equation to calculate HP per psi of boost?

[CSVT#49]

I'm just curious if this is the way to go about it...

I want to figure out how much horsepower is required to obtain 5psi on a 2.5L.

(HP x 63025)/RPM = (PSI x displ.)/ 6.28, 6.28 being 2(pi)

so...

2.5L -> 153in^3

solving for HP...

HP = (3500rpm((5psi x 153in^3)/6.28))/63025

HP = 6.76

Is that correct assuming I'm looking to have 5psi at 3500rpm? Then the plot for HP required to maintain 5psi through the powerband would be as follows...

 

[CSVT#49]

I was talking with a collegue and he was telling me it should be this...

HP = [flow(gpm) x Pressure(psi)] / 1714

flow = engine speed(rpm) x displacement/2
Pressure = gauge pressure at intake

So..

2.5L = 153in^3 = 0.66gal

flow = 3500rpm x (0.66gal/2) =1155gpm
Pressure = 5psi

HP = (1155gpm x 5psi) / 1714 = 3.36hp

and at 7200rpm redline (for me anyway)

HP = 6.93hp

 

[gorman]

that seems a very low value... is that for a twin screw supercharger ? .. G.

 

[beyondloadedSE]

I dont think there is really any good equation to estimate hp per each psi. Each turbo is different and will yield a different amount of hp.

 

[gorman]

yeah; i think that equation should have temp or adiabatic efficiency in there somewhere.. G.

 

[CSVT#49]

I dont think there is really any good equation to estimate hp per each psi. Each turbo is different and will yield a different amount of hp.

Well there should be something out there...

Also its not based on the turbo. It's based on how much work needs to be done in order to keep up with the engines demand for air.

yeah; i think that equation should have temp or adiabatic efficiency in there somewhere.. G.

I would tend to agree with the statement.

 

[CSVT#49]

Wow I should really take time to go back and read through some of my Fluid Mechanics books...

Gotta love Yahoo...
Best Answer - Chosen by Asker
*Please clarify regarding suction,discharge,type of liquid and working temperature as NPSH available is vital for pumping a fluid.
*Q=A.V
Where,
V = fluid velocity (m/s)
Q = capacity (m^3/s)
A = tube area (m^2)

*V = Q x 353.6/ D^2
WHERE,
V = fluid velocity (m/s)
Q = capacity (m^3/h)
D = tube diameter (mm)

*V = Q x 0.409/D^2

V = fluid velocity (ft/s)
Q = capacity (US gall/min)
D = tube diameter (in)

*Re = D x V x RHO/MEW
D = tube diameter (m)
V = fluid velocity (m/s)
forces) RHO = density (kg/m³)
MEW = absolute viscosity (Pa.s)

The RHO is where you take into account your air temp, but since we (I) are looking for specifically 5psi it doesn't matter. However I haven't put a lot of thought into this... I would imagine you would want to design for the worst case scenario of say intake temps of roughly 10-20deg above ambient... which may require more flow to obtain 5psi, but the equation for power doesn't really take this into account

*Static Pressure/Head:
P = RHO x g x h
where:
P = pressure/head (Pa)
RHO= fluid density (kg/m^3)
g = acceleration due to gravity (m/s^2)
h = height of fluid (m)
*P=F/A
WHERE,
P=PRESSURE
F=FORCE
A=AREA.
*Total head H
= Ht – (± Hs) where:
Ht = total discharge head
Hs = total suction head
*Total discharge head Ht
= ht + hft + pt
where:
ht = static discharge head
hft = pressure drop in discharge line
pt > 0 for pressure
pt < 0 for vacuum
pt = 0 for open tank.
*Total suction head Hs
= hs - hfs + (± ps)
where:
hs = static suction head
> 0 for flooded suction
< 0 for suction lift
hfs = pressure drop in suction line
ps > 0 for pressure
ps < 0 for vacuum
ps = 0 for open tank

*Friction loss Pf [(Miller equation)]
= fD x L x RHO x V² /2*D
where:
Pf = friction loss (Pa)
fD = friction factor (Darcy)
L = tube length (m)
V = fluid velocity (m/s)
RHO = fluid density (kg/m3)
D = tube diameter (m)
*NPSHa (Net Positive suction head available):

=NPSHa
= Pa ± hs – hfs – Pvp
(+hs for flooded suction)
(– hs for suction lift)
Pa = pressure absolute above fluid level(bar)
hs = static suction head (m)
hfs = pressure drop in suction line (m)
Pvp = vapour pressure (bar a)
or
where:
Pa = pressure absolute above fluid level
(psi)
hs = static suction head (ft)
hfs = pressure drop in suction line (ft)
Pvp = vapour pressure (psia)

*Power (W) = Q x H x rho x g
where:
Q = capacity (m^3/s)
H = total head (m)
rho = fluid density (kg/m3)
g = acceleration due to gravity (m/s^2)

and FTW. This is where my friend must have gotten his equation...

