How Fast Can A Squarebody Go?

[Blue Ox]

Let me begin with the obligatory disclaimer by saying that I'm not encouraging or suggesting that anybody go out and break any laws or try to set a record in one of these things.

But since it came up in another thread I thought it would be an interesting question. I was thinking that "In Theory" a factory truck would be hard pressed to make it to the triple digit mark. Given the relatively low horsepower of the engines of the era, and the stellar aerodynamics that has earned them their nickname, I'm going to guess that 100 MPH is out of reach. Or is it?

Anybody have one of those maximum speed calculators for gear ratios and tire diameter? Does anybody know the drag coefficient of one of our bricks?

What says the GMSB brain trust?

 

[DoubleDingo]

I think over 100 isn't out of the question as long as it had 3.42 or taller gearing. I've done 120 in Mean Green ('65 3/4 ton) with a crate 350/sm420 and 3.54 gears. I think the tires LT245/75r16, at about 30" diameter. I didn't realize I was going that fast until I pulled into my parking spot at work and only 8 minutes had gone by from when I left my house. 16 miles house to parking spot and open highway in between.

 

[nabeshin]

I can't go above 55 cause of driveline vibrations.

 

[Big Chip]

I googled world's fastest square body and came up with this:

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[Blue Ox]

Found a calculator:

https://spicerparts.com/calc/transratio/index.html

According to that my truck's theoretical top speed is 89.67 MPH. Without the overdrive I'd be down to 76.22.

 

[WFO]

I've never had a truck that wouldn't go better than a 100. Some, you couldn't stay there very long though.

Come to think of it, I don't think I've ever had a vehicle that I didn't know it's top speed.
A benefit of wide open spaces, I reckon.

 

[jjester6000]

I've done over 90mph in my square with a 250 i6, no overdrive, and 4.10 gears (I don't recommend it).

 

[Blue Ox]

I think over 100 isn't out of the question as long as it had 3.42 or taller gearing. I've done 120 in Mean Green ('65 3/4 ton) with a crate 350/sm420 and 3.54 gears. I think the tires LT245/75r16, at about 30" diameter. I didn't realize I was going that fast until I pulled into my parking spot at work and only 8 minutes had gone by from when I left my house. 16 miles house to parking spot and open highway in between.

What's the final transmission ratio on a SM420?

 

[Blue Ox]

I googled world's fastest square body and came up with this:

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Given enough power I'm sure you could get one airborne. That wasn't quite what I was referring to.

 

[Big Chip]

Given enough power I'm sure you could get one airborne. That wasn't quite what I was referring to.

I know but it was the first thing I found. I did 80+ with mine coming through Idaho. Not recommended.

 

[Blue Ox]

I've never had a truck that wouldn't go better than a 100. Some, you couldn't stay there very long though.

Come to think of it, I don't think I've ever had a vehicle that I didn't know it's top speed.
A benefit of wide open spaces, I reckon.

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.

 

[legopnuematic]

I've had my 76 up to 110 coming home from buying some hoods one night, friend had the gps speedo running. That wasn't wide open, maybe 3/4 throttle, so I could have squeezed a little more out of it if I kept in it. 350/350 3.08 235/75/15 and a wee 0 5 block in the bed. Now I have 31/10.5/15s so I could squeeze a little more out of it in theory. Even with the gutless rebuilders crate motor i could hit triple digits with it.

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[Jethro224]

I had my last one up to 100 on the speedo once. Just for a second to see if it could. It did but it didn't like it.
It had 4.10s, 35s, 4spd, 205. The engine wasn't stock tho. '78 350 with flat top pistons (9.5:1?), a little cam, Holley, Edelbrock , headers, MSD.

I've had my "new" one up to 55.

 

[Bextreme04]

According to that calculator, the theoretical limit for my gearing right now is 101mph @4000rpm... once the overdrive is installed it would be 135mph at the same RPM. I can't imagine my current motor makes enough horsepower to push that speed. The new motor that is going in with the OD might though.

 

[Bextreme04]

350/400/205 with 4.11's and 35's