By now about all SM engines have been rebuilt to the same cubic inch as a 450. If both used original gasoline heads the 450 would have more compression with standard pistons and its original camshaft and manifold also gave it a little more power. Lots of combinations of parts that could be put in over the years results in no clear cut answer to the question of performance. Also up into the 1960 tees IH sold replacement blocks with C281 on them that got used in SM tractors. Several around that just have the block changed with all SM parts used with the block. If thats what the tractor is you probably have the same setup as a SM with a replacement block hurting originality.
IH tests with fire crater standard altitude pistons used show only a 1.5 horse power increase with the 450. They recomended a 400 camshaft be used for more power in the SM and I think they used it testing the SM.
Also interesting was the fuel use at 1450 RPM. 450- 4.8 to 5.2 a hour.
SM-4.5 to 4.9 a hour.
This post was edited by D Slater at 07:28:26 09/26/12.
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Today's Featured Article - Tuning-Up Your Tractor: Plugs & Compression Testing - by Curtis Von Fange. The engine seems to run rough. In the exhaust you can hear an occasion 'poofing' sound like somethings not firing on all cylinders. Under loaded conditions the tractor seems to lack power and it belches black smoke out of the exhaust. For some reason it just doesn't want to start up without cranking and cranking the starter. All these conditions can be signals that your unit is in need of a tune up. Ok, so what is involved in a tune up? You say, swap plugs and file the points....now tha
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