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    Thread: Timing Curve

    1. #1
      Join Date
      Sep 2005
      Location
      Enville TN
      Posts
      61

      Timing Curve

      Let me know what you guy's think about the timing curve. I've not tuned the mechanical or vacuum advance yet. I'd like to get some opinions on a starting point for my setup. I started with 35 deg total, but pinged a little. I lowered it to 32 deg and I'm not hearing any ping.

      Current Timing Curve:
      • 20 deg initial (sounds high, but is due to mech advance only 12 deg)
      • 32 deg total @ 3000rpms (12 deg mechanical)
      • 45 deg total @ 1000rpms w/ vacuum advance (25 deg vacuum)
      Engine Setup: (68 Camaro)
      • 383 Gen 1 SBC (.060 over) Eagle rotating assembly
      • 2 Valve relief flat pistons
      • 5.7 rods
      • Bowtie Phase 2 heads fully ported and shaved to 58cc
      • RPM Performer intake
      • 284 Comp Xtreme flat tappet hydruaulic cam
      • 750 Speed Demon carb
      • MSD 6A Ignition w/external coil HEI setup
      • 350 Turbo w/3000 stall
      • 4:10 rear gear
      Thanks for the help,
      Jim



    2. #2
      Join Date
      Oct 2004
      Posts
      2,544
      Country Flag: United States
      Looks good. With that initial, I bet you have a nice idle even with that cam too. Any problems with starter load (on restart) after the car is fully warmed up? If not, leave it.
      Red Forman: "The Mustang's front end is problematic; get yourself a Firebird."

    3. #3
      Join Date
      Sep 2005
      Location
      Enville TN
      Posts
      61
      Quote Originally Posted by amcmike
      Looks good. With that initial, I bet you have a nice idle even with that cam too. Any problems with starter load (on restart) after the car is fully warmed up? If not, leave it.
      It starts fine hot or cold, but it does have an aftermarket high torque starter. I don't notice it sounding like it's loaded while starting. You would think I'd have more mechanical advance than 12 degrees. I think it's close enough for now.

      Thanks for the opinion,

      Jim

    4. #4
      Join Date
      Aug 2009
      Location
      Langley BC, Canada
      Posts
      264
      My set up is pretty close to yours and I run a total of 35 deg total including I believe 19 of mech adv all in by 3000 rpm (I guess that leaves me with 16 of initial and 25 including vac adv at idle and cruise). This was set up on a dyno too. I also have 9 deg of vac adv hooked up to FULL manifold vac NOT ported. This has made a huge improvement on idle performance and mileage.

      Just my 2 cents

    5. #5
      Join Date
      Sep 2006
      Location
      Southern Indiana
      Posts
      4,699
      Country Flag: United States
      If you look under the centrifical weights and plate they mount on the limit pin may have a bushing thats removable (dist upside down looking at bottom of advance assembly or pulling it apart to view) you can also enlonggate that hole or weld up as needed to limt or increase advance.
      I gnerally habe best luck with stock advance weights, no limiter on cent, advance, I generally give my cars in the 16 to 18 degree range, as much centrifical advance as they will take and not ping and get longest amount out of vac advance as possible. oh and I start with lightest advance springs then add one at a time stiffer as needed.
      Heck my 402 big block ran 62 degrees total , hardly ever pinged unless I ran less than 93 octane (we had 94 around at sunoco station). That engine still around and going into a 80s 2dr Caprice and with 355 gears, th400 made 14.5 to 15 mpg, so if I can get a 700r4 I hope to break 20 mpg with my big block.

    6. #6
      Join Date
      Oct 2004
      Location
      Papillion, NE
      Posts
      203
      I think you are good as described, the smaller and more turbulent the chamber and higher the compression (separate issues even though it seems like its the same) the less it will need total, and if it starts, nothing wrong with high initial.

      You may experience stinky exhaust at idle that you want to blame the carb, but its only that the EGTs are so much cooler with the high initial it doesn't burn the stink off

      Finally, not sure where you are from, but lots of initial (and a quick curve) is bad for emissions testing too, so dont expect it to pass a sniffer if required.
      70 Mustang - 489 cid FE, KC ported Edelbrock heads, Modified Victor Intake, Mass-flo EFI, Erson valvetrain, Supercomps, TKO-600, 4.10 9 inch.
      71 F-100 4x4 SB 4x4, 461 cid FE stroker, Edelbrock Pro-flo 4 EFI
      13 Ram Laramie 2500 4x4 6.7 diesel - trailer puller





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