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Old 09-29-2012, 10:30 PM   #76
Korvint
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Yah i get the flow but i still don't get why that is. If you have a 2.5 L engine theres only so much vol you can push into the cylinders during a revolution at whatever comparable RPM you are using. Pressure, vol and temp are all related to each other. Of course both the small and bigger turbo have to be running in their efficient ranges to be comparable. 2.5L is all you get and if you are at 20 PSI at lets say 103F in the intake manifold then the vol you are pushing is the same. more flow from the bigger turbo is not making the engine faster in order to use the addition flow. The only thing i can think of is the smaller turbo can't keep the 20 psi throughout the rpm range and looses its efficiency and tapers off when a larger turbo keeps 20 psi throughout till 7000 rpm.
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Old 09-29-2012, 10:48 PM   #77
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You won't be pushing the same. That's where VE comes in, and PR of a turbo plays into that.
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Old 09-30-2012, 05:18 AM   #78
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WOW.

Almost everyone in this thread is seriously misunderstanding why big turbos make more power.

Someone posted in this thread that a fire hydrant flows more water then a garden hose would at the same pressure. This is true and it would be a great way to describe why a 2.5L engine makes less power at 20 psi than a 7L engine at 20psi.
The fire hydrant flows more water because the nozzle is bigger. If a fire hydrant and a garden hose had the same size nozzle, at the same pressure, they would flow the EXACT same amount. Just imagine the nozzle is the engine and the water source is the turbo.

So yes a bigger turbo can flow more then a smaller turbo at the same psi. But this is what everyone is misunderstanding. The turbo CAN flow more, but the engine is what limits the flow. 20psi in the manifold, is 20 psi in the manifold. (Before you get mad, keep reading) It doesn't matter if you have the biggest turbo in the world, or a pea shooter, it's still 20 psi. And without modifying the engine, 20psi is going to flow the same amount regardless of the turbo.

I purposely left out one factor, temperature. Bigger turbos make less heat. That 20psi in the manifold makes more power with the bigger turbo because the air is cooler and more dense.
So yes, I guess everyone is right when they say the bigger turbo flows more at the same psi. But it flows more because the air is colder, not because its bigger.

I only explained all that because there is a lot of misinformation in this thread.

The short answer that everyone should have given the op is:

A bigger turbo makes more power at the same psi, on the same motor because it produces less heat, so the air is more dense.
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Old 09-30-2012, 07:39 AM   #79
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Jim2752, heat isnt the only factor, I assure you that
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Old 09-30-2012, 08:52 AM   #80
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WOW.

Almost everyone in this thread is seriously misunderstanding why big turbos make more power.


yeah....YOU included
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Old 09-30-2012, 09:10 AM   #81
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Uncle Scotty!! I'm so happy to see you back! I knew you couldn't stay away for long:laughing:
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Old 09-30-2012, 09:45 AM   #82
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Quote:
Originally Posted by BlazeRex
Jim2752, heat isnt the only factor, I assure you that
When comparing different turbos there are a million different factors and its not as simple as "big turbos produce less heat" But the op asked a very simple question. So if there are any factors related to the op's question that I didn't include, then correct me.
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Old 09-30-2012, 11:31 AM   #83
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Quote:
Originally Posted by Jim2752 View Post
When comparing different turbos there are a million different factors and its not as simple as "big turbos produce less heat" But the op asked a very simple question. So if there are any factors related to the op's question that I didn't include, then correct me.
Just because the MAP sensor is reading the same PSI going through the manifold doesn't mean the volume is the same. Also,

if you're maintaining a certain pressure in the intake then both turbos are putting out enough air. temperature is a variable. Temperature effects volume. 20psi at 150deg is less volume of air than 8psi at 100deg. The turbo with the lowest air temp will make more power assuming the exhaust sides are the same.

The exhaust side makes a big difference in power as well. Lower exhaust backpressure increases volumetric efficiency, and can make more power with allowing more cam overlap.
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Old 09-30-2012, 02:51 PM   #84
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I haven't seen drive pressure mentioned.. take a dip into the diesel world and it would have been mentioned 8 times already.

OP, read: http://www.rx7club.com/single-turbo-...estion-637225/
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Old 09-30-2012, 04:07 PM   #85
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Ok here's how it works after thinking about it. Let's say the smaller turbo flow is 40 lbs/ min and the larger turbo is 50 lbs/min. Peak HP is measured usually near peak RPM so around 6000 rpm. A small turbo can't hold 20psi at 6000 rpm because the flow of 40lbs per min is not enough for 6000 revolutions per min when it may need 50 lbs to keep 20 psi. So comparing max HP of the smaller turbo at 6000 rpm it's actually at 15 psi and you get 300 whp. And the larger turbo which flows enough at 6000 rpm to maintain 20 psi gets peak HP of let's say 350-400 whp. I agree with the above that the larger turbo also runs cooler more dense air at comparable psi which increases HP.

/thread
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Old 09-30-2012, 04:10 PM   #86
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Quote:
Originally Posted by cdoliver View Post
Just because the MAP sensor is reading the same PSI going through the manifold doesn't mean the volume is the same. Also,

if you're maintaining a certain pressure in the intake then both turbos are putting out enough air. temperature is a variable. Temperature effects volume. 20psi at 150deg is less volume of air than 8psi at 100deg. The turbo with the lowest air temp will make more power assuming the exhaust sides are the same.

