Idle tuning LS1 with 237/242 Magic Stick 3

[Chevy406]

I've got my friend's '98 Corvette running well with ported 5.3 heads, headers, LS6 intake and a TSP "Magic Stick 3" (237°/242°) cam on 112°. I do have a question with the idle tune though. When I scan the cold startup (using Russ K's configuration), the Desired Idle Airflow numbers are a lot smaller than what the car seems to need. I manually increased the base RAF table to get the idle stable, and now I am wondering if the idle airflow numbers I ended up with are typical of this size cam. The car runs well, LTFT <= 3, and typically idles well but occasionally it will dip and then start surging until you blip the throttle. Here is the RAF table I ended up with:
ECT -40.00 -4.00 32.00 68.00 104.0 140.0 176.0 212.0 248.0 284
Gear 25.70 23.65 21.20 20.59 18.79 17.09 15.79 15.59 13.79 12.40

Of course I'll also attach the tune and scan log from a cold startup.

I'm looking for any comments on the idle tune in particular, but please also let me know if there are other areas I need to improve. I'm still quite the rookie tuner, and most everything I have picked up has been from this forum.

[Dirty 30]

Looks similar to the tune I did for a friend with an MS3 cam and 2.5 LS6 heads. The RAF is a little higher than yours. His has stock style 42lb injectors and is a 2002 tho...
Base it off this, see how it does (be advised, Im a rookie tooner too)

29.871 25.914 21.957 20.638 > 18.000 18.000 18.000 18.000 18.000 18.000 < Work on these

[DSteck]

Adjust the startup airflow and the delay/decay if it's having trouble firing using the logged RAF values. Some cars don't need anything touched with startup airflow, and some need it modified significantly. I couldn't tell you why.

[Chevy406]

DSteck - the car starts up well both cold and hot. I bumped up the IAC Park Position a couple g/sec higher than the values in the RAF table, and that along with a little more startup airflow takes care of the hot re-start.

Dirty 30 - thanks for posting your RAF table. I'm going to try to swing by this evening and bump his idle airflow numbers up like you show. Seems like going 3 times more than stock (at 176° and up) is a big adjustment, but whatever it takes I suppose.

I am learning a lot about what an engine needs through this process. Now I can understand more why my carb'd SBC with a 260° roller cam just wouldn't idle very well in gear. I needed to drill those idle air bleeds bigger. But the carb is gone, and a fuel injected LSx 408 is going into the old '69 Nova now...

[DSteck]

Use the RAF numbers from the scan, and adjust other parameters to accommodate the operating conditions. Don't just try to use tables that worked for somebody else. You won't learn that way.

What are your IAC counts when hot?

[Chevy406]

I understand what you are saying about learning from reading data and trying new settings. That's what makes this so interesting and challenging.
Going back to my scan I see that I need to work on the configuration so that it reads the '98 ECM better. The IAC and LTIT are not logging the way it is currently setup.

I must have something mis-matched in my tuning, because both my '99 and this '98 show a lot smaller idle airflow desired than what the engine "seems" to want. I'll work on the scan configuration and see if I can get some better data to analyze.

[DSteck]

Define how you're interpreting what it "seems to want". If you're talking about dying issues, that's going to fall to your follower/cracker tables.

[Chevy406]

The idle becomes more stable at the particular temperature ranges as I have increased the base RAF table. I know that at some point if I command too much idle airflow it will start hanging the idle RPM higher than commanded. But I haven't reached that point yet.

The car doesn't ever totally die, and it typically returns to idle just fine if you pop it out of gear and coast to a stop. It will idle at say 900 rpm and just randomly dip and start surging. Once it gets into the surge it seems to get stuck with over/under compensation but it doesn't ever stall. A little blip of the throttle will settle it back down to a steady 900 rpm.

Got a rookie question - does this vehicle with electronic throttle even show IAC count?

[DSteck]

If it's an electronic throttle, then you won't have an IAC count. Stock throttle body?

[Chevy406]

Yes, it has a stock C5 LS1 throttle body and an LS6 intake manifold.

Define how you're interpreting what it "seems to want". If you're talking about dying issues, that's going to fall to your follower/cracker tables.

Both the follower and cracker tables address throttle position at various MPH, but this isn't really a problem on this car. It's when the car is stationary and at idle.

[DSteck]

What kind of timing are you running at idle? I'm at work and can't open the file.

[Chevy406]

I have it idling around 24° to 25° ignition advance. I matched the hi & low octane ignition tables along with the in-gear & P/N idle ignition tables.

[S2H]

on an MS3, try bumping your timing up in your idle areas to 28~30 ish

carry that downwards to 800 and 400 rpm, and make your idle spark tables match the high/low octane tables.


try getting your over and under speed spark tables up to +/-16* by +/-400 rpm and carry it out to the end of the table.

[Chevy406]

I appreciate the help soundengineer... I modified the 4 ignition tables and over/under as you recommended. I plan to try it on the car this afternoon.
Here is what I ended up with:

[S2H]

carry your 800 rpm row values down into 400 and 0 rpm as well in your idle tables...

[DSteck]

on an MS3, try bumping your timing up in your idle areas to 28~30 ish

carry that downwards to 800 and 400 rpm, and make your idle spark tables match the high/low octane tables.

Agreed. That cam wants a lot of timing at idle.

[S2H]

as a good example...
I have a 240/244 duration cam...
and I'm at 30* at idle....

[SargeZ06]

as a good example...
I have a 240/244 duration cam...
and I'm at 30* at idle....

How about a RapTR 236/242 615/615 111 +2 LSA?

[Chevy406]

Big thanks to all that helped in this thread. Adding more ignition timing at idle was a big improvement.

I would also like to thank Ed (edcmat-l1) for some off-line pointers that he threw my way. After having my eyes opend a little, I can see just how much I don't understand about engine tuning. It's kind of like welding - most of us can stick two pieces of metal together, but it takes skill, training, and practice to become a true welder. Ed Hutchings has truly mastered computer tuning, and it is super cool of him to help out on the forums like he does. I've got to wander up to Virginia Speed someday to meet Ed and Shawn. Those guys are adding a lot to the LSx community.