Full Race Turbo Kit Update PICS
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Joined: Jul 2005
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From: Gie
After thinking about this for a while I'm not sure it is going to matter much whether you coat the downpipe or not. It would help, but probably not much. My reasoning:
First off, take a look at this turbine map. Note the relationship between mass flow rate and pressure ratio. Pressure ratio refers to the absolute pressure upstream of the turbine divided by the absolute pressure downstream of the turbine. A safe assumption (for this discussion) is that the turbine rotational velocity is directly related to mass flow rate. So as mass flow rate goes up, so does the turbine speed.
If the air downstream of the turbine is allowed cool down excessively, the velocity decreases and the static pressure increases. This leads to a lower pressure ratio as the absolute pressure downstream ends up getting larger. A lower pressure ratio results in a lower mass flow rate, hindering turbine speed.
Honestly, I only think this has an effect in the spool up period. Once the turbine is spooled and the wastegate is in full operation, none of this coating talk matters anymore. Any additional flow rate is going to go out the wastegate, and any cooling effect downstream will no longer lower the mass flow rate (and therefore turbine speed).
And...I'm not sure if that makes any sense at all. I'm rambling at this point but here is my opinion:
Coating a downpipe (and all exhaust bits for that matter) always has a positive effect for a few reasons. It helps keep the energy in the gas, which allows the gas to travel as quickly as possible with the least pressure loss. More importantly, it limits the chances that you will burn the crap out of your engine bay.
First off, take a look at this turbine map. Note the relationship between mass flow rate and pressure ratio. Pressure ratio refers to the absolute pressure upstream of the turbine divided by the absolute pressure downstream of the turbine. A safe assumption (for this discussion) is that the turbine rotational velocity is directly related to mass flow rate. So as mass flow rate goes up, so does the turbine speed.
If the air downstream of the turbine is allowed cool down excessively, the velocity decreases and the static pressure increases. This leads to a lower pressure ratio as the absolute pressure downstream ends up getting larger. A lower pressure ratio results in a lower mass flow rate, hindering turbine speed.
Honestly, I only think this has an effect in the spool up period. Once the turbine is spooled and the wastegate is in full operation, none of this coating talk matters anymore. Any additional flow rate is going to go out the wastegate, and any cooling effect downstream will no longer lower the mass flow rate (and therefore turbine speed).
And...I'm not sure if that makes any sense at all. I'm rambling at this point but here is my opinion:
Coating a downpipe (and all exhaust bits for that matter) always has a positive effect for a few reasons. It helps keep the energy in the gas, which allows the gas to travel as quickly as possible with the least pressure loss. More importantly, it limits the chances that you will burn the crap out of your engine bay.
Joined: Mar 2005
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From: V I C E C I T Y
Originally Posted by foxer10,Feb 11 2007, 04:01 PM
Here is an update from my last post here LINK
Didnt have time to start the project but finally getting some time this month. Got the motor/tranny out and got the 2mm cometic, ARP studs on. Mounted the manifold, turbo, w/g and part of the downpipe. Next step is to plumb the whole setup and it should be ready to go back on the subframe and into the car.
Didnt have time to start the project but finally getting some time this month. Got the motor/tranny out and got the 2mm cometic, ARP studs on. Mounted the manifold, turbo, w/g and part of the downpipe. Next step is to plumb the whole setup and it should be ready to go back on the subframe and into the car.
I gotta swing by one of these days so i can check it out in person 
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Joined: Aug 2003
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From: The Beach, CA
Actually that's just basically thinking you were right 
The pressure ratio being lowered is just assuming that a cooler post turbine is going to hinder flow and that's by just going by the one notion that the density of the gas will increase to a point where it will just negate any other factors there is there.
The high energy gases will still hit the wall and impart more force against the wall of the piping which is what pressure is. Lowering the energy levels of the gases will lower the pressure and though it will be more dense, the overall pressure should reduce.
