This is driving me somewhat nuts. I've got a 412" sbc, with a NX276HR cam. I'm idling at 900rpm, around 14:1 on the wideband, and 24 degrees. After 3-4 minutes at idle the headers glow red.

I'm tempted to throw more advance at idle, but I find it odd that I'll end up with less advance at WOT under boost than at idle.

-- Joe

 

I do know running lean will make everything run hot, headers motor ect pistons will soon give if something aint done. Look into it.

 

I am running 22 degrees at an idle of 950-RPM, 34 degrees total, and 19 degrees full boost running 93 octane. Air/fuel at idle is targeted at 14.2, cam is 23x/23/x on the duration installed straight up, spark reference is set to 8 degrees matching base timing...

 

I'm at 24 degrees. I have to shut the car down after 5 minutes at idle cuz the headers will be glowing red.

Wideband reads around 14:1.. If I richen it up all I end up doing is making my eyes water.

-- Joe

 

Makes me cry just thinking of glowing hot headers at idle!

Richer would be cooler... what happens if you turn the advance down?

You sure the timing at crank with a timing light is correct to bin?

 

That is exactly what came to mind and why I mentioned spark reference w/matching base timing with mine. That, or possibly his cam timing may be off...

 

Hello,

The target advace is the same as the light shows. I know the balancer is right because I set the mark myself to zero at TDC. The cam is straight up. It's a billet comp cams core, and I've never seen them screw up a grind more than a half degree in either direction..

I'm tempted to re-adjust the valves, but I'd think 8 tight exhaust valves wouldn't idle steady at 60kpa.

-- Joe

 

Right. My bias is set to 10. It's a little simpler with the MS than a stock cal, cuz there is no est to disconnect. I've had combos that wouldn't even idle with the est disconnected which made it impossible to set the initial. Anyway, you tell the software what your bias is, then a window pops up showing you what you should see on the light. You verify the light shows that.

-- Joe

 

Glowing headers sounds like too little advance more than too little fuel. Give her some idle timing. My stock Vortec Express ran like 26° at idle and liked 28°. I have a much smaller cam in the 210° @ .050" range and it likes about 30-32°with the cam. I can see idle timing being quite a bit more than WOT timing on a boosted setup.

 

I forgot your running Megasquirt. Another area I would inspect would be an inaccurate/skewed wideband reading, do you have another WB you can test with just to eliminate that as a possibility? That, and other than a possible vacuum leak, everything else sounds like it is right on the money...

 

For what it's worth, the books say you can't get enough timing at idle. Now of course that's not true however it's not uncommon to run upwards of 35 degrees at idle.
This applies to fuel injected or otherwise although I can't comment on a boosted application. One of our NA small blocks runs a Holley EFI and the hand held programmer shows idle advance well into the 30's.
Glowing headers can be an indication of the exhaust gases continuing to burn as they exit the cylinder. With idle timing retarded from optimum, this is often the case.
By way of explanation, I made a change from ported vacuum to full manifold vacuum advance and other arguements aside, the additional 22 degrees from the vacuum has all but eliminated the temperature rise I used to see idling. Total idle advance is now 36 degrees. Seeing as the vacuum advance is non-functional at WOT, here's an example of how idle advance can be greater than WOT advance.
The other consideration is that it seems to be accepted that at idle, a wide band/O2 gauge might not give an accurate representation of what the air/fuel mixture really is. I've taken to tuning my idle for maximum vacuum and live with what the gauge is indicating.

 

Hey Guys,

Thank you for the advice.

I spent about an hour in the shop this morning playing with it. I wanted to rule out tight valves so I did a hot running adjustment. Valves were fine anyway, and now they are certified so.

I tried timing first. I advanced it out to 32 degrees at idle. Headers still glow within a few minutes of running. Coolant temp is very interesting. Sensor in the left head reads around 240, while the one in the manifold reads 205. I shut the car down and let it cool.

Next I tried combinations of fuel and timing. I leaned it out to 15:1, no difference. I richened it out to 12.8 - 13.0:1, no difference. Tried 20 degrees, 24, 28, 30, 32 be it rich or lean. No difference.

When I snap the throttle from idle, I AFR goes to 18:1 and It pings.

I can't rule out that the brand new wideband isn't junk, but it seems to somewhat follow true. I checked the plugs this AM before firing it up and they look really clean. No blistering or white.

I'm stumped. Either I grossly missed the tune, or something mechanical is wrong..

Not sure what to try here. Nothing I can do with the laptop seems to make a difference. Audiably, it runs best around 13:1 AFR and 24 degrees. I can gradual the throttle out and the VE table seems consistent. I suspect the throttle snap ping is just because I have not dialed in AE.

-- Joe

 

Joe, its been awhile since I looked at TunerStudio so bear with me. I had to pull up and reread a few saved links. Did you set your fixed timing the following way...?

http://www.diyautotune.com/tech_arti...ing_how_to.htm

 

Yeah but, I'll do it again just to be sure.

-- Joe

 

I have the nx288 hr with a carb. I tried tuning the idle with a wideband and chased my tail forever. it was about useless for that.

my o2 would bounce between 13- 15 and idle perfect with 7in of vac.

mine seemed to run the best at 38 deg total timing.

 

I'm an idiot.


So anyway. the distributor was tight, and as such I didn't consider that the timing might be off from when I had set it in the spring before I painted the car.

I checked it with a light, and it was so off I didn't know which side of the balancer I was on..

Set my initial to 10 degrees, redid my ignition table to idle at 24 degrees and it's all better now.

So now it runs without the headers glowing, and if I snap the throttle it revs fine and my BOV blows the excess without a lean pop or ping.

Of course, from messing with it I blew the left collector gasket

-- Joe

 

amateur LOL

 

No kidding huh?

Maybe I can blame it on the dog...

-- Joe