Secondary compressor restriction

motorwood

motorwood

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Jun 16, 2010
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We use a smallish turbine to spool then gate around it. At what point does a small compressor on the secondary become too much of a restriction?
 
When your overall boost is down on pr compared primary boost..
I can't impart enough force on the exhaust wheel to overcome the pressure from primary and keep drive pressures in check. With an he351cw... So i an going to a larger turbined turbo and see what opens up.
 
motorwood said:
We use a smallish turbine to spool then gate around it. At what point does a small compressor on the secondary become too much of a restriction?
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How much power you making on what size secondary? I'm going to try and make 1000hp with a 60mm secondary compressor.
 
I have always doubted a 60mm turbo could ever be more of a restriction than a cummins cylinder head.
 
Restrictive of flow, or horsepower...

Because strictly speaking, if it makes ANY boost at all, mass flow of air into the motor is not restricted by the turbo. But that doesn't mean a larger compressor wouldn't make more power.
 
RyanMayo said:
How so?
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I'll try to be as simple as possible for those who aren't aware of this.

Lets say for arguments sake you're running a single S360

If the stock head is completely untouched and you're running 45 psi, then would you be making less, or more, power at a given rpm, as compared to a ported head that with the same turbo produces 45 psi? (this is assuming all other factors are the same eg: temp, humidity, injectors, lp, etc)

Boost is only a measurement of resistance, not power.

In a perfect world, the ported head would make more power with the same boost due to boost pressure equaling restriction. Therefore you end up with more air based on the amount of resistance.
 
khaoskustoms said:
Primary turbo size dictates max power. Not secondary.
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Honestly, I'm not inclined to disagree with you there. In my mind, the secondary compressor is not a restriction until it is so small that it cannot make boost over what the primary provides, i.e. cannot "outflow" the engine itself.

adamsmarshall said:
I'll try to be as simple as possible for those who aren't aware of this.

Lets say for arguments sake you're running a single S360

If the stock head is completely untouched and you're running 45 psi, then would you be making less, or more, power at a given rpm, as compared to a ported head that with the same turbo produces 45 psi? (this is assuming all other factors are the same eg: temp, humidity, injectors, lp, etc)

Boost is only a measurement of resistance, not power.

In a perfect world, the ported head would make more power with the same boost due to boost pressure equaling restriction. Therefore you end up with more air based on the amount of resistance.
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No disagreement here either. In your example, mass flow improved due to an increase in volumetric flow through the engine. I'll add to your list of assumptions that you would need adequate room to move to the right on your compressor map, but other than that I agree 100%.
 
Ive 92mm primary and a 71mm secondary. So I could go smaller on secondary for a quicker dyno spool and still be ok? Could I go bigger on the primary?
 
I've seen some drag trucks with a S366 over S595. So to answer your question. I'd say yes lol
 
Ill try a smaller 64 or a 67 compressor on the HX55 maybe throw a billet I've been saving for a rainy day in the HT80.
 
Yeah, right now my turbine,housing,hot piping, ect. need to stay together.
 
At khaos, not much, (630hp) I discovered I'd bought a poor set of used injectors and never checked them. (Dual fed nozzles single bodies, 5x.025VCO)
 
motorwood said:
We use a smallish turbine to spool then gate around it. At what point does a small compressor on the secondary become too much of a restriction?
Click to expand...

What would happen if you ran a 60mm secondary, but cut the compressor cover open to say a 64mm inlet?

It would still compress air wouldn't it. (Off the line bottom end)

And since the primary has to push through the secondary, it would have a bigger port to flow through...increasing power, or not?
 
Extended Power said:
What would happen if you ran a 60mm secondary, but cut the compressor cover open to say a 64mm inlet?

It would still compress air wouldn't it. (Off the line bottom end)

And since the primary has to push through the secondary, it would have a bigger port to flow through...increasing power, or not?
Click to expand...

While it would still compress SOME, it would do an extremely poor job.

The turbo is designed in such that it requires the tight tolerance in the tip to begin compressing the air. Without it you'd have little to no compression before it reached an area of the compressor cover that was still within tolerance.

While not quite the same, picture it like this.

In a perfect world an ETT wheel makes more power than a standard wheel because you have that extra bit of compressor wheel prodruding into the cover. That piece of the wheel is also at a set tolerance in order to cause it to begin compressing the air therefore by the time the air makes it to where it normally would be with a standard compressor it would already be somewhat compressed adding to total volume of air.
 
I pulled it most of last year with the hx55-80 combo. It pulled good for a fairly basic 180 pump and lousy injectors. Im building a pump and bought better injectors and figured id give it a whirl at the local dyno day in march. I was just curious if dowsizing my secondary compressor only, would lay down a better dyno number?
 
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