How Fast Can A Squarebody Go?

[82sbshortbed]

Oh yeah o had my dad's 84 3/4 ton burb with 6.2 pegged at 85 for a long time coming home from the lake one night. I don't know why but, that thing ran high speeds no problem. Not shaking just smooth running. My buddy looked over and said that's been pegged a while. I don't know maybe 95 or 100. But, she was a great running square back then. I punished it a lot and she could always take more.

 

[SquareRoot]

I **** you not....my 84K20 with CUCV axles will run out of gas trying to get to 100. The quarter mile on the other hand, well let's just say you're glad when the trip is over.

 

[Bextreme04]

In theory... you did see my signature, right?

That's just the math for what the powertrain numbers are capable of. Obviously aerodynamics are going to get you long before you get there. I'm trying to find a drag coefficient for these trucks. There is a formula for power required based on frontal area and drag. I'll warn you now, it's not pretty. Drag increases at the square of speed so horsepower requirements are exponential. IOW there comes a point where you need to double you horsepower to get one more MPH.

That's why I was questioning how fast a stock truck could actually go. Most of the engines of that era didn't really produce that much HP, so the parachute aerodynamics would become a limiting factor.

***edit: The engine power curves are available in the GM Heritage Center documents. If we get to aerodynamic engineering we can look that up.

There's quite a few things to consider to determine horsepower required. The big hit for these trucks is going to be coefficient of drag, frontal area, and rolling resistance. Especially a big lifted 4x4. The rolling resistance is going to be biggest on a 3/4 or 1 ton 4x4 suburban due to the weight. Here's a neat calculator, with some generic coefficients. http://www.bgsoflex.com/aero.html

When you start going really fast you have to start considering producing enough downforce to keep enough resistance on the tires to apply the required horsepower without the tires spinning. It can be quite a balancing act, because producing downforce increases drag, which requires more horsepower. You want to produce just enough downforce to maintain traction.

 

[jtridgley79]

Finally. Someone else with a burb!
They're long and don't have alot of drag because they don't have a pickup bed or anything.

Had my 87 burn on 37s pegged with stock 5.7 with 4.10s in overdrive once. Then I thought about old tires and a hot road and brought it back down to about 70.

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[SquareRoot]

The bug shield, moon visor, CB whip antenna, hickey pushbar and led light bar doesn't help my drag coefficient, but it looks cool and chicks dig it.

 

[OldBlueDually]

My '78 454 Suburban does 100+ rather easily. That's stock with headers. In my younger days I would have run it for all it was worth. Not these days though.

That's interesting! My dads 78 Camper Special Suburban, 454, would hit 100 also easily (white top & bottom, tan/cream color middle, dark tinted windows, was just a beauty). The only thing he did to it is put a new crankshaft in it, because when my grandpa got it on a trade in (grandpa worked at a dealer and bought it for $600 for us!!!!) the thing sounded like a diesel. A lobe was broken on the crank.

One year camping in northern MN, we (brother, dad, and grandpa) went into Hibbing and a long straight road he pushed it to the floor and that baby took off, the 42" glasspacks just singing, my brother & I laughing, grandpa and dad just smiling. Man, that baby rode like a cloud!

Years later when I was driving it, she still had it in her and sounded just as nice, looked just as good and could hit 100 like nothing! I raced my buddy with his Iroc Camaro (305 throttle body) from a dead start, he had me off the line for a little bit until the the 78 woke up and the secondaries were sounding like the biggest vacuum cleaner under the hood you ever heard.

Dam, I miss that rig, I wish I could find it

 

[Poppy 87]

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

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Blown big block, nitro or alcohol, and a glide? Definitely a winning combination!

