Relation between displacement, boost, and power

[khvolk1s]

Okay,

1 bar= 1 atmosphere= 14.5psi

Adding 1 bar of boost to an engine effectively doubles its displacement.

At 10 psi, I boost 71% of 1 bar.

My effective displacement should be about 3.4 liters.

I know there's more to horsepower than just displacement, but most 3.4 liter engines make 250-300 hp.

I know I am not making 250-300 hp.

What am I not understanding about the relationship between displacement, boost, and horsepower?

Thanks

 

[hornsfan10609]

You are saying our FSDE engine designed and built in the late 80s and improved through the 90s and discontinued for over a decade now should make the same power as a modern V6? Apples to oranges, technology and efficiency have increased significantly the past few decades with VVT, cylinder deactivation, stop/start, etc etc. The chevy 454 7.4L was rated at about 215hp back in the 80s, do the math on that lol

 

[kytuner]

There is no simple calculation for how much hp per psi of boost a car is making. It can vary a ton just on tuning and temperature

 

[hornsfan10609]

Just look at how much boost modern engines run, I guarantee it is far more than the 6-7psi the MSP was pushing stock.

 

[tweety2300]

5.0 v8 mustang was around the same time as the fsde was and made a whopping 220 hp. Fsde was not meant to make power at all. Why mazda decided to throw a turbo on it instead of the well proven 1.8 bp is beyond me

I'm not sure who came up with 1 bar doubles displacement but they're idiots. On a vj11 at 18 psi I was making around 190whp. On my gt28 on 16 psi I should be in the low 300 area. Now tell me how does your formula make sense now?

And going by dyno charts most people runing 10psi in a protege make around 200 whp. Now convert that into crank numbers and it'll be closer to 250hp.

 

[khvolk1s]

I thought my little math up there was self-explanatory, if an engine is ingesting twice as much air and fuel or 1 bar over atmosphere, then i is the same effect as doubling its displacement.

 

[tweety2300]

Ok I'll try it again take 2 protgs put a t2554 on one at 14 psi then a gt35 on the other at 14 psi ones going to make way more power.

Psi means nothing. Hell 2 cars same setup can make different power by adjusting the afr and timing

Displacement doesn't mean much either. 1.6 b16 makes 170 hp 2.0 fsde back then made 120. 1.8 b18c makes 197. Small displacement Ferrari v8s make more power than the new 5.0 mustang

In short version the amount of boost and displacement doesn't mean anything at all in terms of hp

 

[khvolk1s]

I understand that volume and pressure are not the same, so a bigger turbo at lower pressure pushes a greater volume of air than a small turbo at higher pressure. All i am saying is at one bar, the air pressuure is 2x that of atmospheric, so doessnt that mean twice as much air in terms of volume is ingested, and therefore twice as much fuel? If everything else is being doubled, why isnt output doubled? If this seems like a stupid point/question, and you can't give an answer that isnt condeaending or insulting, then i don't need it. Thanks

 

[tweety2300]

No because there are dozens of variables when it comes to power output. The amount of air and fuel are just 2 they are major ones yes but other things take away and add to final hp numbers. Drive train loss, temperature, tune, altitude, those are a few.

Fsde is a horrible example to use, inefficient and weak. There are scenarios where doubling the amount of air will double power but it will still have nothing to do with displacement. It will have everything to do with the engine, turbo, setup, temperature, tune list goes on

I'm not trying to be condensating or insulting I'm just trying to say that the amount of air going in doesn't have everything to do with the amount of power or displacement many other things factor into it.

You're questioning it too much, it's not about how much power your car makes. It's about if it makes you happy when you drive it, if you don't like it change it. Whether that means modifying it or trading it in is up to you. But don't expect formulas you pull from the internet to answer why the fsde doesnr make enough power for you.

 

[khvolk1s]

This is a question born of curiosity, and a desire for understanding, not discontnent. I love my car, and with the mods i have done, i think i may have hit my goal of 200 whp. The "formula" isnt anything I pulled from the internet, just a manifestaion of what i know about forced induction. Since you said whoever came up with the formula was an idiot, you did inadvertedly insult me. You also said "psi means nothing" and "displacement doesnt mean much either", and thats hyperbole. If that were true we would all drive RX8s lol. I know these two factors are just two in many like you pointed out, but i think they are signiffigant. At any rate, I think I have my answer. Thanks to everyone who took the time to reply.