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Need to rebuild my 345 engine, I have the 20hp engine with a bad block. I have a good 18hp block. Can someone tell me the difference in the engines. How did they get the two extra horsepower? Could I put the internal 20hp parts into the 18hp block? Thanks
 

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Need to rebuild my 345 engine, I have the 20hp engine with a bad block. I have a good 18hp block. Can someone tell me the difference in the engines. How did they get the two extra horsepower? Could I put the internal 20hp parts into the 18hp block? Thanks

I'd start with measuring the cylinder and piston from both engines. What you are looking for is bore (diameter of the pistons/cylinder) and stroke (amount of movement up & down in the bore). This is how you determine the displacement of an engine. It's usually expressed in cubic inches or cubic centimeters. Say a 8 hp engine is 250cc's a 10 hp could be 350cc's. (Just an example not actual numbers). So the bigger the displacement the more power it should make. In this case the internal parts won't be interchangeable. Some can be used with additional machine work. Like boring out the cylinders to fit a bigger pistons.

Now if the displacement is the same. The horsepower difference could be from higher compression pistons and possibly a different cam shaft profile. Seeing it is only a 2 hp difference. Honestly if the 18 hp was good to just bolt in I would do that and not worry about it.
 

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I'd start with measuring the cylinder and piston from both engines. What you are looking for is bore (diameter of the pistons/cylinder) and stroke (amount of movement up & down in the bore). This is how you determine the displacement of an engine. It's usually expressed in cubic inches or cubic centimeters. Say a 8 hp engine is 250cc's a 10 hp could be 350cc's. (Just an example not actual numbers). So the bigger the displacement the more power it should make. In this case the internal parts won't be interchangeable. Some can be used with additional machine work. Like boring out the cylinders to fit a bigger pistons.

Now if the displacement is the same. The horsepower difference could be from higher compression pistons and possibly a different cam shaft profile. Seeing it is only a 2 hp difference. Honestly if the 18 hp was good to just bolt in I would do that and not worry about it.
It could be a difference in carburetor. Maybe the 20HP breaths a bit better and has bigger jets. If bore and stroke are the same then the compression would be the same unless the heads are different. Also wasn't there a change in how HP ratings were measured on engines. Though I think that was fairly recent (something like the last 5 years or so). But it is possible that it is just a paper rating and doesn't mean anything. I do remember reading about this with the Kawasaki engines on the ZTraks. I want to say the engine was the same model but the HP rating changed from the Z925 machine to whatever is the equivalent in the newer Z930. Something like that anyhow.

I agree that if he has an 18hp that fits, just go with that and don't worry about it. The amount of time spent swapping parts around and potential problems that this will introduce is greater than what it is worth in the end game. He will likely never notice 2HP. In fact as that 20HP engine got weak over time it might have only been producing 16HP so he would still end up ahead.
 

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I'd start with measuring the cylinder and piston from both engines. What you are looking for is bore (diameter of the pistons/cylinder) and stroke (amount of movement up & down in the bore). This is how you determine the displacement of an engine. It's usually expressed in cubic inches or cubic centimeters. Say a 8 hp engine is 250cc's a 10 hp could be 350cc's. (Just an example not actual numbers). So the bigger the displacement the more power it should make. In this case the internal parts won't be interchangeable. Some can be used with additional machine work. Like boring out the cylinders to fit a bigger pistons.

Now if the displacement is the same. The horsepower difference could be from higher compression pistons and possibly a different cam shaft profile. Seeing it is only a 2 hp difference. Honestly if the 18 hp was good to just bolt in I would do that and not worry about it.
Bore and stroke is the same
Per JD parts the cam is the same
Heads are different, that could be it.
OR Rated RPM might be higher on the 20hp so it rates higher, such as 18hp @ 3400rpm and 29hp @3600rpm?


Need to rebuild my 345 engine, I have the 20hp engine with a bad block. I have a good 18hp block. Can someone tell me the difference in the engines. How did they get the two extra horsepower? Could I put the internal 20hp parts into the 18hp block? Thanks
18hp Crankcase (block) has the same part # thru engine FD611V ES01 & FS01 20hp. Part # change for FD611V AS02 & BS02 20hp
 
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