factory relieved blocks

Yep, they certainly did. It ain't a fancy hotrod style shaped relief. Just a kind of milled straight sided slot.
When they started or finished I don't know for certain, but got a 99A here (1939 Merc type) with factory relief.
I have been led to believe that the relief was done because the stock area tween the valves and bore forms a sharp ridge, and this sharp part acted as a stress point, and when used on the big trucks with air brakes, the mixture leans out when theses braked are applied, and this lean out would cause that Sharp part to go silly hot, and then crack. This is what I was told, and it sorter makes sence. I say sorter cause I'm not fully versed on these old air brakes and how they worked.
Martin.
Just re-read this and didn't clearly say, the relief removed that Sharp part (stress riser if you will) and helped to combat the crack. So I wad told.
 
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I have the same answer as scooder. I have one and it was in a truck, am guessing around 39 or 40. It had a 3 3/16 inch bore.

Neal
 
I've rebuilt quite a few 59 blocks factory reliefed. They all came out of big truck engines. I understood the factory did this to the big truck engines to keep them from pinging with a big load on. Some street rodders think they have something with this block but to me there just loosing compression. I'm sure they work good with high RPM engines and with a super charger. Walt
 
Walt, good call on the ping, spose the sharp bit that's removed with this relief could also with its stupid hot possibility could also onset ping and or detonation.
Martin.
 
I have a factory relieved 59 block 239 with a raised area for the intake manifold. I'm not sure what year it was produced. Were 59 blocks with raised intakes produced prior to 1946? If so, were they only for trucks? Thanks for any input.
 
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