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Why bigger turbos make more power than stock turbos at same PSI

Started by EcoPowerParts, November 05, 2013, 09:02:36 AM

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EcoPowerParts

I'm using someone else's post referring to a stock turbo vs a GT35r but the technical basis is the same:
Taken from http://www.e90post.com/forums/showthread.php?t=401958


The debate regarding this topic has come up over and over again in various forums, but I have yet to see a satisfactory explanation other than "big turbo flows more air at given psi". So I am going to attempt to explain this phenomenon while trying to include real world variables such as turbine backpressure, CFM, compressor efficiency, etc.

Now I am not an engineer with a degree in thermodynamics or mechanical theory, so while I believe my rationale is close to the truth, I don't believe it to be the absolute truth. So feel free to correct me or add as you wish.

For simplicity sake, let's say we have an n55 engine, GT35r and n55 stock single turbo in this comparison. As everyone knows, turbo has two main components: compressor and turbine. Let's break it down into components and evaluate it separately.

Compressor:
The GT35r compressor is larger than n55 stock turbo's. This means GT35r's compressor has greater surface area. Let's assume that two compressors are rotating at identical speed, let's say 25,000 rotations per minute. The compressor with larger surface area will obviously move higher volume of air than the smaller compressor. Also, while doing this, the work done by the larger compressor is translated into heat in lesser degree than the smaller compressor, thus giving it higher efficiency.

CFM: (cubic feet per minute)
It's a non-SI unit that measures the volume of gas that passes a given point in one minute. We have established that GT35r's compressor moves higher volume of air. We also know that this air has to pass through the intake manifold that's fixed in volume. Since the higher volume of air has to pass through the fixed space (intake manifold) in one minute, the velocity of the air is higher compared to air generated by the stock turbo which has lower CFM, thus lower velocity.

PSI: (pounds of pressure per square inch)
Pressure is measured at intake manifold. This pressure is generated by air molecules moving rapidly and hitting the inner surface of the intake manifold.
This kinetic energy of the air molecules are proportional to the temperature.
In other words, higher temperature will allow air molecules move at faster speed and create higher pressure.
Real world example of this is a can of butane gas. When you heat this up what happens? The pressure inside the can increases due to higher kinetic energy and the can blows!! But if you were to blow the can just by shoving in more butane at room temperature, you will have to put in ALOT more butane to do that.
We have established that stock turbo compressor blows hotter air compared to GT35r compressor. The hotter air has higher kinetic energy. So it's relatively easier for stock turbo compressor to generate 10psi of pressure because they are moving around so fast bouncing off of the surface of the intake manifold. The GT35r compressor, on the other hand, blows cooler air. So it requires more air to generate the same 10psi of pressure.
Since we know that density = # of moles of substance/volume, we know that the air from the GT35r compressor has higher density.

Turbine back pressure:
The turbine wheel is in the right smack in the middle of the exhaust flow, creating resistance. When the piston engines completes it's combustion cycle, it has to let out exhaust gases. Since the smaller turbine creates more resistance or back pressure, the motor cannot effectively expel all of the exhaust gases it produced. Large turbine wheel of GT35r reduces the resistance (back pressure), enabling more exhaust gases to be expelled at the end of the combustion cycle.

So let's put it all together.
What happens when the intake port opens? :
So let's assume that we have an n55 engine that's operating at 4000rpm.
The intake port of the n55 engine with stock turbo and n55 engine with GT35r are opened for same period of time. Intake manifold pressure for both reads 10psi. Few things happen in the car with a GT35r:
1. The air from GT35r moves at higher velocity into the cylinder due to higher CFM, so more air can go in before the valve closes.
2. Not only more air has entered the cylinder, the air from GT35r is denser because of higher efficiency of the compressor.
3. There is less exhaust gas remaining in the cylinder due to reduced exhaust back pressure. This allows more fresh air to enter the cylinder.


So, during the short period the intake valve is opened, air from the GT35r goes into the cylinder FASTER, and MORE air (oxygen) is available for combustion because the air is denser and there is more room for refresh air.

This is why a larger turbo makes more hp at given psi than a smaller turbo.
Now, go and upgrade..
Mike B | info@ecopowerparts.com
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bigmoneycloser

Ok...
So here is my question... ( I have no mechanical experience)
Can you use these turbos on a XSport? And do you have to upgrade anything else in order to do this?
What is the HP/TQ gain with this upgrade? Are there any potential down sides to this for a non track daily driver?

I guess I should say "questions"...
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EcoPowerParts

Quote from: bigmoneycloser on November 05, 2013, 09:44:27 AM
Ok...
So here is my question... ( I have no mechanical experience)
Can you use these turbos on a XSport? And do you have to upgrade anything else in order to do this?
What is the HP/TQ gain with this upgrade? Are there any potential down sides to this for a non track daily driver?

