rear mounted turbo question
Thread Starter
Registered User
Joined: Sep 2006
Posts: 459
rear mounted turbo question
would having lt headers + an ory help or hinder a rear mounted turbo set up. im sort of concerned because with more area for the exhaust gas to flow, that means velocity would go down. unless im completely wrong. also, should i run a rear mounted set up without a cat because it would be obstruct flow?
Registered User
Joined: Sep 2003
Posts: 579
From: Rock Hill, SC
Long tube headers will hurt the performance of a rear mount turbo according to STS. The benefits of long tubes for breathing are lost when you put a big restriction (turbo) after them. Also they have a lot more volume and heat loss potential compared with stock manifolds or a log style header.
Registered User
Joined: Mar 2005
Posts: 676
From: Ft.hood/Ft.worth/Iraq
about the best you can do is wrap the entire exhaust. when i was still messing around with the sts on my car i wraped from the Y pipe back to the turbo and saw a difference in spool time.
for the cat NO DONT RUN ONE it will end up killing it and you also run into the chance of particles coming off the cat and making its way to the exhaust turbine and cause damage to it. if you are worried about emissions and what not just make a delete pipe to replace the cat and when you go in for emissions put the cat on.
for the cat NO DONT RUN ONE it will end up killing it and you also run into the chance of particles coming off the cat and making its way to the exhaust turbine and cause damage to it. if you are worried about emissions and what not just make a delete pipe to replace the cat and when you go in for emissions put the cat on.
Thread Starter
Registered User
Joined: Sep 2006
Posts: 459
Long tube headers will hurt the performance of a rear mount turbo according to STS. The benefits of long tubes for breathing are lost when you put a big restriction (turbo) after them. Also they have a lot more volume and heat loss potential compared with stock manifolds or a log style header.
Registered User
Joined: Feb 2002
Posts: 5,645
From: Bridgewater, MA
Dave is talking about retaining the heat in the exhaust piping befoe the turbo. You seem to be thinking of the charge piping from the turbo to the Throttlebody.
Registered User
Joined: Aug 2007
Posts: 801
From: New York
This is striaght from STS's site:
and
Basically, Headers are a waste of money with an STS, and heat isn't necessary, but it helps.
Do I need to put headers on to optimize the turbo system?
No, the extra expense and work to install aftermarket headers isn't necessary. Headers are designed to eliminate backpressure in the exhaust system and facilitate exhaust scavenging and flow on normally aspirated engines. Turbocharged engines work on slightly different principles. Namely, there is exhaust "Pressure" between the cylinder heads and the turbocharger because the turbocharger is the smallest diameter orifice in the exhaust system. The turbine housing gets smaller in diameter to increase the velocity of the exhaust gasses before they hit the turbine wheel. This is how you get 100,000 rpm wheel speeds.
Turbocharged exhaust gas pressures can see as high as 30+ psi on high boost applications. So spending money on higher flowing exhaust components designed to lower exhaust backpressure is usually a waste of money. This money would be better spent on an upgraded turbocharger which would produce more efficient boost with less backpressure or just spending the money on upgrading the engine and fuel system to handle more boost.
No, the extra expense and work to install aftermarket headers isn't necessary. Headers are designed to eliminate backpressure in the exhaust system and facilitate exhaust scavenging and flow on normally aspirated engines. Turbocharged engines work on slightly different principles. Namely, there is exhaust "Pressure" between the cylinder heads and the turbocharger because the turbocharger is the smallest diameter orifice in the exhaust system. The turbine housing gets smaller in diameter to increase the velocity of the exhaust gasses before they hit the turbine wheel. This is how you get 100,000 rpm wheel speeds.
Turbocharged exhaust gas pressures can see as high as 30+ psi on high boost applications. So spending money on higher flowing exhaust components designed to lower exhaust backpressure is usually a waste of money. This money would be better spent on an upgraded turbocharger which would produce more efficient boost with less backpressure or just spending the money on upgrading the engine and fuel system to handle more boost.
Doesn't heat create the velocity in the exhaust gasses to spool the turbo?
No, heat doesn't create velocity. Heat creates volume. If you look at any of the physics laws for gasses, you will find that pressure and volume and heat are related. PV=NRT is a popular one, The V isn't for velocity, it is for Volume.
The turbine housing is what creates the velocity. The scrolling design that reduces the volume of the exhaust chamber as it scrolls around causes the gasses to have to increase in velocity and pressure to maintain the same flow rate.
Hotter gasses have more volume, thus requiring a higher A/R which in effect means that it starts at say 3" and scrolls down to approximately 1". Lower temperature gasses are denser and have less volume, so they require a lower A/R housing which would start at the same 3" volume, as the turbine housings use standard flanges, and scroll down to say 3/4".
Now if you were to reverse the housings in application, the conventional turbo would spool up extremely quick, at say around 1500 rpm but would cause too much backpressure at higher rpms because the higher volume of gas couldn't squeeze through the 3/4" hole without requiring a lot of pressure to force it through. On the reverse side, the remote mounted turbo with its cooler denser gasses, wouldn't spool up till say around 4000 rpms but once spooled up would make efficient power because it doesn't require hardly any backpressure to push the lower volume of gas through the larger 1" hole.
