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Discussion Topic:
'51 8BA RPMs
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Big Red 51 |
11-28-2009 @ 3:33 PM
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New Member
Posts: 192
Joined: Oct 2009
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Thanks for the formula Stroker and the comments Super. Looks like 2500 rpm puts me at about 49 MPH with my setup. My rebuild has about 3000 miles on it. So I have been running about 55 which is out about 2800 rpm. Is 2800 harmful? Super, about how much is a Mitchell OD if I can find one? Thanks, Don
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supereal |
11-28-2009 @ 8:25 AM
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Senior
Posts: 6819
Joined: Oct 2009
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Most truck gearing is for power, rather than hiway speed, so they are set up to place the maximum engine speed close to the power band, where horsepower and torque are at peak. That occurs around 2,500 rpm. Most of the trucks I've seen hit that at about 50-55 mph. You will need access to a tachometer to determine where you are. The sticker is that to alter the engine speed, it can only be done by a change in rear axle gears, for a large change, or wheel and/or tire size for modest adjustments. Many of us have installed aftermarket overdrives for modern hiway driving. I have one in my '47 that reduces the engine speed by 33% when engaged. I use it above 40-45 mph. Mitchell and others make them, but you will have to do some searching for your '51. As to the tach, most diagnostic types hook up between the input terminal of the distributor and ground, and are calibrated to number of cylinders.
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Stroker |
11-28-2009 @ 8:02 AM
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Senior
Posts: 1460
Joined: Oct 2009
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(0.00595) * (RPM * r) / (R1 * R2) = vehicle speed in miles/hour where: RPM = engine speed, in revolutions/minute r = loaded tire radius (wheel center to pavement), in inches R1 = transmission gear ratio R2 = rear axle ratio
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Big Red 51 |
11-28-2009 @ 6:19 AM
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New Member
Posts: 192
Joined: Oct 2009
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I run my stock '51 PU on the hiway with a HD 3 speed and 4.27 rear end. I usually run around 50 MPH which sounds like a "comfortable" speed but I do not want to over burden the engine on a 600 mile run. Is there a formula for calculating the RPM and what is a good speed or RPM with this setup for sustained running? If a tach is required, what is the best way to hook one up? Thanks, Don
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