Carb 5.3 timing curve?
09-05-2016, 06:23 PM
#1
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Carb 5.3 timing curve? I know this is a very talked about subject but I havent seen what im needing yet so i figured id ask,,,, i have a 02 5.3 carbed 600cfm vac sec, msd 6010 box, bone stock engine ,,, getting a dead spot off idle then smooths out,, ive played with carb and got it better but think its time to tune it and get away from the pills wondering if anyone had a stock carbed engine tune on here,,, thanks
09-06-2016, 06:21 PM
#3
Timing curve for a distributor? It depends on the compression and fuel type. If you say 9:1 and 93 octane, you can throw full advance in by 2600rpm usually safe. Sometimes even 2400. That full advance being around 27*.
So you start with around 15* and work up to 27* by 2500~ in a naturally aspirated 93 octane application with 9:1 then you can dyno the vehicle with 25 and 29 and check the difference. I.e. if it picked up 5-10% power with 2* additional then great move. Likewise if you reduce timing and it loses only 1-2% then also great leave it reduced. Always use the minimal timing that shows an average output (this will register with a reasonable EGT if you have an EGT gauge)
Old chevys (2-piece sloppy leaky Iron head engines from 80's) used to run 36* all in, but these days modern engines typically use 6-7* less than that for best performance (they do not need as much timing)
So you start with around 15* and work up to 27* by 2500~ in a naturally aspirated 93 octane application with 9:1 then you can dyno the vehicle with 25 and 29 and check the difference. I.e. if it picked up 5-10% power with 2* additional then great move. Likewise if you reduce timing and it loses only 1-2% then also great leave it reduced. Always use the minimal timing that shows an average output (this will register with a reasonable EGT if you have an EGT gauge)
Old chevys (2-piece sloppy leaky Iron head engines from 80's) used to run 36* all in, but these days modern engines typically use 6-7* less than that for best performance (they do not need as much timing)
09-07-2016, 04:38 AM
#4
There is an entire stickie of timing curves
https://ls1tech.com/forums/carburete...iming-set.html
Carb'd LS motors generally like more timing than fuel injection. Most guys seem to get up into the low to mid 30's before the benefits max out.
Running a MAP sensor will help with your issues. If you don't have the sensor than remember to zero out the map curve, otherwise the dumbass box will apply full vac advance all the time. On the 6010 with pills that is something like 12 degrees. Also remember if you plug in a pill even for a second it wipes out your custom curve.
https://ls1tech.com/forums/carburete...iming-set.html
Carb'd LS motors generally like more timing than fuel injection. Most guys seem to get up into the low to mid 30's before the benefits max out.
Running a MAP sensor will help with your issues. If you don't have the sensor than remember to zero out the map curve, otherwise the dumbass box will apply full vac advance all the time. On the 6010 with pills that is something like 12 degrees. Also remember if you plug in a pill even for a second it wipes out your custom curve.
09-08-2016, 03:04 AM
#5
actually I believe what you are seeing is a phenomenon related to the ratio of carb'd to N/A 'race' applications, where a much larger percentage of sample populations are attempting to gain power by turning their distributors with hopes of a few % and printing about it. you can almost always increase cylinder pressure and torque slightly by advancing the timing; that is why we consider whether the vehicle is a race car, or a street car first. Street cars run the timing much closer to the escalating temperature of exhaust gas, as far from the peak of diminishing returns as possible, whether carb or FI this is true. And as I said first sentance, carb application is more likely to include as "carb tuning" what are "race car numbers" for their applications. They are not suitable for street use, rarely do you find carbs on the street (They are not considered daily driver vehicles much anymore) thus the correlation to threads about race car timing events.
09-08-2016, 12:49 PM
#6
actually I believe what you are seeing is a phenomenon related to the ratio of carb'd to N/A 'race' applications, where a much larger percentage of sample populations are attempting to gain power by turning their distributors with hopes of a few % and printing about it. you can almost always increase cylinder pressure and torque slightly by advancing the timing; that is why we consider whether the vehicle is a race car, or a street car first. Street cars run the timing much closer to the escalating temperature of exhaust gas, as far from the peak of diminishing returns as possible, whether carb or FI this is true. And as I said first sentance, carb application is more likely to include as "carb tuning" what are "race car numbers" for their applications. They are not suitable for street use, rarely do you find carbs on the street (They are not considered daily driver vehicles much anymore) thus the correlation to threads about race car timing events.
09-08-2016, 01:58 PM
#7
sorry if it sounded cryptic. All I mean is, when you have FI, you have 1000 options for adjusting for max power. You can play with phasing and A/F ratio very easily. Whereas, with a carb, you cannot so easily. It takes time to pull apart a carb and modify the 144 mysterious settings a Holley has for example. Its alot easier to turn a distributor, so you get alot more "Chatter" about distributor tuning with carbs. Whereas with FI, you get thousand different threads about thousand other ideas.
Its kind of like, all carb guys really have is the distributor. Besides that, they have to open the engine and change/modify it. FI people can tap keys on the keyboard that does things besides timing adjustments and still pick up power; so there is less of that 'chatter' consolidated, its all split up into various subjects over a wide range.
So in theory, the FI engines run with less timing because they make the window smaller for diminishing returns at the bleeding edge. In other words, you push timing into an FI setup and you will get less and less than the same engine carb'd. So FI tuning theory says "don't bother pushing it, too dangerous, play with something else" whereas carb tuning theory says "This is all we can do to it" In both cases, more timing gives you more pressure; its just not necessary or safe with FI tuning, whereas with carb tuning it is considered acceptable to push the limits of the fuel (its probably not a boosted application, something like 88% less likely) and most of those engines will not see 15k/year like some FI applications do, where you wouldn't want the additional timing (it would still be dangerous).
Its kind of like, all carb guys really have is the distributor. Besides that, they have to open the engine and change/modify it. FI people can tap keys on the keyboard that does things besides timing adjustments and still pick up power; so there is less of that 'chatter' consolidated, its all split up into various subjects over a wide range.
So in theory, the FI engines run with less timing because they make the window smaller for diminishing returns at the bleeding edge. In other words, you push timing into an FI setup and you will get less and less than the same engine carb'd. So FI tuning theory says "don't bother pushing it, too dangerous, play with something else" whereas carb tuning theory says "This is all we can do to it" In both cases, more timing gives you more pressure; its just not necessary or safe with FI tuning, whereas with carb tuning it is considered acceptable to push the limits of the fuel (its probably not a boosted application, something like 88% less likely) and most of those engines will not see 15k/year like some FI applications do, where you wouldn't want the additional timing (it would still be dangerous).
Last edited by kingtal0n; 09-08-2016 at 02:04 PM.