The best visual aid ever for understanding the limits of a turbo

[Bzinsky]

Just figured I’d post this. I used to build big turbo honda’s in my early 20’s. Also read maximum boost by corky bell.

As I was watching this nissan Z review, the presenter shows us the Z has a turbo rpm gauge and a boost gauge and you can watch them in action side by side. It was the first time in my life I have ever seen real evidence/data of this. It will help so many people understand the limitations of a turbo and tuning them.

You might want to watch the whole video, but rpm vs boost sequence starts at 7:10


I just figured this would be a perfect visual aid for some people.
You can see the turbo builds full boost at lower engine rpm, and then as the engine rpms increase, the turbo speed has to increase to maintain that boost pressure while the engine is ingesting more air because of the higher rpm.

So what does an aftermarket tuner do to stock motors on stock turbos? Well they usually increase boost pressure, and the turbo does that by increasing rpm. That’s also why if you look at most aftermarket tuning companies, you will see the powerband make way more torque down low and then the torque starts to taper off. That’s because turbo can’t keep up, it has already reached it’s maximum rpm. And if you were to look at the boost pressure of these tunes, the boost would start to drop off as your engine rpm started increasing. Basically the oem’s typically choose a boost pressure that the turbo can maintain through the whole powerband. The aftermarket tuners are basically like, “to hell with that.”
Why do oem’s do that? Well because they build most of the drivetrain to a torque specification, not a hp specification. If you simply let the turbo go wild, you will not have increased the cars peak hp much, but you will have increased the peak torque a lot.

This is also why the key to making real power is upgrading the turbo. You can increase boost with an aftermarket tune, but you can’t maintain that. Increasing boost is just torque. The problem with artifically boosting the torque but it running out of steam on the top end is that your entire drive-train is rated for torque.
Just throwing numbers out of my ass to help let people understand. But lets say your 2.0 make 300ft lbs of torque at 2000rpm, and maintains that until 5250 rpm. That motor would make 300ft lbs and 300hp. Now lets say you threw a tune on it. The tune might give you a 150ft lb jump in torque at 2000rpm for a total lf 450ft lbs, it will feel like an animal. But then as the rpms increase the boost starts dropping, and by 5250rpm you’re down to only 350ft lbs of torque. So your tune extracted 150ft lbs additional, but only a 50hp bump. So what happens when you upgrade the turbo. Well you could just do a 150ft lb torque bump and maintain that all the way to 5250rpm. This is about the same amount of abuse on the drivetrain as your tune only 2.0t because the peak torque is the same, but now you have 450hp instead of 350hp.

Now personally I have a 4xe with a 2.0t, nobody is tuning them yet. Just wanted to point this out if you have a 2.0t and are interesting in modding it.

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[commbubba19]

boost is a measurement of restriction and not always a represenation of more power, but more inefficiency.

 

[Zandcwhite]

Just figured I’d post this. I used to build big turbo honda’s in my early 20’s. Also read maximum boost by corky bell.

As I was watching this nissan Z review, the presenter shows us the Z has a turbo rpm gauge and a boost gauge and you can watch them in action side by side. It was the first time in my life I have ever seen real evidence/data of this. It will help so many people understand the limitations of a turbo and tuning them.

You might want to watch the whole video, but rpm vs boost sequence starts at 7:10


I just figured this would be a perfect visual aid for some people.
You can see the turbo builds full boost at lower engine rpm, and then as the engine rpms increase, the turbo speed has to increase to maintain that boost pressure while the engine is ingesting more air because of the higher rpm.

So what does an aftermarket tuner do to stock motors on stock turbos? Well they usually increase boost pressure, and the turbo does that by increasing rpm. That’s also why if you look at most aftermarket tuning companies, you will see the powerband make way more torque down low and then the torque starts to taper off. That’s because turbo can’t keep up, it has already reached it’s maximum rpm. And if you were to look at the boost pressure of these tunes, the boost would start to drop off as your engine rpm started increasing. Basically the oem’s typically choose a boost pressure that the turbo can maintain through the whole powerband. The aftermarket tuners are basically like, “to hell with that.”
Why do oem’s do that? Well because they build most of the drivetrain to a torque specification, not a hp specification. If you simply let the turbo go wild, you will not have increased the cars peak hp much, but you will have increased the peak torque a lot.

This is also why the key to making real power is upgrading the turbo. You can increase boost with an aftermarket tune, but you can’t maintain that. Increasing boost is just torque. The problem with artifically boosting the torque but it running out of steam on the top end is that your entire drive-train is rated for torque.
Just throwing numbers out of my ass to help let people understand. But lets say your 2.0 make 300ft lbs of torque at 2000rpm, and maintains that until 5250 rpm. That motor would make 300ft lbs and 300hp. Now lets say you threw a tune on it. The tune might give you a 150ft lb jump in torque at 2000rpm for a total lf 450ft lbs, it will feel like an animal. But then as the rpms increase the boost starts dropping, and by 5250rpm you’re down to only 350ft lbs of torque. So your tune extracted 150ft lbs additional, but only a 50hp bump. So what happens when you upgrade the turbo. Well you could just do a 150ft lb torque bump and maintain that all the way to 5250rpm. This is about the same amount of abuse on the drivetrain as your tune only 2.0t because the peak torque is the same, but now you have 450hp instead of 350hp.

Now personally I have a 4xe with a 2.0t, nobody is tuning them yet. Just wanted to point this out if you have a 2.0t and are interesting in modding it.

But it's a Jeep that will spend most of its life at lower rpms, 150ftlbs down low is perfect. We need torque over horsepower for the vast majority of wheeling anyway.

 

[Bzinsky]

boost is a measurement of restriction and not always a represenation of more power, but more inefficiency.

under that logic going up in elevation isn’t a representation of less power

more manifold pressure = more power

also NA motors all under operate under atmospheric pressure. Yeah modding the motor for more hp = more power under the same atmospheric pressure. It doesn’t make the motor more efficient. It simply allows it to consume more air and more fuel.

 

[Bzinsky]

But it's a Jeep that will spend most of its life at lower rpms, 150ftlbs down low is perfect. We need torque over horsepower for the vast majority of wheeling anyway.

That is true, but keep in mind your trans, diffs, transfer case, and axles are torque limited, not hp limited.

I totally understand just doing a tune with no mods. This is more of a learning how shit works thread then a “don’t do that” thread. I just figured that simple gauge display on that nissan Z would be very helpful for those trying to understand turbos.

 

[commbubba19]

under that logic going up in elevation isn’t a representation of less power

more manifold pressure = more power

also NA motors all under operate under atmospheric pressure. Yeah modding the motor for more hp = more power under the same atmospheric pressure. It doesn’t make the motor more efficient. It simply allows it to consume more air and more fuel.

you are over simplyfing this.

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