Onan 18 & 20 Hp ratings

[OhioGregg 6]

Being a relative newbie here on the forum, I have a question about the Onan 18 & 20 hp engines. I have a 518H & a 520H, both great tractors. Everything I have seen in the specs on both engines are the same. Same bore, stroke, etc. Where does the extra 2 hp come from? Carburation? If so, could you just put the carb from a 20hp Onan on the 18hp version and end up with the same thing? Or am I missing something that isn't obvious to me?

 

Thanks,

Gregg

[decksetter 50]

I have heard the cam and carb are different between the 16/18/20, but not sure. Can anyone confirm this?

There is also a p224 that is 24hp (they put it on the wheel horse 724z), but it is a different block / forged steel rods / lots of different stuff.

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[312Hydro 474]

I have heard the cam and carb are different between the 16/18/20, but not sure. Can anyone confirm this?

There is also a p224 that is 24hp (they put it on the wheel horse 724z), but it is a different block / forged steel rods / lots of different stuff.

Sent from my DROID RAZR using Tapatalk 4 Beta

So, When are you starting a build thread on that Mega 524H? I've got questions!

[decksetter 50]

It's not done yet, and it's actually not mine, belongs to a buddy. It was pretty straight forward though!

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[ericj 1,578]

basically the 16 is a motor of it own. the 18 and 20 are the same block, bore and stroke, but hr 18 uses the cam out of the 16 and the carb of the 16. pull up the onan service manual and you can compare the spec. and see for your self. i have an 18 on the back burner that's waiting  for a rebuild an a 20 hp cam and carb to be reborn as a 20 hp motor

 

eric j 

[Desko 610]

Little late but the p216-220 blocks are the same the 16 hp use's a different crank and rods. The 18-20 hp use the same crank and rods but the 18 use's the 16 cam (as stated) for a lower valve lift and the same carb.