How Fast Can A Squarebody Go?

[eskimomann209]

Are we only taking about stockers?

 

[Blue Ox]

Are we only taking about stockers?

That was the premise, but feel free to contribute whatever you want.

 

[DoubleDingo]

What's the final transmission ratio on a SM420?

1:1 70 is about 2,600 with that setup. The engine preferred 3,000, but it had no problem going faster than that. I typically ran it at 3,000 on trips, and if I saw a CHP I would let off the gas and they would look at the truck in disbelief that it could be going that fast. Back then there were more of the old high revving trucks on the road so hearing high revs wasn't out of the ordinary on the open road.

 

[DoubleDingo]

I think the fastest I've ever had mine up to was 75. No wide open spaces to be had here, plus too much law enforcement.

I got lucky on my 120 run as there are usually at least one CHP and one Sheriff on that stretch of road. But it was early and I must have caught it just right...lol...

 

[DoubleDingo]

I forgot to mention, if it even makes a difference, but it had an edelbrock performer intake, ramhorn exhaust manifolds running 2 inch pipes into a borla dual-in/dual-out muffler and the pipes exited at the right rear. I think the exhaust may have helped in this case due to the scavenging effect.

 

[Turbo4whl]

What's the final transmission ratio on a SM420?

SM420 is 1:1 in high gear, same as a SM465.

 

[DoubleDingo]

SM420 is 1:1 in high gear, same as a SM465.

But those 3.54 gears, great highway gears!

 

[77 K20]

In high school I got my '78 K5 and even my current '77 over 100 (around 110 for both). The K5 was stock with a 400. By current truck has 35" tires and a 383.

One of the more interesting things I noticed was both of the hoods have kinks in them from the hood being bent a bit. There is a low pressure area that forms above the hood and the hood starts flexing upwards at those speeds.

I don't recommend ever doing that again.

 

[DoubleDingo]

In high school I got my '78 K5 and even my current '77 over 100 (around 110 for both). The K5 was stock with a 400. By current truck has 35" tires and a 383.

One of the more interesting things I noticed was both of the hoods have kinks in them from the hood being bent a bit. There is a low pressure area that forms above the hood and the hood starts flexing upwards at those speeds.

I don't recommend ever doing that again.

Run a strap across the hood from fender wheel well to fender wheel well...lol...

 

[Blue Ox]

Run a strap across the hood from fender wheel well to fender wheel well...lol...

Or use NASCAR 200 MPH tape.

 

[Turbo4whl]

SM465

Gear ratios are:

• First - 6.55:1
• Second - 3.58:1
• Third - 1.70:1 -Sometimes incorrectly listed as 1.57:1.
• Fourth - 1.00:1
• Reverse - 6.09:1

SM420

Gear ratios are:

• First - 705:1
• Second - 3.57:1
• Third - 1.70:1
• Fourth - 1.00:1
• Reverse - 6.87:1

What's the final transmission ratio on a SM420?

Do you have an SM420 installed in your square. I believe the last year GM installed them was 1968

 

[Catbox]

I have ran mine pretty easily up to 75 on the freeway.
That is just under 3,000 or so on the tach.
The engine has another 1,000 rpm or so in it until it falls on its peanut port face.
I would think 100 is easily achievable.

 

[Vbb199]

I got my 90 burb, 5.7 tbi, 700r4, 3.08, stock gear about 120 mph in a street race with a Dodge Dakota.

Never been faster in a squarebody

(I had a GPS app on my phone because speedo liked to occasionally work)

No lie. Lol, swear to God. It was on a straight 4 lane we got out here.

That son of a bitch felt like it was either gonna fly away, or fall apart.

 

[Vbb199]

That was a couple years ago, since then, I would NEVER do that **** again.

 

[Vbb199]

Not me, but my cousin took his 74 c20 out down the road past like... 85 mph? That damn thing really did feel like it was gonna fly off the road. That was scary as ****.