how many rpms are you turning when cruisin at 70 -75 mph ?

i have a 6.0l 2003 gmc 1500hd 6in lift 33.5s magna charger supercharger superchips chip and flowmaster exhaust

at 70-75 mph i turn 2500rpm is this normal?

 

What gears do you have? Sounds about right I'd think if you have 4.11's

 

Thats seems right. There are alot of calculators on net. for gear/tire/rpm your running etc.
has it changed on you lately making you worry?

 

that sounds about right if you have 4.10's and a 30" tire.

 

30-31 inch tires 3.73's with a 4L80 and I'm doing about 2200. Seems the OD ratio in my buddy's truck with the 5 speed manual conversion (nv somethin) with 3.73's and same size tires revs just about the same.

 

Did you have your truck tuned for the larger tires? You may actually be going faster than your speedo is indicating. Stock tires are 30.4" so your 33.5" tires are 10% larger in diameter. You may be going 10% faster than your speedo is indicating if you have not tuned for those larger tires.

 

I must be in a different math world. If you're running a 33.5" tire you shouldn't be running 2500rpm in overdrive at 70-75mph. Alot of the 1500HD's come with 3.73's, but a few did come with a 4.10 gear. Even with the 4.10 gear you aren't going to be close to 2500rpm with a 33.5" tire. A 4.10 gear isn't really enough gear either with that much tire.

 

Yeah, factoring in a .70 4th gear, 4.10 rears, and 33.5" tire a calculator shows 2000RPM. Kick in the converter lock and you would be under.


http://www.csgnetwork.com/multirpmcalc.html ( i use the bottom calculator where you can enter final trans gear ratio, 60E is .70 and 80E is .75)

 

With the 1500HD he should have the 4L80E, but either way you see what I'm getting at.

 

im ton sure what the gears are in it i bought it with the lift and tires and charger on it so im not really sure what gears it has but i just know that 2500rpm seems fairly exsessive to me is there a way i can figure out my gearing without pulling the inspection plate and counting?