What happens inside a motor run too lean!

[powwerjon]

Several weeks ago there was a discussion on leaning the motor down or run lean burn. Earlier tonight I was going thru several fiber pacs sorting parts and found a piston out of our 1985 alcohol funny car. The motor was a 540 cu.in. with a 12/71 blower and was mostly Keith Black parts. Back in the day and mostly today there are no electronics allowed on the alcohol funny cars. Most of the cars of the day had what was called a “go fast" button that would lean the motor in the top end just before the lights and give it a boost in power. Most of the time you didn’t damage the motor, but sometime when you already had the motor on Kill and it was the final round you would push the button and you let the smoke out of the motor. The satisfaction was that we did win the round and the race.

There are 6 pictures of one of the pistons that came out of the motor on that run. Notice that the intake pocket is melted and pushed in with a hole in the top of the piston. The ring land is gone on that side and on the exhaust side too is scuffed badly and the skirts are scuffed too. Needless to say the sleeve was in poor shape too! This is also was can happen in our motors too.

http://www.gmcmhphotos.com/photos/general-pictures/p65263-img-14881.html
http://www.gmcmhphotos.com/photos/general-pictures/p65262-img-14871.html
http://www.gmcmhphotos.com/photos/general-pictures/p65261-img-14861.html
http://www.gmcmhphotos.com/photos/general-pictures/p65260-img-14851.html
http://www.gmcmhphotos.com/photos/general-pictures/p65259-img-14841.html
http://www.gmcmhphotos.com/photos/general-pictures/p65258-img-1483.html

J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 30’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan

 

[Carl Stouffer]

Here are a couple of photos of pistons that came out of Dave Wood's 403:

http://www.gmcmhphotos.com/photos/g7162-david-wood-27s-403.html

It had a heater hose come in contact with the AC belt on the way to the Tucson GMCMI last Spring and was severely overheated besides running lean due
to the mysterious vacuum leaking device that had been installed in the PCV line.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member

 

[Jim Hupy]

Think in terms of an oxy/acetelyne cutting torch. Nothing too much exciting
happens when you heat parts with the preheat flames, but "Ohhh Mama" when
you push on the oxygen lever, bad stuff happens quick. Rapid oxidation
occurs within nano seconds when excessive oxygen is present.
Parts can, and do, glow red hot in the absence of oxygen, like exhaust
valves in a running engine, turbocharger wheels and cases, exhaust
manifolds and headers, etc. and no harm comes to them short term. BUT, add
too much oxygen to the exhaust gas stream and look out, bad stuff happens
in the form of damaged pistons, exhaust valves, turbo wheels, uncontrolled
combustion processes which results in detonation, overheating, cracked
castings, broken crankshafts etc. Quicker than you can describe it.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> Here are a couple of photos of pistons that came out of Dave Wood's 403:
>
> http://www.gmcmhphotos.com/photos/g7162-david-wood-27s-403.html
>
> It had a heater hose come in contact with the AC belt on the way to the
> Tucson GMCMI last Spring and was severely overheated besides running lean
> due
> to the mysterious vacuum leaking device that had been installed in the PCV
> line.
> --
> Carl Stouffer
> '75 ex Palm Beach
> Tucson, AZ.
> Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive,
> Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American
> Eagles,
> Solar battery charging. GMCSJ and GMCMI member
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[Keith V]

OK so what is 'too lean' 16:1? 15:1? 14:1?
________________________________
From: Gmclist on behalf of James Hupy
Sent: Thursday, September 27, 2018 11:04 AM
To: gmclist
Subject: Re: [GMCnet] What happens inside a motor run too lean!

Think in terms of an oxy/acetelyne cutting torch. Nothing too much exciting
happens when you heat parts with the preheat flames, but "Ohhh Mama" when
you push on the oxygen lever, bad stuff happens quick. Rapid oxidation
occurs within nano seconds when excessive oxygen is present.
Parts can, and do, glow red hot in the absence of oxygen, like exhaust
valves in a running engine, turbocharger wheels and cases, exhaust
manifolds and headers, etc. and no harm comes to them short term. BUT, add
too much oxygen to the exhaust gas stream and look out, bad stuff happens
in the form of damaged pistons, exhaust valves, turbo wheels, uncontrolled
combustion processes which results in detonation, overheating, cracked
castings, broken crankshafts etc. Quicker than you can describe it.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> Here are a couple of photos of pistons that came out of Dave Wood's 403:
>
> http://www.gmcmhphotos.com/photos/g7162-david-wood-27s-403.html
>
> It had a heater hose come in contact with the AC belt on the way to the
> Tucson GMCMI last Spring and was severely overheated besides running lean
> due
> to the mysterious vacuum leaking device that had been installed in the PCV
> line.
> --
> Carl Stouffer
> '75 ex Palm Beach
> Tucson, AZ.
> Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive,
> Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American
> Eagles,
> Solar battery charging. GMCSJ and GMCMI member
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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