Just got the cam broke in. Now headers glow??? [Archive] - Chevelle Tech

: Just got the cam broke in. Now headers glow???

Oct 12th, 03, 12:57 AM
well everything went well with the cam break in. I am still using the edelbrock 600cfm carb. i did notice the more i jetted the edelbrock up the less the headers were glowing. is the glowing headers from a lean condition? i have the edelbrock 600 jetted as far as it will go in the rich direction. will puting my 750 double pumper on it and richening it up make the headers quit glowing? the timming at 2200 rpms with vaccum advanced hooked to ported sorce was 36. no vaccum leaks that i can tell.?

thanks again for the trouble shooting on the carb that turned out to be a BAD cam lobe.

Oct 12th, 03, 1:30 AM
The only thing that makes the headers glow is lean mixture or late timing. The timing issue is a quick thing to check so I would get out the light and rule that one out!
Good luck.

Bob Tiley
Oct 12th, 03, 2:57 AM
Advance the timing - Just turn your distributor until the idle goes up a couple of hundred RPM and start from there.

Oct 12th, 03, 3:12 AM
I had the same problem. When I broke my motor in I had the timing at 8 degrees advanced at about 1200-1500 RPM. When I finally got it to idle down to about 900 Rpm I was at TDC ( Top Dead Center) I advanced my timing and the header dont get near as hot and dont glow anymore.

Oct 12th, 03, 7:58 AM
Ditto on the above,i have seen retarded timming which makes the engine run hotter cause headers to glow orange/red on a fresh motor/cam breakin

Also,just the fact that your car is sitting still
for the cam breakin @ 2k rpms for 30 mins with little to no airflow through the radiator/engine compartment doesn't help matters either. I always setup 1 if not 2 20inch box fans in front of the grill area on on hi for all new motor startups to aid in keeping things from getting too hot which works well.


Oct 12th, 03, 8:20 AM
Cornbread, that vacuum advance should be hooked to MANIFOLD vacuum, not ported vacuum. Ported vacuum rises with throttle opening causing an overadvanced condition at WOT. Disconnect the vacuum line, set the timing, then hook up the advance can to manifold vacuum. The advance will increase at idle (like it should) but when you get on the gas, the vacuum advance will fall away and the mechanical advance will control the maximum total advance.


Oct 12th, 03, 9:31 AM
Overadvanced at WOT? Not possible with any vac advance.

Cornbread, my headers glowed cherry as well on fireup. Timing was spot on, but the 3X2 intake is set a bit lean. I think an exhasut leak contributed to one set of glowing pipes.

It all went away by itself. I don;t know why.

Oct 12th, 03, 10:09 AM
Glowing headers is very common on engines running at elevated rpm's. We see glowing headers all the time on the dyno, even when we are just running medium load and speed with good a/f ratios. We have a guy who comes in and does fuel curves on his F.A.S.T. setups and you can watch the headers change temperature as he is tuning.
When you break your engine in, you fire it up and run it at 2500 for 20 minutes or so ( and probably never do again ), so things are going to get hot. I would be willing to bet that if you went out and started your car and ran it at 2500 rpm for 20 minutes, you would see your headers start to glow.

Oct 13th, 03, 2:56 AM
His header glow is not from over advance. More probably just the opposite. But, yes, you CAN overadvance the thing under hard load IF the vacuum advance is hooked to the PORTED side as he stated his is. Think about how it works. The vacuum advance is there to help street driveability and economy at light to moderate throttle opening. At that point, the mixture volume in the cylinder is low 'cause the throttle plates are nearly closed and restrict the flow of air/fuel mixture into the cyl. Because this mixture is harder to light cause there's less of it, the burn needs to start slightly earlier. Vacuum in the manifold is high under these conditions. So, if the advance can is hooked to the MANIFOLD source, the vacuum advance adds 10*-20* at this point to the mechanical advance of say 38*@2800 rpm with light throttle opening like going slightly downhill at 60 mph. For a total of 48*-58*.

Now, when you open the throttle blades, the motor is now receiving full air/fuel volume. The amount of timing necessary to achieve burn is lessened. The manifold vacuum drops to virtually zero. The spring pressure in the vacuum diaphragm overcomes the lessened vacuum and pushes the advance plate back and now the timing is controlled for the most part by the mechanical curve.

If you hook it up to the PORTED source, the vacuum RISES as airflow thru the carb venturii increases and pulls the vacuum pot open. This will ADD the 10*-20* to the already fully advanced (say 38*@2800rpm.) to give you a total of 48*-58*.
My motors don't like that much timing under full load and I doubt yours does either. Try it with a timing tape and you'll see what I mean.


Oct 13th, 03, 9:34 AM
The ported vacuum source only sees vacuum as the throttle is opened, but vacuum decreases as the throttle is opened further. This is true for both manifold and ported sources.

Connect a vacuum gauge to the line supplying your advance pot and you'll see vacuum drop as throttle is applied under load or at WOT. This reduces advance. If it were the other way around you'd get crazy detonation every time you had to drive up a hill.

As far as the glowing headers during break-in are concerned, ported or manifold vacuum to the advance isn't gonna affect it. Since the throttle is opened well above idle during the break-in period, either source will advance the timing.

As long as you know you have sufficient timing and you're not running lean, there's nothing to worry about.

Oct 13th, 03, 12:34 PM
Randy, yes, I see your point.

Oct 13th, 03, 12:50 PM
Crank up the advance on the break in - the high intake manifold vac mimics forces the effective dynamic compression ratio wayyyy down - as soon as it fires and stabilizes - grab the cap and twist it up. You'll hear the exhaust tone change and the firing smooth right out.

HOT plugs for the break in help too.