The ‘less than 373” cubic inch limitation was derived using the existing cubic inch break down that has been in place for several decades for the cars running under the SCTA rules.  The AIR (American Iron Roadster) class is limited only to the C class engines whereas many of the other classes are permitted to run a variety of cubic inches within their respective classes.

The engine class designations break down as follows:
AA      501.00 cid and greater
A         440.00 - 500.99 cid
B         373.00 - 439.99 cid
C         306.00 - 372.99 cid
D         261.00 - 305.99 cid
E         184.00 - 260.99 cid
F          123.00 - 183.99 cid
G         93.00 - 122.99 cid
H         62.00 - 92.99 cid
I           46.00 - 61.99 cid
J          31.00 - 45.99 cid
K         up to 30.99 cid  

Lorena, Texas (South of Waco)

..Just curious where the rules makers came up with the under 373 cu inches?  It doesn't appear to fit any known engine & doesn't even work out evenly in Litres.. A litre is a hair over 61 cu inches.  So ??..


Paul

Here’s a picture of the engine in the car.
  

Lorena, Texas (South of Waco)

Thanks for the interesting information. It must be obvious I'm not too familiar with what goes on in the racing world, especially on the salt.  First time I've heard of downsizing in the race environment but it makes sense where necessary for qualification purposes.  Period iron M E L parts are not too plentifull and there must be a very strong spring on breaker point(s) to remain stable for  the insane upm's out there. 

64F100 57FAIRLANE500

For this MEL combination, the bore is 4.350” and the stroke is 3.123”.  The crankshaft is a Mercury 383 crankshaft that has been destroked using 2.200” journals while the rods are 7.100” long to keep the wrist pin in a better raised position on the pistons.  The crankshaft is 383, the block is ‘early’ 430, and the heads are 462.  The intake manifold is a AFR single plane for a 460 Ford topped off with a 1050 cfm Holley Dominator carb.

The rules for C-AIR (American Iron Roadster) engines dictates that the engine be less than 373 cubic inches while using 1972 or earlier production heads and blocks.  Those over the counter performance parts that were available during that time frame but were not available in a production car are not legal in that class.  Electronic ignitions are also not allowed either which relegates ignition chores to either breaker point distributors or magnetos using breaker points.

Lorena, Texas (South of Waco)

Great news about #560 running a M E L engine.   I thougnt the base L E M was 383".  If that's true, was this engine down-sized?

64F100 57FAIRLANE500

Nice surprise when going through the Jan 2022 issue of Hot Rod Magazine (page 18) and saw Keith Cornell’s 560 AIR car pictured in the Bonneville Speed Week article.  The 560 car is powered by a 371” M-E-L engine.
  

  

  

Lorena, Texas (South of Waco)