*Power (hp) = Q x H/k,
where,
Q = capacity (US gall/min)
H = total head (psi)
K=1715.

 

[TRicker]

blah blah blah blah......

how about.... turn up the boost until it makes the HP you want? lol.

 

[Dyoel182]

I dont think there is really any good equation to estimate hp per each psi. Each turbo is different and will yield a different amount of hp.

Right. When you just look at PSI you're missing the other half which is flow rate. Run a stocker at 9psi and an aftermarket at 5psi and you might still come out ahead in terms of power. We played with boost pressures on my old Mazda before the hybrid went in.

 

[CSVT#49]

Right. When you just look at PSI you're missing the other half which is flow rate. Run a stocker at 9psi and an aftermarket at 5psi and you might still come out ahead in terms of power. We played with boost pressures on my old Mazda before the hybrid went in.

You guys are not getting this...

I'm looking to find out how much horsepower it takes to PRODUCE the boost I'm looking for... not how much I can make off of it.

 

[striker2]

You guys are not getting this...

I'm looking to find out how much horsepower it takes to PRODUCE the boost I'm looking for... not how much I can make off of it.

well, thats still dependant on the turbo.

 

[Dyoel182]

I'm looking to find out how much horsepower it takes to PRODUCE the boost I'm looking for... not how much I can make off of it.

What does horsepower have to do with exhaust flow? And he's right its totally dependent on the turbo you use since a small exhaust trim will spool up quick on any engine and bigger one may never fully spin up.

 

[CSVT#49]

What does horsepower have to do with exhaust flow? And he's right its totally dependent on the turbo you use since a small exhaust trim will spool up quick on any engine and bigger one may never fully spin up.

This is not necessarily for a turbo or a supercharger, but rather any means of forced induction. The equation should be able determine the amount of horsepower required to create the boost desired.

On another note regardless of what trim your turbo or supercharger is, it is still doing the required work to produce the boost at a certain RPM.

 

[DemonSVT]

This is not necessarily for a turbo or a supercharger, but rather any means of forced induction. The equation should be able determine the amount of horsepower required to create the boost desired.

On another note regardless of what trim your turbo or supercharger is, it is still doing the required work to produce the boost at a certain RPM.

Negative!

Boost is a measurement of intake resistance versus the compressor map and dynamic cylinder volume of said engine.

There is no overall finite answer for what boost makes what power and there never will be one!

You can ask what boost on a specific compressor map (i.e. one specific supercharger) on a set engine setup (including displacement, compression, ratio, cam timing, normal VE, etc, etc) makes what HP increase per 1 psi of "boost" pressure increase. However all of the numerous variables must be accounted for to do this!

 

[CSVT#49]

You guys are not getting this...

I'm looking to find out how much horsepower it takes to PRODUCE the boost I'm looking for... NOT how much I can make off of it.

Negative!

Boost is a measurement of intake resistance versus the compressor map and dynamic cylinder volume of said engine.

There is no overall finite answer for what boost makes what power and there never will be one!

You can ask what boost on a specific compressor map (i.e. one specific supercharger) on a set engine setup (including displacement, compression, ratio, cam timing, normal VE, etc, etc) makes what HP increase per 1 psi of "boost" pressure increase. However all of the numerous variables must be accounted for to do this!

Demon see the post I quoted above.

Obviously there is no one equation to determine how much horsepower can be gained from each 1psi of boost as there are way to may variables from application to application...

However with that said there should be an equation to determine how much horsepower is required to create the boost for the engine at a specific rpm because you have a fixed displacement for your engine, in this case 2.5L. So one could figure out how much work the turbo/supercharger is doing to produce Xpsi at Y engine rpm.

 

[striker2]

no, because even if you have a given exhaust flow, PSI is still dependent on the turbo. different turbos create different PSI at different compressor wheel RPMs, which is determined by the turbine side AR and wheel trim.