So does high boost pressures that so many seem to use as a barometer for performance.

The higher the boost pressure, the more pumping losses the engine suffers from as the piston fights to compress a cylinder volume of, say, 35 psi instead of 25 psi of boost.

It takes more kinetic energy out of the crank to further compress the greater potential energy and push back of higher boost pressure.

There is a balance to all things. A lot more is not always better, even if a little more is.

 

🤯 I fully agree with that statement y2k

 

Ooooh, this could be a fun discussion!!

I don’t ‘fully’ agree - but you could change my mind.

In a nutshell, an extra 10psi of ‘resistance’ is insignificant to cylinder pressures - but more oxygen is always beneficial. More O2 allows us to burn more fuel, which accelerates the exhaust velocity, which is capable of producing even more boost. There is always a limit, but to strengthen your argument - you will see the highest MPG if you can drive without making boost... Adding ‘more O2’ is limited by the turbo map. I agree, a stock turbo pushing 35psi is cramming a bunch of HOT air (less O2) into the combustion chamber. This is not efficient - but almost exclusively makes more power (35 vs 25psi).

Maybe ask a mod to move this to a dedicated thread?

 

I'll ask, but only after asking the mod to delete any of your disagreement. (just kidding, for anyone concerned)

Where would you like it moved to? Make a new thread, or add it to BDP's new thread?

If we leave BDP's thread to strictly injectors, what posts from THIS thread would you like in the new thread (use post #s).

I will do whatever you suggest.

 

Oh my, that’s a lot of responsibility!!

I would say let’s have a boost discussion separate from the ICP discussion and move posts to those places.

But only if it pleases the mods.

 

Done. As you directed.

 

I'm with Jason - more boost will always give you more power, provided you put enough fuel in to use the extra oxygen. From that point of view, save for theoretical 'pathological' cases, the more boost you put in, the more power you get out.

However, the rest of the engine will generally not be able to deal with things past a certain point: you can run out of cooling, you can run out of mechanical strength...

 

More boost can also equal hot air or an unequal balance between boost and back pressure which leads to performance loss. If a 1:1 boost/back pressure can be maintained at higher boost levels the stress on the motor will be less.

 

I generally always thought that making power (say 300 rwhp) on 15 psi was better than having to push 25 psi to make the same power, but I don’t really know how it works.

 

Aint it all about moving maximum amount of air with minimum amount of boost / restriction (boost is measurement of restriction)..🙄

 

All turbos have an efficiency range where they operate best in. Saying “more boost equals more power” is only true up to a certain point. If
you try to push it too far past the efficient range of a specific turbo it will heat the air up too much and also drastically shorten its life.

 

Right, remember when I was talking about 'pathological' cases? This would be a great example.

Yes, each turbocharger and engine combination has a range in which it will work well. Outside of that range, as you point out, you run into compression heat issues among (many) possible others.

This was not, however, what the OP was asking: the original question related to the cylinder 'fighting' the pressure and therefore generating less power with a greater charge of air/fuel mix in the cylinder. As far as I know, this is not possible within the posted context (i.e. a relatively modern direct injection turbocharged diesel with 'reasonable' levels of boost). You will start overheating things or bending rods well before that is even theoretically possible.

And yes, it is possible to get less charge (or at least, not as great an increase in charge) by using the wrong turbocharger, overloading it and causing the charge air to increase dramatically in temperature (that is the main reason to have an intercooler, by the by, together with managing the heat load on the engine: the amount of oxygen that goes into the cylinder decreases because of the temperature and, as Brandon has suggested, you can dramatically shorten the turbocharger's life. That's why you keep an eye on EGT and IAT, but that's common knowledge...

 

This is my understanding as well based on my own experiences and research. Since learning this lesson the hard way, I have said many times on the FTE that more boost does not always mean better performance. People should not be shooting for a high boost measurement alone, they should be shooting for the right boost measurement, right fuel measurement and right EGT measurement.

Some people are not familiar with reading a turbo map and I am not good at it. I can decipher the secrets they tell, but I need to study them for a period of time. Years ago I had a thread on here where a few of the old timers (Rich AKA White Buffalo for example) helped teach me how to read a turbo map.

Even then, it still took me a while to realize a high boost measurement alone does not necessarily mean good performance.

How much boost is too much, well that depends on the build of the engine, the injectors, the fuel required and supplied and the turbo size in regards to compressor and AR.

With my modified stock turbo I was pushing 32 PSI of boost at 3000 RPM and now with the upgraded turbo I am accomplishing the same amount of work and same tasks with 20 PSI of boost at 2100 RPM.

 

This. ⬆️
Once out of the turbo’s designed map it will not function efficiently (and probably not live as long). I feel this is much more of an impact than any engine related losses. My opinion on the matter anyways.

I also believe the spirit of the OP’s question was to generate discussion on the matter and was not specifically addressed towards pumping losses. Correct me if I’m wrong Mr Y2KW57.

 

Uh, no, respectfully.

That is to say: if we're comparing apples and oranges, things may behave differently (the classic example is, you get a bigger turbocharger housing, pressure goes down but CFM go up, yes, in that case you will read less pressure but move more air and therefore have higher performance, though even that is pretty uncommon because the manifold and the heads, we're postulating, stay the same). But if we take a given configuration and run 15 PSI of boost vs. 10, as an example, while remaining within the correct performance parameters of the turbocharger, i.e. *without seeing temperatures diverge*, and *provided that we're adding the correct amount of fuel in both cases*, then higher boost will mean a higher quantity of air/fuel mix in the cylinder. That will mean more power unless and until we end up in an edge case, but we can't generalise an edge case and call it a good generalisation. There exist valid counterexamples to almost anything with engines.

Of course, sure, if you JB weld the wastegate shut and the DME (sorry, PCM) doesn't put out the correct amount of fuel you will generally not see horsepower gains (and there are exceptions even to that, though generally less so in diesel engines).

We really need to define a bit better what we're talking about, otherwise any statement can be valid. 'More boost does not equate to higher horsepower' as a statement in isolation is actually less frequently true than 'more boost, more power'.