Red hot pipes !

[tgracing]

Dear All,

Whilst spinning up Pamela to temperature before putting her to bed for the winter I had the engine revs up at about 2000 for 15 mins. I noticed that (counting from the front) number 2 exhaust pipe wasn't red hot but the others were. Does the panel think this is normal for an 8V VX 1600 lump. Or is this the root cause of my lack of power ?

 

Yours anxiously,

 

Davebo

C7 CAR

 

Edited by - davebo on 18 Dec 2000 12:49:54

[John E]

I experienced this phenomenon earlier this year whilst bedding in the cam on my x flow. Apparently, on the x flow at least, its quite normal and is due to lack of airflow around the pipes and the proximity of one pipe to another.

[Marius]

This reminds me of a mysterious X-FILE I also once had: after building the car and firing the engine the first time (Vauxhall 16V) the pipes started to turn red and smoke but it disappeared after some minutes. I concluded that some non visible grease (from touching the pipes during build) caused this as it never appeared afterwards.

Now, 2 years later, after rebuilding and tuning the engine it appeared once more the first time I fired it up, but no smoke this time (no grease this time, too, used the same manifold as 2 years ago).

Peter "the tech" Moulder-Carmichael, maybe Davebo´s case has the same reason as mine. Do you have any explanation for these "X-FILES"?

 

Marius

[murph7355]

Caveat - I'm incompetent with mechanical objects.

 

Now I have that out of the way, I seem to recall from the se7ens list that glowing pipes could also be caused by too weak fuel mixture being supplied to the engine and/or cam timing being out (the former was definitely the cause of a couple of K-series cars doing this, and it also happened on mine too).

 

Whether it's normal on other engines and why it should go away after a couple of minutes (all else being equal) I don't know. But I think I'd check these things out as I'm sure exhausts aren't designed to run like that for any length of time (especially at low revs).

 

C7 AJM

[Tim Sture]

Davebo

 

Are you still trying to blame the car?

 

Tim 9th

[murph7355]

Incidentally, I'd guess that if the mixture and/or timing was out then your power figures may well be affected (by how much though, who knows...). smile.gif

 

C7 AJM

[J.R.]

Exhaust headers running red (except under power on rolling road) is usually caused by retarded ignition timing - dependant on the advance curve sometimes only a couple of degrees can do it. I commonly experience it when first running a new engine as I initially run them retarded.

 

If one header is much cooler than the others either carbs mixture / balance is incorrect for that cylinder or plug / lead etc misfire.

 

When I first run up an engine after a rebuild I always spit on my finger & touch each header after 1 minute, no variation of sizzle tells me all is well, pipes always smoke during first run up.

[Roger King]

This is a perfectly normal phenomonem with an engine (almost any engine) that does not have 3D ignition mapping.

 

Under the very light throttle conditions that you were running, the actual compression pressures inside the combustion chamber are quite low (this is simply because the nearly closed throttle will not allow much air in). Fuel/air mixtures under these conditions burn more slowly than those under high compression pressures (full throttle running).

 

Such a slow burning mixture really needs to be ignited earlier (more ignition advance) to ensure efficient burning in the combustion chamber. A 3D mapped system has a sensor on the carbs so that the management system can know about the light throttle position and add in this extra ignition advance, whereas a 2D system like yours has no idea what throttle postition you have and just sets the ignition timing to suit full throttle which is really too late.

 

Now an internal combustion engine works by turning heat energy into mechanical energy, but unfortunately your slow burning light throttle mixture is being ignited too late for this to happen efficiently. The result is that a lot of the heat stays as heat and is then chucked out of the exhaust leading to the glowing pipes.

 

Mixture problems can also make the problem worse.

 

Edited by - roger king on 18 Dec 2000 23:22:56

[Tony Martyr]

You should be aware that about the same amount of energy is going out via the exhaust pipe as is being transmitted to the wheels. Without any airflow or a management system that is compensating for near closed throttle running it is not suprising that the pipes heat up. The exhaust gas during full power running will be around 650 degrees C but you normally have your mind and eyes on other things.

[tgracing]

All,

Thanks for the replies. i think a rolling road session is needed to tell the full picture. I wasn't particularly worried about the pipes glowing (but I am now) it was the fact that one pipe wasn't glowing that concerned me.

 

Cheers, Davebo.

 

Tim,

Hey, show me a straw and I'll clutch at it.