Stress on engine from boost without fuel

[me4ka86]

A bit theoretical question...

Imagine an engine
A) boosting 1 bar and 200hp power
B) boosting 2 bars and 300hp power
C) boosting 2 bars but spray fuel for only 200hp

So my question is for C) . We have high boost, we compress the air but the power output is low. What kind of stress would this situation be on the engine and especially con rods compared to A and B

 

[Windex]

Boost pressure? 2 bars.
Compression Pressure? 26 bars (give or take)
Combustion Pressure? 240 bar or more

The engine is more than capable of taking the extra boost pressure. The issue will arise that either the turbo will be overstressed and fail at some point, or if the engine has a turbo made to deliver 2 bars of boost, then the engine will have turbo lag.

 

[me4ka86]

Disregard turbo overstressing, turbo lag or other real world concerns. How much more does 2 bar boost stress the engine than 1 bar having same power output

 

[Windex]

You will just supply the engine with excess air. There will be more air in the cylinder than needed for the combustion cycle. Given the pressures above, there will be magnitudes more pressure on the power stroke of the piston, but that stroke will be no more powerful at 2 bar boost than at 1 bar boost, assuming as you have stated that you are only delivering fuel for 1 bar of boost.

It's only when you match the fuel to the increase air do you get increased combustion pressures and additional force on the connecting rod.

Suck-Squeeze-Bang-Blow - in your theoretical scenario, you are only increasing the squeeze part slightly, it's the "bang" that bends rods.

 

[GlowBugTDI]

Sooo, pardon my dumbness (never actually messed with this kind of stuff)....but... hypothetically you optimize fuel/air.
If you were to slightly retard the timing would that help reach higher output without beating on the rods as much. Granted it would also rob some power but would you be able to generate enough of an offset that you could be gaining power still, but not being quite as hard on the rods? Or is that just worthless shenanigans?

Edit: I guess then you have to figure at what output would it bend rods and be more worth it to just have a built set up...right?

 

[adamss24]

When asking for more boost than the engine needs for a set amount of air you actually lower it’s efficiency, EGT increase and AFR is lean- nothing majorly
wrong with it as the engine can take it however you don’t need to.
As others said, engine and turbo are effectively a heat pump, It’s these peak cyl pressures that bend rods and lift heads, secret is to produce most power to less boost while keeping things together !