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HP Ratings
#1
Hello,

Can someone please explain the accurate HP rating for the above engine in a Mustang conv. ? I have been told 250 HP, 157 HP 177 HP. I know in 72 they started rating differntly with the accesories and exhaust connected. Were the ratings at the rear wheels, flywheel etc. ? thanks

steve
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#2
The "MOTORS" manual lists 3 different ratings for 1973 351C 2V, 154, 156, and 159. These are SAE flywheel NET ratings. This means all accessories, air cleaner, and complete exhaust were installed for the test. The change occurred in 1972 although GM listed Gross and Net in 1971. Compression ratio is listed as 8.0:1 for all three ratings. Someone may have more definitive information. Chuck
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#3
True, Ford went to SAE-net horsepower ratings beginning in '72. As mentioned above, all available accesories ( alt, ps, water pump, etc...) were installed as was a complete exhaust and air cleaner. This was thought to give a more accurate rating for customers.
The old way was "gross" horsepower: still measured at the flywheel, but with no accesories on the engine...no alternator, water pump, etc. Open carb,and open headers. Water and electricity fed to the engine externally. The engine had near-zero parasitic loss from accesories. This resulted in an unrealistic rating.

Gross to net typically resulted in a 10-20% loss in rated horsepower, depending on which engine was tested.

Now, the crappy part is for anyone with a 71 and older motor when bench-racing today. For example, my "monster" 429 CJ was rated at 370 horses( gross), which if in todays net ratings would be somewhere around 300-325 horses...pretty poor for a stinkin' 7-liter "Cobra Jet".

I dont pull on this thread too often...it all unravels too easily.
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#4
naa10104;189636 Wrote:Hello,

Can someone please explain the accurate HP rating for the above engine in a Mustang conv. ? I have been told 250 HP, 157 HP 177 HP. I know in 72 they started rating differntly with the accesories and exhaust connected. Were the ratings at the rear wheels, flywheel etc. ? thanks

steve

thanks for the info.... hoping it made a little more HP.

Kit Sullivan;189648 Wrote:True, Ford went to SAE-net horsepower ratings beginning in '72. As mentioned above, all available accesories ( alt, ps, water pump, etc...) were installed as was a complete exhaust and air cleaner. This was thought to give a more accurate rating for customers.
The old way was "gross" horsepower: still measured at the flywheel, but with no accesories on the engine...no alternator, water pump, etc. Open carb,and open headers. Water and electricity fed to the engine externally. The engine had near-zero parasitic loss from accesories. This resulted in an unrealistic rating.

Gross to net typically resulted in a 10-20% loss in rated horsepower, depending on which engine was tested.

Now, the crappy part is for anyone with a 71 and older motor when bench-racing today. For example, my "monster" 429 CJ was rated at 370 horses( gross), which if in todays net ratings would be somewhere around 300-325 horses...pretty poor for a stinkin' 7-liter "Cobra Jet".

I dont pull on this thread too often...it all unravels too easily.


thanks for the info....hoping that it made a little more HP.
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#5
Hello Steve and welcome to the site. Please post an introduction thread and tell us about your new 73 Convertible. Looking forward to meeting you at one of the local meetings.
http://www.7173mustangs.com/forum-introductions



Mike AKA Ole Pony & Rare Pony

Our current Mustang garage/driveway
1973 Mustang Convert - Bought in 1974 - Still have it!
2004 Mach 1 Oxford White Auto, Bought Sept 06


[Image: 20180127_082009.jpg]

upload a photo on internet




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#6
The power ratings are disappointing but please remember there are a few fairly low cost improvements to help alleviate that.

Jeff T.

Low buck, touring style, '73 Convertible "rolling restoration", 351c, 2v heads with a shave and a haircut, Performer intake, Holley 650(ish), roller rockers, screw in studs, guideplates, stainless valves, Duraspark / Motorsports MSD, T-5 conversion. 1-1/8" front, 3/4" rear swaybars KYB shocks and some home brewed subframe connectors. Future plans; JGC steering box, Cobra brakes and... paint, interior, etc.

When I die I want to die like grandpa, peacefully in my sleep... not screaming, like his passenger.

[Image: 1_12_09_14_10_15_11.png]
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#7
Horsepower smorshpower, all that matters is Torque!!!
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#8
Very true, very true.

Torque is what we feel when we press down on the go pedal, not horsepower.
Horsepower is nothing more than sustained torque as rpm increases.
Engines in the 70s and 80s were designed to deliver as much torque down low as they could to give a feeling of high performance "off the line", where a lot of the stop-light drag races would occur.
Most people did not take thier cars to an actual dragstrip, so an impromptu street race was typically all over by 50-60 mph...well low in the RPM range and over with before the engine has any chance to climb into the higher RPM ranges. These smogged-out motors could not breathe well for various emission-mandated reasons, and just could not maintain any decent torque numbers in the higher RPMs, hence the lower horsepower figures.
That is why cars equipped with BOSS 351s, 428 and 429 CJs, etc...produced decent HP #s: They could continue to breathe well at higher RPM enabling them to maintain higher torque as RPMs increased. Thus, higher horsepower.

