The Stovebolt Site Forums The Parking Lot Tons 'o Fun 1-Ton Engine & Ground Speed Puzzle

Gents,

Got a puzzle here -
1949 1-Ton GMC
270 cid engine
4:56 rear end
4 speed on the floor
Original size tires on 17" rims

What speed can I expect to be able to drive this truck without stressing the engine too much? Hoping for 45mph on country back roads. Maybe 50mph???

What about RPMs? I believe the max recommended engine speed by GMC/Chevrolet is 3400 RPM for this engine. Any idea what 45 to 50mph will will take engine RPM to?

Thanks for the help.
Marc

not knowing how tall the tires are you wont be able to figure it out. so using the link grigg posted it says my 40 250 will run 2261 rpm @ 45mph and 2512 rpm @ 50 mph. that is with a 4.56 rear, 30.5" tires(7:50x16's). that's exactly what my tach in the truck read at 50 all the way to aths southbend show and back for a total of 1300 miles. lots of seat time to listen to the 270 sing. while i was there a friend of mine ran it up over 3000 rpm for a short duration. because i was too busy freaking out what he was doing to my engine i didnt get a chance to see how fast we were going while he was laughing at my drama. he assured me it could do that all day long and probably can just get used to the noise. being it a 49 the cab design will make it quieter and you shouldnt notice it as much at least thats how it is in the "Ashton". i run that at 53mph and its turning that 270 2700-2800 rpm and you can have a conversation in the cab. in the 40 no way.

id wait until you have the truck to worry about that. your driving yourself nuts. been there done that
hope that helps.

The trick is knowing the rolling radius of your tires. Common tires you can look up on "The Tire Rack" and find out the revs/mile. That figure multiplied by the rear end ratio gives you the RPM at 60 mph.

Grigg / 51 Ashton / Truckernix - thank you for the replies. I plugged some numbers in calculator Grigg posted and looks like engine speed would be 2550RPM at 50mph. I'm guessing tire radius is 30" with the 17" rims on that truck. Puts me a little more at ease in regards to not being too much of a burden on the flow of traffic...

51 Ashton - yes, I think I am driving myself nuts... Obsessive Compulsive behavior carries right over to buying an old truck! Good think I don't have much hair to pull out anymore.

Thanks,
Marc

I ran my 5:14 rear truck with 216 for years as fast as I could. 50-60 mph. It had original engine and finally died from burnt valves and excessive piston clearance at 103,000 miles. Had 89,000 hard farmer miles on it when I bought it. Just run it and enjoy yourself. I could tell when to let off when the noise got to a certain pitch.

I drive at 50 mph every day. I've got the 5.14 in there. My motor was rebuilt in '89. I don't know how many miles were on it before it sat for years and years ('till I got it), but I've put 17,000 breakneck miles on my truck in the past three years.