408 Reversion effect on Idle tuning - Can it be tuned out?
12-08-2007 | 05:52 PM
#1
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Joined: Mar 2006
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408 Reversion effect on Idle tuning - Can it be tuned out? Sorry for writing an essay, but I am stumped. What do people who know far more than I do think about this???
Just finished putting in a 408 LQ9 in a 2002 T/A. Decided to go with a Powerbond UD pulley, Fidanza Alum flywheel (12.5 lbs) and ACPT Carbon Fiber Driveshaft. The rest of the mods are listed below.
In the past, I've tuned several LS1's successfully with LS1Edit, HP Tuners. With a quick trip to Dyno for WOT. But I'm having a bitch of a time getting this new combo to idle properly. After trying 6 ~ 7 different combo ideas, it still surges when coming down from cruise to idle, sometimes to the point where it stalls.
I've started to suspect the U/D Pulley + aluminum flywheel + carbon fiber driveshaft are factors because together so much mass has been taken out of the driveline rotation. Not enough mass is there to help in dampening variations or reversion in crank rotational speed due to the bigger cam.
It's important to note that the motor runs perfect at mid and deep throttle. RPMs snap like a whip when you tap the throttle. Still a little lean but I wanted it that way during engine break-in to avoid washing rings during this period. Only issue is idle.
Mods:
TSP 408ci stroker (11.5 CR running 93 octane)
TSP MS3 camshaft
90mm FAST w/90 mm TB
Descreened Stock MAF w/MAF Ends
Stage II Patriot LS6 style heads
Coated Longtubes
3" exhaust all the way to the back
New O2 sensors
New ECT Sensor
New Knock Sensor
New MAP Sensor
New Camshaft Pos sensor
New Crank Pos sensor
New Plugs (no misfires)
Smoke tested and found no vaccum leaks around intake or injectors.
Just finished putting in a 408 LQ9 in a 2002 T/A. Decided to go with a Powerbond UD pulley, Fidanza Alum flywheel (12.5 lbs) and ACPT Carbon Fiber Driveshaft. The rest of the mods are listed below.
In the past, I've tuned several LS1's successfully with LS1Edit, HP Tuners. With a quick trip to Dyno for WOT. But I'm having a bitch of a time getting this new combo to idle properly. After trying 6 ~ 7 different combo ideas, it still surges when coming down from cruise to idle, sometimes to the point where it stalls.
I've started to suspect the U/D Pulley + aluminum flywheel + carbon fiber driveshaft are factors because together so much mass has been taken out of the driveline rotation. Not enough mass is there to help in dampening variations or reversion in crank rotational speed due to the bigger cam.
It's important to note that the motor runs perfect at mid and deep throttle. RPMs snap like a whip when you tap the throttle. Still a little lean but I wanted it that way during engine break-in to avoid washing rings during this period. Only issue is idle.
Mods:
TSP 408ci stroker (11.5 CR running 93 octane)
TSP MS3 camshaft
90mm FAST w/90 mm TB
Descreened Stock MAF w/MAF Ends
Stage II Patriot LS6 style heads
Coated Longtubes
3" exhaust all the way to the back
New O2 sensors
New ECT Sensor
New Knock Sensor
New MAP Sensor
New Camshaft Pos sensor
New Crank Pos sensor
New Plugs (no misfires)
Smoke tested and found no vaccum leaks around intake or injectors.
12-09-2007 | 12:06 PM
#4
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On The Tree
Joined: Mar 2006
Posts: 125
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Simple really, tried doing it by the numbers. Log -> tweak -> test, repeat. It got close, but surge was still there on hard braking coming to a stop. So, experimented a bit more with Throttle Cracker, Throttle Follower, etc and started noticing that every time I set the Base Running Airflow back to stock to try something else, it ran better!!!
So after a couple more experiments, the pattern I found was that the car simply didn't like the calibrated RAF table with the numbers coming out of my calculations (following the procedure that's been beat to death around the boards).
Put everything back to stock. Bumped up the entire VE table about 12%, and reduced the 400, 800 & 1200 RPM range by 70%, 80%, 90%. Reset the IAC after cracking it open a few turns of the set screw till IAC were in the 20's and SUBTRACTED .5 g from the Base Running Airflow table. Bingo!!!
Car comes down to a soft landing at 850 from 70MPH, clutch completely in and hard braking. No overshoot, no "bounce", just a stock-like soft landing.
So after a couple more experiments, the pattern I found was that the car simply didn't like the calibrated RAF table with the numbers coming out of my calculations (following the procedure that's been beat to death around the boards).
Put everything back to stock. Bumped up the entire VE table about 12%, and reduced the 400, 800 & 1200 RPM range by 70%, 80%, 90%. Reset the IAC after cracking it open a few turns of the set screw till IAC were in the 20's and SUBTRACTED .5 g from the Base Running Airflow table. Bingo!!!
Car comes down to a soft landing at 850 from 70MPH, clutch completely in and hard braking. No overshoot, no "bounce", just a stock-like soft landing.
12-09-2007 | 02:57 PM
#5
i have a 240/250 110 lsa cam in my 370 and i have it idleing just like stock. I didnt' have to mess with the cracker, or follower at all. Reducing the ve table below 1200 rpms, and messing with the desired airflow table with doing rtacs. That and i have it idleing at 950, drops down to 950 everytime and doesnt seem to be hunting at all.
12-10-2007 | 09:16 AM
#6
i have a 240/250 110 lsa cam in my 370 and i have it idleing just like stock. I didnt' have to mess with the cracker, or follower at all. Reducing the ve table below 1200 rpms, and messing with the desired airflow table with doing rtacs. That and i have it idleing at 950, drops down to 950 everytime and doesnt seem to be hunting at all.
