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Discussion Starter · #1 ·
In my Mustang restoration guide the specs are,
320 @ 4800 (brake horsepower) and 427 @ 3200 (torque). What exactly is brake horsepower and torque? Mainly, how much HP would a stock "S" code 390 4V pump out?
 

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brake horsepower is just that....the engine dyno is a kind of brake

The hi-performance engines back then were given low HP estimates so the insurance companies would chill out......I've read the 390 4V would squeak out at least 365, and TONS of torque.

Good motor....heavy, but good!
 

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Brake horse power is the horse power measured where the tires hit the pavement. The other way to measure is at the engine output before it goes into the transmission. The reading will be higher there, but does not really indicate how the car will perform. A lot of power is lost through the tranny. Torque is the ability of the engine to turn the tires. This is mostly controlled by your total gear ratio. Torque is measure on foot-pounds. Think of it as applying torque to tighten a nut. Hope this kinda helps.
Dave
 

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actually, the factory rated 320 hp is grossly overrated for the S-code 390GT motor. The fact that Ford rated the 428CJ only 15 hp more than the 390GT kinda proves that point. I have driven Mustangs, similiar in weight, with both engines and the difference between a 390 and a 428 is like the difference between a Pinto and a 289 hipo K-car. The "best" quarter mile times I recall posted by the 390 Mustangs were all in the 15s - 428s stock were good for high 13s. I believe a closer horsepower rating for the 390 would have been under 300 hp.....

randy
 

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Some of us can remember what 390 GT's ran like in stock form.... Embarassing!

Torqey motors, moved the car effortlessly, but wouldn't win very many drag races....

But with the addition of CJ heads, intake, lo gears, and headers, they could hold their own!
 
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Discussion Starter · #6 ·
Actually the CJ's horsepower was way under-rated and should never be compared with a 390 !!
 
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