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mcdarrunt

Straight 8 top speed

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Have driven my 37 Special ocean to ocean and border to border at left lane freeway speeds and always figured it was probably a 100mph car. I was going to a nearby town on a zero wind day and with a long stretch of dead level river bottom road and thought, "Why not". It topped out at 93mph at a dead accurate GPS speed. Set up is a 1952 263 0.040 over, turbo 350 with non-lockup converter, 2.73 rear, and 28" tall tires. The rpm was only 26 hundred so I think it lacked the torque to push that brick of a body any faster through the air resistance. I have a set of 4.11 gears and an overdrive transmission which this has proved are needed even though I'm planning on no more speed runs; once in 40 years is enough. I think 3000 to 3200 rpm would be just right at this speed. If Ben comes up behind with his 50 I'll just pull over and let him by.

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Ben, I prefer to think "chickened out at 93" as the beginning of wisdom arriving in your thought process while you were cruising along. One of my problems is the "Someday" even after a good dose of wisdom arrives. Be safe. A little wisdom is better for the car and you as well.

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8 hours ago, Mark Simmons said:

Ben, I prefer to think "chickened out at 93" as the beginning of wisdom arriving in your thought process while you were cruising along. One of my problems is the "Someday" even after a good dose of wisdom arrives. Be safe. A little wisdom is better for the car and you as well.

  But where is the fun!

 

  Ben

Edited by Ben Bruce aka First Born (see edit history)
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Ben's 50 would EASY hit a HUNDRED, if it didn't have the world famous V- - - -.

 

Got to love that Ben, he knows a ton about dim dare Straight Eights. 

 

Dale in Indy

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Had a '39 Coupe back in the day that, according to the speedometer, would run well over 100. I can tell you that it would out run a 57 TBird top end any night of the week! Crazy? Yes but a lot of us did some crazy stuff behind the wheel back in the day.

 

Gary

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93?  Out where Ben is, that's the "slow lane".  Where I'm at, west of Fort Worth, near I-20, the speed limit drops to 70 from 75, about 10 miles west, but many are still running 80 or even 85 when I get on I-20 headed east.  If you're pacing traffic, then thinking it's a little slow, when you slow down for a "slower" vehicle, you ease down on the throttle to leisurely get past them, then look down and you're running 85, with people then passing YOU, you wonder when 75 mph just got to be so "slow" or what they're in such a hurry to get to?

 

Enjoy, responsibly!  Every so often, "diagnostics" are necessary . . .

 

NTX5467

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Read with interest , have a 53 straight eight 263 , think was rebuilt when renovation carried out , but worried as she's still an old girl so have until now have only taken her up to 60ish , would like to cruise on the nearby motorway about 70/75 , do you guys think I safe to do so.

cheers

pilgrim

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6 hours ago, Pilgrim65 said:

Read with interest , have a 53 straight eight 263 , think was rebuilt when renovation carried out , but worried as she's still an old girl so have until now have only taken her up to 60ish , would like to cruise on the nearby motorway about 70/75 , do you guys think I safe to do so.

cheers

pilgrim

 

 Absolutely!  I had a "Ruby" back in the late '50s.  75? Any time.  Go for it. Assuming tires are up to the task. 

 

  Ben

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Up to 65 for a comfortable prolonged cruising speed with short bursts up to what it will do.  Driving faster than 65, the water pump can't keep up and the temp will creep up.  Back in the 1950's and early 60's in Texas the speed limit was 60 day and 55 night.  Even at 55 you were out running the headlights on those old 6v cars.

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Willie, Willie, Willie. I can drive mine, either the 248 that came out of it, or the modified 263 all day at 70-75 and temp stays normal. I have never had a car that would overheat at any speed if ever thing is in good shape..

 

I have never heard of water pump not keeping up.

 

  Ben

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If the belt slipped, would it slow the pump, thus NOT keeping up?  High speed/rpm would cause more engine heat, thus it's possible the pump wouldn't keep up, MAYBE.

 

With all this said, I'M NOT THE EXPERT.  

 

Dale in Indy

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4 hours ago, old-tank said:

Up to 65 for a comfortable prolonged cruising speed with short bursts up to what it will do.  Driving faster than 65, the water pump can't keep up and the temp will creep up.  Back in the 1950's and early 60's in Texas the speed limit was 60 day and 55 night.  Even at 55 you were out running the headlights on those old 6v cars.

Old tank , good knowledge and advice , appreciated,  noticed the headlight problem already 

cheers 

pilgrim 

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Through the 50's and 60's I had a 53 Special.  Drove back and forth between Winnipeg and Moose Jaw (400 miles) in all seasons and generally after midnight.  Not counting one stop for gas and a burger the trip normally took 5 hours.  I did this once or twice a month for seven or eight years.

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6 hours ago, Tinindian said:

Through the 50's and 60's I had a 53 Special.  Drove back and forth between Winnipeg and Moose Jaw (400 miles) in all seasons and generally after midnight.  Not counting one stop for gas and a burger the trip normally took 5 hours.  I did this once or twice a month for seven or eight years.

Did you ever marry her?

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dMight it be the water pump "not keeping up" or too much turbulence in the water jackets or "pump cavitation"?  OR . . . . yet-unheard mild detonation/lean mixture?

