Boost level and torque curve

[thx78]

enjoy the surge of a turbo, it's fun and part of the appeal of these engines. however I always believed that the torque was flat or diminished directly after the spool so that what comes after is of less interest. I am not a specialist in turbo engines, far from it, but to my great surprise I discovered engines whose torque increases after spooling and the pressure (psi) increases  with the revs. like the curves that I post the cams can play a role in this and the use of a boost control also. Can we limit the psi during spooling and increase the boost level with the revs or this type of curve is unpredictable. in other words, can I create this crescendo of torque after spooling voluntarily on any engine, with the right size turbo etc

here are the examples

[thx78]

[thx78]

[thx78]

[thx78]

[Dose Pipe Sutututu]

45 minutes ago, thx78 said:

Can we limit the psi during spooling and increase the boost level with the revs or this type of curve is unpredictable. in other words, can I create this crescendo of torque after spooling voluntarily on any engine, with the right size turbo etc

That's all dependant on your boost strategy and your tuning abilities (or your tuner's abilities).

[thx78]

ok but so this is still possible?

[Dose Pipe Sutututu]

Just now, thx78 said:

ok but so this is still possible?

Yes, with a modern ECU and a capable tuner.

[Duncan]

I'm really not following....are you saying you want peaky (ie laggy) torque?

generally the plan is to get as much as you can, as low as you can so it is usable.

[thx78]

I'm not necessarily talking about a peak torque, on the first curve the spool arrives a little after 3500. but the torque increases  until 6000. I'm only talking about having even more torque after the spool rather than a flat curve

[thx78]

basically like the power curves posted above

 

[thx78]

made with turbo and tuned by (hypergear)

[GTSBoy]

It is completely normal. Your original understanding is what was wrong, not what you see in the charts.

[thx78]

ok I understand, but the majority of turbo vehicles lose torque, or have a flat torque curve after the spool. 

hence my initial misunderstanding.

I didn't think this type of curve was possible

 

[Duncan]

That is typical (for a rb at least) with a medium to large turbo, noting the format of the graph is probably misleading what you see a little (half portrait width but full height, in landscape it would look quite different)

Basically until it hits target boost the torque curve is rising steeply, when that is 4000+ rpm it is not great to drive since almost all of your life is between 1,000 and 3,000 rpm. Once you hit target boost the wastegate opens and torque stops rising so quickly. From there the shape of the curve depends mostly on the cams and where they have a peak vs the rev limiter

[thx78]

yes indeed the graphic format makes a visual difference but there is on average 120nm more between 4000 and 6000rpm on the curves it is not nothing. you are right, the cams influence the torque curve. I was able to chat with one of the Hypergear tuners, he confirmed that a boost control allows you to manage the pressure after the spool. the absolute pressure (psi) on the graphics is measured where? It seems that the cams affect the maximum pressure depending on the regime but I may be wrong.

 

not pleasant to drive before 4000? if we spend our lives between 1000 and 3000 rpm as you say then we might as well just run diesel turbos

[Kinkstaah]

I'm not sure you understand the physics of what you are asking.

Can you draw on the dyno graph what you want to have happen? I'm thinking this is a functional impossibility here, unless you chose a turbo literally so laggy that torque is at max at 7000rpm and artificially choked prior to that.

Power and Torque are intrinsically linked. Power is just Torque over time. What you're really seeing in the torque graph is "Power per RPM" if that makes any sense whatsoever.

You still get more power at 7000rpm than 5000rpm, because it is "power per RPM" and you have more RPM. at 7000 than you do at 5000.

You still feel more powerful at 7000rpm. The torque graph will influence the rate of power increase per RPM.

[thx78]

don't want anything more or less, I don't really understand why the torque still goes up to 6000-6500, while the boost peak is around 4000. if it only comes from the cams or from the boost controller etc.

 

[Kinkstaah]

Because there is still an engine underneath that turbo.

PSI is not a measurement of power, it's a byproduct of resistance. What would be really decent is to have a CFM gauge on the output of a turbo to see how much it's actually pushing.

21psi (as an example) is not the same amount of air at 3000rpm as it is at 7000rpm, even if the boost controller is controlling boost at "21psi". The engine is inhaling and exhaling way more air at 7000 than at 3000, even if it's less efficient.

[thx78]

 most turbos look like this. spool, flat torque curve and drops.

 

the boost rises to the target psi and remains fairly constant. like this graph.

 

In what I presented above, the torque and boost increase after the spool. I'm asking what settings change this. that's all