Engine number tag decoding help please.

[Mcwho]

I have a 65 monza, I am confused as it has dual exhausts and I cannot make sense of the engine numbers. See attached...

Sent from my SM-G965U using Corvair Forum mobile app

[bbodie52]

T1221RB

T = Tonawanda, New York (GM Tonawanda Engine Plant)
http://media.gm.com/media/us/en/gm/comp ... wanda.html
1221 = Engine manufacturing date (month and date). December 21st.
RB = 1965-66 140 hp — 164 CID 9.0:1 Compression Ratio, with Manual Transmission — Corsa Only
Probable Cylinder Head Casting No: 3856727, 3878565, 3878570, 3883861

That particular suffix code "RB" was usually assigned to an engine designated for a 1965-1966 Corsa only. It was the standard engine in the Corsa, with the 180 hp Turbocharged engine as the only option in the Corsa.

The 140 hp engine was also offered as an option with the Corvair 500 and Monza, coupled to a Powerglide or manual transmission, from 1965-1969. It has large valve heads, 4x1 carburetors (2 Primary and 2 Secondary with a progressive linkage) and dual exhaust.

[bbodie52]

This will give you some idea of the differences between the 140 hp engine and the 110 hp engine.

140 hp vs. 110 hp...

• Same high-performance camshaft on both 140 hp and 110 hp engines. Low performance camshaft in the 95 hp engine.
• Same 164 Cubic Inch displacement with same bore and stroke on all 1964-1969 engines.
• Stronger, nitrided crankshaft on the 140 hp and 180 hp turbocharged engines. (Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface).
• On the 140 hp engine, a 4x1 carburetor arrangement, with two primary and 2 secondary 1-barrel carburetors, connected with a progressive linkage to open the secondary carburetors as you approach full throttle. (Equivalent to a 4 barrel carburetor on the 140 hp engine, vs. a 2 barrel carburetor (2x1) on the 110 hp and 95 hp engine).
• Dual muffler, dual exhaust with larger exhaust ports and larger exhaust manifolds on the 140 hp engine. Single exhaust on the 110 hp and 95 hp engine.
• 9.0:1 Compression Ratio in both 140 hp and 110 hp engines. 8.0:1 CR on the 95 hp engine.

140 hp Heads...

It's all about better breathing at full throttle at the high RPM ranges. At lower RPM the big valves and dual exhaust don't make much difference, and the secondary carburetors are not open for business.


110 hp Heads...

[azdave]

It is simple enough to put dual exhaust on nearly any Corvair so no big deal there. The case code indicates it's likely a 140 HP engine so it would have came with dual exhaust from the factory, even if the engine was in a base model 500 or a Monza.