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How much HP should you get out of a 70 gas?

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Jon

11-23-2002 18:07:15




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I have rebuilt a 70 gas with 45 over pistons 8.8:1 compresion, ported the head and opened the intake manifold up. On the dyno I get 52Hp all the time. I have 100 octane fuel in it also. I live 3000 ft above sea level. Should a person get more Hp or is that all a 70 will do? I would appreciate any info on getting more power out of the old girl. thanks,
Jon




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phil

11-24-2002 09:48:16




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 Re: How much HP should you get out of a 70 gas? in reply to Jon, 11-23-2002 18:07:15  
Jon, I looked up the effects of altitude on a piston engine. If the HP is 100% at Sea Level it would be 82% at 5000 feet, 66% at 10,000, 52% at 15,000 feet, etc. That calculates to about 89% at your local altitude of 3000 feet. So you should expect to loose about 5 HP.



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2 cylinder

11-24-2002 08:30:21




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 Re: How much HP should you get out of a 70 gas? in reply to Jon, 11-23-2002 18:07:15  
Have you tried adjusting the timing (distributor)when you dynoed the tractor? When we dyno our A and G for tractorpulling, we start with the carb. abjust it for peak HP on the dyno, then adjust the timing for peak HP. Our JD-G varies about 10-12HP just by how the timing is set.



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G Taylor

11-23-2002 18:58:37




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 Re: How much HP should you get out of a 70 gas? in reply to Jon, 11-23-2002 18:07:15  
50.4HP for a stock 70 gas at 975 rpm on the pulley. This combo should be making at least 55HP on the pto. 57 to 60 HP if 6-1/8" G pistons had been used. Head porting and milling the intake divider out from between the runners can cause turbulence. Also a loss of velocity/ram effect and centrifuging/ dropping suspended fuel mist out of the air stream . Airflow is limited by the valve and port or combustion chamber shape an inch each way from the seat. Hogging the ports out just increases the volume and reduces the velocity on heads with valve limitation. Bigger intake valves without getting into the water jacket or being shrouded by the "eyebrow" with cut down stems and back cut heads make HP.Port matching the intake/head and making certain the choke and throttle blades are 100% open. Have you tried it with the carb intake casting installed but the aircleaner removed? Is the heat riser fully in the cold position? Is the high compression piston shrouding the spark plug interrupting flame travel? Is the spark strong and at the correct time? 100 octane will limit power if it doesn't knock with 92 octane. Is a cylinder running too rich or lean? Try a LP intake/exhaust manifold, set the valve lash 1-1/2 nut flats loose from where you can't spin the push rod by hand. Was the cam/lifters trued up or were the used pieces just re-installed? A Pertronics ignition module and MSD 6 unit won't make extra power but they will ensure spark isn't the limiting factor.

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