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JM 
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Joined: 12 Sep 2009
Location: United States
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 Topic: how much motor?
Posted: 17 Jul 2016 at 9:30pm |
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I have a wc I want to pull with in div. 2 , 3mph --4000lbs. If I put 15.5-38 what is the least cubes I need to have enough hp? I have the original block with 45 crank and oem d17 pistons, head has been worked over by speed shop, zenith carb.Thanks
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DrAllis
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Joined: 12 Sep 2009
Points: 20548
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Posted: 18 Jul 2016 at 9:02am |
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As I read the Div #2 NATPA Rules, the maximum tire size you can use are 13.6 x 38's or 14.9 x 28's which are 168 and 170 square inches. If it was my tractor, I'd be thinking the 3500 lb class and maybe 3000 lb class with 4000 lbs as an option. It's also an 18 inch high drawbar, not 20 inch, which takes less HP. If you stay with the 28 inch rubber your 3 MPH gearing should work with your engine as-is (I think), or an RC rear end for 38 inch rubber. There are probably better carbs (more air flow/larger venture) than what you have ??
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DiyDave
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Joined: 11 Sep 2009
Location: Gambrills, MD
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Posted: 18 Jul 2016 at 6:02pm |
Hook her to the sled, and see what happens... 
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DrAllis
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Posted: 18 Jul 2016 at 9:12pm |
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I've got a restored WD-45 with D-17 pistons and sleeves and new 14.9 x 28 rear tires. I've pulled it twice weighing 4,000 pounds with a 20 inch high drawbar. On a pretty good black dirt track, I've got just enough power to spin it out in SECOND gear. That's my comparison to what JM is trying to do.
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JM
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Posted: 18 Jul 2016 at 9:40pm |
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I did some test pulling at 4500 lbs. It would spin out in first, but not second. My speed in first was 2.7 mph, free gov speed is 1550. I have 14.9-28 firestons on it. I have a 45 too, and the wc is geared higher. The track was rock hard cleats were spinning on top of the clay. I pulled it at half throttle first gear and it still spun out. I have been thinking about going to 4000 that is the lightest class in my area, have a shop top cut the tires that is allowed and most tractors have done it. I think my gearing is really good because the engine is lugging hard but seems to have plenty in first. When I pulled second gear and pulled it down, I was only about 15-20 feet behind where I spun out in first.
I asked about building a motor to turns 38s because Ive been told many time 28s wont get the job done.
Last nite I talked to a puller who says he saw a d17 on 28s beat a bunch of big tire tractors.
Maybe I should cut the tires and try it a while, set my rpm up to get a little more speed.
What do you think?
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DrAllis
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Posted: 18 Jul 2016 at 10:06pm |
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I thought Div 2 rules allowed 10% over on the RPM....I'd sure take advantage of that.
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Charlie175
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Location: Shenandoah, VA
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Posted: 19 Jul 2016 at 7:06am |
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You can win with 28s for sure
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Charlie
'48 B, '51 CA, '56 WD45 '61 D17, '63 D12, '65 D10 , '68 One-Ninety XTD
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CAL(KS)
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Joined: 18 Sep 2009
Location: Chapman, KS
Points: 3786
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Posted: 19 Jul 2016 at 7:58am |
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you CAN win with 28's. I would say a majority of the time the taller tires win, but yes 28 will sometimes win. there is no magic setup, as conditions always change. currently i dont think you have enough motor for taller tires to compete. in my club we have 5-6 AC's in the light classes and not 1 is running 28 inch tires. several of them attend Natpa pulls, they dont run the circuit but do attend depending on pull location. I dont have details on motor specs but they are built div 2 and most pull div 3 also. the light weights are so competitive and that was part of the decision to pull the UC. not that 5-6k is gonna be easy as i have M's with 7 inch cranks to deal with. but something different for me.
Edited by CAL(KS) - 19 Jul 2016 at 7:59am
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Me -C,U,UC,WC,WD45,190XT,TL-12,145T,HD6G,HD16,HD20
Dad- WD, D17D, D19D, RT100A, 7020, 7080,7580, 2-8550's, 2-S77, HD15
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JM
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Posted: 19 Jul 2016 at 5:17pm |
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I might cut the 28s and put them on 15 inch wheels for max contact and try it. I think the gearing and hp is matched pretty good.
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Robacpuller
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Joined: 07 Apr 2016
Location: Wisconsin
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Posted: 27 Jul 2016 at 9:54pm |
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Robacpuller
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Location: Wisconsin
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Posted: 27 Jul 2016 at 9:57pm |
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Robacpuller
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Posted: 27 Jul 2016 at 9:59pm |
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These r some pics of my carb and we're mounts to manifold
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