Final thoughts on driveablity and cam selection
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
I disagree. As pointed out, my spark is wavering less than 1-deg. This is when it's above 900 (actually 800 is my hot idle speed). I also review my logs for the 1200rpm starts I used late last week. I only got one knock count RIGHT at start-up. Even though my KS seems a hair sensitive, I'm really not getting knocks with my timing. (I get about six in a 15-minute drive). FYI: I'm using 4032 pistons. Higher silicone, tighter fit.
Mostly, I'm throwing ever POSSIBLE thought out there I can think of. I'll probably end up back at my original conclusion about the definition of driveable. But, I'm certainly hoping to be proved wrong.
1.25 may be meaningless -- unless I try lowering my idle speed again. The logical assumption is my PW will go down with any reduction in idle speed. (What would have happened if I hit the minimum PW with prior tunes? Keep in mind the injectors should have been fine. It just would have been bumping off an ECM parm).
My guess is it was ignored. I've seen a couple of other parms ignored by the ECM. For example, maximum total timing had been exceeding in my earlier efforts.
So, without knocks, the ESC being enabled -- or not -- could not have made any difference. Also, having the ESC enabled for rpms lower than say...1200 might help guard against accidental lugging at higher loads. (Notice how low the factory sets low rpm/high LV8 spark advance.)
Mostly, I'm throwing ever POSSIBLE thought out there I can think of. I'll probably end up back at my original conclusion about the definition of driveable. But, I'm certainly hoping to be proved wrong.
1.25 may be meaningless -- unless I try lowering my idle speed again. The logical assumption is my PW will go down with any reduction in idle speed. (What would have happened if I hit the minimum PW with prior tunes? Keep in mind the injectors should have been fine. It just would have been bumping off an ECM parm).
My guess is it was ignored. I've seen a couple of other parms ignored by the ECM. For example, maximum total timing had been exceeding in my earlier efforts.
So, without knocks, the ESC being enabled -- or not -- could not have made any difference. Also, having the ESC enabled for rpms lower than say...1200 might help guard against accidental lugging at higher loads. (Notice how low the factory sets low rpm/high LV8 spark advance.)
Dave
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Worrying about too much timing at low speeds is something a rental car company might be concerned about what do you care what it is as long as you know not to lug the car in a high gear. Just for fun engage ESC below your idle rpm and drive the car and see how it reacts useing the stock timing tables I think you will be surprised. The knock you see on starting is the starter motor and nothing to be concerned about. With out ESC enabled at idle it will never run right I think you are placing way too much value on the timing not moving around it is suppossed to move around but not wander from what the ECM commanded. With 6 to 10 degrees of timing at idle to 900 rpm it is always going to feel soft under a load the surge you complain about is getting past the ESC off point and the engine wakeing up by finally getting enough timing and it's effeciency going way up.
Dave
Dave
Our cars have WAY more timing than 6-10 degrees at idle. Your advice seems way off base.
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
I am understanding ESC to be 'electronic spark control' and to encompass everything from knock retard, idle spark / stall saver and ignition advance and retard as needed basically not a fixed amount of timing if this is not what it is then yes I am off base. My business is tuning primarily aftermeaket ECM equiped cars and bikes Motec Haltec EFI Tech that sort of thing so am not proclaiming to be a wizard at a stock GM system but have faced my fair share of off idle stuff in the past.
Dave
Dave
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
To address the timing issue: GM ODB1 cars have anywhere from 25° total advance (at 800rpms) to 40° total advance (at 1200 rpms). Thats before any start-up spark bias is thrown in. (These numbers are for light loads. Timing raises slightly, then drops for heavier LV8s). So far, my alterations for cold start-up have been to the start-up spark bias table, the start-up enrichment table, and the two OPEN LOOP AFR % tables. I'm pretty happy with my primary SA table as I've smoothed all transitions, adjusted for the AFR heads, and it runs WAY smoother than the stock motor did. (There are no noticable transitions from large advance or PE engagement).
So far, I'm getting some improvement from SlickFX3 and TPI-421's guidance to lean out the rediculously rich factory AFR. Instead of a rapid surge, COLD start-up idle is down to a leisurely drift. Again, this is for a cold start-up and lasts only about 60 seconds. Once it's warm, there is no drift or surge.
My idle is stable at any other time/rpm. (Assuming I don't set the idle below 800 rpms.)
Last edited by GREGGPENN; Mar 8, 2011 at 03:42 PM.
