more often bad then not.
(sorry i'm venting)


a guy was bragging about glowing headers... i'm thinking...umm more often then not.. thats bad.

A. your timing is off
B. you have shitty headers
C. YOUR TIMING IS OFF
D. i guess a radical cam might do it... but i've never seen it happen in anything under 8000rpm

anything else... this is all i can think of now
(now if it was a turbo somepeople do this on perpose to spool faster but would wrap said header if this was the goal)

3/1/2006 12:39:53 AM

What do he and his timing have in common???



THEY'RE BOTH RETARDED

3/1/2006 12:42:51 AM

OHHHH SNAP!!!!

3/1/2006 1:07:48 AM

leaning out

3/1/2006 1:57:57 AM

3/1/2006 2:02:36 AM

If your bottom end sucks your pistons will "glow" on that lean condition tooo.

[Edited on March 1, 2006 at 2:07 AM. Reason : .]

3/1/2006 2:06:51 AM

1st gen ford probe gt's will have glowing headers even when everything is right

3/1/2006 2:24:11 AM

^^^ I recognize that motor..

3/1/2006 3:54:53 AM

Quote :

"D. i guess a radical cam might do it... but i've never seen it happen in anything under 8000rpm"

We used to drag race a lot back in the days, and we weren't rich people, meaning, high dollar race car and trailer, but a very budget motor home (like a mid 70s 30 footer). I went with my uncle to Darlington one year and one the way down he hears a pop trying to accelerate up a hill and was like "Damn, guess we'll have to chain it up when we get there"... meaning a motor mount broke. To shorten the story, he loses in the first round, comes back and we load the shit up in minutes because he is pissed. He stays pissed off the whole way and basically has his foot to the floor whenever possible. We get back to the Rockingham area and a guy flags us down saying he sees a lot of smoke coming out of the motor home. We stop, pull the dog house off and immediately see a sagging to one side motor, cherry red exhaust manifolds, and oil leaking out onto them and burning. Turns out the short steep hill we had just climbed twisted the motor even more which is what caused it to start leaking the oil out of the valve cover. That was a fairly tense few minutes getting it put out.

And I'll assure you that motor never saw 8 grand.

3/1/2006 9:26:27 AM

explain the physics behind retarded timing causing glowing headers

3/1/2006 9:51:47 AM

firing with the exhaust valve open puts more heat into the exhaust

firing with closed valves keeps the heat in the combustion chamber

3/1/2006 10:08:39 AM

^yup, the expanding hot gas is allowed to escape into the header because of the firing when the exhaust valve is open.

3/1/2006 10:13:34 AM

Quote :

"What do he and his timing and this thread have in common??? THEY'RE BOTH RETARDED "

3/1/2006 10:13:46 AM

I like how that bike engine has the carbon fiber intake manifold. Can't really tell from the pic.

3/1/2006 10:21:25 AM

running rich/exhaust restriction

3/1/2006 12:10:57 PM

how does running rich = heat?

running rich keeps things cool

3/1/2006 12:27:00 PM

Quote :

"firing with the exhaust valve open puts more heat into the exhaust firing with closed valves keeps the heat in the combustion chamber"

A little more detail here. Firing isn't actually initiating when the exhaust valve is open; rather, firing occurs too late, and fuel is still actively burning when the exhaust valve opens and blowdown occurs. Instead of exhaust gases consisting mostly of combustion byproducts, they consist of quite a bit of burning mixture. Yeah, it produces a lot of heat. It's a good way to burn your valves as well (so is having insufficient valve lash on the exhaust valves).

With a radical cam, the same thing can occur, especially if the lobe separation angle is very large and/or cam timing is advanced.

[Edited on March 1, 2006 at 12:32 PM. Reason : more shit...]

3/1/2006 12:30:13 PM

^^ yep.... once the o2 is burned outta the mix the rest of the gas just sits there because there is nothing to combust with... this gas obsorbs energy by evaporation cooling things down.

basically the same thing idea w/ water injection only water keeps things cooler & regulates burn speed & is cheaper ( and you don't have to worry about 02 keepin the fire burning too long.

if the gas is still on fire... then the motor isn't rich... when the gas quits burning (but is still there) then the motor is rich.

