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Depends on your measuring stick.

The market says, emphatically, that the Boss 429 is the best Boss. And I would agree with that, both in performance and looks and interior/comfort.

But I also love the Boss 351, and came damn close to buying one at the last Mecum Orlando event.
 
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I wouldn’t kick her out of bed for sure but 429 all day for me.
 
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I'd take the '69-'70 Boss 429 over the '71 (1 year only) Boss 351 any day, but the Boss 351 was actually faster 0-60 MPH and had a faster 1/4 mile time than either the Boss 429 or the 428 CJ back in the day, all being bone stock of course. One other little note that the Boss 351 had besides the 11.7:1 CR forged pistons was a solid lifter cam, 4 bolt mains and rods that were shot peened and magnafluxed with a 7,500 RPM limit straight from Ford.
 

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It may be as strong or even stronger performance wise than some of the 69/70 Boss platforms but the appearance just can’t compare to the 69/70 Boss cars. But beauty is in the eye of the beholder I guess.
 

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I'd take the '69-'70 Boss 429 over the '71 (1 year only) Boss 351 any day, but the Boss 351 was actually faster 0-60 MPH and had a faster 1/4 mile time than either the Boss 429 or the 428 CJ back in the day, all being bone stock of course. One other little note that the Boss 351 had besides the 11.7:1 CR forged pistons was a solid lifter cam, 4 bolt mains and rods that were shot peened and magnafluxed with a 7,500 RPM limit straight from Ford.
Sadly the "BOSS" name took the limelight and other faster 1971 Mustangs stayed in the backgound. I believe 13.8 is quoted/fastest 1/4 mile time for the 1964.5 to 1973 Mustangs and the 71 BOSS 351 got that badge of honor from the major magazine publications back "in the day"................but Drag Times magazine got multiple 13.4/13.5's out of a Ford loaner one year only 1971 429 Super Cobra Jet Mach 1, with its oem 375HP, 11.3 to 1 C.R., 2.23 intakes, solid lifters, factory D1Z Holley 780, C6 and 4.11 gear........But that was just a Mach 1, who cares.........The last of the Big Block Mustangs ran rather well on the street, and drag stripped well in Drag Pack form with either 2.32 close ratio top loader or C6 and either 3.91 Traction Lock or 4.11 Detroit Locker.........

^^^^^ I will also say that there were many in the Mustang world who did not care (and do not care today) for the bigger 1971-73 Mustang body style and I think the "BOSS" attached to one in 1971, and its good performance, was the saving grace for some kudos back then and up to today.............The rest of the 71-73's seem to be secondary discussions, even the 1972 R-Code which is rare in today's world......

R
 

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Sadly the "BOSS" name took the limelight and other faster 1971 Mustangs stayed in the backgound. I believe 13.8 is quoted/fastest 1/4 mile time for the 1964.5 to 1973 Mustangs and the 71 BOSS 351 got that badge of honor from the major magazine publications back "in the day"................but Drag Times magazine got multiple 13.4/13.5's out of a Ford loaner one year only 1971 429 Super Cobra Jet Mach 1, with its oem 375HP, 11.3 to 1 C.R., 2.23 intakes, solid lifters, factory D1Z Holley 780, C6 and 4.11 gear........But that was just a Mach 1, who cares.........The last of the Big Block Mustangs ran rather well on the street, and drag stripped well in Drag Pack form with either 2.32 close ratio top loader or C6 and either 3.91 Traction Lock or 4.11 Detroit Locker.........

^^^^^ I will also say that there were many in the Mustang world who did not care (and do not care today) for the bigger 1971-73 Mustang body style and I think the "BOSS" attached to one in 1971, and its good performance, was the saving grace for some kudos back then and up to today.............The rest of the 71-73's seem to be secondary discussions, even the 1972 R-Code which is rare in today's world......

R
I love the Boss name. Yes, 13.8 in the 1/4 mile is/was the quoted time for the Boss 351 as well as 0-60 in 5.8 seconds. The Boss 351 had the same 2.23 intakes, but had the Autolite spreadbore carburetor on top of it's aluminum intake. Also only the BB's got the 2.32 CR trans while the SB's got the WR with a first gear of 2.78 for better acceleration. The Boss 351 only came with the 4 speed top loader with no auto option. The 429 SCJ really should have beat the Boss 351, which had 330 BPH, considering the huge BHP and TQ advantage of the 429 SCJ. The Drag Pack also had optional 4.30 gears.

I do not particularly care for the '71-'73 body style. The 1972 R-Code had the 351C HO engine which was a detuned version of the Boss 351. Also there were 351 CJ cahs in the early '70's too.
 