The exhaust side makes a big difference in power as well. Lower exhaust backpressure increases volumetric efficiency, and can make more power with allowing more cam overlap.
I agree with you 100% and that's what I was trying to explain, although I forgot to mention the exhaust part...
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Old 09-30-2012, 04:11 PM   #87
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If both turbos are running 20 psi at 4000 rpm with other stuff stock the wHP will be similar but the larger turbo will have the advantage with less heat and more dense air.
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Old 09-30-2012, 04:42 PM   #88
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And more efficiency so less back pressure on the exhaust.
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Old 09-30-2012, 06:16 PM   #89
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Less timing and same boost can make more or equal power too which is nice
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Old 09-30-2012, 06:44 PM   #90
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Quote:
Originally Posted by Korvint View Post
If both turbos are running 20 psi at 4000 rpm with other stuff stock the wHP will be similar but the larger turbo will have the advantage with less heat and more dense air.
Maybe...heat shielding will come into play. And we haven't even touched turbo spool.
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Old 09-30-2012, 06:59 PM   #91
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Uncle Scotty!! I'm so happy to see you back! I knew you couldn't stay away for long:laughing:
d000000000000000000d

post LESS

read more

and you will be far better off
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Old 09-30-2012, 07:21 PM   #92
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Quote:
Originally Posted by cdoliver View Post
The exhaust side makes a big difference in power as well. Lower exhaust backpressure increases volumetric efficiency, and can make more power with allowing more cam overlap.
Quote:
Originally Posted by Slimsti View Post
Less timing and same boost can make more or equal power too which is nice
Yes, Both are a result of the lower PR at the same PSI and higher VE like I was talking about earlier.
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Old 10-01-2012, 01:59 AM   #93
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Quote:
Originally Posted by Korvint View Post
Ok here's how it works after thinking about it. Let's say the smaller turbo flow is 40 lbs/ min and the larger turbo is 50 lbs/min. Peak HP is measured usually near peak RPM so around 6000 rpm. A small turbo can't hold 20psi at 6000 rpm because the flow of 40lbs per min is not enough for 6000 revolutions per min when it may need 50 lbs to keep 20 psi. So comparing max HP of the smaller turbo at 6000 rpm it's actually at 15 psi and you get 300 whp. And the larger turbo which flows enough at 6000 rpm to maintain 20 psi gets peak HP of let's say 350-400 whp. I agree with the above that the larger turbo also runs cooler more dense air at comparable psi which increases HP.

/thread
My 16g (35lb/min) held 20psi at redline (and it could hold more). My 68hta held 28psi at redline. You can absolutely hold high boost at redline with small turbos. Of course it's usually not beneficial because the turbos are not efficient at that point. Check compressor maps.
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Old 10-05-2012, 01:04 AM   #94
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Originally Posted by dgm_wrx

F*** me? Sorry sweetie I don't swing that way but if I did I would request that I could call you Daddy Scotty:happy:
More like grandpa scotty, B****ing and complaining like an old man.
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Old 10-05-2012, 08:22 AM   #95
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More like grandpa scotty, B****ing and complaining like an old man.


sick of stupid puppies like YOU and that other idioit posting stupid **** out yer asses here


w t f ???
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Old 10-05-2012, 02:53 PM   #96
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More like grandpa scotty, B****ing and complaining like an old man.
Dude you are a loser boo hoo cry your self to sleep your one of those retards that asks stupid questions that if you typed into Google like you do when you jerk off you jerk off and how old are you cause If I was as stupid as you at your age id just give up on life. Oh yeah. Take or deep buddy and don't say you don't swing that way cause you do ******

End rant. Sorry lol
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Old 10-05-2012, 03:21 PM   #97
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yi342534
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Old 10-05-2012, 03:22 PM   #98
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It's like when I'm eating pizza. I put two slices on top of each other (cheeze on cheeze), and I can literally eat double the amount of total slices.

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Old 10-05-2012, 03:33 PM   #99
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Quote:
Originally Posted by cdoliver View Post
Just because the MAP sensor is reading the same PSI going through the manifold doesn't mean the volume is the same. Also,

if you're maintaining a certain pressure in the intake then both turbos are putting out enough air. temperature is a variable. Temperature effects volume. 20psi at 150deg is less volume of air than 8psi at 100deg. The turbo with the lowest air temp will make more power assuming the exhaust sides are the same.

The exhaust side makes a big difference in power as well. Lower exhaust backpressure increases volumetric efficiency, and can make more power with allowing more cam overlap.
I think you're confusing volume and mass there. The volume is determined by the size of the intake manifold. It doesn't change based on the pressure of the air that's flowing through it.

Temperature affects either volume or pressure or sometimes both. If the container can expand, like a balloon, then when you increase the temperature, the volume is going to change. But if it's a rigid container, like an intake manifold, then the only thing that's going to change when you increase the temperature is the pressure.

That's also why running a turbo way outside its efficiency range doesn't make a lot of power. The pressure is still there because the temperature is very high, but there isn't anywhere near as much mass of air molecules to burn as there would be in a cooler intake charge.
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