Warrenavenue
Active Member
Hey guys, feel free to redirect me to a better place to post this but im looking for some tuning advice with a fresh 496 build in a truck. I figure you B Body guys are a wealth of info on the subject of tuning. Build specs are down at the bottom.
I have about 450 miles on this build and broke it in on a chassis dyno at a friend's shop a few weeks ago. When I broke it in I had the initial timing set around 12* and overall was around 33*. After seating the rings we did a couple full pulls and made 423hp at 4980RPM and 465tq at 4040RPM at the tires on 91oct with a very linear torque curve and a clean and consistently increasing HP curve. Im assuming somewhere around 18% parasitic loss since this is in a 4x4 with 35" tires so not too disappointed in the numbers. I was running an MSD Atomic EFI that did well to fire up and quickly learn the engine but I maxed out the capabilities of the Injectors at 5200 RPM and noticed over the next week that it smelled fat at idle and would diesel when I shut it off. I went around and around trying to track down issues with MSD Tech but ended up finding out that the Atomic can't handle a 107* lobe separation and decided to change it out for a 750 double pumper last week.
Now with the 750 I set the floats, pulled the 73 main jets and put in 72s since im at 2000ft, evenly adjusted all 4 idle screws to a 12.9-13.2 AFR at idle, and an idle speed of around 700 RPM. All 4 screws are a tad less than 3/4 of a turn out from seated. At first I was running 12* initial timing and an idle around 800 but found that it still smelled really fat at idle and wouldn't tolerate anything leaner than 13.5 AFR. It would also want to run on when I shut it down which is really frustrating since its almost winter and ambient temps are down in the 50s so summer is gonna be a real joy! So I bumped initial timing to 16* which has slightly helped with the dieseling (slightly) and it doesn't smell quite as fat but now im concerned that I might be flirting with detonation, especially since this is in a truck with a stick.
Are any of these numbers looking crazy to you guys? Should I be chasing a different idle or bringing initial timing up even more? Im assuming an overall timing in the neighborhood of 36* is healthy for a build like this but I can use all the tuning input I can get from you seasoned tuners out there. Am I running the right plug gap? Are my plugs too hot for the application?
Thank you ahead of time for any insights with this, my head and my wall are getting to know each other way too well.
383 Block
4.310 Bore
4.25 Stroke
11.3cc dish Ross forged pistons
84cc Edelbrock Performer RPM Heads
Comp Ratio is right around 10.39
Long tube Hedman headers
Edelbrock Performer RPM Intake
Holley 750 Double Pumper w/Elec Choke
MSD 6AL
MSD Pro Billet Distributor w/Vac Advance
NGK R5671A-7 gapped at .034"
Manual Transmission
NP435
4.10 Axle Gears
Cam- LS 107*
Dur. @.050 I-229* E-242*
Lift- .345 x .345
I have about 450 miles on this build and broke it in on a chassis dyno at a friend's shop a few weeks ago. When I broke it in I had the initial timing set around 12* and overall was around 33*. After seating the rings we did a couple full pulls and made 423hp at 4980RPM and 465tq at 4040RPM at the tires on 91oct with a very linear torque curve and a clean and consistently increasing HP curve. Im assuming somewhere around 18% parasitic loss since this is in a 4x4 with 35" tires so not too disappointed in the numbers. I was running an MSD Atomic EFI that did well to fire up and quickly learn the engine but I maxed out the capabilities of the Injectors at 5200 RPM and noticed over the next week that it smelled fat at idle and would diesel when I shut it off. I went around and around trying to track down issues with MSD Tech but ended up finding out that the Atomic can't handle a 107* lobe separation and decided to change it out for a 750 double pumper last week.
Now with the 750 I set the floats, pulled the 73 main jets and put in 72s since im at 2000ft, evenly adjusted all 4 idle screws to a 12.9-13.2 AFR at idle, and an idle speed of around 700 RPM. All 4 screws are a tad less than 3/4 of a turn out from seated. At first I was running 12* initial timing and an idle around 800 but found that it still smelled really fat at idle and wouldn't tolerate anything leaner than 13.5 AFR. It would also want to run on when I shut it down which is really frustrating since its almost winter and ambient temps are down in the 50s so summer is gonna be a real joy! So I bumped initial timing to 16* which has slightly helped with the dieseling (slightly) and it doesn't smell quite as fat but now im concerned that I might be flirting with detonation, especially since this is in a truck with a stick.
Are any of these numbers looking crazy to you guys? Should I be chasing a different idle or bringing initial timing up even more? Im assuming an overall timing in the neighborhood of 36* is healthy for a build like this but I can use all the tuning input I can get from you seasoned tuners out there. Am I running the right plug gap? Are my plugs too hot for the application?
Thank you ahead of time for any insights with this, my head and my wall are getting to know each other way too well.
383 Block
4.310 Bore
4.25 Stroke
11.3cc dish Ross forged pistons
84cc Edelbrock Performer RPM Heads
Comp Ratio is right around 10.39
Long tube Hedman headers
Edelbrock Performer RPM Intake
Holley 750 Double Pumper w/Elec Choke
MSD 6AL
MSD Pro Billet Distributor w/Vac Advance
NGK R5671A-7 gapped at .034"
Manual Transmission
NP435
4.10 Axle Gears
Cam- LS 107*
Dur. @.050 I-229* E-242*
Lift- .345 x .345