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I love the Boss name. Yes, 13.8 in the 1/4 mile is/was the quoted time for the Boss 351 as well as 0-60 in 5.8 seconds. The Boss 351 had the same 2.23 intakes, but had the Autolite spreadbore carburetor on top of it's aluminum intake. Also only the BB's got the 2.32 CR trans while the SB's got the WR with a first gear of 2.78 for better acceleration. The Boss 351 only came with the 4 speed top loader with no auto option. The 429 SCJ really should have beat the Boss 351, which had 330 BPH, considering the huge BHP and TQ advantage of the 429 SCJ. The Drag Pack also had optional 4.30 gears.

I do not particularly care for the '71-'73 body style. The 1972 R-Code had the 351C HO engine which was a detuned version of the Boss 351. Also there were 351 CJ cahs in the early '70's too.
I was thinking 2.19 intakes on the BOSS 351, here is what I found on the internet......

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The Boss 351 was a very unique motor. It had all of the best Ford could offer:
Heads just like the Boss 302 with canted-valves Canted-valves (2.19" intake and 1.71" exhaust)

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...............and the 1970/71 429 Torino had a 4.30 gear option, the 1971 Mustang Drag Pack was 3.91 and 4.11......

Back in the 1999-2008 timeperiod I had 3 1971 429 Mach 1's, 1- 375HP SCJ 4 spd. 4.11 D.L......1-375HP SCJ C6 3.91 T.L. and 1-370HP CJ, C6 3.25 T.L. and that one was fully optioned and the Emminger invoice had an price of $6100, it was Corvette money back them......I also had the Emminger invoices on the two Drag Pack cars and they were in the $4500-$4800 range each.

The 370HP 325 gear CJ was not a drag racer, but it could pull into some scary higher speeds and even at those higher speeds that car held the road well which the 71-73's were known for........It almost seemed like it squatted down as the speed increased......

They were decent car show cars, not restored, all needed a little bit here and there, but they all had their matching number drive trains, all original glass, and all around nice cars.....

One of the best improvements for 1971, well there were several, but getting rid of that P/S ram/assist was nice........No more hoses hanging down and leaking.......and going to a "then new" canted valve 351C and 429 was also nice from an engine technology performance advancement for the higher end performance options.....I still swear they saw what Chev. did back in 1965 with their lighter weight canted valve engine design and then got to the design board on building Fords modern performance engine......

R
 

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I was thinking 2.19 intakes on the BOSS 351, here is what I found on the internet......

----------------------------------------------

The Boss 351 was a very unique motor. It had all of the best Ford could offer:
Heads just like the Boss 302 with canted-valves Canted-valves (2.19" intake and 1.71" exhaust)

--------------------------------------------

...............and the 1970/71 429 Torino had a 4.30 gear option, the 1971 Mustang Drag Pack was 3.91 and 4.11......

Back in the 1999-2008 timeperiod I had 3 1971 429 Mach 1's, 1- 375HP SCJ 4 spd. 4.11 D.L......1-375HP SCJ C6 3.91 T.L. and 1-370HP CJ, C6 3.25 T.L. and that one was fully optioned and the Emminger invoice had an price of $6100, it was Corvette money back them......I also had the Emminger invoices on the two Drag Pack cars and they were in the $4500-$4800 range each.

The 370HP 325 gear CJ was not a drag racer, but it could pull into some scary higher speeds and even at those higher speeds that car held the road well which the 71-73's were known for........It almost seemed like it squatted down as the speed increased......

They were decent car show cars, not restored, all needed a little bit here and there, but they all had their matching number drive trains, all original glass, and all around nice cars.....

One of the best improvements for 1971, well there were several, but getting rid of that P/S ram/assist was nice........No more hoses hanging down and leaking.......and going to a "then new" canted valve 351C and 429 was also nice from an engine technology performance advancement for the higher end performance options.....I still swear they saw what Chev. did back in 1965 with their lighter weight canted valve engine design and then got to the design board on building Fords modern performance engine......

R
You are correct on the valve sizes. I was thinking of something else when you mentioned 2.23 intakes, like intake runner size. I knew the 4.30 gears were an option for the Torino. Funny how they were an option for one model, but not for another.
 

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You are correct on the valve sizes. I was thinking of something else when you mentioned 2.23 intakes, like intake runner size. I knew the 4.30 gears were an option for the Torino. Funny how they were an option for one model, but not for another.
I know, that is interesting how the 4.30 was an option for the heavier Torino and not for the lighter Mach 1........4.11 was the top drag race gear in the Mustang in 1971.....

R
 

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I know, that is interesting how the 4.30 was an option for the heavier Torino and not for the lighter Mach 1........4.11 was the top drag race gear in the Mustang in 1971.....

