QuickVet

Hey guys, long time since I checked out this section. Hope all your projects are going well. Anyway, I started the vette up tonight and let it idle at about 2200rpm and saw that the headers were bright red.

Do I need to lean it out or richen it up?

Oh yah, forgot to mention, After i turned off the car at about 1500rpm the car had a few bangs/pops out the exhaust. What does that mean?? is that a clue to which way the carb should be jetted?

Thanks
Aaron


[Modified by QuickVet, 9:22 PM 3/2/2004]

LD85

when mine glowed this weekend it was because my timing was retarded and my distributor was off one tooth, sorry I cant say if it was rich or lean, usaully rich is burning fuel in the pipes from what I have read

SWCDuke

There's probably something wrong with your spark advance map.

I bet it doesn't have a vacuum advance, or its "ported" and not providing a vacuum signal to the can at low throttle openings.

Duke

DeenHylton

Your either running way too lean or your timing is off or both. Running rich will tend to cool everything so your headers would be "cool" also (no bright red).

Deen

big632

Way lean and probably sucking air somewhere.Make sure all vacuum hoses are on.

CFI-EFI

I think BOTH rich or lean can cause glowing headers. MY experience was with a rich mixture and retarded timing. That caused some of the combustion to take place in the exhaust manifolds. The popping at shut off seems to strengthen the rich/retarded theory. Good luck, and...

RACE ON!!!

grapeknutz

:iagree:

stinky

:iagree:

pws69

<img src=" :iagree: " border=0>

Same happened to me.


[Modified by pws69, 1:43 PM 3/5/2004]


[Modified by pws69, 1:44 PM 3/5/2004]

QuickVet

interesting. i dont know which way to go. I drove the car the other day and it seems to run pretty good. I will be racing it this weekend.

I dont have the vacume advanced hooked up from the distributor. I pretty much only race the car and have heard it doesnt really make a difference if you only race it. Do you guys think that is why it was having a problem. The headers were glowing at idle and i didnt drive it anywhere. I didnt notice the glowing the day i drove it because, well, it was in the daylight. Perhaps, on Thursday evening when i do the oil change I will drive it and see if they are red then.

Thanks for all the replies.
Aaron

CFI-EFI

I would imagine it is a little hard to observe the headers, while driving. Vacuum advance makes little or no difference at the track. Once you go WOT, the vacuum is gone.

RACE ON!!!

Lionsden

Within reason a lean mixture will have high combustion temperatures (piston melting) and lower exhaust temperatures. Mixture is consumed in the cylinder.

A rich mixture will have lower combustion temperature and high exhaust temperatures. Mixture has incomplete burn in the cylinder and burns in the exhaust (red hot exhaust).

Retarded timing has the same effect as a rich mixture.

SWCDuke

This thread has witnessed a lot of misinformed theories that originate
from who knows where. Here's the deal.

Within reason there is not a great deal of difference in EGT for rich or
lean mixtures that have correct ignition timing for any operating condition until the mixture gets so lean that you have intermittent misfires and the mixture burns in the exhaust system. That will cause exhaust system temperatures to go sky high in nothing flat. Severely retarded timing relative to what is required for the specific operating condition will also dramatically increase EGT.

For every engine operating condition there is an ideal spark advance value that maximizes peak temperature and pressure in the cylinder (which usually occurs just past TDC) and minimizes EGT and fuel consumption. The ideal timing is both a function of load (manifold vacuum) and relative richness. Lean, low density mixutures need more spark advance than rich, high density mixtures. Lots of exhaust gas dilution, such as is the case at idle with a high overlap cam further increases the ideal timing requirement.

Between idle and WOT there are literally an infinite number of operating
conditions, but for a high performance SBC total idle timing of 25-30degrees is about right and 36-38 at WOT. Cruise timing in the 2000-4000 range should be up to 50-54 degrees, which is a combination of initial, full vacuum advance, and full centrifugal advance.

If you don't have a functioning vacuum advance system your idle and part throttle EGTs are going to be several hundred degrees higher than if you have a vacuum advance curve that is properly matched to the vacuum characterisitics of the engine.

If you have a vacuum advance can merely hooking it up to a full manifold vacuum source with enough vacuum to pull the plunger to the limit at idle will noticeably lower EGT. You can verify with a IR gun, but just your awareness of radiant heat or header color will confirm the drop in EGT. The NAPA/Echlin VC 1810 vacuum can (0@4", 16@8") is a suitable can for a high performance engines and it must be connected to a full manifold vacuum source that provides full idle vacuum signal to the can, not a "ported" vacuum source that does not provide a vacuum signal until the throttle is above idle. Most vacuum cans don't have specs that are suitable for a high performance
engine, so just any vacuum advance is not the answer.

Racing engines on real race cars don't need a vacuum advance because they spend very little time at idle or part throttle cruise.

A "weekend racer" needs a vacuum advance assuming you do any street driving. You can disconnect it when you race, but assuming you're talking about drag racing you are probably better off leaving it hooked up so you don't overheat waiting your turn to run.

Obviously at WOT when there is virtually no inlet manifold vacuum, there will be no vacuum advance, so it has no effect on power or detonation, but may have a transient effect as you go off and on the throttle while shifting.

Duke

Lionsden

:iagree:

'Within reason' is pretty subjective. As a mechanic on fixed load engines with EGT monitoring and air/fuel ratio controls I could watch the change in exhaust temperatures by varing the A/F ratio. A small increase in fuel caused an increase in exhaust temp. A small decrease in fuel caused a decrease in exh temp. But there is a point -lean or rich- that the cumbustions start doing interesting things.

Rich doesn't always cause XXXXX or Lean doesn't always cause YYYYYY. At different point in the A/F ratio bell curve the flame front is affected differently.

Giving a short all inclusive answer to a "Is my engine running rich or lean" question is difficult. Then throw ignition timing into the equation............

TONYDEE64

Just to throw my $.02 in here... You didn't state what kind of ignition you are running. But, if you are running an HEI make sure your EST bypass wire is still connected (or still has good contacts). If it is not connected you will not have anywhere near the advance you need and your headers will indeed glow. If you are running an HEI you may also want to look at your ingition module in the distributor since if it goes bad it supposeldy defaults to a "limp home" mode which I'm guessing would also screw up your timing. I once also had a bad (shorted out) prong in my ignition module that caused this condition.

thomasdeanjr

Thank you! You provided some great info!!!!