RPM’s
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Mountain Pass
Joined: May 2018
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From: Webster
RPM’s
I purchased a Bosch tachometer from Jets to put on my 61 F100. I know you get what you pay for so this could be the case with this, that being said how many RPM’s (approximately) should my 223cu, 3 on the tree be turning at say 55 mph?
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With a 29 inch tire and your 1:1 3rd gear, at 55 mph you will turn the rpms shown by each possible rear axle ratio:
3.25 = 2071
3.50 = 2230
3.70 = 2358
3.89 = 2479
4.10 = 2613
3.50 might be the most common gear.
Your warranty/data plate has the VIN, trans, color, axle etc codes on it. Your differential came with a sheet metal tag on one of the studs, about the "5 o'clock" position. Big IF regarding either of those still being there, and another big IF regarding you axle being OEM.
3.25 = 2071
3.50 = 2230
3.70 = 2358
3.89 = 2479
4.10 = 2613
3.50 might be the most common gear.
Your warranty/data plate has the VIN, trans, color, axle etc codes on it. Your differential came with a sheet metal tag on one of the studs, about the "5 o'clock" position. Big IF regarding either of those still being there, and another big IF regarding you axle being OEM.
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Does the tach have a switch for 4/6/8 cylinders?
3.0 gears would rev 1912, but then we don't know your tire size, axle ratio etc.
To turn 5000 rpm at 55, you would need 7.85 gears, so I think we can count that out.
Seriously, at 1800 rpm at that speed your motor should hum and sound very happy.
3.0 gears would rev 1912, but then we don't know your tire size, axle ratio etc.
To turn 5000 rpm at 55, you would need 7.85 gears, so I think we can count that out.
Seriously, at 1800 rpm at that speed your motor should hum and sound very happy.
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Mountain Pass
Joined: May 2018
Posts: 114
Likes: 3
From: Webster
Thanks for everybody’s reply! First lesson, read the directions! Found the switch on the back of the tach, set on 6 and tried it again. I was turning 2200 RPM at 55 mph on speedometer app on my phone (speedometer doesn’t do anything but bounce around). I also took off the aftermarket breather and put the original oil bath breather back on it sounds a lot better.
Thanks for the info.
Thanks for the info.
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Fleet Mechanic
Joined: Aug 2016
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From: Great White North
Thanks for everybody’s reply! First lesson, read the directions! Found the switch on the back of the tach, set on 6 and tried it again. I was turning 2200 RPM at 55 mph on speedometer app on my phone (speedometer doesn’t do anything but bounce around). I also took off the aftermarket breather and put the original oil bath breather back on it sounds a lot better.
Thanks for the info.
Thanks for the info.
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