3/1/2006 12:40:18 PM

The glowing headers on the motorcycle engine was running about 0.9 La, which is about a 12.5:1 A/F ratio. No lean problem there, it was just running under full brake load around 8500 rpm for about 30-45 seconds or so. Lean mixtures actually burn cooler than rich mixtures. The timing would have to be waaay retarded if it was firing when the exhaust valve is open, and the engine wouldn't run.

3/1/2006 12:41:50 PM

1st the engine will run
i've seen a person wire an engine 1 piston off on the distributer and it still run (glowing headers after 1 min @ idle)

and actually you can't say 1 is cooler than the other.. you just don't want it perfect because we don't have the materials to make motors hold up to the perfect 14.6:1 mixture. (or things slightly lean of that) with direct injection you can make a motor run much much leaner but only because you inject much less fuel and have better control of it.


energy needs to be absorbed by the fuel or by the nitrogen in the air.. either way its burning cooler than a perfect mix.

[Edited on March 1, 2006 at 12:51 PM. Reason : .]

3/1/2006 12:49:30 PM

leaner is cooler?

Ive always heard high exhaust gas temps = glowing hot manifold = lean

3/1/2006 1:37:57 PM

well he's sorta right man its all about energy vs mass (or evaporation energy)

if you don't put enough gas in the air to let it get too hot it won't
if you put enough gas in the air to absorb the extra heat it will make things run cool too.

3/1/2006 4:55:29 PM

The extra fuel provides evaporative cooling of the mixture and has nothing to do with the actual combustion or exhaust temperatures. I was always told that leaner was hotter, but that's not the case. If you want to learn about it, check out Engineering Fundamentals of the Internal Combustion Engine by Pulkrabek. If lean was hot, then diesels would burn the hell up anywhere other than full load. I don't know where you got the thing about materials handling stoich ratios, that's just BS. Read said book. 1 piston off on a V8 distributor is only about 60 degrees of crank timing late, which would still be before the exhaust valve opens. My point still remains that if plugs are firing with the exhaust valve open, the engine won't run or start, it'll only backfire.

[Edited on March 1, 2006 at 6:34 PM. Reason : ]

3/1/2006 6:32:19 PM

correct, the engine would fire, but there wouldnt be enough compression to start it. probably make an interesting sound, and look cool with no manifold on the ex. ports. will it make the manifold glow? no way. unless its like .020 mild steel then maybe.


i dont know if the misdirection of the flame front would be an issue to the ring lands or not, probably depends on haha ok im bullshitting now. i have no clue about that shit.

3/1/2006 6:47:46 PM

I agreed with you (sorta)
But i can tell you that Vaporizing fuel slows down a flame front alot more than not putting enough gas in there.

But.. if you run lean you have to retard everything because the flame front will move alot faster... possibly causeing a temperature & pressure spike as the piston compresses the expanding gasses.

ohh and diesel and gas burn at 2 completely different rates.... a gas motor would blow itself apart if run at diesel compression ratios....

i didn't know your point was based of the exaust valve being open when the piston ignites... but it can still be open near the end of the burn or atleast before the heat disapates into the block.
and is carried off by way of water.

[Edited on March 1, 2006 at 7:37 PM. Reason : .]

3/1/2006 7:36:18 PM

Quote :

"A little more detail here. Firing isn't actually initiating when the exhaust valve is open; rather, firing occurs too late, and fuel is still actively burning when the exhaust valve opens and blowdown occurs. Instead of exhaust gases consisting mostly of combustion byproducts, they consist of quite a bit of burning mixture. Yeah, it produces a lot of heat. It's a good way to burn your valves as well (so is having insufficient valve lash on the exhaust valves)."

I think I said that a couple of posts earlier...

