340 Engine... Top Speed "120 mph?"

[Mr. 440SixPack]

You are right about gear ratios but when you are going for a high top speed, aerodynamics are very important. If you can "cut" fast through air you don't even need that much horsepower to reach 130+ mph.

By the way I' ve heard somewhere that 'cuda hit more than 190 mph on le mans race back in the 70s...

[NoMope Greg]

I'm not saying that aero doesn't play a part.  In fact, above 50 mph, the biggest job the engine has is pushing air out of the way and the amount of power needed to do the job is a logarithmic progression in relation to velocity.  To double your speed takes not twice as much power but four times as much. 

My point is that is that the original poster thought those vehicles should be easily able to exceed 135 mph because they had 300 hp.  Aero definitely plays a part, but the main thing was the overall gearing of the package - fewer gears, shorter gearing, shorter tires - all combined to limit top-end speed. 

Another thing - given the times, the odds are that the top speeds noted were on the speedometers of the cars, not over a measured flying mile.  We all know that the gauges on our old cars are typically pretty inaccurate, especially at higher speeds.

[LAA66]

 From another respectable forum:

" Sports Car Graphic tested a JS23U0B Challenger and published the results in their November 1969 edition.

They claim their test car had at 100mph;

370lbs of front end lift.

75lbs of downforce at the rear (due to weight transfer from the front lifting)

and 340lbs of drag pulling the car back."

 I would guess that front end lift gives us that "vauge" feeling above 100 mph.

 

[Mr. 440SixPack]

Is that why most of the racing e-body mopars have front spoilers?

Like this one:

[NoMope Greg]

That's why all race cars have some sort of aero aid up front, be it a spoiler or splitter or wing.  It's all about keeping air from getting underneath the car and lifting the front end.  Very important when you expect the front wheels to actually contribute to getting the car around a corner.

[Super Blue 72]

I can't imagine going that fast in one of these cars unless the suspension was tuned for high speeds.  Anything under 100mph, ok, but over 100mph must start getting hairy.  I never had the pleasure of going that fast in one of these cars but it must be a handful at speed.

I've done 130mph in my Integra with Mugen Racing suspension and 130 was scary and the curves come up real fast and hard around here at that speed on the highway.  Can't imagine in an old muscle car that has stock suspension.

[Mr. 440SixPack]

Hehe, i would like to try how it is in an old muscle car when going 120 mph and more

[Fleet 500]

Here is a good point. From a letter printed in Motor Trend (Oct., 1973):

"I was quite happy when I saw your article on the 1st Annual Flat-Out Classic. But I was also quite disgusted when I saw the results.
How come you people can only get a 455 Firebird going 124.3 mph when another magazine claims 129 for a fully-loaded Lincoln Town Car?

121.13 for the Charger is nothing considering the Chrysler Imperial will do 122 with the same drivetrain minus dual exhaust.

The Riviera does 123 while the hot little GS only pumps 115.97 and 20 more horses to boot?"

- Randy Smith, Stillwater, Minn

[torredcuda]

Gearing-my cuda with 3.91`s doesn`t have much for top end.My speedo bounces around 120 or so( not very accurate I think) when my tach is at redline.This car had plenty of power to do a 13.2 1/4 mile so I know with lower gears a much higher top speed would be easy.

[NoMope Greg]

Here is a good point. From a letter printed in Motor Trend (Oct., 1973):

"I was quite happy when I saw your article on the 1st Annual Flat-Out Classic. But I was also quite disgusted when I saw the results.
How come you people can only get a 455 Firebird going 124.3 mph when another magazine claims 129 for a fully-loaded Lincoln Town Car?

121.13 for the Charger is nothing considering the Chrysler Imperial will do 122 with the same drivetrain minus dual exhaust.

The Riviera does 123 while the hot little GS only pumps 115.97 and 20 more horses to boot?"

- Randy Smith, Stillwater, Minn

If Randy Smith of Stillwater, Minnesota is still with us after 36 years, I wonder if he's learned to do the math of rpms, tire height and gear ratios yet...

[sprecks]

I see that know, I was looking at your chart wrong.

There is a formula you can use that combines horsepower, tire size, rear gears & so on to arrive at the actual top speed mathematically possible. I do not have the formula avaliable, but I bet one of our racer members does?

Here are the formulas you all may find useful. Keep in mind these don't take into account any transmission slippage losses etc.

MPH = (RPM) X (Tire diameter) X (0.003) / Gear ratio

RPM = (MPH) X (Gear Ratio) / (Tire Diameter) X (0.003)

Tire diameter = (MPH) X (Gear Ratio) / (RPM) X (0.003)

Gear Ratio = (RPM) X (Tire Diameter) (0.003) / MPH

[Mr. 440SixPack]

Gearing-my cuda with 3.91`s doesn`t have much for top end.My speedo bounces around 120 or so( not very accurate I think) when my tach is at redline.This car had plenty of power to do a 13.2 1/4 mile so I know with lower gears a much higher top speed would be easy.

You have 340 engine? This is damn fast for a small block

[Fleet 500]

Here are the specs from the Motor Trend article mentioned above.
"Flat-Out American Classic" (July, 1973 Motor Trend.)

Car--------- Pontiac-- Dodge-- Chevy--- Ford---- Buick--- AMC
------------ Firebird-- Charger- Chevelle- Mustang Century Javelin

Engine------ 455----- 440----- 454----- 351----- 455---- 401
Rated net hp 310----- 275----- 245----- 266----- 270---- 255
Rated torque 390----- 380----- 375----- 301----- 390---- 345
Compression- 8.4:1--- 8.2----- 8.25----- 7.9----- 8.5----- 8.5
Axle ratio---- 3.42:1-- 3.23---- 3.08----- 3.25--- 3.42---- 3.54
0-60 mph---- 7.3 sec- 7.4----- 8.2------ 8.9----- 7.4----- 7.7
1/4 mile----- 15@98-- 15.2@93 15.8@87 16.3@86 15.3@90 15.5@90

Top speed-- 124.30-- 121.13-- 118.73-- 118.57-- 115.97-- 115.53

Fuel mileage- 11.74-- 11.11--- 12.28--- 11.65---- 12.20--- 11.58

Noted in the text was the fact that Charger developed a stuck valve lifter during practice and never seeme to clear up at high rpm but did free itself at idle. And, to quote: "Nevertheless, the Charger ran second fastest with a 121.13 mph down the straight, maybe on 7 and 1/2 cylinders, which is a moral victory."

[torredcuda]

You have 340 engine? This is damn fast for a small block

Pretty basic 340,9.3-1,ported factory cast "J" heads w/ 2.02`s,runs 13.2`s -13.5`s right off the street but I`d like to see a 12.99 out of it with some more tuning.I really want to biuld a stroker small block to go faster!

[426HEMI]

I know I had my 340 faster than most when I had it on the road back a few years ago.  I had it over 140 and it was cool.