Horsepower Equation Revisited
#1
Supreme Member
Thread Starter
iTrader: (2)
Join Date: May 2007
Location: right behind you
Posts: 2,574
Likes: 0
Received 0 Likes
on
0 Posts
Car: '85 maro
Engine: In the works...
Transmission: TH700 R4
Axle/Gears: 3.73 posi
Horsepower Equation Revisited
I put this equation into tunerpro awhile ago and it worked somewhat, but it's not perfect. Here's where the equation can be found, but there's no explanation of what 792001.6 is. Does atmospheric pressure need to be 14.7 or is it actual atmospheric pressure (about 12.1psi where I live), and how do I make this work with forced induction?
A * C * (X * .01) * B * R / 792001.6
Where A is atmospheric pressure, B is engine dispalcement, C is static compression ratio, R is RPM and X is VE.
A * C * (X * .01) * B * R / 792001.6
Where A is atmospheric pressure, B is engine dispalcement, C is static compression ratio, R is RPM and X is VE.
Last edited by bl85c; 12-22-2013 at 01:27 PM.
#2
Supreme Member
Thread Starter
iTrader: (2)
Join Date: May 2007
Location: right behind you
Posts: 2,574
Likes: 0
Received 0 Likes
on
0 Posts
Car: '85 maro
Engine: In the works...
Transmission: TH700 R4
Axle/Gears: 3.73 posi
Re: Horsepower Equation Revisited
Maybe manifold pressure be substituted in for A to make it work with forced induction?
#3
Supreme Member
Thread Starter
iTrader: (2)
Join Date: May 2007
Location: right behind you
Posts: 2,574
Likes: 0
Received 0 Likes
on
0 Posts
Car: '85 maro
Engine: In the works...
Transmission: TH700 R4
Axle/Gears: 3.73 posi
Re: Horsepower Equation Revisited
Seem to get reasonable estimates when I put manifold pressure in for A, but only above atmospheric. I need a way to limit the minimum for A to atmospheric pressure, is there a way to do this with a formula?
Last edited by bl85c; 12-23-2013 at 12:04 AM.
#4
Moderator
iTrader: (1)
Join Date: Mar 2002
Location: Chasing Electrons
Posts: 18,409
Likes: 0
Received 217 Likes
on
203 Posts
Car: check
Engine: check
Transmission: check
Re: Horsepower Equation Revisited
For a rough estimate I use the BSFC, injector flow rate, number of injectors, and the injector duty cycle. Gets close to flywheel HP.
RBob.
RBob.
#5
Supreme Member
Thread Starter
iTrader: (2)
Join Date: May 2007
Location: right behind you
Posts: 2,574
Likes: 0
Received 0 Likes
on
0 Posts
Car: '85 maro
Engine: In the works...
Transmission: TH700 R4
Axle/Gears: 3.73 posi
Re: Horsepower Equation Revisited
I'm looking for something dynamic though. I could throw a guess of .5 BSFC at it, but how can I calculate actual BSFC without horsepower? I think the above formula is the way to go. Just need to find a good way to tweak it for forced induction.
#6
Member
Join Date: Aug 2006
Location: Tampa, FL
Posts: 484
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1988 Iroc-Z Red T-tops
Engine: 305 TPI LB9 55k miles
Transmission: Auto 700r4
Axle/Gears: 2.73 posi
Re: Horsepower Equation Revisited
I used 14.7, live RPM and airflow data and at idle I get 5-6 HP and the VE calculates out to .02-.04 sound right?
#7
Supreme Member
Thread Starter
iTrader: (2)
Join Date: May 2007
Location: right behind you
Posts: 2,574
Likes: 0
Received 0 Likes
on
0 Posts
Car: '85 maro
Engine: In the works...
Transmission: TH700 R4
Axle/Gears: 3.73 posi
Re: Horsepower Equation Revisited
VE should be higher. You can calc it using this-
M * .132 / (491.67 / (A + 459.67) * .0808) / (E * R / 3456) * 100
Where A is IAT, E is engine displacement, M is MAF (in g/sec) and R is RPM.
M * .132 / (491.67 / (A + 459.67) * .0808) / (E * R / 3456) * 100
Where A is IAT, E is engine displacement, M is MAF (in g/sec) and R is RPM.
Thread
Thread Starter
Forum
Replies
Last Post
Bohemian
Aftermarket Product Review
11
11-25-2015 09:38 PM
dbrochard
Engine/Drivetrain/Suspension Parts for Sale
8
09-25-2015 04:56 PM
Street Lethal
Miscellaneous Third Gen Items!
0
09-07-2015 01:09 PM