Morbid Intentions

Just like last time I was spurred by a previous discussion to crunch numbers

the discussion was simple... turbocharged small displacement engines trying to compare horsepower per liter to N/A engines... made no sense to me

so I found two little simple equations you can do #1, to convert given PSI through an engine and add the PSI to it's displacement for a theoretical final displacement... #2 to break down a percentage of how much power the actual turbo is making as opposed to the engine


#1 (with help from 3.0taurass)

((boost pressure + atmospheric PSI/atmospheric PSI) displacement)

so to test this I used a 2004 GTI... but to hit a little closer to home I will use the 2010 Taurus SHO

The Taurus SHO is a 3.5L twin turbo car developing 365BHP/350TQ @ 12PSI from it's turbos

using the equation...

12 + 14.7 = 26.7
26.7/14.7 = 1.8
1.8 x 3.5 = 6.3L


making the car a theoretical N/A 6.3L


which leads me to the next equation... finding out just how much power the turbo is making over and above the power your engine is making... again, I used the GTI but I will use the SHO here


#2

(boost pressure+atmospheric PSI/atmospheric PSI)

this should give you a number which you need to look at as a percentage...

you then need to subtract your percentage from 100%

then take that percentage and times it by your total BHP and ft. lbs tq

and theoretically that is how much power your turbos are making

should look something like this for the SHO

(12+14.7/14.7) = 55%
55% - 100% = 45%
365*45%= 164BHP
350*45%= 158ft lbs tq.

so in conclusion those turbos are making 164BHP @ 158ft lbs tq and without those turbochargers given the same compression ration specs and dimensions of the engine the car would only be making 201BHP @ 192ft lbs at it's given 3.5L of displacement N/A

as boost pressure increases... these figures will change, and these equations can be applied to any form of aftermarket FI cars as well


also... the second equation can be applied to my previous equation of factoring in altitude to your turbocharged application... seen here

https://mustangforums.com/forum/stre...lping-you.html

so in other words... that same Taurus SHO @ 6000ft would use the rule that for every 2,000ft the atmosphere loses 1.1PSI (meaning the atmospheric pressure is 11.4PSI)... which means that the turbocharger is making more power while the engine itself is making less power.

so first we would have to see how much power the car is losing at the given DA

the Taurus SHO loses 49BHP/42TQ @ 6000FT taking into the account it's turbocharged and using the equation supplied in my other thread

so now we are dealing with a car that makes 316BHP/308TQ

now @ 6,000ft the equation would look like this

12PSI+11.4 = 23.4
11.4/23.4 = 49%
49% - 100% = 51%

so in conclusion at a DA of 6,000ft the turbochargers make 51% of the cars power while the engine only makes 49%. This means at the increased elevation and lower power level the turbocharges make 161BHP/157TQ out of the total 316BHP/308TQ available @ 6000FT

this is all of course theoretical but comes together pretty much perfectly in the scheme of things... and yeah... I got bored again lol

Stone629

Nice write up Morbid! Nothing gets me more than some dummy saying, "your pathetic v8 needs all that displacement just to hang with a 4 banger"... When that 4 cylinder is being force fed by a turbocharger. The damn turbo is the other 4 cylinders, lol. Anyway, good info, Morbid.

Morbid Intentions

thanks

for sh*ts and giggles I ran this civic as an extreme to see if it sounded right or screwed everything up

http://www.dragtimes.com/Honda-Civic...lip-12459.html

28PSI + 14.7 = 42.7
42.7/14.7 = 2.9
2.9 x 2.2 = 6.4

6.4L for 680WHP @ 441WTQ seems kind of low but his low end power is almost next to nothing... so I'm thinking that the use of low displacement to make more peak power by sacrificing low end power travels with the equation as well... I mean, he doesn't make north of 200WHP and torque until after 5K lol

Maraman

Too much math for me, I know I have 5.0 liters, which is equal to 2 1/2 bottles of mountain dew.

perfect.disguise

I got 7.1. Though what about the fact that two diff turbo's can flow/put out way diff numbers at the same boost level?

Morbid Intentions

what are you running like 28PSI?

and at that PSI are you pushing around or over 500WHP?

if so that sounds about right to me

perfect.disguise

29psi on my old D44 and the D65 will be tuned to 28-29psi. Though power diff between the two will be huge. That's what I meant.

Yes, over 500 on this set-up, though My old set-up was the same 7.1 and it was only ~420whp.

Morbid Intentions

I see what you are saying... I think I have a solution and with your digging it will be a better formula too... that is why I post it here lol

Let me sit on this for a couple... it seems I have to incorporate the size of the turbo into the equation... or at least that is what I think that will help the most

I don't do this because I think it's the end all everything to everything... I just like to crunch numbers when I'm bored, I think I should have been born an asian lol

3.0Taurass

I think incorporating the efficiency of the turbo for the cfm of the motor could be good. Like if the turbo had an efficiency of 80% you could change the first equation to

(((Boost pressure * 0.80)+atmospheric pressure)/atmospheric pressure) * displacement

The efficiency map thing should correct for the size of the turbo

perfect.disguise

Wouldnt that be diff per turbo as well? What about the lbs-min the turbo is actually puttng out.