Carbed LS3 Tuning Help
07-25-2010, 08:47 PM
#1
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Carbed LS3 Tuning Help Well im new to the carbed LS setup.Im needing some advice tuning this thing.Its a stock LS3 with a Livernois stage 2 cam.Intake duration is 230@.050 exhaust 236@.050 intake lift .590 exhaust lift .600 with 114lsa.Running a GMPP single plane intake with a 4150 Holley 850DP.The car is a 78 nova full wieght car with th350 10inch 3800 stall, 4:10 gear and 27 inch tall tire....right now its running pretty rich from looking at the plugs.The carb is jetted 80/80 im thinking dropping it to 76/76.It has a stumble at when accelerating from partial throttle to mid then it smooths ut once the rpms get up some.Also im using the MSD 6012 ignition box.Right now im using the number 3 pill.Gonna put the MAP sensor in and coustom tune it soon as i get a serial port adapter for my laptop.What would you guys suggest far as jetting on the carb and accelerator pump,squirters,ect.I bought it reconditioned back to factory specs.Should have a 8.5 power valve in it.Should have 31 squirters front and back also.....Thanks for any help!
07-27-2010, 11:46 PM
#2
all the pills in the 6012 SUCK!! they all have to little timing for a carb application. I have a stock cam in my engine right now, but i will be changing to 1 with 227/235 @ .050", and 114 lsa, very soon
Here is arough idea of my timing curves:
0-1000rpm - 15*
1000 - 2000 - ramping from 15* to 33*
2000 - 4000 - 33*
4000 - 6000 - 33* dropping to 32*
6000 and above 32*
Map: ( I may have to change this a tiny bit when I put my cam in)
15* from 0 to 4psia
15* dropping to 0, from 4psia, to 10psia
Carb:
put the holley supplied jetting in it, and check to see that the idle setting on the throttle blades does not have the butterflies open more than about .020" into the transfer slots. If you need more idle speed when this is set, then slightly open secondary blades. There is 2 settings on the pump cam (little plastic coloured cam on the throttle linkage) - select the 1 that will give the biggest shot of fuel. After that, if it still stumbles as you transition into more throttle, then increase squirter size a couple numbers at a time 'till it goes away. there is more too it, but this should get you in the ball park. it will seem rich at idle no matter what you do, because the cam has overlap. I have wideband O2 on my car and it really helps tune, but idle is still tough to get right. Remember - main jets, are mostly for WOT, dont mess with them till last.
Lastly - you can almost ignore plug readings, unless you run leaded fuel. It is virtually impossible to read plugs with unleaded.
Here is arough idea of my timing curves:
0-1000rpm - 15*
1000 - 2000 - ramping from 15* to 33*
2000 - 4000 - 33*
4000 - 6000 - 33* dropping to 32*
6000 and above 32*
Map: ( I may have to change this a tiny bit when I put my cam in)
15* from 0 to 4psia
15* dropping to 0, from 4psia, to 10psia
Carb:
put the holley supplied jetting in it, and check to see that the idle setting on the throttle blades does not have the butterflies open more than about .020" into the transfer slots. If you need more idle speed when this is set, then slightly open secondary blades. There is 2 settings on the pump cam (little plastic coloured cam on the throttle linkage) - select the 1 that will give the biggest shot of fuel. After that, if it still stumbles as you transition into more throttle, then increase squirter size a couple numbers at a time 'till it goes away. there is more too it, but this should get you in the ball park. it will seem rich at idle no matter what you do, because the cam has overlap. I have wideband O2 on my car and it really helps tune, but idle is still tough to get right. Remember - main jets, are mostly for WOT, dont mess with them till last.
Lastly - you can almost ignore plug readings, unless you run leaded fuel. It is virtually impossible to read plugs with unleaded.
Last edited by 3pedals; 07-28-2010 at 12:00 AM.
07-28-2010, 01:07 PM
#3
i was told to always keep the jetting within 10 sizes from each other. im running 70/80s in my 750 hp street holley.
after i jetted it down i adjusted the timing to 15* from 0-1000 rpm the ramped it up to 29* total at 3000 rpm then re adjusted the transfer slots and idle screws. my plugs have a nice light tan brown color to them with the idle screws all 3/4 of a turn out.
junk those pre tuned pills.
reset all of your carb adjustments after a jet change, start with your idle screws 1 turn out then set then reset your transfer slots. maybe you could switch to a 6.5 power valve or a different accelerator pump to solve your off idle stumble.
after i jetted it down i adjusted the timing to 15* from 0-1000 rpm the ramped it up to 29* total at 3000 rpm then re adjusted the transfer slots and idle screws. my plugs have a nice light tan brown color to them with the idle screws all 3/4 of a turn out.
junk those pre tuned pills.
reset all of your carb adjustments after a jet change, start with your idle screws 1 turn out then set then reset your transfer slots. maybe you could switch to a 6.5 power valve or a different accelerator pump to solve your off idle stumble.