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[Bextreme04]

Well, I hadn't really tried to push it before but after this thread I was curious. On my way home from the airport last night I decided to take a straight stretch of highway instead of going through town. She does 75-80 pretty easy, but man is she load and rough at that speed. It was bucking and shaking all over the place and the steering was LOOSE. Still had plenty of power though, I'm pretty sure she could easily hit 100 once I get the suspension worked out. I'm pretty sure the front spring bushings are shot and it needs the steering box tightened up, rebuilt, and an alignment done.

 

[Poppy 87]

In the most recent high speed drive, Ole Bessie with 415,000 miles, 305 tbi, TH400, and 3.08 gear, fitted with 235/75R15 tires was able to sustain 78mph on I-16 in middle Georgia. She had 3 engines, 2 engine stands, and 4 tires in the bed! Oh, she was on a trailer behind a 26 foot Uhaul truck.

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[SquareRoot]

So theoretically, if you had a 80 mph headwind you would eventually come to a standstill?

 

[bucket]

That's interesting! My dads 78 Camper Special Suburban, 454, would hit 100 also easily (white top & bottom, tan/cream color middle, dark tinted windows, was just a beauty). The only thing he did to it is put a new crankshaft in it, because when my grandpa got it on a trade in (grandpa worked at a dealer and bought it for $600 for us!!!!) the thing sounded like a diesel. A lobe was broken on the crank.

One year camping in northern MN, we (brother, dad, and grandpa) went into Hibbing and a long straight road he pushed it to the floor and that baby took off, the 42" glasspacks just singing, my brother & I laughing, grandpa and dad just smiling. Man, that baby rode like a cloud!

Years later when I was driving it, she still had it in her and sounded just as nice, looked just as good and could hit 100 like nothing! I raced my buddy with his Iroc Camaro (305 throttle body) from a dead start, he had me off the line for a little bit until the the 78 woke up and the secondaries were sounding like the biggest vacuum cleaner under the hood you ever heard.

Dam, I miss that rig, I wish I could find it

Yeah I believe it! I don't know how much it has past 100 mph or so, but it gets there easy and just rides along nicely. The 454 likes the 3.73 gear and 285/75 tire.

 

[bucket]

Also, my first squarebody was a 2wd K5 Blazer with the 250 six. It had 32" tires and iirc, a 3.08 gear. I really pushed it hard one day. It got up to about 75 mph and started leaking oil profusely out the rear main seal. So I'd say that's the top speed of a 20 year old 6-cyl truck, lol.

 

[OldBlueDually]

Yeah I believe it! I don't know how much it has past 100 mph or so, but it gets there easy and just rides along nicely. The 454 likes the 3.73 gear and 285/75 tire.

I think this one also had 3.73's in it too. I remember dad having to take the axle apart to repair something on it, and at the same time he threw in a pair of helper springs to help with pulling the late 70's Wilderness camper.

Honestly from a dead stop I was surprised how all that steel just took right off and went. My dad also being a GM mechanic made sure the emissions BS was not inhibiting it's ability to pull the family camper, us, and a load of stuff in the back of it. What a great suburban that was. I was a bit sad the day dad traded it in for a mid 90's GMC Suburban. Plenty of power that one had too, but the entire "cool factor" was gone. It was more economical, and much safer, but not very cool.

 

[RecklessWOT]

Truth in screen name.

Hey I'm not hiding it lol. I've toned it WAYYY back as an adult, but any time I drove anywhere as a kid my gas pedal had two positions, OFF and ON. I think the brakes might have had 3 positions, but I mostly used that as an on/off switch too

 

[Vbb199]

Well, I hadn't really tried to push it before but after this thread I was curious. On my way home from the airport last night I decided to take a straight stretch of highway instead of going through town. She does 75-80 pretty easy, but man is she load and rough at that speed. It was bucking and shaking all over the place and the steering was LOOSE. Still had plenty of power though, I'm pretty sure she could easily hit 100 once I get the suspension worked out. I'm pretty sure the front spring bushings are shot and it needs the steering box tightened up, rebuilt, and an alignment done.

Hey now!!! He said NOT to try to run it as fast as you can!!
First post!!