I guess I should say "questions"...
Yes, these turbos will fit any of the transverse vehicles (all stock turbos are same part #).
Mike - BPD is supplementing his stock fuel system with meth, I don't know how the car will do on just a stock fuel system on the low boost setting yet. Somebody will have to blaze that trail for us. The ATP turbos will definitely make great HP in their lowest best setting, we just need more people with them on their cars for feedback. I don't see any reason why you would have any issues on your Xsport with these turbos.
Mike B | info@ecopowerparts.com
www.ecopowerparts.com -
please use my website for any price quotes and to submit any orders.
Please email me via info@ecopowerparts.com if you have any questions on new or existing orders, PM's via the forum are hard to track your purchase as I can't relate user name to actual name.
https://www.facebook.com/ecopowerparts

bigmoneycloser


Quote from: 4DRHTRD on November 05, 2013, 09:56:44 AM
Quote from: bigmoneycloser on November 05, 2013, 09:44:27 AM
Ok...
So here is my question... ( I have no mechanical experience)
Can you use these turbos on a XSport? And do you have to upgrade anything else in order to do this?
What is the HP/TQ gain with this upgrade? Are there any potential down sides to this for a non track daily driver?

I guess I should say "questions"...
Yes, these turbos will fit any of the transverse vehicles (all stock turbos are same part #).
Mike - BPD is supplementing his stock fuel system with meth, I don't know how the car will do on just a stock fuel system on the low boost setting yet. Somebody will have to blaze that trail for us. The ATP turbos will definitely make great HP in their lowest best setting, we just need more people with them on their cars for feedback. I don't see any reason why you would have any issues on your Xsport with these turbos.


Th fuel system is a problem for me, because there aren't many if any(except at track) places to get anything other than standard 93 octane here in NJ...


2014 Explorer Sport 401A
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Pirelli Scorpion Zero Asimmetrico 285/35/22
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EcoPowerParts

93 Octane should be fine, it would be great if we could get BPD to get LMS to do a 93 octane tune/dyno and 93 octane + meth tune/dyno to see where it's at. Hopefully they can also do a boost plot with AFR on their dyno to see the boost curve.
Mike B | info@ecopowerparts.com
www.ecopowerparts.com -
please use my website for any price quotes and to submit any orders.
Please email me via info@ecopowerparts.com if you have any questions on new or existing orders, PM's via the forum are hard to track your purchase as I can't relate user name to actual name.
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bigmoneycloser


Quote from: 4DRHTRD on November 05, 2013, 10:02:33 AM
93 Octane should be fine, it would be great if we could get BPD to get LMS to do a 93 octane tune/dyno and 93 octane + meth tune/dyno to see where it's at. Hopefully they can also do a boost plot with AFR on their dyno to see the boost curve.
Lol
That statement is way above my Pay grade... Lol
I'm guessing LMS would write me updated tunes if I did the turbos without the fuel system.
But would I need or be in my best interest to have it dyno'd somewhere?
Not sure who in NJ I could trust to do that since LMS is where everything I have has come from and I have no idea anyone with an AWD dyno here?
2014 Explorer Sport 401A
22x10.5 Vossen CVT- powder coated Matte Graphite
Pirelli Scorpion Zero Asimmetrico 285/35/22
H & R lowering springs/LMS 93 high boost/AirAid CAI/170* thermostat/3 Bar Map Sensor/Full LED interior /HID head and fog lights/weather tech digital floor mats/SharkFin antena/custom Billet foot pedals/Wilwood big brake kit/ LMS-Corsa CatBack Exhaust/LMS Catted Downpipes

EcoPowerParts

Mike - BPD has the ATP turbos on his SHO, he's going to go see LMS to get a dyno tune soon. That will tell us how much HP the turbos make on stock fuel + meth, I'm also hoping he'll convince them to do a dyno without meth to see what the car does and if it behaves without meth.
Mike B | info@ecopowerparts.com
www.ecopowerparts.com -
please use my website for any price quotes and to submit any orders.
Please email me via info@ecopowerparts.com if you have any questions on new or existing orders, PM's via the forum are hard to track your purchase as I can't relate user name to actual name.
https://www.facebook.com/ecopowerparts

bigmoneycloser

That would be great to see without meth....
A possible good outcome would be all I need to pull the trigger!
2014 Explorer Sport 401A
22x10.5 Vossen CVT- powder coated Matte Graphite
Pirelli Scorpion Zero Asimmetrico 285/35/22
H & R lowering springs/LMS 93 high boost/AirAid CAI/170* thermostat/3 Bar Map Sensor/Full LED interior /HID head and fog lights/weather tech digital floor mats/SharkFin antena/custom Billet foot pedals/Wilwood big brake kit/ LMS-Corsa CatBack Exhaust/LMS Catted Downpipes

EcoBrick Bob

Me thinks this thread is all my fault....  Thanks Mike for posting.