No, heat doesn't create velocity. Heat creates volume. If you look at any of the physics laws for gasses, you will find that pressure and volume and heat are related. PV=NRT is a popular one, The V isn't for velocity, it is for Volume.
The turbine housing is what creates the velocity. The scrolling design that reduces the volume of the exhaust chamber as it scrolls around causes the gasses to have to increase in velocity and pressure to maintain the same flow rate.
Hotter gasses have more volume, thus requiring a higher A/R which in effect means that it starts at say 3" and scrolls down to approximately 1". Lower temperature gasses are denser and have less volume, so they require a lower A/R housing which would start at the same 3" volume, as the turbine housings use standard flanges, and scroll down to say 3/4".
Now if you were to reverse the housings in application, the conventional turbo would spool up extremely quick, at say around 1500 rpm but would cause too much backpressure at higher rpms because the higher volume of gas couldn't squeeze through the 3/4" hole without requiring a lot of pressure to force it through. On the reverse side, the remote mounted turbo with its cooler denser gasses, wouldn't spool up till say around 4000 rpms but once spooled up would make efficient power because it doesn't require hardly any backpressure to push the lower volume of gas through the larger 1" hole.
Registered User
Joined: Mar 2002
Posts: 2,743
From: Baton Rouge, LA, USA
Heat is absolutely necessary in a turbo setup. Heat drives the turbine. Read any Thermodynamics book. The power produced by a turbine is. . .
Power = Mdot x (enthalpy in - enthalpy out)
Mdot - mass flow rate
enthalpy - is proportional to the temperature of the gas.
10 mile of exhaust pipe leading to the turbine loses alot of the heat, so it loses alot of the very thing that drives the turbine.
I could pick apart that info from STS, but there are so many errors it would take a while.
Either way. . . headers will cause the exhaust to cool and you'll lose power so don't get them.
Mike
Power = Mdot x (enthalpy in - enthalpy out)
Mdot - mass flow rate
enthalpy - is proportional to the temperature of the gas.
10 mile of exhaust pipe leading to the turbine loses alot of the heat, so it loses alot of the very thing that drives the turbine.
I could pick apart that info from STS, but there are so many errors it would take a while.
Either way. . . headers will cause the exhaust to cool and you'll lose power so don't get them.
Mike
Registered User
Joined: Mar 2002
Posts: 2,743
From: Baton Rouge, LA, USA
Heat is energy.
From Engineering Thermodynamics, by Jones and Dugan, "Because of Joule's work, the conclusion that the internal energy of an ideal gas is a function of temperature only is known as Joule's law."
Internal energy change multiplied by mass flow rate is the power produced by a turbine. Likewise, internal energy change multiplied by mass flow rate is the power required to drive a compressor. Note that not all the exhaust gas goes through a turbocharger. This demonstrates that the turbine is capable of producing far more power than the compressor needs. Why? Because the exhaust gas is so much hotter than the incoming air, so there is much more energy available.
Mike
From Engineering Thermodynamics, by Jones and Dugan, "Because of Joule's work, the conclusion that the internal energy of an ideal gas is a function of temperature only is known as Joule's law."
Internal energy change multiplied by mass flow rate is the power produced by a turbine. Likewise, internal energy change multiplied by mass flow rate is the power required to drive a compressor. Note that not all the exhaust gas goes through a turbocharger. This demonstrates that the turbine is capable of producing far more power than the compressor needs. Why? Because the exhaust gas is so much hotter than the incoming air, so there is much more energy available.
Mike
Registered User
Joined: Aug 2007
Posts: 801
From: New York
I guess how I've taken it from everybody these past years, is that when someone says "heat makes a turbo work" I interpret it as "if you take a blow dryer to a Turbo's turbine side, then it'll produce boost." Which is stupid on my part, I know.
But I agree with everything you last posted, heat is definitely an integral part of producing an efficient Turbo setup. I just wish people would say that heat expands the air, creating a larger volume of air, and thus the air holds more energy when it hits the turbine. So the heat works through the air to power a turbine, not directly on a turbine....
picky, I know, and I'm sorry
But I agree with everything you last posted, heat is definitely an integral part of producing an efficient Turbo setup. I just wish people would say that heat expands the air, creating a larger volume of air, and thus the air holds more energy when it hits the turbine. So the heat works through the air to power a turbine, not directly on a turbine....
picky, I know, and I'm sorry
Registered User
Joined: Mar 2002
Posts: 2,743
From: Baton Rouge, LA, USA
The point of all combustion driven devices (steam turbine, gas turbine, recip engine, etc. . .) is to convert heat into shaft power. When you burn fuel, it creates heat. We just want to convert that heat into power. It's actually best if you think of it this way.
