74 k10 going 55 mph is at 3,500 rpm

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Oregon
First Name
grant
Truck Year
1974
Truck Model
k10
Engine Size
350
My question is why do you think you have 3.73 gears? it Sounds more like 4.56s or your only getting first and 2nd gear.
I’m not 100% sure but that’s what the build sheet says and it looks stock. Last night I was driving and it did go into third gear.
 

Bextreme04

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Eric
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K25
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350-4bbl
How do you know what your RPM is? Factory tach? Aftermarket one? Where are you at in Oregon?
 

gmbellew

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It’s an aftermarket tach, I’m in McMinnville oregon

good question about the tach. I am not that familiar with aftermarket tachometers or if there are different types, etc.. but at 3500 rpm the engine should definitely be making some noise. that can be used as a quick reality check on the tach readout. is the engine really screaming at 55mph?
 
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grant
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350
good question about the tach. I am not that familiar with aftermarket tachometers or if there are different types, etc.. but at 3500 rpm the engine should definitely be making some noise. that can be used as a quick reality check on the tach readout. is the engine really screaming at 55mph?
She’s not quite screaming but she’s definitely up there in the rpm according to my ears lol
 
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grant
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She’s not quite screaming but she’s definitely up there in the rpm according to my ears lol
Okay I just drove it on a backroad, she is shifting into third gear. The tach was saying 3,400 rpm at 55 however it is up by around 220 rpm. The speedometer is pretty spot on. So given that info the rpm’s at 55 are close to 3,180.
 

TotalyHucked

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I'm gonna venture to guess either you have way more gear than 3.73 (either the original axle has been regeared or it's been swapped with another axle) or your tach is off more than 220rpms. How did you verify it was off by 220?
 
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grant
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1974
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k10
Engine Size
350
I'm gonna venture to guess either you have way more gear than 3.73 (either the original axle has been regeared or it's been swapped with another axle) or your tach is off more than 220rpms. How did you verify it was off by 220?
By a timing light
 
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grant
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1974
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k10
Engine Size
350
According to this the axle is a 3.73 gear stock axle, how do I go about figuring out wether someone changed the gear ratio?
 

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Joined
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Posts
31
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Location
Oregon
First Name
grant
Truck Year
1974
Truck Model
k10
Engine Size
350
I remember some aftermarket tachs having a small 4-6-8 switch for the number of cylinders on the engine….
Oddly enough this tach (which I bought on Amazon) advertises it works on 4-6-8 cylinders engines however it doesn’t have any switch to change between them
 

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