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shieldslx

HELP! (tractor pullin)

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shieldslx
Is there any way to modify the briggs ohv engines for more power cheaply (I/C). I want to pull my 808GT that I put a ohv in, it has pullin tires and now weights, but I think I need more power. HELP!

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Al
Hi, One thing that you can do and it would usually be considered stock, is to grind the valves to obtain a power gain. Usually in race engines, the valve seats are ground until the outside contacts the valve about 1/32 of an inch from the outer edge of the valve. Next narrow the seats to about 1/16th on the intake and 3/32 on the exhaust valve. Do this with a 60 degree stone or Neway cutter on the inside of the seat This is sometimes referred to as hanging the valves. Narrow seats seal much better than wide ones. Grind the seats 45 degrees and the valves 46 degrees, I have seen dyno tests done where a about a 5% power gain can be obtained by grinding a 2nd face on the valve about 15 to 20 degrees. This face should come to with in 1/32 of an inch of the inside of the seat. Even more can be gained by tuliping the valve. I have done this a few times by putting the valve in a lathe and using a hand "port" grinder and stone. Turn the lathe on (cover the bed and cross slide ways to protect the lathe ways from grit) then using the hand grinder and a cone shaped stone grind the metal from the bottom side of the valve head. Grind until the transition from the stem to the head is smooth and the metal flows smoothly to the point about 1/32" inside the seat. This makes the valve lighter and the intake and exhaust efficiency much greater. The engine breathes so much better. Many clubs don't allow porting in stock classes. But the 2nd face is usually OK. Tuliping may or may not be acceptable in stock classes. The advantage of this is that it does not hurt the low and mid range torque, but still provides a gain. If you go to a longer duration cam shaft, you will lose low and midrange torque, but will gain more power at high rpm. Remember that a well detailed pretty stock engine will usually provide more power than a poorly set up modified engine. The more radical the engine is the more perfect it has to be and the more sensitive it is. Things like degreeing the cam in and ignition timing changes are critical with high performance parts. Alcohol is another issue. It is so sensitive to outside air temps etc. Many of the guys I know have over $6000.00 in K series pulling engines. This includes the after market k341 blocks with no fins and thicker cankcases. These can take over 4 inch bores and not have to have straps on the head and draw bolts from the head to the bottom the crankcases. Strapping keeps the blocks from breaking at the base of the cylinder and the cylinder leaving the crankcase. With these engines developing in the 75 hp area on the dyno, at 6500 rpm they are being taxed to the limit. I hear that Juiien Bond at Mid West Super Cub is doing Kohler Command (small Blocks 25 -30 hp)that dyno 100 hp for $10,000.00 and you provide the core. Three years ago my very close friend Scott Minnzenmeyer owner of Recreational Motorsports (www.recmotor.com)was running one on the dyno gettimg about 88 hp when the crank shaft broke and created many pieces of scrap. Now they have to use steel billet crankshafts when they get in this area up. Scott was my first full time employee in our current business. He was a state motorcycle trials champ when I hired him at 17. We were adding Simplicity to our golf car business. I was working at Rockwell days and at the shop nights and Sats and Sundays. I hired Scott and said essentiially here's the check book, make it work. Then I soon hired a lady to help him. In a couple or 3 years he went on his own and partnered in a John Deere outdoor power business. Later he and his partner sold to a larger dealer and became the service manager and while there he did a lot of work with Polaris on performance stuff. My old race machinist friend died and Scott had worked with and around him on his race stuff. They were close and when John became unable to continue he bought John's equipment and started Recreational Motorsports. If you need any performance work done he would be a good person to contact. I still use his dyno room and engine dyno occasionally. He builds engines and ships them world wide. They do a lot in the small Kiddee Snowmobiles (5hp)and grind their own racing cams for them etc. Anyway you can go as wild and spend as much as you want pulling. Let your pocket book be your guide

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MikeES
As Rod said...get the rule book first, that will tell you what you can and cannot do. Also Al brought up a good point about a poorly set up modified engine. The engines in our pulling tractors are absolutely stock but run like a well oiled sewing machine, we beat the modifieds all time. One miss, one hesitation is a killer in pulling. First get your stock engine running as smooth and strong as it can before tearing into modifications. Friction...get your drive line to be as free as possible, no drag anyplace. Watch the veteran pullers, they can push their tractors around with 1 finger.

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