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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: blazing816 on December 02, 2013, 12:43:09 pm
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Okay so my temporary K10 I am using, until my project is done, has a 305 with a eldelbrock 1406 carb and TH350/NP208 in it. I tow a 23 travel trailer 4600lbs about twice maybe 3 times a year. It pulls it, but does not have much grunt to get it moving from dead stop well and my project probably will not be done for another two summers. So I have 2 questions:
1. I do not know the gear ratio because sticker says they are suppose to be 3.08 but all the running gear (trans and axles and engine in it when bought it) were change to mid-late 70s gear. So my question is there a way to determine gear ratio without taking off the diff cover??
2. What would help my 305 with a little more low end, however I still want to be able to go 65mph on freeway without the truck revving to high if possible. I am assuming a cam swap is what I am after, just curious what you guys would recommend for a 305, type and brand??
Thanks
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To determine the gear ratio without removing the diff cover. Jack up the truck and place on jack stands. Mark each rear drum to the backing plate, and mark the rear end yoke to the differential. 2 guys turn equally the rear wheels 1 complete turn. Count the drive shaft revs. Slightly under 3 revs you have 2.73, right at 3 revs 3.08. Almost 3.5 revs would be a 3.42. 3 3/4 revs a 3.73 and so on. Those I have mentioned are 1/2 ton stock ratio's GM had
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You can do the same thing out in the parking lot. Mark the bottom straight down on the sidewall of the tire with chalk. Lay 5' away from the truck on the pavement where you can see the driveshaft and have someone ease the truck forward in Drive one revolution, until the mark is straight down again. Count the driveshaft revolutions, etc.
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Comp and Lunati cams have a cam recommendation section. I'd suggest going there and filling out all the fields; they usually get back to you in a day or two. In the meantime, headers would help, and maybe advance the timing two degrees. That alone made a noticeable difference when I had a 305.