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Tractor Pulling Discussion Forum

JD 70 gas cam

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Oppy

06-21-2004 08:06:05




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I need some recommendations for a cam. We're trying to up the horsepower w/o stroking the motor and getting too radical. To date, we've bored it to 396 cu. in., aluminum pistons, milled the head .050, new valves etc. (nothing oversize), rebuild the carb (roberts carb shop), installed and new electronic ignition (Petronix) and dry air filter. We'll be running in a stock rpm class (I believe they allow 20% over rated rpm).

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Ron

06-21-2004 19:52:01




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 Re: JD 70 gas cam in reply to Oppy, 06-21-2004 08:06:05  
I will be posting pictures of the valves I just cut for my 630 JD.. Polish the combustion chambers--this will take a while to get it to Shine..! With a full re-contour of the upper side of the valve (FULLY POLISHED), and a 4 angle cut from the seat, down into the throat of the port, I seem to always get a Very Good increase in power-wheather it is a tractor, OR an automobile engine... NOW, combine THAT with a GOOD cam, and you will make some power..

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buickanddeere

06-21-2004 08:54:40




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 Re: JD 70 gas cam in reply to Oppy, 06-21-2004 08:06:05  
The 70's limiting point is flow through the intake valves and the ports/combustion chamber eyebrow. A set of 70 all-fuel valves can be shortened to fit after the seats are ground larger. Do a three angle valve job and blend all the rough edges out of the intake port bowls. Match all the carb/manifold/gaskets/head ports to prevent overlap. Opinions vary on grinding the eyebrow out from around the intake side of the combustion chamber to improve flow.

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