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Tractor Pulling Discussion Forum

73hp jd G?

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slyfox

02-20-2004 05:41:36




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I have a jd G with stock stroke,powerblock,worked over flathead with 6 3/4 pistons tractor runs great with good low rpm hp and mid range hp and only show 68hp. How are some of you guys showing 73hp with 75 less cubes?




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a puller

02-22-2004 18:43:49




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 Re: 73hp jd G? in reply to slyfox, 02-20-2004 05:41:36  
there is something wrong with it. we have a G that has a flathead that is just ported and polished, 3 angle valve job, .090 pistons, and that is it other then it has the big nut 51 carb on it. it ran 68hp constant no matter when, but we have had it up to 72 in just right conditions. Lately, the head cracked, and it blows water alot, so it only has 65 as I speak. We need to tear it down and weld it up. I will let you know what it has when we get it back together. We use a p 2000 M&W dyno and test it at 540.

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ronjohn

02-24-2004 08:06:48




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 Re: Re: 73hp jd G? in reply to a puller, 02-22-2004 18:43:49  
what is a 3way valve job, i never heard of it



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lynn

02-21-2004 06:20:03




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 Re: 73hp jd G? in reply to slyfox, 02-20-2004 05:41:36  
slyfox..one thing you can do to check the motor is to measure the torque at different rpms..put the tractor on a dyno and check hp at 535 rpms pto..pull down to 500 rpms and measure the pressure on the gauge..pull to 450 and do the same and on to 400..take your pressure readings and convert to hp at the different rpms..calculate the torque at these points and you can see what kind of torque curve you have..fixed a styled g few years ago for a friend..6.250 x 8.000 490 cubes with the g pistons which i think take hp because of the ring friction..heres what we got out of it..
71 hp at 535 rpm 975 motor rpm torque 383 ft lb
67 hp at 500 rpm 911 motor rpm torque 386 ft lb
61 hp at 450 rpm 820 motor rpm torque 391 ft lb
54 hp at 400 rpm 729 motor rpm torque 389 ft lb
this gives 1.5% torque rise between the 975 and 729 rpm reading..this motor had the head worked on and jerrys manifold but stock cam..also had 11:1 compression which takes away some of lower torque..most of the john deeres i have worked on have about 8% torque rise..
another g i fixed for my friend was a 6.250 x 9.500 jerrys head 9.5:1 compression jerrys manifold..this tractor measured this..
82 hp at 535 rpm 975 motor rpm torque 442 ft lb
69 hp at 400 rpm 729 motor rpm torque 497 ft lb
torque rise 12.4%
it had a stock 51 big nut carb and stock cam which restricted the upper rpm airflow but when pulled down had a very large torqur rise..larger carb would help 975 rpm hp but i think marginal help at 729 rpm along with the $500 cost..if you can do this to your tractor you can get an idea if there is some restriction or other problem..lynn

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ChadS

02-21-2004 06:51:11




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 Re: Re: 73hp jd G? in reply to lynn, 02-21-2004 06:20:03  
I have to put my 2 cents in here, Lynn, are these actual dyno tests? Why wouldn't the engine pick up HP when you lug it past 540? In all cases I have built and tuned tractors, the Hp should increase a few HP when you lug it past 540, or 535, then drop off. Even on our 730 it goes up about 9 hp when we lug it below 540 before it drops off. Now, on a stock unaltered carb, that, what you described will do that. go up to a cretain HP at 535, nad when you lug it past, it drops off during to pull down. Somewhere in there, a factor is not right,, from one dyno man to another, It should get stronger when you go past 540, increase maybe 5-10 hp, then drop off. Here is what I am talking about...
A 240 ci Farmall H 4 cyl
225 psi compression
at 535 it is 72 hp. at 400 it is alomost 85 before the hp drop off. Now I know that comparing apples to oranges here, but it is all the same theory in my opinion. How I got the engine to increase HP when it lugs, is the amazing part, carb, and governor work, good fuel, and ignition. Tuning the engine to run at 540 is fine, but when you have an engine that has a strong power curve, and a carb that does not match it, it will drop HP, before it makes it. It has to be designed to lug, not just at 540, but all rpm ranges. Just my opinion,,, ChadS

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lynn

02-21-2004 16:52:18




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 Re: Re: Re: 73hp jd G? in reply to ChadS, 02-21-2004 06:51:11  
ChadS..the dyno i use is one of the old m & w ones..the gauge on it shows 535 pto rpm and the point where you take the direct reading of hp..when you go below that point there is a pressure reading you have to take and compute it out on the wheel chart to get the actual hp..the gauge reading goes up as you pull it down but the rpm also is going down..i of the opinion you cannot gain hp when the rpm is going down unless there is a problem with cam or intake system which limits higher rpm..an example of this would be the deeres..i measured my friends g and it made 54 hp at 535 and also 54 at 600 so the rpm didn't help..lynn

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ChadS

02-22-2004 06:18:14




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 Re: Re: Re: Re: 73hp jd G? in reply to lynn, 02-21-2004 16:52:18  
Lynn, I have one of those M&W conversion charts too. Nice to have it. I guess the way to describe what I am saying, is,, it is like measuring brake HP, or close to it. It measures how much lug power an engine has. If it does not lug, and make more power under a heavier load on the rated rpm, your carb is off. Not trying to dispute dyno know how, LOL,, it is finding power that many don't know it is there!! Even on the JD 2 lungers, they have a power curve, just for kicks, I got out my 730 JD, and dynoed it. It is 68 hp at 540, then at 400 it was 75hp before it started losing power. I had gone through the carb to make the engine lug and have the carb be able to feed it fuel while lugging that low. Makes a big difference on the track. ChadS

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Jack

02-20-2004 14:23:31




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 Re: 73hp jd G? in reply to slyfox, 02-20-2004 05:41:36  
Are you stopping at 540 pto rpm's or pulling it on down to 450 pto rpm's to get your reading?540 is the way to do it but on these ole JD's pullin them down past 540 the horsepower will go on up which is not considered the actual hp.Mine had 55 hp at 540 but went up to 59-60 at 450 pto rpm's so I went with the 55 hp claim.Another thing to remember is that dyno's don't all read the same.If the tractor or tractors your talkin about all used the same dyno theres a good chance some figures may differ from what they were.

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JDGnut

02-20-2004 15:54:20




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 Re: Re: 73hp jd G? in reply to Jack, 02-20-2004 14:23:31  
Most dynos are only accurate at the 540 and 1000 rpms... (some have a 600 rpm and other ranges.) if they are pulled down lower.. or the reading is taken at a different RPM you have to convert the HP reading on the dyno using a chart to a wheel.. that usually came with the dyno... That is will dial type dynos... Most digital read out dynos will convert the results for you...
JDGnut
(My Div II G is in that hp range.. two different dyno's less than 2hp difference.. )

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Tyler Neff

02-20-2004 08:19:40




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 Re: 73hp jd G? in reply to slyfox, 02-20-2004 05:41:36  
Jerrys head and manifold would help , along with some high ratio rockers. You can cut your own rockers or use Murphys roller rockers. I dont think changing the cam will help a whole lot. Plus chnging the cam is a pain in the butt. Hope this helps Good Luck.



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