Like:rockon:
5.4L vs. 5.0L at same boost :(
- Thread starter Pure_Evil_GT500
- Start date
Like:rockon:
it's funny that you mention this, only after you've been proven wrong:kaboom:
sixties
60s Muscle
GT / GT500 Comparison with 15 lbs. of boost. I'll compute the force each generates
on the piston.
Definition: 1 atm = 14.7 lbs/sq. in. = standard atmospheric pressure
Boost = 15 lbs.
----------------------------------------------
GT
Comp. ratio = 11.0:1
Stock:
1 atm x 11.0 = 161.7 lbs./sq. in.
Boosted:
(1 atm + 15 lbs.) x 11.0 = 326.7 lbs./sq. in. (Humongous)
----------------------------------------------
GT500
Comp. ration = 8.4:1
Boost = 9 lbs.
Stock:
(1 atm + 9 lbs.) x 8.4 = 199.1 lbs./sq. in.
Boosted:
(1 atm + 15 lbs.) x 8.4 = 249.5 lbs./sq. in.
----------------------------------------------
Stock:
GT puts 161.7 lbs./sq. in. on the piston.
GT500 puts 199.1 lbs./sq. in. on the piston. GT500 generates more HP
15 lbs. of boost comparison:
GT puts 326.7 lbs./sq. in. on the piston. GT generates more HP
GT500 puts 249.5 lbs./sq. in. on the piston.
The additional 30 cu. ins. that the GT500 posseses is not enough to overcome the force difference with 15 lbs of boost.
----------------------------------------------
By the way, the equivalent boost if the GT had 8.4 pistons is ...
(326.7 lbs./sq. in. / 8.4) - 1 atm = 24.2 lbs. of boost.
I don't see the 5.0 lasting very long with that force on the piston.
PS: please check my thinking and calculations
on the piston.
Definition: 1 atm = 14.7 lbs/sq. in. = standard atmospheric pressure
Boost = 15 lbs.
----------------------------------------------
GT
Comp. ratio = 11.0:1
Stock:
1 atm x 11.0 = 161.7 lbs./sq. in.
Boosted:
(1 atm + 15 lbs.) x 11.0 = 326.7 lbs./sq. in. (Humongous)
----------------------------------------------
GT500
Comp. ration = 8.4:1
Boost = 9 lbs.
Stock:
(1 atm + 9 lbs.) x 8.4 = 199.1 lbs./sq. in.
Boosted:
(1 atm + 15 lbs.) x 8.4 = 249.5 lbs./sq. in.
----------------------------------------------
Stock:
GT puts 161.7 lbs./sq. in. on the piston.
GT500 puts 199.1 lbs./sq. in. on the piston. GT500 generates more HP
15 lbs. of boost comparison:
GT puts 326.7 lbs./sq. in. on the piston. GT generates more HP
GT500 puts 249.5 lbs./sq. in. on the piston.
The additional 30 cu. ins. that the GT500 posseses is not enough to overcome the force difference with 15 lbs of boost.
----------------------------------------------
By the way, the equivalent boost if the GT had 8.4 pistons is ...
(326.7 lbs./sq. in. / 8.4) - 1 atm = 24.2 lbs. of boost.
I don't see the 5.0 lasting very long with that force on the piston.
PS: please check my thinking and calculations
Interesting calculations, but you are only using static CR, which only tells part of the story. This assumes that the cylinder is sealed at BDC, which never happens. The true dynamic CR could be much different, and change those numbers dramatically. VVT can further influence this in a major way.
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The 5.4 has a massively long stroke. The longest of any production engine. It actually has a longer stroke then a 500ci montain motor in prostock. A big thing is mean piston speed. A 5.4 at 7,200 rpm has a mean piston speed of 5,000 ft per minute. That is the same as a F1 engine at 19,000rpm. Once you hit 6,800 fpm the piston is actually "out running" the flame front of gasoline. It's not technely but BMEP(effective pressure) is dropping very rapidly beyond that point. For the 5.4 stock stroke that is 9,800rpm. A prostock engine is about 6300fpm at 10,000rpm. I use these two because they are the top of the mountain for engine development.
Rod ratios come into play but are often overstated for dwell time. A longer rod to stroke ratio does hold the piston within a certain distance of TDC for a longer period of time/degrees. But a diffence of about 1% a difference of about 2hp and 2lbft is what prostock engine builders have found. They are not worried about engine longevity but more worried about packaging everything like F1. Prostock is trying to get the straightest shot to the cylinder and pushrods as straight as possible. F1 they are trying to get the center of gravity the lowest. In F1 they couldnt get anything below a 2.xx if they wanted to due to packaging. The prostock guys are in the 1.7x range. A higher rod ration does keep down on side loading and decreases piston acceleration limiting Gforces exerted on the assembly. However if you talk to F1 and Prostock engine builders rod ratios are usually not in the top ten items to consider really important.
The G-force from acceleration exerted on the piston/pin/rod/rod bolts/crank are also higher in the 5.4 then the 4.6 and 5.0 again reducing total max rpm given same materials.
That is the short answer without getting overly technical but getting out some of the basics. As stated above there has been 5.4s turned to 8,800 rpm with steel rods and lived. But doesn't make it a good idea.
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For a forged steel rod I'm comfortable with 5,500 fpm in a drag only car that gets freshened up every season as the max. That's 9300 for a 4.6, 9,000 for a 5.0 and 7,900 for the 5.4. There are other factors to consider there but as far as forged steel rods, crank and forged pistons go that is my personal opinion from some experience. In a street car that number drops to 4500 roughly for my comfort level to live 100,000 miles. Which would be 7,600 for the 4.6 7,400 5.0 and 6,500 for 5.4 to live a long happy worry free life for the rotating assembly.
After reading this, Steve gave us a response in 5.0 Magazine
-- Find it here ---http://www.svtperformance.com/forums/road-side-pub-17/772300-i-only-one-see-read.html
-- Find it here ---http://www.svtperformance.com/forums/road-side-pub-17/772300-i-only-one-see-read.html
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