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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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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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Guest Kit Sullivan

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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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.


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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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

20180127_082009.jpg

 

 

 

 

 

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

[align=left]Jeff T.

 

When I die I want to die like grandpa, peacefully in my sleep... not screaming, like his passengers. [/align]

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Guest Kit Sullivan

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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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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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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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.


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.

 

If you need help a friend of mine whom I'm pretty sure bleeds BLUE, does some magic on Clevelands. He'd rather put more hp AND torque in a Cleveland than eat. But he's three hours away just outside of Lynchburg.

 

67 Diamond Blue Vert

 

images?q=tbn:ANd9GcRveIaRU6OAzTfd2Mv6ypGH49BZcPU7MS_7PBKhiOmpmJJrHJ_B_Q

 

DUDE

 

LOL even my sig line offended somebody!

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Guest Kit Sullivan

When thinking about the legendary "Cleveland", it is best to think about the engine's potential, as opposed to it's out-of-the-box performance, with exception to the 71 BOSS 351/HO and the 72 HO versions. Those were actually fairly well optimized as an OEM offering. I actually prefer the 72 HO over the BOSS 351 engine( I know: Blasphemy!). Only slightly less powerful on paper, yet produces nearly identical performance as the 71 B1/HO in reality. And idles better and runs on regular gas.

 

All other Clevelands, both the 2V and the 4V variety were delivered from Ford with the potential to be awesome, with just a few hop-up mods.

There are are several emissions'-mandated items that hindered Ford's ability to release the engine as the engineers would have liked, and they got more intrusive and severe each year through '74.

 

Basically, the areas to optimize in order would be (in my opinion...others may differ)

 

1) Breathing: Aluminum aftermarket intake and carb would be first. Headers or an opened-up exhaust is in there too.

 

2) Gearing: A dud rear axle ratio will make any engine modification seem like a waste of money. 3.25 at an absolute minimum, 3.50 is a great all-around gear. Lots of 3.00 axles were stuck in cars with Clevelands, and they suck.

 

3) Ignition: A decent electronic ignition is a must. Doesn't have to be expensive: A simple Pertronix alone is a vast improvement.

 

4) Distributor blueprinting: Not difficult to learn and makes a huge off-the-line improvement. Cheap to do on a stock distributor and just as effective (nearly) as expensive aftermarket distributors.

 

#3 and #4 both assume you have optimized the settings for performance, not mileage or emissions.

 

5) A good zero-degree timing-chain set (applies mostly to '73 Clevelands). You will never get the awsome and legendary "Cleveland" performance with a retarded emissions-friendly timing set installed. I have seen MANY people throw thousands of dollars of parts on a '73 Cleveland only to end up with nothing better than the sluggish stock pereormance.

 

These are all external mods, with posibly the exception of the timing set. Do these few mods correctly to a stock non-BOSS/HO Cleveland, and you will think you added another 100 cubes of displacement. Most people are astounded at how much performance can be added to these engines relatively simply.

 

From here, you will do the more involved mods, such as cam, rockers, head work, etc...

 

Do the easy stuff first and you may never have the desire to do anything more involved.

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When thinking about the legendary "Cleveland", it is best to think about the engine's potential, as opposed to it's out-of-the-box performance, with exception to the 71 BOSS 351/HO and the 72 HO versions. Those were actually fairly well optimized as an OEM offering. I actually prefer the 72 HO over the BOSS 351 engine( I know: Blasphemy!). Only slightly less powerful on paper, yet produces nearly identical performance as the 71 B1/HO in reality. And idles better and runs on regular gas.

 

All other Clevelands, both the 2V and the 4V variety were delivered from Ford with the potential to be awesome, with just a few hop-up mods.

There are are several emissions'-mandated items that hindered Ford's ability to release the engine as the engineers would have liked, and they got more intrusive and severe each year through '74.

 

Basically, the areas to optimize in order would be (in my opinion...others may differ)

 

1) Breathing: Aluminum aftermarket intake and carb would be first. Headers or an opened-up exhaust is in there too.

 

2) Gearing: A dud rear axle ratio will make any engine modification seem like a waste of money. 3.25 at an absolute minimum, 3.50 is a great all-around gear. Lots of 3.00 axles were stuck in cars with Clevelands, and they suck.

 

3) Ignition: A decent electronic ignition is a must. Doesn't have to be expensive: A simple Pertronix alone is a vast improvement.

 

4) Distributor blueprinting: Not difficult to learn and makes a huge off-the-line improvement. Cheap to do on a stock distributor and just as effective (nearly) as expensive aftermarket distributors.

 

#3 and #4 both assume you have optimized the settings for performance, not mileage or emissions.

 

5) A good zero-degree timing-chain set (applies mostly to '73 Clevelands). You will never get the awsome and legendary "Cleveland" performance with a retarded emissions-friendly timing set installed. I have seen MANY people throw thousands of dollars of parts on a '73 Cleveland only to end up with nothing better than the sluggish stock pereormance.

 

These are all external mods, with posibly the exception of the timing set. Do these few mods correctly to a stock non-BOSS/HO Cleveland, and you will think you added another 100 cubes of displacement. Most people are astounded at how much performance can be added to these engines relatively simply.

 

From here, you will do the more involved mods, such as cam, rockers, head work, etc...

 

Do the easy stuff first and you may never have the desire to do anything more involved.

 

thanks very much for the info ! good stuff...

