AFM Adjustment

[Kossco]

Wow, thank you for that amazing reply!

[tommu]

On a side note id love to get a larger clearer file from the original post. the images and text are great, but it's a real strain to be able to make out all of the text and fine details. if the originals are larger/clearer id love to see them sometime.

Me too. Maybe you could put them in a book...

Bump

[Amskeptic]

On a side note id love to get a larger clearer file from the original post. the images and text are great, but it's a real strain to be able to make out all of the text and fine details. if the originals are larger/clearer id love to see them sometime.

Me too. Maybe you could put them in a book...

Bump

I will be working on the illustrations at some point and will try to improve clarity.
How many DPI shall I save them at? How many pixels you all want?
Colin

p.s. no Steve Kent, no. A lean mixture that is real lean does NOT extend the burn into the exhaust causing Armageddon, because the whole point of this exercise (that shows up on the CHT gauge, hello)
is that we are starving the burn. There is no further combustion left by the time the exhaust is going out the port. My late model bus exhaust system with the headless bolt flange on the left manifold is now at 133,000 miles since new, 70,000 miles past when I dremelled all the bolt heads off, it is terrible to look at, but not a wisp of soot leaking from the gasket. Let's chill on the catastrophisizing shall we?)

[72Hardtop]

Nothing wrong with running 15-16 afr at cruise. It is actually cooler than 14.7 at cruise. The added heat comes into play with throttle position (excess) not part throttle condition/s.

[sgkent]

On a side note id love to get a larger clearer file from the original post. the images and text are great, but it's a real strain to be able to make out all of the text and fine details. if the originals are larger/clearer id love to see them sometime.

Me too. Maybe you could put them in a book...

Bump

I will be working on the illustrations at some point and will try to improve clarity.
How many DPI shall I save them at? How many pixels you all want?
Colin

p.s. no Steve Kent, no. A lean mixture that is real lean does NOT extend the burn into the exhaust causing Armageddon, because the whole point of this exercise (that shows up on the CHT gauge, hello)
is that we are starving the burn. There is no further combustion left by the time the exhaust is going out the port. My late model bus exhaust system with the headless bolt flange on the left manifold is now at 133,000 miles since new, 70,000 miles past when I dremelled all the bolt heads off, it is terrible to look at, but not a wisp of soot leaking from the gasket. Let's chill on the catastrophisizing shall we?)

a overly lean mixture places the fuel molecules farther apart. As a result the burn is much slower. As a result the exhaust port and stack temp WILL go up as the burn extends into the exhaust port. Google "Lean backfire".

[Amskeptic]

a overly lean mixture places the fuel molecules farther apart. As a result the burn is much slower. As a result the exhaust port and stack temp WILL go up as the burn extends into the exhaust port. Google "Lean backfire".

Yes, thank-you for the explanation, now talk to Len Hoffman and the guys over at Lycoming and the graphs that *show* EGTs dropping as you lean past lean.

[sgkent]

the egt will drop once you get really lean but the burn will continue into the port and overheat the exhaust valve. On an air cooled VW engine your best mixture is not the most efficient one. That is why VW discontinued their air cooled engines in smog countries. If you read the Lycombing literature you will also see that any head temp over 380F - 400F is considered damaging to the engine. There is a reason drag racers burn alcohol - it burns really rich so they can use the extra fuel to cool the engine. When that un-burned fuel hits the outside air it creates the flames you see. The moral is don't run your air cooled bus engine at 14.7 or leaner unless you are on flat and level at low speeds. Waste the fuel and run in the low 13's except at light cruise which 14.5 - 14.7 is ok, no hills no headwinds. At light cruise the EGR will add inert air and let the engine run more efficiently and cooler. Like Len, I raced and won plenty of trophies in GP and FP also. Built heads like Len does today.

[Amskeptic]

the egt will drop once you get really lean but the burn will continue into the port and overheat the exhaust valve. Like Len, I raced and won plenty of trophies in GP and FP also. Built heads like Len does today.

... but did you like my photographs? Those bleached intake valves? The white frosted pistons?
Now at 142,000 miles.
Colin

[72Hardtop]

ROP = Rich of Peak

LOP = Lean of Peak

Us airplane guys have a lot in common with us ACVW guys.

Chart will explain it...

[Amskeptic]

SEE? SEE?
(thank-you 72Hardtop)

[72Hardtop]

the egt will drop once you get really lean but the burn will continue into the port and overheat the exhaust valve. On an air cooled VW engine your best mixture is not the most efficient one. That is why VW discontinued their air cooled engines in smog countries. If you read the Lycombing literature you will also see that any head temp over 380F - 400F is considered damaging to the engine. There is a reason drag racers burn alcohol - it burns really rich so they can use the extra fuel to cool the engine. When that un-burned fuel hits the outside air it creates the flames you see. The moral is don't run your air cooled bus engine at 14.7 or leaner unless you are on flat and level at low speeds. Waste the fuel and run in the low 13's except at light cruise which 14.5 - 14.7 is ok, no hills no headwinds. At light cruise the EGR will add inert air and let the engine run more efficiently and cooler. Like Len, I raced and won plenty of trophies in GP and FP also. Built heads like Len does today.

A lean burn of 15-16 at a part throttle condition is better and cooler than at 13-14 (same throttle condition).