Horsepower on John Deere Compacts

[Tractor King]

I opened up the post and my question seems somewhat unanswered if there really is an answer. The cubic size and compression of the 770 and 790 are comparable...where is the 6 hp difference?

 

[RoyJackson]

I opened up the post and my question seems somewhat unanswered if there really is an answer. The cubic size and compression of the 770 and 790 are comparable...where is the 6 hp difference?

I thought JD755's post (#6) and attachments was pretty clear

 

[Craig B]

The combustion chamber design, valve size, intake and exhaust ports and manifolds (or injectors if so equipped), and also camshaft profile can dramatically alter H.P. in I.C. engines with the same bore and stroke.

 

[RoyJackson]

The combustion chamber design, valve size, intake and exhaust ports and manifolds (or injectors if so equipped), and also camshaft profile can dramatically alter H.P. in I.C. engines with the same bore and stroke.

Very true and some or all may have something to do with the difference in engine output...but the 790's engines have more cubic inches then the 770's...which very likely accounts for the increase.

 

[picker77]

An interesting comparison in this vein is the 3032E vs the 3038E. They are exactly the same tractor, but the 32E uses Yanmar's 3TNV88 (naturally aspirated with 97.6 cu in) for 31.4 hp @2500 RPM, and the 38E uses the 3TNV84T (turbocharged with 91.5 cu in) for 37.1 hp @2500 RPM.

Clearly, JD gained the 6 extra hp by running a smaller displacement engine harder (6 extra hp from 6 fewer cubic inches), and adding some very expensive moving parts (a turbo). All other specs of the two tractors are identical, including weight, etc.--except cost, of course.

To me, the extra 6 hp would have meant value for the dollar if it had been gained via more cubic inches and less complexity instead of the other way around, and had been delivered with some extra weight to help get the added power to the ground. In my case, I opted for the lower hp, larger displacement, and lower cost of the 3032E. Doesn't mean a 3038E would have been a bad choice, I just believe in weight first and power second, and since these are light tractors to begin with I think paying $1200 more (IIRC) for 6 hp would not have been a good investment.

 

[ctlguy]

It's too bad the University of Nebraska does not have tractors below 40hp. Always found their web site interesting and when there is differences in advertisement it is listed. I have always been a little baffled why some companies choose not to participate in the oecd testing makes me really wonder about their claims.