Theoretical Question

[Janusz1]

I am fairly new to turbo engine and need some help in understanding it.

I have a modified '78, 1 bar spring. Lets assume that my boost gauge works 100% accurate and I am driving along in say 3th gear 5,000 RPM with boost pegged at 1 bar and accelerator not quite floored. At this very moment my engine produces a specific torque/power.

Is this torque/power defined now, at this very moment, by any other parameters then boost? Boost defines cylinder pressure, right? If my accelerator were floored now would I have more power? I THINK not because any additional fuel power potential (it means boost) would be dumped by wastegate, right? Will the ignition adjustment make any difference AT THIS VERY MOMENT? A/F ratio? I even think that the quality of fuel (lets disregard potential engine knocking) would not matter right now.

Please tell me if it is so or not and why?

By the way; thank you guys for this forum and your input. I learned a lot since last year from all of you.

[s5uewf]

ignition timing and AFR will make a significant difference in power at any rpm or at any level of boost or non boost.
Once you start bleeding off boost because you have hit your boost peak, you can still make more or less power if your ignition timing or fuel AFR is off. Otherwise, we would never have to tune our engines, we'd just have to ensure we hit the boost limit.

[T77911S]

if fuel and timing are set for peak HP and 5k is where your peak HP is produced, the only way at that moment to increase power is if you had adjustable boost and increased pressure.
is that what you are looking for?

[Speedy Squirrel]

If you don't have the throttle pedal all the way down then you have less than 1 bar in the intake manifold, on the engine side of the throttle. You have 1 bar on the intercooler side, and the wastegate maintains that. That's why they call it a throttle, so stop messing around and stomp on it!

[proffighter]

Originally Posted by Speedy Squirrel

If you don't have the throttle pedal all the way down then you have less than 1 bar in the intake manifold, on the engine side of the throttle. You have 1 bar on the intercooler side, and the wastegate maintains that. That's why they call it a throttle, so stop messing around and stomp on it!

1+

Power is result of the pressure in the combustion chamber after ignition and all involved factors.

Boost is just one and as Speedy said, you read boost before TB so no max combustion chamber pressure (means power at the end) until full throttle

BTW if your max boost is 1bar, you won't have it when just driving along. As soon you lift a little, boost will decrease, even at 5000rpm and whatever speed

[Janusz1]

I have this big boost gauge which is replacing clock in the dash, not the stock electric mickey mouse gauge. It shows vacuum and boost and I think it is very responsive and precise. I know for sure that its pressure line goes directly from the brake booster (2.5 mm hose). So, do my pressure (vacuum and boost) readings come not from engine side of the throttle but intercooler side?

I always believed, until now, that my gauge showed the actual combustion chamber pressure. Could you please confirm that it is not so?

[JFairman]

If you're boost gauge is getting it's pressure reading from the brake booster line it's showing you the air pressure in the intake manifold and not pre throttle body in the intercooler which will be a little higher than in the intake manifold because of the pressure drop post restrictive stock throttle body.

You didn't say you have an aftermarket boost gauge taking it's reading post throttle body so people figure you're talking about the stock boost gauge that takes it's reading from a questionable accuracy sending unit pre throttle body.

Seems to me the motor will always make the most horsepower with the single throttle body butterfly open all the way as long as AFR and timing is correct regardless of what your boost gauge displays.

[Janusz1]

But isn't the horsepower/torque directly the product of combustion chamber pressure and only that?

Because if it is then, logically, once you have 1bar achieved then the maximum power at this RPM is already there and the throttle position makes no difference.

Am I wrong here and if yes, why?

[aschen]

There is a pressure drop across the throttle that is the very definition of throttling actually. 1 bar boost at part throttle has somewhat less pressure past the throttle plate

[RarlyL8]

Boost pressure is irrelevant in this scenario.
Think normally aspirated (one atmosphere pressure), when you drive at less than full throttle the C/R of the engine is static. At full throttle is is still the same but you are making more power due to more fuel and air and RPM.

[proffighter]

At the end it's just the pressure which pushes the piston down. Where due all the factors the pressure is the highest, the most torque of the engine is.

The basic formula for engine power is:

P = VH * pi * n / 1200

P = Power
VH = Displacement
pi = medium pressure on piston
n = RPM's
1200 = Definied amount for 4-stroke (600 if 2-stroke)