hudman

I got my car back with the new motor and new Jet Hot headers. I am aware of the rich/lean fuel mixture that can cause extreme exhaust temps. The warning in the package mentions that the headers will glow while tuning if you do not use a big fan etc. My were glowing after idling for a while in the driveway, but it was dark outside so it was very noticeable.

Do you think I have an incorrect mixture, or is it because the engine and/or headers are new and the thing was just idling in the driveway for too long in the dark which made it very easy see the glow.

Once they glow, are they ruined? They did look duller to me.

joeveto

It sounds as though you are running lean. I don't know if the headers are ruined.

KATMAN

Possibly timing set too retarded?

gkull

You way rich. Unburned gas is burning inside the pipes.

wayne_69_427

I agree with joeveto your runing lean :iagree:

Corey_68

:iagree: My first thought when I read the title.
Check your timing. :yesnod:

Jvette73

When I was tuning and my old Q-jet was way lean, my headers glowed cherry red. They did loose some sheen but theyre not ruined. They'll loose that sheen eventually anyway.

sb69coupe

I think it's probably related to your other post. Do you still have the vacuum advance disconnected? At idle, your timing is probably too retarded, causing excessive exhaust temps.

Shannon

79VetteMike

Unburned gas would not sit in the headers and burn causing them to glow. It would either come out of the exhaust pipe or flood the carb. Either you are very lean or your timing is way off. An extreme vacuum leak might also create a hotter than normal exhaust.

79VetteMike

Forgot to mention....sometimes breaking in an engine causes much more extreme than normal temp- I am not sure of the reasoning behind this, but I am sure that someone here knows-It may have something to do with having to idle at 2000rpm at break-in or maybe everything is not lubed to it's optimum- I would be interested in knowing the true reason.

Stefan69

Yupp. They're ruined. Send them to me :D
I will dispose them for you for free.....
Seriously though it may be OK. To be sure: check timing. It could also be that the mixture is waaaaayyyy off. Do you get "lean roll" in idle? That would indicate that you're running too lean. Also check spark plugs. If you don't know how to read them, I can scan some pictures for you. I had (european) cars that always had glowing headers or even cast exhaust manifolds. It just can get hot down there. :jester

Good luck!

Stefan

SanDiegoPaul

Forgot to mention....sometimes breaking in an engine causes much more extreme than normal temp- I am not sure of the reasoning behind this

When I broke in the cam after starting my virgin engine, IT WAS HOT!! Temp stayed at 185 :) but with both headers cherry red for fifteen minutes, I couldn't stay under the hood holding the carb open any more. I grabbed a rag and saved my fingers but my arms still cooked. I didn't make it to 20 min. I think I shut her down after 12 to 15 minutes. I've got 3K miles on it now and the cam ain't flat yet :yesnod: so I guess I'm OK for now!

The hair on my arms has grown back :) :blueangel: :lol: :flag


[Modified by SanDiegoPaul, 8:00 PM 4/4/2003]

Vetterodder

My guess is too rich or too little timing. You are definitely seeing the effects of fuel being burned in the headers. Late timing, even with a correct fuel mixture, will put more unburned fuel into the the exhaust. It can also increase engine temps by causing combustion to continue while the piston is farther down in the cylinder. In that scenario, more of the cylinder wall is exposed to combustion temps and heat that would otherwise be making power is transferred to the water jackets.

If you've gone to a bigger cam, that in itself could cause both richer exhaust mixtures and also a need for more timing at idle. The slower air/fuel velocites that result from longer valve openings also prevent the air and fuel from mixing well at idle. Even if the carb is providing the proper amount of fuel with the proper amount of air, they can't mix well and some of that fuel isn't burned in the combustion chamber (that why big cams "lope").

What is your initial set at?

hudman

I do not know what the initial is set at. The shop that installed the motor set it up for me. I am just suspect because the plugged the vacuum advance into the wrong inlet on the carb. So I disconnected it tonight and now I have the glowing headers.

I have 2 similar posts running from 2 different days, so I apologize for floating similar questions.

It makes sense that since I disconnected the advance tonight there is now too little initial timing. However, given the discussion of the absence of vacuum at idle when hooked up the correct port, why would disconnecting the vacuum advance cause the initial timing to be slack. Without vacuum, would the vacuum advance do anything at idle?

The correct port has a little bit of vacuum, but not much. Maybe that is enough to advance the timing slightly.

Alwyn678

Car is running LEAN.... no question there

Chuck Harmon

I am running a long duration cam that I advanced 4 degrees when I installed it. My headers were glowing in the dark at idle too. I believe the exhaust valve was opening a little too soon while still in the power stroke allowing the incredibly hot combustion gasses to enter the headers a little too early. Changing the cam to straight up specs seemed to help big time. It no longer glows at idle "on a dark and stormy night".

Otherwise, I would say that the engine is either too lean, or the ignition timing is too retarded.

Chuck

Duke94

I had the same problem with the new engine in my 78' (XE-262 cam and alum heads). The headers glowed orange after 30 seconds. The timing was et at 10 degrees (no vacuum advance) at idle. The engine seemed to labor at idle and popped out the carb when I nailed the gas. Turns out that with the XE-262 cam it wanted way more initial advance (like 18 degrees). No more orange headers and it runs great.

LemansBlue68

If your carb mixture was excessively rich, you'd see black smoke coming out of the exhaust. Besides, when we want to decrease exhaust temps during development we ALWAYS RICHEN A/F mixture (sometimes up to 11:1). I do calibrations for a living. If you were too lean, you'd know it because the the engine would idle rough and and would hesitate on acceleration. In fact, extreme lean conditions cause a reduction in exhaust temps too because of incomplete combustion. The reason your exhaust is so hot is because your base ignition timing is too retarded. If you're not running vacuum advance, hook it up. Lars has issued a great tech paper on setting your ignition timing. Check it out it the tech section of the forum. You should find a big increase in bottom end and midrange torque when you get the timing dialed in. If you're still really unsure about your A/F mixture, have an O2 sensor bung installed in your exhaust and check the A/F mixture on a chassis dyno. After you've got it tuned you can remove the sensor and plug the hole. The access port will always be there if you want to to further tuning. It'd be well worth the effort.

clem zahrobsky

if they glow red at idle you have retarded timing and/or too rich and fuel is burning in the headers. connect the vacuum advance to manifold vacuum so you have more advance at idle and will help cure this.at full throttle the exhaust temp is close to 1400 degrees and even cast iron manifolds will glow if not enought air is passing by them. i have seen this on motorhomes. :chevy

jimtreber

Personal experience:
Fresh engine and I was breaking in the cam. New headers were red enough to light up my garage. I called the header mfg and they said the headers were drawing raw gas into the tubes and to lean the idle. I was skeptical but I did what they said and no more red headers while breaking in the cam or ever after.

1976 406 TH400 4.11 nitrous 12.14