Bernoulli's equation states that static pressure + .5 (density of gas) V^2 = Pressure
Just from that formula, lowering the velocity has a much greater effect than density does. However that's only for incompressible masses and it gets complicated because there is heat transfer and thermodynamics comes into play.
The pressure ratio being lowered is just assuming that a cooler post turbine is going to hinder flow and that's by just going by the one notion that the density of the gas will increase to a point where it will just negate any other factors there is there. The high energy gases will still hit the wall and impart more force against the wall of the piping which is what pressure is. Lowering the energy levels of the gases will lower the pressure and though it will be more dense, the overall pressure should reduce.
Bernoulli's equation states that static pressure + .5 (density of gas) V^2 = Pressure
Just from that formula, lowering the velocity has a much greater effect than density does. However that's only for incompressible masses and it gets complicated because there is heat transfer and thermodynamics comes into play.
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Joined: Jul 2005
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From: Gie
Originally Posted by kane.s2k,Feb 14 2007, 03:35 PM
Actually that's just basically thinking you were right The pressure ratio being lowered is just assuming that a cooler post turbine is going to hinder flow and that's by just going by the one notion that the density of the gas will increase to a point where it will just negate any other factors there is there.
The high energy gases will still hit the wall and impart more force against the wall of the piping which is what pressure is. Lowering the energy levels of the gases will lower the pressure and though it will be more dense, the overall pressure should reduce.
Bernoulli's equation states that static pressure + .5 (density of gas) V^2 = Pressure
Just from that formula, lowering the velocity has a much greater effect than density does. However that's only for incompressible masses and it gets complicated because there is heat transfer and thermodynamics comes into play.
The pressure ratio being lowered is just assuming that a cooler post turbine is going to hinder flow and that's by just going by the one notion that the density of the gas will increase to a point where it will just negate any other factors there is there. The high energy gases will still hit the wall and impart more force against the wall of the piping which is what pressure is. Lowering the energy levels of the gases will lower the pressure and though it will be more dense, the overall pressure should reduce.
Bernoulli's equation states that static pressure + .5 (density of gas) V^2 = Pressure
Just from that formula, lowering the velocity has a much greater effect than density does. However that's only for incompressible masses and it gets complicated because there is heat transfer and thermodynamics comes into play.
I believe the pressure ratios from the charts are measure of absolute static pressure up and downstream of the turbine, not dynamic (1/2*ro*v^2), or total pressure (Pstatic + Pdynamic).
I'm definitely curious about this stuff. The crazy part is that I work on stuff like this all the time and I still don't have a 100% understanding of how everything works. Haha...and I've found that neither do many of the engineers at big companies like Borg Warner...
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From: Miami FL
Here are some updated pics a little after getting the motor back into the chassis. There are going to be a bit of modification and/or fabrication to get things going. The kit includes relocation brackets for the fuse box, p/s box, and heater valve. All heater hoses have to be rerouted as it is close and one hose touches the manifold. This is not a friendly kit to install. This is not to discourage anyone, just get an experienced shop to install this if you plan to get one. It will be worth it at the end. At this point, its going to be about plumbing all pipes, lines, oil filter relocator, oil cooler, EMS components and trying to keep everything as clean as possible.
- Test fitting the intercooler. Installed on the front horns (not the rebar) so we should be able to trim the grill and retain it to keep a nice clean OEM look and not overexpose the intercooler.
- A/C lines moved to the left away from manifold. Used DEI heat screen and cool tape to wrap it up. Heater hoses and all s/s braided lines will use DEI fire sleeves.
- Intercooler pipe goes between cross beam and steering rack. Its a tight fit but
- Test fitting the intercooler. Installed on the front horns (not the rebar) so we should be able to trim the grill and retain it to keep a nice clean OEM look and not overexpose the intercooler.
- A/C lines moved to the left away from manifold. Used DEI heat screen and cool tape to wrap it up. Heater hoses and all s/s braided lines will use DEI fire sleeves.
- Intercooler pipe goes between cross beam and steering rack. Its a tight fit but