07-28-2010, 08:41 PM
#4
80 jets in the primary are probably too rich. Look at the sticky thread on who has used a carb and dist on LS motors. Lots of tuning advice and set ups in there. Most guys run primary jets in the low 70's. There is another thread titled something like LS carb database. Some good info in there too.
i would highly recommend a wide band O2 with logging capability. Like someone else said on here anything less is just guessing.
LS motors with a single plane intake can be tough to tune off idle. Most guys "fix" it with a 50 CC primary accel pump and bigger squirters. In my case the real fix was to put in smaller idle air bleeds. That really woke up the engine. I can be at 1500 RPM in 5th gear and a mear touch of the throttle just makes it pull. No bog or hesitation.
Have to disagree with the advice to set the jets last. IMO set them first, then start tuning the low RPM circuits.
Adding a MAP sensor made my car much easier to start.
i would highly recommend a wide band O2 with logging capability. Like someone else said on here anything less is just guessing.
LS motors with a single plane intake can be tough to tune off idle. Most guys "fix" it with a 50 CC primary accel pump and bigger squirters. In my case the real fix was to put in smaller idle air bleeds. That really woke up the engine. I can be at 1500 RPM in 5th gear and a mear touch of the throttle just makes it pull. No bog or hesitation.
Have to disagree with the advice to set the jets last. IMO set them first, then start tuning the low RPM circuits.
Adding a MAP sensor made my car much easier to start.
07-28-2010, 09:16 PM
#5
80 jets in the primary are probably too rich. Look at the sticky thread on who has used a carb and dist on LS motors. Lots of tuning advice and set ups in there. Most guys run primary jets in the low 70's. There is another thread titled something like LS carb database. Some good info in there too.
i would highly recommend a wide band O2 with logging capability. Like someone else said on here anything less is just guessing.
LS motors with a single plane intake can be tough to tune off idle. Most guys "fix" it with a 50 CC primary accel pump and bigger squirters. In my case the real fix was to put in smaller idle air bleeds. That really woke up the engine. I can be at 1500 RPM in 5th gear and a mear touch of the throttle just makes it pull. No bog or hesitation.
Have to disagree with the advice to set the jets last. IMO set them first, then start tuning the low RPM circuits.
Adding a MAP sensor made my car much easier to start.
i would highly recommend a wide band O2 with logging capability. Like someone else said on here anything less is just guessing.
LS motors with a single plane intake can be tough to tune off idle. Most guys "fix" it with a 50 CC primary accel pump and bigger squirters. In my case the real fix was to put in smaller idle air bleeds. That really woke up the engine. I can be at 1500 RPM in 5th gear and a mear touch of the throttle just makes it pull. No bog or hesitation.
Have to disagree with the advice to set the jets last. IMO set them first, then start tuning the low RPM circuits.
Adding a MAP sensor made my car much easier to start.
When you first start the engine you are on the idle circuit, and as soon as you touch the throttle you are in the transition and pump/cam/nozzle area, it makes no sense to leave a problem in that area alone and tune the main jet first. The main jets dont start in untill the throttle is at least 20+% open. There are many ways to acheive the goal of tuning the carb, and you can tune the mains first if you want, but If a guy simply leaves the factory installed jets in the carb, untill after the idle, and transition are setup correctly, you are going to be close. Mainjet changes should be the last thing on your mind if it has a stumble when you step on the gas. but the air idle bleeds are worth a look after the basics are dealt with.
Barrett.
Last edited by 3pedals; 07-28-2010 at 09:23 PM.
07-29-2010, 07:58 AM
#6
The main jets affect every circuit in the carb. go ahead and set them last if you like, but if your changing them 5 or 6 jets sizes like I think the OP will need to be prepared to retune the low RPM circuits again.
07-31-2010, 02:23 AM
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took the holley apart and and rejetted it and repalce the power valves in the front with a 6.5 and put a block off in the back and jetted it up...........ran like total complete ***!!!!!!!!!!!!!!!!ran so rich the back two cylinders wouldnt even fire.you could grab the header tubes while it was running and it was cold!!!!!
solved the problem though.went and bought a edelbrock 750 manual choke put it on and it runs great.has more power and will start up without even touching the gas pedal.
solved the problem though.went and bought a edelbrock 750 manual choke put it on and it runs great.has more power and will start up without even touching the gas pedal.