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When thinking about the legendary "Cleveland", it is best to think about the engine's potential, as opposed to it's out-of-the-box performance, with exception to the 71 BOSS 351/HO and the 72 HO versions. Those were actually fairly well optimized as an OEM offering. I actually prefer the 72 HO over the BOSS 351 engine( I know: Blasphemy!). Only slightly less powerful on paper, yet produces nearly identical performance as the 71 B1/HO in reality. And idles better and runs on regular gas.

 

All other Clevelands, both the 2V and the 4V variety were delivered from Ford with the potential to be awesome, with just a few hop-up mods.

There are are several emissions'-mandated items that hindered Ford's ability to release the engine as the engineers would have liked, and they got more intrusive and severe each year through '74.

 

Basically, the areas to optimize in order would be (in my opinion...others may differ)

 

1) Breathing: Aluminum aftermarket intake and carb would be first. Headers or an opened-up exhaust is in there too.

 

2) Gearing: A dud rear axle ratio will make any engine modification seem like a waste of money. 3.25 at an absolute minimum, 3.50 is a great all-around gear. Lots of 3.00 axles were stuck in cars with Clevelands, and they suck.

 

3) Ignition: A decent electronic ignition is a must. Doesn't have to be expensive: A simple Pertronix alone is a vast improvement.

 

4) Distributor blueprinting: Not difficult to learn and makes a huge off-the-line improvement. Cheap to do on a stock distributor and just as effective (nearly) as expensive aftermarket distributors.

 

#3 and #4 both assume you have optimized the settings for performance, not mileage or emissions.

 

5) A good zero-degree timing-chain set (applies mostly to '73 Clevelands). You will never get the awsome and legendary "Cleveland" performance with a retarded emissions-friendly timing set installed. I have seen MANY people throw thousands of dollars of parts on a '73 Cleveland only to end up with nothing better than the sluggish stock pereormance.

 

These are all external mods, with posibly the exception of the timing set. Do these few mods correctly to a stock non-BOSS/HO Cleveland, and you will think you added another 100 cubes of displacement. Most people are astounded at how much performance can be added to these engines relatively simply.

 

From here, you will do the more involved mods, such as cam, rockers, head work, etc...

 

Do the easy stuff first and you may never have the desire to do anything more involved.

 

 

That is great info kit. I've done most of the usual mods to my 2V and it has responded very well from them. My engine is actually a 1970 version that I put in the car according to the casting number on the block if it makes any difference. In straight from the factory configuration it sure wasn't a barnstormer by any means, so the low factory horsepower rating is entirely believable.

351w - Ford racing GT40X 178 cc aluminum heads - Ford racing(crane) 1.7 roller rockers - Comp Cams 280H magnum cam .544" / .544" lift - ARP hardware - hedman longtubes - magnaflow exhaust with X pipe - Duraspark - MSD digital 6al box - MSD TFI coil - optima red top battery - tuff stuff 140 amp alternator - weiand stealth intake  - edelbrock 1406 600 carb  - march pullies and brackets - Be cool fan controller - derale electric fan - FMX trans - motive 4.11 gears - traction lok - lakewood traction bars.                                            

 

 

 

 

 

 

 

 

 

 

 

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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!...

Kit,

While I agree with much of what you said, I am a bit confused about whether you believe low speed torque is a good thing or a bad thing. It seems you don't think highly of the late 70s Olds 403 with gobs of low speed torque nor the 351C 4v cars that have significantly less low speed torque. It seems to me that how much torque you need, and where in the RPM band you need it, depends on many variables such as intended purpose and the ability to effectively transfer the torque to the pavement. As to why someone would build a car that's performance capability would only be used a fraction of the time, even less than 5%, it is because it is what people wanted and still do. That is why Ford built the 1971 429CJ and 351C 4V Mustangs and why Ford, GM, and Chrysler build muscle cars in the current era. Just one opinion. Chuck

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Guest Kit Sullivan

My statements were that a big-torque, low RPM motor may feel like a real powerhouse on the street to someone unfamiliar with 1/4 mile runs...which demonstrates the totality of an engine's performance capabilities far more thouroghly than a typical stop-light drag race on the street.

I totally agree with you about "useable" torque. If you can't effectively get the power to the street, it makes no difference how much torque you have.

My dislike of the olds 403 as a performance engine is based on it comparison to an early 70s poncho 400. Both run great 0-50 or so, but the pontiac motor will walk the olds from that point on.

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Glad to hear there is another closet Pontiac fan on the site!:) Mine was a 1964 Tri-Power, 4 speed, Convertible, GTO. I needed the the money at the time (1971) so the $600 profit, while working for $1.05 an hour, was to too much to resist the sale. Good on yah, Chuck

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This is what happened after I put a 4V intake and 600cfm carb on my 73 H code:

 

 

No idea what the HP is but it feels good! :)

Doc

Project started 8-7-10

Completed: All new suspension, rebuilt 351C H Code bored .030 over with mild cam and intake, new 3.50 TracLok, custom exhaust system

Current "mini-project": interior upgrade :-/

[button=http://www.7173mustangs.com/forum-garage?filterxt_uid=76]Doc's Garage[/button][button=http://www.7173mustangs.com/thread-1973-mustang-convertible-restoration-and-modification]Doc's Wiki[/button]

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The best "power" upgade I did to mine was swithcing out the C-6 for a T-5 manual. It made a significant difference in how the car feels and drives. It frees up about 50-60 hp.

[align=left]Jeff T.

 

When I die I want to die like grandpa, peacefully in my sleep... not screaming, like his passengers. [/align]

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