What is my trucks recommended highway speed?

[OffRoad]

hey, i have an old chev and i was wondering how fast i can take it on the highway for long trips.

it's a 90 c10, regular cab, long box, with 4.3 / sm465 / 10 bolt w/ 3.08s and 235/75/15 tires (29" tires)

it didn't come with a tach for whatever reason. what is the maximum safe rpm of this truck? what does that translate to in speed?

i only drive about 100 kph (62 mph) now. can i go faster? i don't want to ruin the motor, i can't afford another one.

 

[chevy wrangler]

on tuesday i drove my truck going about 75 for an hour and i blew a feeze plug !!LOL it took me like half an hour to replace, good thing i broke down near a checkers

 

[W7NB]

At 2500 RPM with 29 inch tires and a 3.08 rear end you are doing 113 kph. It would depend on what RPM you consider acceptable.

 

[Russell]

I used to run my 350 at just over 3000 rpm for hours at a time, and it is no worse for wear

With gearing like you have, run it the full 110 km/h speed limit, and don't worry about it. Just as long as you are keeping oil pressure, thats all that matters

 

[81jimmyslt]

As fast as you can, my truck gets the worst shake above 55 the hood wobbles like crazy scares the crap out of passengers.

 

[blazinzuk]

A 90 is considered old wow my truck must be cro magnan or something. Go as fast as you want its a modern truck. Way more modern than my 73 and I would go 75 in it when it was stock easy

 

[OffRoad]

i don't consider a 90 that old. i realize you guys are driving trucks from the 70s. they just rust away here. 90 is old for the rust belt.

 

[MaxPF]

I routinely do 80MPH (130kph) on trips, and I hold that speed for hours. I have 33's with 3.73's and a 4L60, so I only turn around 2150RPM at that speed. With the SM465(no OD) and your tires/gearing you will be turning around 2850RPM. Boats usually run 4500-5500RPM for hours on end, and your engine won't be turning anywhere near that.

In other words, stand on it

 

[OffRoad]

how do i determine my rpm at speed like you did? what's the math?

 

[GMCJason]

Here's the calculation for RPM:

RPM = ((gear ratio) * (speed in mph) * (336)) / (tire diameter in inches)

Sorry - don't have the factors for the metric version but you can convert the inputs (speed and tire size).