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08-01-2010, 02:46 PM
#8
well that sucks. this thread made me want to tinker with my holley again. I hooked my FAST wideband to the car and took her out for a spin. air/fuel ratios with all within exceptional ranges and she flat hauls ***.
if you changed that much stuff you have to start all over with the base tuning. re adjust the transfer slot, set the air bleeds out 1.5 turns then tune for an idle rpm that produces the greatest vacuum. what size jets did you put in your carb? if its running too rich its possible you have your transfer slots open to far and its causing a rich condition. how far out did you have the air bleeds? also how much vacuum are you pulling at idle? i wouldent give up on that holley yet.
if you changed that much stuff you have to start all over with the base tuning. re adjust the transfer slot, set the air bleeds out 1.5 turns then tune for an idle rpm that produces the greatest vacuum. what size jets did you put in your carb? if its running too rich its possible you have your transfer slots open to far and its causing a rich condition. how far out did you have the air bleeds? also how much vacuum are you pulling at idle? i wouldent give up on that holley yet.
08-02-2010, 10:37 AM
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Eddy suck, I went from 370rwhp to 420rwhp by going with a Holley 750dp. All that changed was the Carb
Last edited by Ravenous T\A; 08-02-2010 at 03:10 PM.
08-02-2010, 07:32 PM
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Eddy suck, I went from 370rwhp to 420rwhp by going with a Holley 750dp. All that changed was the Carb
if you changed that much stuff you have to start all over with the base tuning. re adjust the transfer slot, set the air bleeds out 1.5 turns then tune for an idle rpm that produces the greatest vacuum.
all the pills in the 6012 SUCK!! they all have to little timing for a carb application. I have a stock cam in my engine right now, but i will be changing to 1 with 227/235 @ .050", and 114 lsa, very soon
Here is arough idea of my timing curves:
0-1000rpm - 15*
1000 - 2000 - ramping from 15* to 33*
2000 - 4000 - 33*
4000 - 6000 - 33* dropping to 32*
6000 and above 32*
Map: ( I may have to change this a tiny bit when I put my cam in)
15* from 0 to 4psia
15* dropping to 0, from 4psia, to 10psia
Here is arough idea of my timing curves:
0-1000rpm - 15*
1000 - 2000 - ramping from 15* to 33*
2000 - 4000 - 33*
4000 - 6000 - 33* dropping to 32*
6000 and above 32*
Map: ( I may have to change this a tiny bit when I put my cam in)
15* from 0 to 4psia
15* dropping to 0, from 4psia, to 10psia
08-03-2010, 09:34 AM
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Well I can only go by what happend to me. Had a 750 eddy, changed jets, no increase. Modified into a 850 cfm....no increase but got rid of some hesitation. friends swear by Holley so found a new one online for cheap, swapped. Ran on dyno hit 410rwhp out of the box, changed jets and hit 420rwhp. Compario link below of my 2 dynos
https://ls1tech.com/forums/dynamomet...-dyno-ls1.html
https://ls1tech.com/forums/dynamomet...-dyno-ls1.html
08-03-2010, 01:30 PM
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I may try another Holley after I get some other things on the car done and want to try to get the max potential out of the engine.Right now Im leaving the Edelbrock on it for breaking the engine in and sorting out other small items....May go with one of there 830HP carbs.
08-03-2010, 09:09 PM
#15
I'd go bigger. correct me if I'm wrong, but arent holleys actually smaller than the advertizing states? the 830hp probly only flows 750cfm??? I run a Mighty demon 850 and love it, but if you MUST have a holley at least go with a 950hp , maybe even a 1000hp.
08-04-2010, 09:21 AM
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[QUOTE]I'd go bigger. correct me if I'm wrong, but arent holleys actually smaller than the advertizing states? the 830hp probly only flows 750cfm???[/QUOTE
I couldnt tell you if thats true or not.....I looked at the demon series carbs but ive heard mixed things about them.Guess ive heard more ppl say bad stuff about them but i never owned one.
I couldnt tell you if thats true or not.....I looked at the demon series carbs but ive heard mixed things about them.Guess ive heard more ppl say bad stuff about them but i never owned one.
08-04-2010, 09:54 AM
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http://www.holley.com/applications/C...bSelection.asp
This will help ya. I have an agressive cam, big stall, and low gears....it told me 750cfm...more than that will be overkill
This will help ya. I have an agressive cam, big stall, and low gears....it told me 750cfm...more than that will be overkill
