Tuning gurus....have a question
08-24-2010, 07:55 PM
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Tuning gurus....have a question I have a narrow knowledge of tuning. I need some help understanding.
Recently done a head and cam motor. Had my tune tweaked yesterday. Had an issue with surging and bucking at low speeds. My local tuner looked at the tune that the shop in Detroit(base tune only) installed and we noticed that the idle spark tables were all set to 17 degrees up to 800 rpm anything over 800 was 4 degrees (WTF). The car was bouncing back and forth from the high octane spark table to the idle table and it ran like ****. We reloaded the stock idle spark tables and the surging at low speeds went away completely. We picked up the idle to 975 from about 800 and the car gets underway smoothly with an 11 lb flywheel. Car is a head and cam LS6 with a 90mm Fast LSX set up. The cam is very mild (GM Hot Cam 112LSA). The only remaining issue is the hunting it does to get back to idle after deceleration (mostly at parking lot speeds) and although it will stall occassionally, with the AC on it seldom stays running at all when stopping. The warmer it gets the worse it gets. It can dip to 500 rpms and recover after several bounces. It will idle pretty steady when just sitting still. This is the last issue we need to solve as the car performs quite well other than this hunting back to idle thing. What are the tuning approaches to this problem? Is the first place to look idle air? Throttle cracker? It's an LS6 drive by wire. BTW I have done plenty of lurking around and this seems to be a resounding issue with cam installs. Seems like the responses are all over the map from drilling the TB blade to running open loop. Anyone have a lot experience solving this that can chime in with some suggestions?
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Recently done a head and cam motor. Had my tune tweaked yesterday. Had an issue with surging and bucking at low speeds. My local tuner looked at the tune that the shop in Detroit(base tune only) installed and we noticed that the idle spark tables were all set to 17 degrees up to 800 rpm anything over 800 was 4 degrees (WTF). The car was bouncing back and forth from the high octane spark table to the idle table and it ran like ****. We reloaded the stock idle spark tables and the surging at low speeds went away completely. We picked up the idle to 975 from about 800 and the car gets underway smoothly with an 11 lb flywheel. Car is a head and cam LS6 with a 90mm Fast LSX set up. The cam is very mild (GM Hot Cam 112LSA). The only remaining issue is the hunting it does to get back to idle after deceleration (mostly at parking lot speeds) and although it will stall occassionally, with the AC on it seldom stays running at all when stopping. The warmer it gets the worse it gets. It can dip to 500 rpms and recover after several bounces. It will idle pretty steady when just sitting still. This is the last issue we need to solve as the car performs quite well other than this hunting back to idle thing. What are the tuning approaches to this problem? Is the first place to look idle air? Throttle cracker? It's an LS6 drive by wire. BTW I have done plenty of lurking around and this seems to be a resounding issue with cam installs. Seems like the responses are all over the map from drilling the TB blade to running open loop. Anyone have a lot experience solving this that can chime in with some suggestions?
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08-24-2010, 08:34 PM
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Every tuner I speak with wants to dyno tune my car ($500). I'm looking for driveability. My car has already been dyno tuned. I want a specific driveability issue fixed. What is it I ask for?
08-24-2010, 09:10 PM
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Subscribing to hear what the gurus have to say. The Hotcam kicked my *** a few years ago trying to tune it myself. I finally gave up, but I loved that cam and am considering a rematch. I have had very similar problems to the one you state above so I am interested to hear some suggestions as well.
08-24-2010, 10:41 PM
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Without posting a tune file all we can do is guess.
IMO though find what timing the car likes at idle, remove a few degrees & put this into your base spark tables. Use the idle underspeed spark tables to add the timing back. Work it to values that doesnt give too much of an overshoot.(add gradually)
Then turn on the A/C & see what happens. Too much air will cause it to hunt, too little & it will lug until stit adds air & allows it to find idle.
I have used this method successfully on the few cam cars I have done.
IMO though find what timing the car likes at idle, remove a few degrees & put this into your base spark tables. Use the idle underspeed spark tables to add the timing back. Work it to values that doesnt give too much of an overshoot.(add gradually)
Then turn on the A/C & see what happens. Too much air will cause it to hunt, too little & it will lug until stit adds air & allows it to find idle.
I have used this method successfully on the few cam cars I have done.
08-25-2010, 05:50 AM
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Like 5.7 ute said, it is a combination of idle timing and airflow... I would have to see an EFILive tune file to help you really.
One thing I was unclear on is you TB - is it a cable or drive-by-wire? Wasn't sure what car this was - the one in your sig? If you are using the setscrew to set the blade on the TB, you need to reset the TPS after setting it...
I have tuned a couple of hot cams and they have a great midrange - but as you are finding, the idle is a bit difficult to get right... what you really need is a tuner who knows how to tune drivability, not just throw it on a dyno and call it good for $500... and as you have discovered, those can be hard to find. Where are you located?
One thing I was unclear on is you TB - is it a cable or drive-by-wire? Wasn't sure what car this was - the one in your sig? If you are using the setscrew to set the blade on the TB, you need to reset the TPS after setting it...
I have tuned a couple of hot cams and they have a great midrange - but as you are finding, the idle is a bit difficult to get right... what you really need is a tuner who knows how to tune drivability, not just throw it on a dyno and call it good for $500... and as you have discovered, those can be hard to find. Where are you located?
08-25-2010, 10:23 AM
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I've found that a good idle and a good return to idle are primarily tied to a good VE table, good Base Idle Airflow (RAF) table, proper idle timing, smooth transition between idle and main spark tables, correct IAC counts, trimmed throttle cracker, trimmed throttle follower, and proper underspeed/overspeed spark tables. Getting those right seems to get you 90% of the way there, and then you can fine tune to get it how you like it with idle speed, startup adders, airflow derivitve and integral, A/C torque, etc.
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08-25-2010, 11:31 AM
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Like 5.7 ute said, it is a combination of idle timing and airflow... I would have to see an EFILive tune file to help you really.
One thing I was unclear on is you TB - is it a cable or drive-by-wire? Wasn't sure what car this was - the one in your sig? If you are using the setscrew to set the blade on the TB, you need to reset the TPS after setting it...
I have tuned a couple of hot cams and they have a great midrange - but as you are finding, the idle is a bit difficult to get right... what you really need is a tuner who knows how to tune drivability, not just throw it on a dyno and call it good for $500... and as you have discovered, those can be hard to find. Where are you located?
One thing I was unclear on is you TB - is it a cable or drive-by-wire? Wasn't sure what car this was - the one in your sig? If you are using the setscrew to set the blade on the TB, you need to reset the TPS after setting it...
I have tuned a couple of hot cams and they have a great midrange - but as you are finding, the idle is a bit difficult to get right... what you really need is a tuner who knows how to tune drivability, not just throw it on a dyno and call it good for $500... and as you have discovered, those can be hard to find. Where are you located?
08-25-2010, 06:33 PM
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I've found that a good idle and a good return to idle are primarily tied to a good VE table, good Base Idle Airflow (RAF) table, proper idle timing, smooth transition between idle and main spark tables, correct IAC counts, trimmed throttle cracker, trimmed throttle follower, and proper underspeed/overspeed spark tables. Getting those right seems to get you 90% of the way there, and then you can fine tune to get it how you like it with idle speed, startup adders, airflow derivitve and integral, A/C torque, etc.
09-04-2010, 10:15 AM
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10-10-2010, 11:21 AM
#14