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Discussion Starter #1
I've got horseppower on my mind and hope someone can help educate me a litte.

According to my owner's manual, the 1969 428CJ was rated at 335 brake hp and 440 ft-lb torque. The google says "brake hp" is at the crankshaft with no accessories like alternator or power steering etc.

Is there a formula to translate these into rear wheel hp? What should a guy expect on an unmodified 428CJ?
 

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Drivetrain loss is around 15% to 20%. You also have to consider that these engine were way under rated from the factory because of insurance companies. The CJ realistically made closer to 400-425 out of the box.
 

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Drivetrain loss is around 15% to 20%. You also have to consider that these engine were way under rated from the factory because of insurance companies. The CJ realistically made closer to 400-425 out of the box.
A number of engines of that time were underrated. In addition to the CJ 428, the Boss 302, chevy 302, chevy, 350 HO, 426 hemi were also known to crank out more HP than listed. I don't recall seeing any actual torque ratings for the higher HP ratings.
Does anyone know if the 302 4v, 351 4v, 390 4v Ford engines of the time were underrated?
 

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A better question, is who has dyno sheets on freshly rebuilt "stock" performance engines. Most of these cars, "out of the box" weren't that quick. I think it took some smart option checking to get into the hundred mile an hour club, even back in the day.
 

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A stock 428CJ in good tune will make 275 horsepower at the rear wheels. That will propel a 3400 LB Cougar XR-7 to easy mid - 13's at 100 MPH in the quarter mile.
 

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A better question, is who has dyno sheets on freshly rebuilt "stock" performance engines. Most of these cars, "out of the box" weren't that quick. I think it took some smart option checking to get into the hundred mile an hour club, even back in the day.
I do. My mostly stock 351C 4V with offy dual port intake, holley carb and pertronix ignition registered 193 hp at the rear wheels and 250 ft lbs of torque and that's with the jets changed to 68 and a 10.5 power valve.
 

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My *barely* modified 351C (new cam, Edelbrock intake, headers) made 330 RWHP with full dual exhaust, FMX trans. Dyno'd just a tick under 400HP at the crank in that combo.
IIRC the 1970 351C was "stated" at 300HP but lore has suggested that Ford lied about the power and it made more like 330.

So just assume by my experience that the drivetrain loss is *around* 70HP and the 428CJ was really making 350HP instead of 330HP as advertised, then 275-285RWHP is in order for a stock 428CJ.
 

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Discussion Starter #8 (Edited)
Dyno results are in:


Maximum Power
314.3 @ 4693 RPM / 104.1MPH
with WCF 316.8


Maximum Torque
359.0 @ 4566 RPM / 101.2MPH
with WCF 364.6

Not bad for a grocery-getter. This was done on a PowerDyne Mustang Chassis Dyno. "WCF," the google tells me, means Weather Control Factor - but I don't know how that works.

 

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Cool thread Rob, thanks.
 

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A better question, is who has dyno sheets on freshly rebuilt "stock" performance engines. Most of these cars, "out of the box" weren't that quick. I think it took some smart option checking to get into the hundred mile an hour club, even back in the day.
But back in the day when these cars came out they had really crappy tires and wouldn't hook either. Power is nothing without traction
 

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Dyno results are in:
...
Not bad for a grocery-getter. This was done on a PowerDyne Mustang Chassis Dyno. "WCF," the google tells me, means Weather Control Factor - but I don't know how that works.

I would presume WCF takes into account the current atmospheric conditions and factors them to an ideal situation (cooler ambient temp perhaps lower humidity - a perfect storm for achieving horsepower and torque). Once you know what that ideal weather scenario is, you can calculate an algorithm to adjust your dyno results to PEAK potential, in that given perfect scenario. Just guessing, but pretty confident that is what WCF is.
 
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