spytech

Hey everyone-

I currently have an LS2 with the aforementioned cam. ET performance heads, 92mm ported FAST manifold, 96mm NW tb (dbw).

I have tuned the motor so it can idle at 950 (swings between 850-1000), and its driveable - I can coast to stops and it finds idle fine. If I make sudden stops though, or try parking lot driving...lots of stalls and or heavy/surging.

I know with a cam with 26 degrees overlap, tuning will be a battle, but does anyone have any suggestions on what the idle really should be for a cam this big in a 408 ls2? I set the startup friction airflow so that it starts the motor at 1200rpms or so and that runs GREAT. Sounds and feels great. Once that startup air decays out the idle gets more ragged. Thinking of raising the idle to 1200 and seeing how that works - any suggestions for the more experienced folks here?

DrkPhx

iTrader: (15)

1200 rpms is way too high for hot idle. My cam has about the same amount of overlap and it idles at 900 rpms at hot idle with no surging. It took a lot of work to get it right, but it's fine. It will take working on a combination of spark tables, fuel and the different idle airflow tables to get it right. What software do you use for tuning? Bi-directional controls that allow for real time adjustments are a a huge help. Start at 1000 rpms and work your way from there.

spytech

Thanks for the response.

I use HPTuners for my scanning and tuning. Right now its set to idle at 950. When it sets in at idle it swings from 850-1000ish. Seems fine there, sounds better when its idling at 1150-1250 with startup airflow, though.

Here is a vid from yesterday - when i start you will hear the idle at 1200rpm. When I return and pull in the driveway it settles in at 950. Coasting to a stop like that is fine, but if I were to suddenly depress the clutch, throw it in first, and stop...usually makes it stall. Sometimes though, the idle can be really choppy.

Did you change your RPM idle error settings from the defaults of 50 and 15 to something higher, say 150/100 to account for the bigger swings in rpms?

Most of the guys on the HPT forum are saying there's no way that cam will idle at 950 properly and to move it up to 1150-1200, which is why I posted here for a second opinion. The guy that built my engine says a 1200rpm would be fine...too much feedback, lol. Other forums have said that the 408 with a cam that big will never be easily managed on the street...

http://www.youtube.com/watch?v=XXL6gP7hzR4

DrkPhx

iTrader: (15)

That's really not the best video for idle.

That's too much of a swing even for that cam. The most obvious tables to look at are the idle overspeed and underspeed error tables.

Does this happen while decelerating? If so, it can be the Throttle Follower tables.

I use EFILive so I don't know the HPT lingo. Are you referring to the idle overspeed/underspeed spark tables?

Ehhh. Usually the people who say it can't be done, are the ones who've never done it. It can be done. Like I mentioned above it takes a lot of time and patience to get it right. There is no magic wand to nail it down.

spytech

lol, probably not - all I have so far

how would I adjust the overspeed and underspeed tables? (this is for adapative spark advance right?) Right now my overspeed looks like 0 @ 0, -1 @ 12.5 rpm, -3 @ 25, -5 @ 37-300. Underspeed is 0 @ -300 and -250, 4 at -200, -150, -100, 3 @ -50, 2 @ -37.5, 1 @ -25, 0 @ -12.5 and 0.
Would I decrease those values in both directions towards zero?

Yes when decellerating. No problems when accellerating. If I coast down it is usually fine. If I have to stop faster, like going from one block stop sign to the next, stopping quick for a stop light, stalls are waiting... I lowered the throttle follower decays by 50% in 1st and 2nd gear up to around 20mph, but didn't notice much of a difference. The throttle follower airflow table is pretty small - it doesn't add 1g/sec of air until the TP % is @ 13.5, where it hits 1.2. The throttle follower airflow multipler is also still 1, so it does nothing. I was thinking of changing the multipliers for 400-800-1200rpm and seeing what that does?

in HPT there are 2 settings under the idle rpm section called 'proportional enable rpm error', and 'integral enable rpm error'. Basically idle correction kicks in when the idle swing is greater than the values set. Stock is 50 for proportional, 15 for integral. I've seen other cammed cars with these set to 150/100, but haven't tried that. From what I get, it lets the idle swing more without the computer stepping in with the idle routines.
Thanks again for the response. Learning as I go here

hymey

What is the actual logged timing at idle, sounds like not enough airflow,and you IAC is to aggressive, pretty much turn it off and stop it correcting as it will make the idle hunt to much.

spytech

Thanks for the response. DP has been helping me immensely via email and we got it running great. Never stalls, idles at 975, drops to idle smoothly, idles smooth. Had to end up adding 2.5g/s more air across the RAF, changed some cracker values, reset throttle follower to stock, but added some delays, increased the follower multipliers, and brought up spark timing in idle regions. The tune was still using stock LS1 timing in the idle regions and that helped smooth things out a ton.

Pwebbz28

iTrader: (31)

The 255/265 110 lsa cam in my 408 idles fine at 950

rem308winvtr

iTrader: (24)

find a good tuner the will make it right

Jimbo'sZO6

iTrader: (1)

My 416 with its 248/254 112LSA cam (27* overlap), we set the idle at 1050 and 1150 with the AC on. It does fine around town once warmed up and really doesn't give me any problems with stalling or big surges.
Driveability for me is a non-issue, but might be a bit much for some others!


Jimbo