I have met many people over the years that have told stories of how powerful thier late-70s stock muscle car was, and I always bite my lip to keep from insulting them.
I am particularly referring to the late-70s Trans-Ams with the 403 Olds motors. Rated at a measly 180 horsepower, but loads of low end torque.
Those cars felt like a powerhouse off the line...lots of tire smoke and such, but by 50-60 mph, they were all done. They could'nt breathe well, so the torque just fell off in the higher RPM...no sustained torque, so no decent horsepower.
Most of these owners would never go to a real dragstrip to get a 1/4 time, so they had no clue how really underpowered those cars were.
An engine's breathing capabilities determines in large part its ability to produce power. But it is a compromise. Lots of breathing capability ( big intake valves, big ports, headers, etc...) allow an engine to maintain torque at higher RPM, yet can also hinder its off-the-line performance. These engines are well-suited for dragstrip duty, where all of the RPM range can be used. But if you just want to pop around stop light to stop light, you may never get to use the engine's potential.
OEM 351 4V clevelands are notorious for this. The 4V heads are awesome for dragstrip duty, but trade off some low-end torque for high-end torque ( horsepower).
Street driven 351 4V Clevelands are less impressive off the line than thier fame would suggest.
The 351 2V engine has smaller valves, and swapping an aftermarket 4V intake and carb results in a much more "streetable" engine. Loads of low down torque for the stop light drags...more than even a stock 351 4V. However, it still cannot sustain the RPM as the stock 4V heads can in the upper ranges, therefore produces less power ovsrall.
But if primarily driven on the street, who cares?

Too many people build thier cars for dragstrip duty, yet only spend 5% ( or less!) of thier driving time there, all the while suffering lower performance where they spend most of thisr driving time.

Whew!...
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#9
Kit Sullivan;189732 Wrote:Very true, very true.

Torque is what we feel when we press down on the go pedal, not horsepower.
Horsepower is nothing more than sustained torque as rpm increases.
Engines in the 70s and 80s were designed to deliver as much torque down low as they could to give a feeling of high performance "off the line", where a lot of the stop-light drag races would occur.
Most people did not take thier cars to an actual dragstrip, so an impromptu street race was typically all over by 50-60 mph...well low in the RPM range and over with before the engine has any chance to climb into the higher RPM ranges. These smogged-out motors could not breathe well for various emission-mandated reasons, and just could not maintain any decent torque numbers in the higher RPMs, hence the lower horsepower figures.
That is why cars equipped with BOSS 351s, 428 and 429 CJs, etc...produced decent HP #s: They could continue to breathe well at higher RPM enabling them to maintain higher torque as RPMs increased. Thus, higher horsepower.

I have met many people over the years that have told stories of how powerful thier late-70s stock muscle car was, and I always bite my lip to keep from insulting them.
I am particularly referring to the late-70s Trans-Ams with the 403 Olds motors. Rated at a measly 180 horsepower, but loads of low end torque.
Those cars felt like a powerhouse off the line...lots of tire smoke and such, but by 50-60 mph, they were all done. They could'nt breathe well, so the torque just fell off in the higher RPM...no sustained torque, so no decent horsepower.
Most of these owners would never go to a real dragstrip to get a 1/4 time, so they had no clue how really underpowered those cars were.
An engine's breathing capabilities determines in large part its ability to produce power. But it is a compromise. Lots of breathing capability ( big intake valves, big ports, headers, etc...) allow an engine to maintain torque at higher RPM, yet can also hinder its off-the-line performance. These engines are well-suited for dragstrip duty, where all of the RPM range can be used. But if you just want to pop around stop light to stop light, you may never get to use the engine's potential.
OEM 351 4V clevelands are notorious for this. The 4V heads are awesome for dragstrip duty, but trade off some low-end torque for high-end torque ( horsepower).
Street driven 351 4V Clevelands are less impressive off the line than thier fame would suggest.
The 351 2V engine has smaller valves, and swapping an aftermarket 4V intake and carb results in a much more "streetable" engine. Loads of low down torque for the stop light drags...more than even a stock 351 4V. However, it still cannot sustain the RPM as the stock 4V heads can in the upper ranges, therefore produces less power ovsrall.
But if primarily driven on the street, who cares?

Too many people build thier cars for dragstrip duty, yet only spend 5% ( or less!) of thier driving time there, all the while suffering lower performance where they spend most of thisr driving time.

Whew!...
thanks for the info. well stated and easy to understand. would you recommend going with a period correct intake/carb or aftermarket ? Thanks again for the info.

steve
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#10
I know from my Sportster that the right mods doubled my rear wheel HP. My bike left the factory and dynode around 45 ish.
I now make 90 ish. I am hoping similar magic can be performed on my 351C. 155 HP from a 5.8 liter is not even close to enough. Poor gas mileage and no power is a really bad combo. Would love to know where to thread is where changes have been made and then results dynode. It would also be nice to understand what happens at $1000, $2000, 3,4,5 with that investment for H.P results.

Bright lime 72 Mach 1 with 351C 4V, with summit 600 carb(have a Holley too), Edelbrock dual-plane manifold, Hooker headers, 3 inch exhaust with flowmasters, 17 inch Eleanor wheels, FMX tranny, A/C, P/S, front disks and 350 rear gear. Drive it to work every day.
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