Joe Werner

1940s cadillac top speed?

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Was a bit of a test. As speed goes up there are a number of forces at work - internal friction of the motor, rolling resistance, drivetrain losses, accessory losses but by far once speeds get higher, aerodynamic drag forces are the most important. The formula I gave, F_d\, =\, \tfrac12\, \rho\, u^2\, c_d\, A, is the formula for the aerodynamic drag of an object in motion through a compressible fluid (air).


The drag force (what the engine must overcome) equals 1/2 rho (fudge factor relating to air density and such) times the square of the speed, times the coefficient of drag (how slippery the shape is) times the frontal area of the object (aka CdA).


In simplest terms it takes about 3x the power to go 100 mph as 60 just for the extra drag. Not going to go into Tractive Effort.


But the bottom line is that to maximise speed you want to gear so that the max speed is at or just above the maximum torque.


In the bad old daze torque peaks were pronounced and usually had a quick drop off with a HP (pure math from torque, rpm, and a fudge factor) peak shortly thereafter.


Now modern race cars use fractals to estimate real drag, lift, and cooling. General Motors was using six degrees of freedom in computer models in 1970 which made it easy to adapt to over one gee models for a Corvette. Turned out the 68 rear suspension had better camber characteristics that the 69-up or 63-67. $15 item.


The biggest difference comes from computer controlled spark plus VVT. A modern DOHC - 4 valve (no hemis need apply) head with VVT and DI can have 90% of the torque peak from about 1800 rpm to 7000 rpm on pump gas. In fact a significant part of the silly horsepowers seen today is from raising the torque peak from 4800 rpm to 6800 rpm.


Be glad to go further but first read Sir Harry's "The High Speed Internal Combustion Engine".

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3 hours ago, bryankazmer said:

Agree on the inherent balance.  A straight eight is more susceptible to crankshaft whip, but the better ones had 9 main bearings to address it.  I think the difficult issue is getting uniform flow to all cylinders.  Hence Buick's duals and some aftermarket set ups.


Inline-eight engines also aren’t possible to build in a perfectly harmonically balanced configuration, as is possible with a cross-plane V8.

The crankshaft in an inline-eight would be quite long and would be more prone to flexing and/or failing under the increased torque than a shorter crankshaft. This is also true of the camshafts. 9 main bearing Packards can be made to Idle pretty smooth, but they too have a fuel distribution problem as in all straight eights which are the outside cylinders run lean, the inside cylinders run rich and the two middle are just right.

  BTW. the Buick straight eight is only five main bearings, heck my gen3 Chevy inline six has seven main bearings! now that is a inherently balanced and smooth engine which easily passes the quarter test, although as witnessed my dad's 50 Pontiac straight eight had no problem passing that test as well. 

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