Another point needing to be made is that our stock turbos are VERY SMALL.  That's why these ATP turbos will work and generate more potential CFM due to lower air temps.  However, bigger might not be better if one already had plenty of turbo volume, ie. a single larger turbo. The latter is definitely more efficient, but creates lots of turbo lag. 

So our stock very small turbos get peaky when pushed over 15 psi.  ATP turbos provide steady air, up to and above the volume our engine can use with current Fuel system, without much more turbo lag. Probably the most important issue is that they also include better bearings and heavier duty parts per Mike's comments to me. And they won't work as hard as the stock ones, so should handle the abuse some of us are known to create, much better than the stock turbos. 

The biggest unknown at this time is how much boost & CFM our stock fuel system can handle, with or without Methanol spray.  If you guess wrong... Ford is not your friend....
2010 Red Candy/White EB Flex.. World's first 12 second Brick.. 12.904 @ 106.85 MPH - October 2011
2009 Spt. Red G8 GT - modded. best time 12.074 & 114.02 MPH
2008 White G8 GT - mods... 8.32 1/8 mi.

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Bob has decided not to post here any more, please do not PM him he will not receive it.

Shifrty1

I know that many that have had twin turbo cars. I.E. the mark iv supras and the 300 zx cars have swapped the twins for a single, larger tubo, as the single offered up more horsepower than a twin upgrade.  have you guys put any thoughts to that?
Sorry Officer, thought that sign was merely a suggestion for old folks...  My bad...

2013 SHO  Livernois Tune, AIRRAID CAI traded but always in my heart
2008 Shelby GT500

SRT82ECOBOOST

I think that some of the F-150 owners are going to the single larger turbo since there is room in the engine bay to do so.
2013 SHO PP in White Platinum Metallic Tricoat, PPE Downpipes, Livernois Stage V8/3 Bar, Custom 2.5" Catback, 170 T-stat, Airaid CAI, H+R Springs and debadged
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EcoPowerParts

Quote from: SRT82ECOBOOST on November 05, 2013, 01:43:51 PM
I think that some of the F-150 owners are going to the single larger turbo since there is room in the engine bay to do so.
Nobody has done that yet, Full-Race has a prototype on their truck but nothing in production so far, they also have a big twin setup they have made manifolds for. ATP will be the first released to public turbo that I know of, should be finalized by end of the month, I've been saying that according to info from them for 2 months though :)
Mike B | info@ecopowerparts.com
www.ecopowerparts.com -
please use my website for any price quotes and to submit any orders.
Please email me via info@ecopowerparts.com if you have any questions on new or existing orders, PM's via the forum are hard to track your purchase as I can't relate user name to actual name.
https://www.facebook.com/ecopowerparts

bigmoneycloser

I need a conference call about alternate fuel and fuel delivery...(meth and E)
I just found out that the local ford dealer that has a big mustang Motorsports dept. stocks all that fuel all summer long, but nothing in winter. 
I don't understand how people are using the meth or ethanol, so I don't know how it benefits me.
Would love more power to tool around with, but I'm not racing or going to the track, so not sure if that is just waste of money??
2014 Explorer Sport 401A
22x10.5 Vossen CVT- powder coated Matte Graphite
Pirelli Scorpion Zero Asimmetrico 285/35/22
H & R lowering springs/LMS 93 high boost/AirAid CAI/170* thermostat/3 Bar Map Sensor/Full LED interior /HID head and fog lights/weather tech digital floor mats/SharkFin antena/custom Billet foot pedals/Wilwood big brake kit/ LMS-Corsa CatBack Exhaust/LMS Catted Downpipes

EcoPowerParts

Quote from: bigmoneycloser on November 05, 2013, 02:37:24 PM
I need a conference call about alternate fuel and fuel delivery...(meth and E)
I just found out that the local ford dealer that has a big mustang Motorsports dept. stocks all that fuel all summer long, but nothing in winter. 
I don't understand how people are using the meth or ethanol, so I don't know how it benefits me.
Would love more power to tool around with, but I'm not racing or going to the track, so not sure if that is just waste of money??
There's topics elsewhere on the forum that discuss E85 and methanol which are not the same thing and there's boards specific to those topics.
Not really a discussion point for bigger turbos though and why they make more power at the same PSI
Mike B | info@ecopowerparts.com
www.ecopowerparts.com -
please use my website for any price quotes and to submit any orders.
Please email me via info@ecopowerparts.com if you have any questions on new or existing orders, PM's via the forum are hard to track your purchase as I can't relate user name to actual name.
https://www.facebook.com/ecopowerparts

crash712us

The problem with a single large turbo is lag. Our cars are hitting peak torque just above 2000rpm's. With one single large turbo you wouldn't see power til 4000 rpm's.

2011 tuxedo black non pp, LMS stage 5, Corsa cat back, LMS down pipes, Airaid, Alky control meth injection, Megan Racing coil overs, EBC rotor&pads, Mobsteel grill, 2013 trans cooler. 403whp 417wtq 12.25 @ 110