations the table shows closer to 42* under normal cruising conditions but remember the hard limit and the factored advance.

  2. #62
    LT1 specialist steveo's Avatar
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    Quote Originally Posted by Fast355 View Post
    Burst knock retard does not show up as actual knock retard.

    You won't get more than about 40° advance into a distributor that has the base timing at 0.

    The aluminum head L98 Corvettes ran up to 48° in their timing maps. They had horrible quench as well.
    huh? the opti doesn’t have any problems up to 50 degrees of advance. its a huge cap.

  3. #63
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    Stock lt1 software limit is 46 degrees. I have no idea if it is software limitation or hardware opti limitation. Someone have to guinea pig the setting to 52* and see if the pcm freaks out.
    It is not good idea to compare lt1 with 96-00 vortec engine. They have different intake and suppose different chamber and dynamic flow characteristics.

    Lt1 have unique intake manifold that brings all kind of nightmare tuning situations. It also doesn`t like too much advance at low loads on cammed cars. I had terrible knock at 25-35 kp range and had to lower stock settings. Than found that lt4 also had less advance at that range.

    I forgot to mention that freeing up the exhaust can reduce map and fuel consumption. Confirmed with logs on bad muffler replacement with free flowing one.

  4. #64
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    Quote Originally Posted by kur4o View Post
    Stock lt1 software limit is 46 degrees. I have no idea if it is software limitation or hardware opti limitation. Someone have to guinea pig the setting to 52* and see if the pcm freaks out.
    It is not good idea to compare lt1 with 96-00 vortec engine. They have different intake and suppose different chamber and dynamic flow characteristics.

    Lt1 have unique intake manifold that brings all kind of nightmare tuning situations. It also doesn`t like too much advance at low loads on cammed cars. I had terrible knock at 25-35 kp range and had to lower stock settings. Than found that lt4 also had less advance at that range.

    I forgot to mention that freeing up the exhaust can reduce map and fuel consumption. Confirmed with logs on bad muffler replacement with free flowing one.
    I'll test it out in the next few days. First will be just overriding to add the 6* over the table with EEhack then if it doesn't freak out I'll add it to my table.

  5. #65
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    So I was able to run as much as +10* spark advance without knock or malfunction during cruise. Hotter coolant temp and less throttle used so a win I guess. Fwiw there is a programed 46* spark limit that can be changed. I know I had it maxed for a significant time.
    Last edited by space387; 12-11-2019 at 03:47 AM.

  6. #66
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    So I was able to run as much as +10* spark advance without knock or malfunction during cruise. Hotter coolant temp and less throttle used so a win I guess. Fwiw there is a programed 46* spark limit that can be changed. I know I had it maxed for a significant time.
    Did you change the spark limit scalar before testing? Set it higher before the test or the advance will be capped at 46* no matter how much you command in eehack.

    Be careful, more advance than the optimal will destroy crank bearings in no time. The map change can be used as a guide.


    I am thinking to add a 4cylinder mode as a patch and controlled with external switch. Will it be any beneficial to fuel economy is still unknown. There will be a forced open loop needed to prevent blms from wacking.

  7. #67
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    Quote Originally Posted by kur4o View Post
    Did you change the spark limit scalar before testing? Set it higher before the test or the advance will be capped at 46* no matter how much you command in eehack.

    Be careful, more advance than the optimal will destroy crank bearings in no time. The map change can be used as a guide.


    I am thinking to add a 4cylinder mode as a patch and controlled with external switch. Will it be any beneficial to fuel economy is still unknown. There will be a forced open loop needed to prevent blms from wacking.
    No I found the spark limit of 46 doing this and looked further into the tune for confirmation. The issue with running the car in 4cyl mode and not disabling the valves too is you will still burn almost as much fuel and end up with a higher parasitic draw from the non firing cylinders still making compression. Its wort a try but I wouldn't expect much in the way of gains.

  8. #68
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    Quote Originally Posted by space387 View Post
    The issue with running the car in 4cyl mode and not disabling the valves too is you will still burn almost as much fuel and end up with a higher parasitic draw from the non firing cylinders still making compression.
    It's worth a try but I wouldn't expect much in the way of gains.
    1stly, yes, what space387 said; if all 8 cylinders are inhaling and compressing but only 4 are actually making power, those four will use MUCH MORE FUEL - except maybe during non-DFCO coastdowns.
    I wish every 0%TPS deceleration would DFCO, but many do not, and the O2 sensors are always aiming @ 14.7 AFR.

    NorthStar V8s use a 4cylinder contingency mode when coolant temps hit 266°F / 130°C. https://www.youtube.com/watch?v=0YWOf6u1sb8
    [266°F / 130°C is WAY too late for an all-aluminum engine; 239°F / 115°C would be more sensible. (I'm nuts enough to activate OverHeat Enrichment as early as 221°F / 105°C on my all-iron LT1).]
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  9. #69
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    well it finally happened. I bricked the PCM trying to flash a new tune. As a temporary I am going back to megasquirt as it is already tuned for this car just not great. After the holidays I plan to try and resurrect the bricked pcm.

    So I have a moates Burn 2, can i use that with an adapter to flash a new chip to get the ecu talking? Also what is everyone using for a USB adapter, I diy'ed my own but I think it was not up to the task. Would like to make another one just need the proper chip.
    Last edited by space387; 12-12-2019 at 08:30 AM.

  10. #70
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    Quote Originally Posted by kur4o View Post
    I am thinking to add a 4cylinder mode as a patch and controlled with external switch.
    That's not really going to very beneficial to economy because you'll still be using energy pumping air through the engine. What GM is doing on the late model stuff works as well as it does because it collapses both intake and exhaust lifters at BDC of each de-activated cylinder and then leaves them closed throughout the reduced displacement mode. This causes a minimum amount of pumping loss because the compressed air acts to push the piston back down the bore after TDC. It also introduces no oxygen into the exhaust until it reverts back to normal displacement, so the ecu only has to disable BLM learning for the one engine revolution it takes to re-activate the collapsed lifters.

    Disclaimer - "as well as it does" is highly subjective. By itself, the increase in efficiency isn't very significant unless it's coupled with other fuel saving techniques. You're still losing energy moving the pistons, just not as much as if you were pumping air through the engine.

    Edit: Another consideration to a 4 cylinder mode without cyinder de-activation is catalyst flare / overheating.

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