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Harry Ferguson Tractors Discussion Forum
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z120 over bore HP

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justin14054

02-22-2008 21:01:46




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Rebuilt a to-20 with the overbore kit 3-5/16=wondered if anyone new the HP rateing with larger bore.Tractor data page just shows std bore.just curious.Thanks
Justin14054




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Jim in OH

02-27-2008 10:59:14




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 Re: z120 over bore HP in reply to Jerry/MT, 02-22-2008 21:01:46  

Jerry/MT said: (quoted from post at 12:00:56 02/23/08) ....That"s almost a 4% increase in airflow so the horsepower will go up by almost 4% .....


If you could actually can get 4% more air into it.... The TO30 went to larger intake valves, to take advantage of this slightly larger displacement, which the TO20 does not have.. but then you would be hard pressed to tell the difference of 1 hp in the field anyway... a twenty degree drop in air temperature would get about the same improved result....

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stroked550

02-27-2008 10:30:14




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 Re: z120 over bore HP in reply to justin14054, 02-22-2008 21:01:46  
I rebuilt our to-20 a few years ago with the overbore kit. Pretty much average rebuild, milled the head, new valves, ect. Tractor dynoed 29 hp on the pto last summer with probably 400-500 hours on rebuild.
Ben



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justin14054

02-23-2008 14:04:58




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 Re: z120 over bore HP in reply to justin14054, 02-22-2008 21:01:46  
Thanks Guys
Justin



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Jerry/MT

02-23-2008 11:00:56




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 Re: z120 over bore HP in reply to justin14054, 02-22-2008 21:01:46  
All other things being equal, the horsepower should scale with the sqaure of the bore diameter ratios.For example, if the over bore is 3-5/16 and the standard bore is 3-1/4 then the diameter ratio is (3.3125/3.250)^2 = 1.039. That"s almost a 4% increase in airflow so the horsepower will go up by almost 4% which is about 1.2 HP.



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Jerry/MT

02-23-2008 11:06:47




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 Re: z120 over bore HP in reply to Jerry/MT, 02-23-2008 11:00:56  
Opps. I used 30 hp for the reference HP. But that"s the TO-30. For the To-20 it"s ~27 hp so the change will be ~1 HP.



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NJ howie

02-23-2008 10:21:15




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 Re: z120 over bore HP in reply to justin14054, 02-22-2008 21:01:46  
justin just a guess but the to30 runs a std. bore of 3 1/4 at 30 hp.the connecting rods are the same so 3 5/16 should be close but don't no about the head and how they differ.



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