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Single cylinder briggs engine horse power changes


mwells

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Ok I've been doing some research on the old cast iorn single cylinder engines, and was wondering what they all change on the engines to get more hp. From my understanding and please correct me if I'm wrong, the 10hp-16hp have the same carbs. Are they changing compression of the engines with the raised fin heads? For example my 12hp has a flat head, my 13hp has the raised fin head. As for the 14hp-16hp the bore is again bigger to add more hp. I don't have a 14 hp, but both my 15+16 hp engines have the raised fin heads too, so what is the difference in the 15+16hp engines to gain 1hp more? Are all the cams/valves the same on the 12-16hp engines? Or is that where there getting the extra hp? Thanks in advance for your imput!!
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Some had no change, it was just a marketing ploy. Some were rpm changes from 3300 to 3600rpm's. The raised fin engines were basicly the same. I have heard of some variation in the jet size of the carb, but since there were so many changes in internals of the carbs anyway it's hard to track.
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When ordering carb kits for some of the various models, there are different P/N's, and subsequently, different sized ports in the main jet. There were also different intake manifolds, and I'm guessing minor changes to the fuel/air mixing and intake resulted in changes to combustion/claimed hp. This has always been my thought, anyway.
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Also, the 325xxxx and 326xxxx series of engines had a more "breathable" and less restrictive air cleaner system (using the pre-filter jacket and dry element along with the longer intake manifold. Briggs may have done some additional tweaks with the cam lobe profiles along with what others have said about the head design/changes. Tom(PK)
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I started tractor pulling with a 12hp 30ci bored out to a 16hp piston 32ci. I did find differences in carb bores. The 15/16hp 32ci engines had a larger bore carb than the 12hp. That was 14 years ago, but I think the difference was about 1/16" The later 32ci engines 14, 15, and 16 hp were identical except for a little tab on the throttle stop to prevent the throttle plate to open all the way on the 14 and 15 hp.
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That anwsers a lot of questions! Thanks for you input! Does anyone know if the valves and camshafts are the same on the 12+13hp or the 14-16hp engines?
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quote:
Originally posted by mwells
Does anyone know if the valves and camshafts are the same on the 12+13hp or the 14-16hp engines?
The best way to accurately find out is to downlaod the respective manuals and compare part numbers. I'm willing to bet that there are different specs not on the inatallation of the cams, but on the mechanical valve timing itself between the different size engines.
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I am referring to the actual cam lobe sizes that deal with lift and duration, Bob. Static timing should be the same through the entire engine family. So there must simply be a larger bore and different synchro balancing between the 30 and 32 ci engines, right??
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