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John Deere Tractors Discussion Forum

75hp 720 Diesel!!

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720Deere

11-10-2003 18:59:38

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I responded to a local classified add about a fully restored 1958 720D and was told that the tractor just tested at 75hp on a dyno. I can't imagine getting 30% more out of a 720! Has anybody ever heard of this before, or is this just a case of an inexperienced dyno operator? They are one strong tractor especially with a twist of the rack screw, but let's be reailistic! I should have asked if perhaps he pulled 5-16's with this monster! Oh, by the way, the tractor is located in MD and is priced at $9,000.00.

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Dingaling

11-11-2003 17:38:59

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Re: 75hp 720 Diesel!! in reply to 720Deere, 11-10-2003 18:59:38

Hey I live in MD. and I am interested. Where it is ????? Tomorrow is going to be a rain day, good day to go eye up a 720

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Gpower

11-11-2003 10:36:43

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Re: 75hp 720 Diesel!! in reply to 720Deere, 11-10-2003 18:59:38

It can happen....without a lot of boring and stroking...just not with all factory parts..ie fuel parts.

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stuart

11-11-2003 08:21:11

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Re: 75hp 720 Diesel!! in reply to 720Deere, 11-10-2003 18:59:38

I have a M&W dyno and it is accurate even below 540. We use it to break in tractors that have a new motor in them. and to check our 7220 magnum and 2 JD 4455s after we bring them home from the big farm pulls. The only way he is getting that kinda power is if he is over revving the motor and pulling it down past the 540 mark. unless he has it bored or stroked even then anyone with a brain knows that it takes 100 hp to pull 5-16s. at least in our type of soil

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720Deere

11-11-2003 13:15:26

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Re: Re: 75hp 720 Diesel!! in reply to stuart, 11-11-2003 08:21:11

"anyone with a brain knows that it takes 100 hp to pull 5-16s." Easy there Stuart. The 5-16's thing was a little humor regarding the excessive power claims. It may only be about half, but there is a brain here somewhere.

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720Deere

11-11-2003 13:12:46

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Re: Re: 75hp 720 Diesel!! in reply to stuart, 11-11-2003 08:21:11

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Jed

11-11-2003 06:16:55

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Re: 75hp 720 Diesel!! in reply to 720Deere, 11-10-2003 18:59:38

I run an automotive testing lab and we use a lot of dynos. You need to see when the last certifictaion was done. Dynos require maintance and calibration. I don't believe that HP rating is accurate.

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buickanddeere

11-10-2003 19:14:30

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Re: 75hp 720 Diesel!! in reply to 720Deere, 11-10-2003 18:59:38

Possible but not recommended except for a brief sprint down the pulling track to beat tractors not painted Deere green. When new they wher esupposed to be operated at full rated rpm and 80% load with reserve left for tough spots. Why beat an extra 25-30%HP out of a 45+ year old piece of equipment?

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morgan heaton

11-10-2003 19:09:58

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Re: 75hp 720 Diesel!! in reply to 720Deere, 11-10-2003 18:59:38

I have just had my 730 standard dyno tested and it said 71 horsepower. The thing is that most of the time these figures are not at 540 pto rpm. So say at 540 rpm it dosen't have the most hp. which is the proper way to rate a tractor, but it will make 75 hp at a lower non rated pto speed. And it dont it sound cool to say that a 720 has 75 hp. I think so. Morgan Heaton

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720Deere

11-10-2003 19:19:38

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Re: Re: 75hp 720 Diesel!! in reply to morgan heaton, 11-10-2003 19:09:58

Morgan,

I am assuming that 75hp is max hp at a much lower rpm than rated. The problem is this 75 hp reading won't mean squat when you have a pto load rated at 540 rpm. I have seen 70 diesels max out in the 60's range but again nowhere near 540 pto rpm.

Please correct me if I'm wrong, but isn't there some kind of correction factor for the old M&W dynos? As I recall, they are not all that accurate once you torque the tractor down below the 540 rpm range.

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morgan heaton

11-10-2003 19:33:44

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Re: Re: Re: 75hp 720 Diesel!! in reply to 720Deere, 11-10-2003 19:19:38

Hey, Im with you, I dont think that 71 Hp on my tractor is acurate at all. It was just a little above what it should be a 540 (could be off due to operator error) but te operator of the dyno said that just about any tractor will have a reserve hp at a lower pto rpm. And as for going down the track, Idont know, I supose that the pto hp is a totaly different thing. I mean that you have sveral different veribles (tire size, final drive ratios, weight distribution, ect that cause one tractor to go farther than another. My point was that I could say my tractor has 71 hp, but in truth at 540 it had 61 hp. But I suppose that if you were selling a tractor 75 hp sounds better than 59 like it should. All in all I agree with you and also, I dont pull the guts out of my 730 on a regular basis, I guess it was a special occasion. Morgan

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buickanddeere

11-11-2003 16:37:40

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Re: Re: Re: Re: 75hp 720 Diesel!! in reply to morgan heaton, 11-10-2003 19:33:44

If the dyno test starts at 540 rpm then of course torque and rpm will increase when loaded down and rpm drops about 10%. Thats about where the proportional control style govenor fially has pulled the fuel rack wide open. Try the dyno pull starting at 15% over rated pto rpm and then lug her down. The only electronic or mechanical control system is a PI or PID system (Proportional Integer Derivitive). That will keep rpm from drooping when loaded from 0 to 100% load.

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Puller

11-11-2003 07:12:59

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Re: Re: Re: Re: 75hp 720 Diesel!! in reply to morgan heaton, 11-10-2003 19:33:44

You be amazed what a 720 would put out with a little bore and some extra stroke

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