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How to compare hp diesel v. gas


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#1 middleageddeere OFFLINE  

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Posted April 10, 2011 - 08:21 PM

I often see repower posts that say things like, "You need either a 17 gas or a 14 diesel" Can anyone explain how to tell what diesel hp is equal to what gas hp? Thanks.
Adam

#2 olcowhand ONLINE  

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Posted April 10, 2011 - 08:33 PM

I don't know where to find all the specs, but it's more a matter of torque output than HP.
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#3 middleageddeere OFFLINE  

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Posted April 10, 2011 - 08:47 PM

Right, right, right... and since they list hp most frequently, I am wondering how it typically compares.

#4 olcowhand ONLINE  

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Posted April 10, 2011 - 08:49 PM

I think you can drop 4hp on diesel to match gasoline...my opinion by using them. Then I'd guess it depends on which engines also.
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#5 middleageddeere OFFLINE  

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Posted April 10, 2011 - 08:53 PM

Ok that is what I was looking for..thanks so much Daniel.

#6 DH1 ONLINE  

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Posted April 11, 2011 - 04:36 AM

I think gas engines have a maximum peak rating where diesel has a continuous rating.
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#7 Boss 448 OFFLINE  

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Posted April 11, 2011 - 12:29 PM

Comparing horsepower and torque ratings can be tricky. This can be even more complicated since some published specs I've seen appear to be rated in metric units rather than S.A.E. units we are familiar with in this country.

I think that Daniel is close on his approximation for comparing small gas and diesel engines. Another important factor to consider is the type of duty the engine will see. In general it appears that diesel engines work better under constant heavy loads than do gasoline engines and their stronger design makes them more durable. Under constant loads diesel engines also have better fuel economy to the point that even though diesel fuel is more expensive per gallon you still save substantially on overall fuel costs.

JN
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#8 Texas Deere and Horse OFFLINE  

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Posted April 11, 2011 - 12:34 PM

I think you can drop 4hp on diesel to match gasoline...my opinion by using them. Then I'd guess it depends on which engines also.



Daniel, So if I understand what you are saying, My 14hp kubota engine should have the power of my 18hp Onan?
I am planning to drop it in a 140 H-3.

#9 olcowhand ONLINE  

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Posted April 11, 2011 - 01:32 PM

Daniel, So if I understand what you are saying, My 14hp kubota engine should have the power of my 18hp Onan?
I am planning to drop it in a 140 H-3.


Right at it or close Brian. I know my 12+hp Kubota compares to a 16hp Onan. Isn't your engine a Z482? If so, it's not 14hp, more like 12+. 11HP continuous, 12.7 intermittent. If your engine is a Z482, IMO it would compare to 16HP gasoline.
Here are the Z482 Specs: Kubota Diesel Engine Super Mini series - Model Z482
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#10 DMF OFFLINE  

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Posted April 11, 2011 - 01:41 PM

In a nutshell it's basically what DH1 said about peak ratings. This is from another site that (I think) descibes it well:

You have to consider how horsepower is rated in order to compare diesel engines to gasoline engines in a typical garden tractor. The horsepower ratings that you see are peak horsepower ratings. Gasoline powered engines in garden tractors typically have peak horsepower at about 3000 rpm and horsepower falls off quickly below that . Diesel engines in compact tractors typically have their peak horsepower at about 1000-1500 rpm and horsepower stays up throughout most of the rpm range. How does that make a difference? A gasoline powered garden tractor has to be at full throttle to achieve its rated horsepower. When the tractor has a load put on it by a mower or going up a hill, for example, the rpm will fall from, let's say, around 3000 rpm down to 2500 rpm. At 2500 rpm a gasoline engine will have significantly less horsepower than at 3000 rpm. At 2500 rpm, with much less horsepower, the load will pull the engine down even further until the rpm and horsepower are so low that either the engine stalls or you release the load (by shutting off the mower or pushing in on the clutch) A diesel engine, however, has a much broader power band. Using the same example, the diesel powered tractor running at full throttle encounters the same load as the garden tractor did. The engine rpm will fall from, let's say, 2000 RPM to 1500 rpm. At 1500 rpm the diesel engine will have roughly the same power as it did at 3000 RPM and will continue to pull the load. The horsepower and rpm will not continue to fall because the diesel engines power is not as dependant on the engine's rpm.
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#11 olcowhand ONLINE  

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Posted April 11, 2011 - 01:44 PM

Most of the Yanmar & Kubota engines in garden tractors intended for mowing also.... run 3400 to 3600rpm, same as gasoline. My Massey 1010 runs 2750rpm.
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#12 Texas Deere and Horse OFFLINE  

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Posted April 11, 2011 - 02:02 PM

Right at it or close Brian. I know my 12+hp Kubota compares to a 16hp Onan. Isn't your engine a Z482? If so, it's not 14hp, more like 12+. 11HP continuous, 12.7 intermittent. If your engine is a Z482, IMO it would compare to 16HP gasoline.
Here are the Z482 Specs: Kubota Diesel Engine Super Mini series - Model Z482



I think you are right Daniel, I don't remember the model number, but it's in a T1600 tractor that my friend and I got for him to use as parts machine and for me to have a diesel engine for a conversion...:laughingteeth:
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#13 Boss 448 OFFLINE  

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Posted April 12, 2011 - 04:44 PM

I think that Daniel and several others here that have done a diesel repower will agree - the hardest thing to rate and compare is that diesel sound emanating from under the hood whether it's just idling or when you put a load to it. Priceless!

JN
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#14 olcowhand ONLINE  

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Posted April 12, 2011 - 04:45 PM

I think that Daniel and several others here that have done a diesel repower will agree - the hardest thing to rate and compare is that diesel sound emanating from under the hood whether it's just idling or when you put a load to it. Priceless!

JN


Oh man, did you hit the nail square on the head!!!!! :thumbs:
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#15 Boss 448 OFFLINE  

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Posted April 15, 2011 - 08:30 AM

Come to think of it, the black exhaust smoke don't hurt either! :bigrofl:

I guess we'll have to create a rating system called the sensory value.

I'd also like to point out that there seems to be a very high level of quality workmanship observed on diesel conversions. Every on I've seen on this forum exhibit absolutely top creativity and workmanship. Apparently one attracts the other. Impressive!

JN

Edited by Boss 448, April 15, 2011 - 08:36 AM.

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