Page 1 of 2 12 LastLast
Results 1 to 10 of 17

Thread: DFCO exit timing - Table b5150

  1. #1
    Lifetime Member
    Join Date
    May 2007
    Posts
    254

    Default DFCO exit timing - Table b5150

    After recently having the cat back fitted to release the noise that had been thus far strangled by the stock system I have steadily become tired with the DFCO exit pops and bangs. With the new system it sounds like I am doing the old kill switch trick we used to do on bikes. The subtle pops/bangs are nice but at certain loads the thing sounds embarrasing.

    So looking to smooth the step back into normal fueling from DFCO, the table that looks best placed to do this is b5150 but the question is to lessen the bangs, should timing be increased closer to normal spark timing or decreased further to lengthen the time taken to return to base spark?

  2. #2
    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
    Join Date
    Jul 2008
    Posts
    1,807

    Default

    Quote Originally Posted by stigmundfreud View Post
    After recently having the cat back fitted to release the noise that had been thus far strangled by the stock system I have steadily become tired with the DFCO exit pops and bangs. With the new system it sounds like I am doing the old kill switch trick we used to do on bikes. The subtle pops/bangs are nice but at certain loads the thing sounds embarrasing.

    So looking to smooth the step back into normal fueling from DFCO, the table that looks best placed to do this is b5150 but the question is to lessen the bangs, should timing be increased closer to normal spark timing or decreased further to lengthen the time taken to return to base spark?
    Running a different OS, but can't you just disable DFCO by temperature (a.k.a. LS1's)? If you can't then you want to slow down the spark ramp back to normal timing to lessen the sensation of engine braking. Though that will make it last longer, it is a very gradual braking at that point. I don't know if that will eliminate the 'popping' sound..short of disabling it..
    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
    200cc Heads, 228/232 110+2 Cam, 1 3/4" LT's w/catts, GMMG, Koni Shocks, Hotchkis Springs, 35/21 Sways, 17" ZR1's, 3.90 Gears Roadrunner PCM LM-2 Serial Wideband
    EFILive Closed-Loop MAF/SD Hybrid Tune..


  3. #3
    Lifetime Member
    Join Date
    May 2007
    Posts
    254

    Default

    more than happy to disable and yes even in this OS we have similar enablers/disablers. I was leaning towards lowering the exit spark start point so less spark = less bang though at the same time was thinking the closer to end spark rate you start the ramp in from would lessen the bang cycle so could reduce the actual big bang. You know the nice rumble when dfco exits? Thats what I want to keep but at town speeds the exit from DFCO ends up with a massive pop, its all on stock so the noise is purely related to the lack of silencing but I want to reduce it. Will try both lower and higher settings to see which is closer to what I want. The trade off if lower settings work is that I will spend longer waiting for true throttle response which can be a bad thing if it ends up like a bmw330 which can take up to 2 seconds for throttle response!!

  4. #4
    Lifetime Member
    Join Date
    May 2007
    Posts
    254

    Default

    anyway its time you and Joe both upgrade to e38's to share your enthusiasm on a newer platform!!

  5. #5
    R.I.P Shawn, 1956-2011 WeathermanShawn's Avatar
    Join Date
    Jul 2008
    Posts
    1,807

    Default

    Quote Originally Posted by stigmundfreud View Post
    anyway its time you and Joe both upgrade to e38's to share your enthusiasm on a newer platform!!
    You may be right. I was reading an article in GM High-Performance today that was insinuating the same thing. I know.. I have gotten too specialized and narrow in my understanding of tuning...

    I would be interested in your DFCO Spark results. I have played around with spark ramp rates and amount of DFCO spark. My goal is a little different. Running up and down the Mountains around here, I try to find that DFCO 'sweet-spot' where I can go down a 2-3 mile decline..hold gear and never use the brake.

    If I recall that initial pop is right when DFCO releases? I hear it, but it kinda rumbles with the exhaust. But, I agree under certain circumstances you don't want it to do it.

    Let me know what you end up doing.

    Good luck..
    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
    200cc Heads, 228/232 110+2 Cam, 1 3/4" LT's w/catts, GMMG, Koni Shocks, Hotchkis Springs, 35/21 Sways, 17" ZR1's, 3.90 Gears Roadrunner PCM LM-2 Serial Wideband
    EFILive Closed-Loop MAF/SD Hybrid Tune..


  6. #6
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    27,752

    Default

    Quote Originally Posted by stigmundfreud View Post
    anyway its time you and Joe both upgrade to e38's to share your enthusiasm on a newer platform!!
    I would like to, but GM USA doesn't make a 2 door performance coupe in my price range......anything good is promptly EOL'd.

  7. #7
    Lifetime Member
    Join Date
    May 2007
    Posts
    254

    Default

    You could weld up the rears in the g8!

    Current settings are nice for duration of dfco meaning good brake rate whilst staying off the power but the ramp in is causing the issues. I'll report back on the findings though I might just go and disable dfco (assuming it retains cfco)

  8. #8
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003
    Posts
    27,752

    Default

    Pontiac is being dissolved.

  9. #9
    Lifetime Member
    Join Date
    May 2007
    Posts
    254

    Default

    blimey!

  10. #10
    Lifetime Member
    Join Date
    May 2007
    Posts
    254

    Default

    Well I took 20 degrees off the timing through the range, improved things a lot at sub 2500rpm = much more subtle but feels almost like a slight surge when tipping back in, presumably as it now takes that little longer for the spark to catch up. Still getting big pops about 2500 but much less than before, a bit more timing pulled here could improve things but there is only so much you can do when you have the vacuum issues to contend with.

    So in the end i just disabled it, I cannot see it making that much of a saving but certainly the DFCO cannot be too great for cat life. So bye bye big pops and bangs but still get a nice run down sound and cfco still in effect.

Page 1 of 2 12 LastLast

Similar Threads

  1. timing table maxed out?
    By ryans1000 in forum General (Petrol, Gas, Ethanol)
    Replies: 26
    Last Post: December 1st, 2009, 08:14 AM
  2. Stage 3 timing table
    By dennisscars in forum IL6,IL5,IL4 Atlas Engines - P12 PCM
    Replies: 0
    Last Post: November 14th, 2008, 04:09 PM
  3. DFCO Timing?
    By N0DIH in forum General (Petrol, Gas, Ethanol)
    Replies: 18
    Last Post: September 27th, 2007, 07:01 PM
  4. Boost Timing Table
    By marcink in forum Custom Operating Systems
    Replies: 2
    Last Post: April 24th, 2007, 07:27 PM
  5. DFCO table questions
    By QUICKSILVER2002 in forum General (Petrol, Gas, Ethanol)
    Replies: 17
    Last Post: March 13th, 2006, 12:44 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •