Topping out at 55 mph?

[1965GMCK1502]

Originally Posted by RichG

FWIW, your math is correct 2500rpm with 4.10 gears and 33" tires yields 55mph

Thanks Rich, imagine that's close to max rpm on this engine?

[RichG]

305s had horsepower ratings at either 3600 or 3800 RPM so there is still some room.

[Robert B.]

I have my grandfather’s ‘63 GMC, long bed step-side, 3/4t, 4x4, winch (front), PTO, K1502E, w/ a 511 front/rear end. It tops out at about 60mph. I too have looked at all the options in an effort to attain higher hwy speeds and concluded that w/ all that would have to be done to achieve that, it’s simply not worth it, b/c #1 The expense and cascading effect on other components of the drivetrain, etc. and #2 there’s nothing like original equipment. I concluded I’d keep everything factory original, w/ exception of the split-rim wheels. Good luck. I look fwd to following your decision and course of action.

[1965GMCK1502]

Originally Posted by Robert B.

I have my grandfather’s ‘63 GMC, long bed step-side, 3/4t, 4x4, winch (front), PTO, K1502E, w/ a 511 front/rear end. It tops out at about 60mph. I too have looked at all the options in an effort to attain higher hwy speeds and concluded that w/ all that would have to be done to achieve that, it’s simply not worth it, b/c #1 The expense and cascading effect on other components of the drivetrain, etc. and #2 there’s nothing like original equipment. I concluded I’d keep everything factory original, w/ exception of the split-rim wheels. Good luck. I look fwd to following your decision and course of action.

Thanks for the details Robert! I am most definitely staying original. Two weeks in with this 305 and I'm very pleased with how it runs. May look into power steering options, but other than that just some cosmetic changes in the works.

[POWERSTROKE]

I have to agree with BigBlockV6, swapping in a newer 5-speed or 6-speed overdrive trans would provide best highway cruising MPG and at lower rpm and best lower gears for starting out heavy loads.

When I ordered out my 1987 pickup I had a choice of two manual 4-speeds, NP-435 and a Mazda over-drive trans. 2nd gear starts even when towing were the rule. MPG suffered if trying to cruise over 65 mph. I had 3.55 gears, and 31 inch tall tires, 4th gear was direct drive.

Finally when I ordered out my '96 I had a good 5-speed manual overdrive available. Same 3.55 gears, 31 to 32 inch tires, but the .77:1 overdrive lets me easily cruise at 75 mph. I 've even pulled brush in 4wd Hi in low gear, and was able to spin my tires at idle on blacktop. So I have the best of both ends of the operating range. Took me a while to find a truck with the manual 6-speed, but my dealer finally got one in. One Saturday morning Son and I and the salesman took it for a ride. Same close ratio My 5-speed is, just smaller splits between gears. But 1st and 5th gear ratios the exact same as my 5-speed. I just had to shift one more time to get to my cruising gear. With my 5-speed and 3.55 gears I'm good towing to 20,000#, if I occasionally towed heavier I'd either go 4.10 or 3.73 gears or the 6-speed. If I towed heavy a lot, I'd go 3.73's and the 6-speed.

I think you will find your running your 305 V-6 around 2400-2500 rpm, which is about where it's torque peak is at, and it's horsepower peak is 3600-3800, I've run everything from 3-on-the-tree to 13 speed Road-Rangers and 5+4 twin stick transmissions, and everything in between. More torque and a wider engine rpm range is always better, but more closer spaced gears makes up for a shortage of horsepower in lots of situations. Like my little commuter car, 218 hp, flat torque curve from 1700 to 5000 rpm, and manual 6-speed. Most times I skip a gear or two when not in a hurry.

I missed my calling decades ago, I wanted to be a fleet buyer for a major trucking company. Ended up buying parts for manufacturing for 30+ years. I wanted to match transmissions with engines to provide drivers the best performance with the best mpg and durability for the company.

[Robert B.]

Please let me know what you discover regarding power steering. That’s intriguing. A guy down in Killeen told me an older corvette pwr steering module would work...odd I know.


Sent from my iPhone using Tapatalk

[1965GMCK1502]

Originally Posted by Robert B.

Please let me know what you discover regarding power steering. That’s intriguing. A guy down in Killeen told me an older corvette pwr steering module would work...odd I know.


Sent from my iPhone using Tapatalk

I’m staying original and manual steering on mine....but I too would love to hear about power steering options for the 4x4 versions.