The exhaust gas goes into the turbocharger at 1700 deg F. It leaves the turbocharger at 1200 deg F. So, this 500 deg F temperature drop is where you got your power from. In order to drop the temp from 1700 to 1200, you would need a pressure ratio through the turbine of about 2.5/1. Being that the downstream pressure should be near atmospheric, the upstream pressure would need to be about 22 psig. This is the pressure the pistons need to work against on the exhaust stroke, so the lower the better.
Now, say your exhaust gas is only 800 deg F because it was cooled excessively on the way to the turbine. In order to extract the same amount of energy as we did going from 1700 to 1200 at the same flow rate, we would need to drop the exit temperature down to about 250 deg F. In order to accomplish this, the pressure ratio would have to be about 7.5/1, which would result in an upstream pressure of 95 psig (!!!). You can offset temperature drop by increasing mass flow rate to some extent, but that requires larger turbines and thus, have even slower response times.
Notice on all the latest OEM turbo apps, the turbocharger is placed very close to the cylinder head and the manifold is cast iron. This retains a very high amount of the heat in the gas and the result is lightning quick spool and relatively high system efficiency (though they do sacrifice efficiency for spool time, which increases exhaust pressure). Have you driven a VW GTi, Lancer EVO, or SRT-4 lately?
Mike
The exhaust gas goes into the turbocharger at 1700 deg F. It leaves the turbocharger at 1200 deg F. So, this 500 deg F temperature drop is where you got your power from. In order to drop the temp from 1700 to 1200, you would need a pressure ratio through the turbine of about 2.5/1. Being that the downstream pressure should be near atmospheric, the upstream pressure would need to be about 22 psig. This is the pressure the pistons need to work against on the exhaust stroke, so the lower the better.
Now, say your exhaust gas is only 800 deg F because it was cooled excessively on the way to the turbine. In order to extract the same amount of energy as we did going from 1700 to 1200 at the same flow rate, we would need to drop the exit temperature down to about 250 deg F. In order to accomplish this, the pressure ratio would have to be about 7.5/1, which would result in an upstream pressure of 95 psig (!!!). You can offset temperature drop by increasing mass flow rate to some extent, but that requires larger turbines and thus, have even slower response times.
Notice on all the latest OEM turbo apps, the turbocharger is placed very close to the cylinder head and the manifold is cast iron. This retains a very high amount of the heat in the gas and the result is lightning quick spool and relatively high system efficiency (though they do sacrifice efficiency for spool time, which increases exhaust pressure). Have you driven a VW GTi, Lancer EVO, or SRT-4 lately?
Mike
Registered User
Joined: Apr 2003
Posts: 1,056
From: Marietta, GA
Let me interject here, only to clarify what Mike is saying..
If i am not mistaken, Joule's law is specific to ideal gases. Although in this case Mike is just illustrating how heat engergy can be converted to work.
In our case (turbochargers); exhaust gas cannot be treated as an ideal gas. which is why Mike said this,
"Internal energy change multiplied by mass flow rate is the power produced by a turbine" while the power he is refering to is the work done on the turbochargers shaft, and neglecting heat transfer to the surroundings.
If i am not mistaken, Joule's law is specific to ideal gases. Although in this case Mike is just illustrating how heat engergy can be converted to work.
In our case (turbochargers); exhaust gas cannot be treated as an ideal gas. which is why Mike said this,
"Internal energy change multiplied by mass flow rate is the power produced by a turbine" while the power he is refering to is the work done on the turbochargers shaft, and neglecting heat transfer to the surroundings.
Registered User
Joined: Mar 2002
Posts: 2,743
From: Baton Rouge, LA, USA
3 cars to compare. . .
My old T-trim Vortech at 13 psi ran 133 mph in the quarter at full weight. (~680 hp)
An e-friend of mine has an LS1 car with a remote-mounted T76 R-trim. With the turbo totally maxed out, he's making 15 psi and pulling 134 in the quarter in Las Vegas at full weight. (~700 hp)
My current setup is a front-mount T76GTS. With the wastegate wide open (lowest boost I can possibly run with a 40 mm WG), I'm making 17 psi and pulling 146 mph in the quarter at full weight. (~900 hp)
Mike
Registered User
Joined: Feb 2002
Posts: 5,645
From: Bridgewater, MA
Well you just said it. Heat drives the turbo (making it simple here)... the heat needs to reach the turbine. When exhaust travels a long distance, you have convection happening (heat transfer between the gas and the metal exhaust piping). The piping absorbs some of the heat loss, therfore a drop in overall exhaust temps by the time it reached the turbine. Cast manifolds are thick, and retain heat. Wrapping exhaust helps retain heat.
Last edited by RealQuick; Nov 10, 2007 at 11:12 PM.
Thread
Thread Starter
Forum
Replies
Last Post
Patricklt1
Show and Shine / Paint and Body Care
4
Apr 24, 2015 06:29 AM
95z_28_camaro_4_Ivan
General 1967-2002 F-Body Tech
2
Dec 19, 2014 08:48 PM