The big thing about running lean is lack of a homogeneous mixture...flame front propagation does not occur smoothly or evenly. Up to a certain point, leaner is hotter; the most complete combustion occurs at slightly lean conditions, as an excess of oxygen is available to combine with the fuel, and ALL of the fuel burns. However, too lean DOES eventually lead to lower temps, as nitrogen acts as a combustion buffer, slowing the burn and absorbing heat energy.

Even at 1.0 La (Lambda; 14.7 parts air to one part fuel; the ideal stoichiometric ratio), there remains traces of unburned fuel due to lack of mixture homogeny and local spots of rich mixture, etc. I love how Poe87 pulls these somewhat obscure terms (or at least those used primarily by fuckin' Krauts) out of his arse.

3/1/2006 7:36:44 PM

Too lean Too long Too bad

3/1/2006 7:36:54 PM

mehhh...

some people know what works in a book others know what works in F.A.S.T. Big Stuff & AEM

Dear Poe... i challenge you to run a typical motor off >15.6 a/f ratio. especially if you have a possitive intake pressure.


[Edited on March 1, 2006 at 7:50 PM. Reason : .]

3/1/2006 7:39:50 PM

"Danger to intake manifold"

3/1/2006 8:08:15 PM

I never said lean was good for power or longevity. I merely said that leaner mixtures produced cooler combustion temperatures. The lean mixtures cause problems when the mixture is not homogeneous like Dan said. Best power is slightly rich, best fuel economy is slightly lean. Ideally, fuel should be as vaporized as possible when it gets to the combustion chamber. I'm not new to tuning, I know that 15.6:1 isn't a good fuel ratio for max power, but under part throttle cruise, it's probably fine.

The reason not to run lean under boost is for heat reasons. Running richer than normal has a cooling effect on the intake air charge, which helps resist detonation and pinging. Sorry for the lambda, that's just the terminology the Austrailans use in Motec.

My point with the diesel engine is that a diesel runs extermely lean at anything below full load. Following the logic of lean mixtures produce high combustion temperatures, a diesel would burn up right quickly. Read the book I referenced earlier, you might understand a little more of how this works.

3/1/2006 8:14:34 PM

^Keep in mind, too, that local fuel distribution in a diesel is VERY rich (immediately surrounding the injector) and the flame front propagates extremely rapidly at the injector. Burn time is more of a function of injection duration, and pressures build very rapidly in a diesel. You'll notice that a straight-piped diesel is usually noticeably quieter and has an entirely different exhaust note than a gasoline engine. That's because the combustion period is over and done with in a diesel when the exhaust valve opens and blowdown occurs. A small bit of combustion is most likely still occurring in the gasoline engine.

And yes, diesels run very lean except under full load. They have no throttle plate.

3/1/2006 8:23:59 PM

its also timed where its almost a constant pressure expansion process.

3/1/2006 8:28:49 PM

^ideally, yes.

3/1/2006 8:33:20 PM

Quote :

"They have no throttle plate"

WTFbbq

the more u no

so what kind of AF ratios are we talking to get to the point where lean = cooler?

[Edited on March 1, 2006 at 8:41 PM. Reason : ]

3/1/2006 8:40:45 PM

I merely provided the diesel as an example of lean mixtures not being hot - I know diesels are very much different than gasoline engines, that wasn't my point. Reading the book I talked about earlier will explain a lot of this stuff. Flame speed is slower with a lean mixture than a rich mixture as well (p.280), sumfoo1 said something about that earlier. On p.321, "exhaust temperature of an engine will go up with higher engine speed or load, with spark retardation, or with an increase in equivalence ratio." Equivalence ratio of 1 is stoich, above is rich, and below is lean, so higher equivalence ratios mean a richer mixture produces a higher EGT. However, peak combustion temperatures are cooler under a very rich mixture because more heat energy is going to evaporating the fuel before it can burn.

3/2/2006 1:25:02 AM

ok I didn't know we were talking about average burn temps... if they all stayed near average... motors wouldn't detonate because the expansion happend too fast (spiking pressures and breaking parts).

I've never actually measured egts on a gas motor on a dyno but i've never seen glowing headers (from running rich) either and i've seen motors run down to 10:1

3/2/2006 11:55:25 AM