 

Typically, each engine/vehicle combination has its own "comfort-range" speed.  In the middle '60s it was something like 75% of peak power rpm.  In other cases, it was just past the peak in the torque curve rpm.  It can vary with carb/exhaust configuration, too.  Some engines, by observation, sound "wound-out" over 3500rpm, with a power peak rpm of about 4500rpm or higher.  Just depends.  Some run pretty easy up to a point, then it takes more throttle for each increment increase in speed.  Aero issues combined with power output, I suspect.

 

What ever feels BEST for you and your vehicle!

 

NTX5467

Edited by NTX5467 (see edit history)
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1 hour ago, Ben Bruce aka First Born said:

 

 And what does THAT mean?   Example for the uneducated!  

 

  Ben

 

I assume C Carl was referring to wind resistance as that follows that rule. Rolling resistance is more typically a direct relation to the speed (double the speed requires double the power).

 

However, for cars the rolling resistance is pretty minor compared to the wind resistance above pretty low speeds (depends on vehicle shape and other factors but probably 30 MPH or so).  So just going with the power needed to overcome wind resistance is a reasonably close approximation.

 

Anyway, to explain the cube rule: If you double the speed, the power required goes up by eight times (2x2x2). If you want to go three times faster you will need 27 times (3x3x3) more power. 

 

For example, assume it takes 20 BHP to move a vehicle at 50 MPH on a flat road with no wind. If you want to double the speed to go 100 MPH then you need 2x2x2 (the cube) or 8 times more power. In this case that means you'd need 160 BHP. If you want to drive that same car at 150 MPH (3 times faster than 50 MPH) you will need 20 x (3x3x3) = 540 BHP. Those numbers are probably low as your rolling resistance and other losses also increase but by much smaller amounts.

 

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Might these "power" figures be "at the road surface" rather than "flywheel horsepower"?  In that case, add about 15% to the power figures quoted.  

 

NTX5467

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9 hours ago, Ben Bruce aka First Born said:

Thanks Ply33.  You are cubing HP, are you not?   C Carl said "as the cube of speed".  

 

  Ben

 

Yes.

 

Basics:

  • The definition of work is force times distance (W = F * D). I am using a programmer's notation where the "*" indicates multiplication.
  • The definition of power is work divided by time (P = W / T).
  • Since work is force times distance and speed is distance divided by time (P = F * D / T) and speed is distance divided by time (S = D / T), you can consider power to be force times speed (P = F * S).
  • The forces you are working against to move a vehicle forward (forgetting internal losses in the engine and transmission, just considering the vehicle size and shape, road and air) are rolling resistance and wind resistance. Call the rolling resistance Fr and the wind resistance Fw
  • Rolling resistance (Fr) is reasonably constant but depends on vehicle weight, wheel and tire design, etc.
  • Wind resistance (Fw) goes up as the square of the speed. I've forgotten all the theory behind why it is the square but theory was based on lots of wind tunnel and other real world observations. The general equation is Fw = Cd * A * S * S where Cd is a measured "coefficient of drag" that makes the units work and accounts for the force values found when testing. "A" is the frontal area and "S" is the speed. The vehicle frontal area and shape don't usually change with speed so consider them constants. Instead of writing "S * S", the usual notation is S2. If speed is the goal, you'll notice faster vehicles usually have a small frontal area and a fast looking shape (i.e. low coefficient of drag).
  • If you plug vehicle forces into the power equation you get P = (Fw + Fr)*S = ((Cd x A x S2) + Fr) * S.
  • Above a fairly low speed the wind resistance dominates the equation so you can forget about the rolling resistance and you get P = Cd * A * S2 * S = Cd * A * S3
  • All of this is for a steady speed. If you want to consider how fast the vehicle can accelerate then there is a whole different set of equations that can be dominated by vehicle weight.
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Seems like the late Roger Huntington had some methods to determine wind resistance by using "coast down" time/distance to better fine tune the acceleration results?  Using a mercury column device suction-cupped to the windshield, to determine acceleration G-forces and such.  Then used it to determine negative acceleration from braking tests.  Purely "analog" in the middle and earlier 1960s "instrumented testing".  MOTOR TREND and others had their "bicycle wheel" speedometers and stop watches for timed acceleration testing and brake tests.  Huntington measured the "G-forces" of the brake system in his stopping tests, plus distance.

 

Looking at the performance testing graphs of acceleration of those older road tests, it was easy to see which combinations had "power" and those that had power via gearing than engine power per se.  If the car had a low power/weight ratio, "deep" rear axle ratio gearing, and/or very high power, the speed/time graph had a much more vertical ascent than a normal car which was a much smoother curve that eventually flattened out at the top.  Similarly, 3-speed automatics (vs 2-speed automatics) and 4-speed manuals usually had quicker rises to the upper speeds.  "If it won't go, gear it" 

 

Back then, most cars needed more powerful engines to push the air out of the way.  In some cases, it got out of the way on its own (seeing what was coming toward it!).  "Aerodynamics" was something for airplanes flying faster on existing fuel supplies and helping decrease "wind rush" on automobiles.

 

NTX5467

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