https://www.ford-trucks.com/forums/1403003-3-5l-na-torque-curve.html
Do not believe the 3.5L NA is getting enough credit.

Believe it is interesting to compare the 3.5L NA to the 5.0L NA.
The 3.5L NA torque curve is nearly flat in the 2000-3000 rpm range
& peaks at 4250 rpm.
The 5.0L NA torque curve has no flat rpm ranges. The 5.0L NA has a totally positive linear slope torque curve from 1000 rpm to 3850 rpm at peak torque, then decreases with negative slope.

At 65 mph in 6th gear OD with stock tires, the 3.5L NA engine speed is 1814 rpm with default 3.55 rear end ratio. The engine develops 197 lb-ft of SAE net torque, based on the torque curve furnished by TOM and curve fit adjusted to meet the current F150 peak torque specification, 253 lb-ft @ 4250 rpm.

At 65 mph in 6th gear OD with stock tires, the 5.0L NA engine speed is 1692 rpm with default 3.31 rear end ratio. At that engine speed the 5.0L NA develops 173 lb-ft of net torque, 24 lb-ft less than the 3.5L NA.

The 3.5L NA develops 12% more net torque at crusing highway speed
than the 5.0L NA.

Engine speed is easy to calculate.
MPH road speed x 1min/60 sec x tire rotations/mile x trans gear ratio x rear end ratio = engine speed, RPM.
Tire rotations/mile is published by each tire manufactures for size of tire and easy to find on Tire Rack.com for most tires.
Stock tires for the F150 are 245/70/17.

The only experiece of towing a heavy load with a light duty truck was back in 1992
when towed a 26 ft boat with a flybridge & two stern drive engines from SOCAL to Portland, Oregon. Used my 5.8L/C6 , three speed trans in a Ford Bronco as the towing vehicle with 105" wheel base.
The weight of the boat & trailer was approximately 8000#.
Barely made the trip. Used 2nd gear most of the time at 45 mph with engine speed ~ 2785 rpm with 31x10.5x15 tires. On the 10 mile, 8% down grade from CA state line into Medford, Oregon used 1 st gear all the way down the hill
with ground speed < 25 mph.
Travel a 10 mile up hill, 6% grade almost every day. The Semi Trucks will run you off the road, if traveling < 45 mph.

If traveling 45 mph in 3rd gear, 1.52:1 ratio, with a 3.5L NA ,
engine speed ~ 2767 rpm, which is the middle of the torque curve flat rpm range.
The engine develops 214 lb-ft of net torque.

If traveling 45 mph in 3rd gear with a 5.0L NA ,
engine speed ~ 2580 rpm.
The engine develops 245 lb-ft of net torque, only 14.5% more torque than the 3.5L NA.

The 2015/16, 5.0L even with the upgrade to 387 lb-ft peak torque compared to 2012-2014 with 380 lb-ft of peak torque is not the same 5.OL EFI engine found in the 1986-1996 Ford Bronco/F150.
That engine had a completely different torque curve using a compression ratio of 9.0
compared the 10.5 for the current generation.
engine speed, rpm torque , lb-ft
1000 230
1500 250
2000 265
2400 270 peak rating
2500 270
3000 270
4000 240
This data is published by FoMoCo & posted on this forum

OEM Tire size for that vintage was 235/75/15, according to Tire Rack.
At 45 mph road speed the engine speed is 2928 rmp in 2nd gea,r using the C6 , 3 speed trans and OEM 3.73 rear end.

At that engine speed the engine develops 270 lb-ft torque, operating in the flat region of the torque curve, compared to 245 lb-ft for the current 5.0L operating on the slope of the torque curve with both vehicles traveling @ 45 mph ground speed.
The older generation 5.0L developed 10% greater torque than the current 5.0L NA
at low up hill ground speed towing a heavy load.

Bottom line is in my opinion,the 3.5L NA has a better shaped torque curve for a truck application than the current 5.0L NA and even develops more torque than the 5.0L NA at highway speed.

Believe the 3.5L NA has more merit than it is being given and should not be discounted as a viable engine option.
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