best way to increase top end speed in a 1967 K20

[texanidiot25]

Reasons I don't speed

1) Bad front shocks, small bumps can get big. Never mount nitro shocks shaft down again....
2) Inaccurate Speedo, I don't know how fast I'm really going. I just know 100 is roughly 70 mph and that's all I normally do. Unless I turn on the GPS
3) No tach, if I choose to speed in third, I'd have no idea how fast she's spinning. Though, I can listen to it.
4) Gas money
5) A loud, bright orange truck, does tend to get attention enough at 65. A big orange truck with the engine running hard, gets even more. The police would love me.

[69DISASTER]

I have the same problem I have a 72 GMC with that Bulldog of a tranny (SM465) and 410 rear end and the truck screams at 70mph thinking of going with an NV4500. How big of a job is it?

[Critter]

Originally Posted by 69DISASTER

I have the same problem I have a 72 GMC with that Bulldog of a tranny (SM465) and 410 rear end and the truck screams at 70mph thinking of going with an NV4500. How big of a job is it?

Pretty big, huge in my opinion if you are putting it in a 4x4, even BIGGER if you intend to mate it to your original transfercase. Damn cool if you can afford it and pull it off.

[jamieg]

im running a 400 on SM465 with 4.10's on 31" rubber.
I dont get anywhere fast, but on the bright side it gives people a better look at what a real truck looks like


I am changing up to a 700r4 and 35" rubber tho, which "should" drop me to about 1600ish rpm hiway speed. Which is just perfect for cruzing to the car shows

[1972CheyenneSuper]

I'm surprised nobody mentioned these guys yet. http://www.gearvendors.com/index.html

[texanidiot25]

I think an OD unit would drastically start moving things like the x-case, and its x-members around. Plus having to change drive shaft legths to compensate for it as well..

[72JimmyDiesel]

a 67 k20 would have an eaton rear, 4.10 is the highest gear set offered in the eaton and most 67K 20 trucks would of had 456's especially the 6 cylinders.

[spinning wheels]

Originally Posted by 1972CheyenneSuper

I'm surprised nobody mentioned these guys yet. http://www.gearvendors.com/index.html

I have looked at them. It is not cheap, easily over 2500 bucks. From what I was told, it is a modern version of the OD that the British Morgans' used to use. Not sure if it was the same electronic OD that Volvos used to use.

The commercial unit would be the stronger of the two units that they sell. That was what I found out, when I researched them and spoke to their reps about 4 years ago.

On a bright side, if you can find a newer wrecked or burned up Motorhome, it might have a gearvendors overdrive unit. What cool about these ODs, is that a 3 speed becomes a 6 speed.

[sierra4x4]

My DD 85 K20 has a 250 with a SM465/208 combo with 4.10's and 235/85r16 tires which are 31.5 inches tall I run at 3100rpm at 70 mph.

[jamieg]

http://www.snoman.com/HTML/axlecalc_5a.html
give that link a try to help get ya a little closer to what your looking for

[onlyifihadachevy]

i like that you want to go pass the 100 in a old 4x4 thats my goal too. But different gears or a overdrive should get you a little faster i belive. how do out what your top speed should be.

[JAKES 68GMC]

I had my needle buried a time or two with 4.56 gears, and a time or two with 4.10 gears. Surprising, the truck was really stable at those speeds. But I won't do it again anytime soon.

[onlyifihadachevy]

nice thats my plans for my 350/th350 with 4.10s if it doesnt blow up.