top speed for 1972 k20?

[vardenafil]

I finally got my 72 k20 in a position where i can safely run and drive it. It has a 350 sbc and a 700r4 behind it. The truck only goes about 50 miles an hour. is this normal? i see posts on here where people claim they can cruise at 75 on the freeway with no problems. I dont know if i need to look into the transmission to see if im not hitting all my gears or what.

[dagnabbitt]

Check (with a professional) to see if your TV cable is set up right, and if you are hitting 4th gear.

If all is fine with that then maybe you need taller gears in your rear diff.

[Fbks_Cruiser]

Even if you are not getting to 4th gear, you should still be able to go faster than 55 mph. 3rd gear is 1:1 ratio. I’ve gotten my K2500 up to 65 no problem. Just never felt the need to go any faster so I really don’t know where the top end is. My truck likes to cruise at 55 mph. At that speed it’s turning about 2500 rpm with th350 transmission (1:1 in 3rd) and has 4:11 gears.
Although your tv cable may be out of adjustment that might not be your problem. Do verify it is adjusted properly. A misadjusted one can ruin a 700r4.
Does it accelerate strongly? At 50 mph is the engine speed high even though you are not moving very fast?
You say you just got it to where you can run and drive it. Sounds engine related to me. Check timing. Just yesterday I was working on my truck (replaced ignition module) afterwards timing was off, it could barely get out of its own way. Very poor acceleration and top speed. Next look at fuel. Getting enough from the fuel pump? You say it’s been sitting awhile. Clogged pickup in the tank or gunked up filter? Carburetor may need some attention.

[Ol Blue K20]

Sounds a bit slow to me. I a 427 big block with a th350 and 4:10 gears. 75 is 3500 rpm but it's no problem as long as I have gas. LOL

[RustyPile]

All of the above posts are deserving of your attention.. I'll add one more.... Check your speedometer accuracy....

[vardenafil]

the truck does feel like a dog. it doesnt feel like it has a lot of power. I thought it was just because it was a heavy truck with only 175 horsepower. the transmission does seem to shift hard when it shifts. so maybe you guys are correct about the cable. also it seems like the truck idles high so maybe you guys are also correct about the carb. The truck would always start and idle. i just never drove it around do to brakes and suspension, tire issues.

[truckster]

My C20 with a 250 L6, three speed, and 4.56 gears could do 65, although it was screaming at that speed. Something's definitely not right.

[Stocker]

Agree with above posts, something is not right. My '72 K20 with stock 350, TH350 trans and 4.10 gears is happiest at 55 but will do 65-70 (or a bit more) if you ask it to.

[ratty69]

Probably a VERY silly question, but could it be in 4-low? If the hubs are unlocked, you wouldn't feel it binding around corners.

Seen something similar happen once when the shifter got bumped while getting into the truck.

[Accelo]

Start off in manual low and run up to about 2000 rpm. Manually shift to second and repeat in all gears. You should be able to feel it shift. My guess, without any additional information, is you are missing gears.

[vardenafil]

Thanks guys for all the tips I’ll play around with it this weekend. There is a car show in town so it’ll give me an excuse to drive it around a bit

[Sparky dave]

My c10 has the standard 255 hp 350 engine, 700 r4, 3.73 rear end (I think) and does 110mph in 3rd at 5000 rpm and gets there pretty quickly. Something seems way off

[ratty69]

Originally Posted by vardenafil

the truck does feel like a dog. it doesnt feel like it has a lot of power... also it seems like the truck idles high

Somehow I missed this.

Disregard my previous response. Does the truck run hot? Maybe not boiling over, but up near the top of the gauge? If so, your timing may be WAY retarded, like 10+ degrees ATDC.

Timing set way late like this will give you a slow gutless engine with a high idle, AND running hot.

Did this on purpose once to pass the sniffer test, 00 HC! Couldn't get above 40 mph on the drive to the test station...

[Richard]

Pegged the speedometer in my K20 several times with the 350/465 manual and the TH350 swap. My K10 with the stock 350/TH350 had no problem doing this as well with the tired small block. Something is not right.

[57taskforce]

My 350, 4 speed, 4:11 K20 runs 70+ regularly around here with absolutely 0 issues other than always being on empty.

[vardenafil]

ok so i think i figured it out. i was driving my truck around and had a passanger with a gps trying to tell me when the shift points were. i wanted to to see if the truck went in to all the gears. apparently the speedometer on the truck is not very accurate. the speedometer seems to spaz out when it hits 45 mph or so and only goes up to 50mph. the gps on the phone had the truck doing 60 something mph before i backed off. the rpm guage doesnt work on the truck and apparantly the speedometer is off also.