R
Ford also had some other stuff like a 1 3/8" spline on the BB 4 speed top loader as opposed to the 1 1/16" spine on the SB 4 speed top loader. They made a 9 3/8" removable 3rd member that would not fit in the 9" housing without modification. They also pondered, and I believe they built at least 1, a Hone-o-Drive 2 speed diff that had attached to the front of the 3rd member on the Cougar Eliminator with a lever in the cockpit to change gears ratios say from 3.50 to 4.30. It was never an option though. Too bad IMO.

I remember when the 351C came out in 1970 and all the Chevy guys were crying and complaining to NHRA because they could not catch the high revving, high output power that the 351C made. They bitched and hollered and cried so loud that NHRA penalized the 351C drivers by .1-.2 lbs. per horsepower in the professional catagories. Chevy didn't like the fact that Ford had and engine that their SB couldn't touch.
 

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Magazine test results (0-60 and 1/4 mile times) were such a mixed bag of unscientific nonsense back in the day, that you simply can't point to published tests and really determine anything whatsoever. A Boss 351 performing slightly better than a 428CJ could simply be a matter of cooler/drier weather at a better hooking lower-altitude track. They did not correct their numbers for anything, as has been done for the last 40 years.

I've driven them all, I agree with Robert that the 1971 429SCJ is a formidable runner (probably stronger than Boss 351), and I'd also put out there that the Boss 429 has always been the victim of "urban myth", being accused of being a dog. That was never really the case. The Boss 429 was indeed detuned from the factory, smallish carb, smallish cam and restrictive exhausts manifolds. But lurking within were the makings for an exotic monster that none of the other engines we're discussing could ever hope to match. Buy all of these vehicles brand-new, and then start modding, you'll quickly realize that the Boss 429 gets crazy-powerful at an exponential rate compared to the others. In any case, a bone-stock Boss 429 is a 13.70's-13.80's machine, maybe quicker at the right track. The Boss 351 was never appreciably (if at all) faster than the Boss 429, but there are no good/valid track tests from back in the day to point to. Just rhetoric and rumor and the occasional Boss Nine at a humid track in a terrible state of tune and a horrific driver, only helping to further the misinformation about the car.

Peter Klute, many moons ago, did a GREAT "shootout" of bone-stock muscle cars. He knew they were stock, because they were all restored in his shop. It was about as equal a setting as you could hope for, all cars in proper tune at the same track on the same day running in the same weather. You'll be surprised what comes out on top. And I apologize in advance for the young dork in the NPD shirt... ;)

 
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I may be out in right field all on my own here, but to me the 71 Mustang in general is one of the ugliest mustangs ever produced right behind the Mustang II. I'd take a 4-eye fox body over a 71 any day of the week.
 
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I may be out in right field all on my own here, but to me the 71 Mustang in general is one of the ugliest mustangs ever produced right behind the Mustang II. I'd take a 4-eye fox body over a 71 any day of the week.
You're out in right field, standing on clay, leaning over the wall stretching your best to catch that ball... LOL! ;) ;)
 

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You're out in right field, standing on clay, leaning over the wall stretching your best to catch that ball... LOL! ;) ;)
I also really like the looks of the SN95 and the S550 so my tastes are weird to be sure.
 

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I also really like the looks of the SN95 and the S550 so my tastes are weird to be sure.
I absolutely LOVE the S550 (makes my S197 look like an Amish old maid), and I always liked the SN95's as well, although I always thought the styling of the edge cars (99-04) was a bit clumsy and awkward. Not to the point that I'd kick it out of bed, just not as slick and harmonious as the 94-98.

The S550, IMHO, was a grand-slam home run out of the park.
 

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As I recall, the factories were not above supplying automotive publications ringers that were modified and/or tuned for better performance than the production versions sold in the dealerships.
 

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As I recall, the factories were not above supplying automotive publications ringers that were modified and/or tuned for better performance than the production versions sold in the dealerships.
That indeed tended to be "a thing" from time to time. And even if the car was indeed bone-stock, they'd hand it to the mags with a tank full of high-octane race fuel and timing bumped up significantly, which really makes a big difference just in that.

But even further muddying things is that a lot of the performance/road tests were performed by drag/enthusiast magazines who were diddling with timing, removing air filters, swapping on slicks, etc, and talking about it in the article as they made the car go quicker, but casual "web surfers" today don't bother to read the article, they just go straight the the final results and cite it as fact/history.
 

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I absolutely LOVE the S550 (makes my S197 look like an Amish old maid), and I always liked the SN95's as well, although I always thought the styling of the edge cars (99-04) was a bit clumsy and awkward. Not to the point that I'd kick it out of bed, just not as slick and harmonious as the 94-98.

The S550, IMHO, was a grand-slam home run out of the park.
Well we agree on some things then. Duckbill spoilers on the trunk, custom headlights, race seats, vents on the hoods, matte black stripes, and black wheels seem to be how I prefer my curvy mustangs.

Car Wheel Tire Land vehicle Vehicle
 
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