FWIW on floors chassis etc which have been subjected to open headers and soot, carbon caked on, I have used Wal Mart / dollar store HD oven cleaner with great results, FWIW the non smelly stuff isn't worth the time or effort.
The fuel tank was ridiculously covered in carbon from open headers.
The axle housing had 1/8-3/16" thick carbon flaking off when we got the car....
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~JAG~
NCRS#65120
68 GTO HO 4 spd Alpine Blue /Parchment 2 owner car
#21783 71 Corvette LT1 45k miles Orig paint - Brandshatch Green - National Top Flight - last known 71 LT1 built.
71 Corvette LT1 42k miles Original paint - Black - black leather - only black LT1 known to exist.
NUMEROUS Lemans blue Camaros,
Monza Red and Daytona Yellow Corvettes
& a Chevelle or two...
Survivors, restored cars, & other photos
https://picasaweb.google.com/lh/myphotos