Stock Turbo + External Wastegate
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Joined: Jul 2009
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From: SFL
Stock Turbo + External Wastegate
Hey guys, I was wondering what you guys thought about this setup.. To my knowledge and previous searches no one has done it yet.
I'm planning on running an ATP diverted downpipe that has an external wastegate mounted on it. I was planning on running it with the artisan 3" testpipe and catback exhaust with the stock turbo setup.
I wanted to get the 38mm tial wastegate and a Forge MBC and keep the boost lvl at stock until I get tuned for 27 lbs. Wiill 27 lbs be safe on 93 pump? Do you guys think it will still taper with the Ext Wastegate setup? If so, how much? I plan on getting my car tuned by jester in orlando. Any opinions are greatly appreciated. Also, I've read that the stock diverter valve will start to leak with boost any higher then 25 lbs. I'm planning on getting a Forge Diverter Valve to solve that issue.
Also for future reference, I also plan on getting a couple more bolt on's such as uicp, licp, cai, and a fmic. After those, cams, ported intake mani, fuel pump & injectors, etc.
Thanks,
Jay
I'm planning on running an ATP diverted downpipe that has an external wastegate mounted on it. I was planning on running it with the artisan 3" testpipe and catback exhaust with the stock turbo setup.
I wanted to get the 38mm tial wastegate and a Forge MBC and keep the boost lvl at stock until I get tuned for 27 lbs. Wiill 27 lbs be safe on 93 pump? Do you guys think it will still taper with the Ext Wastegate setup? If so, how much? I plan on getting my car tuned by jester in orlando. Any opinions are greatly appreciated. Also, I've read that the stock diverter valve will start to leak with boost any higher then 25 lbs. I'm planning on getting a Forge Diverter Valve to solve that issue.
Also for future reference, I also plan on getting a couple more bolt on's such as uicp, licp, cai, and a fmic. After those, cams, ported intake mani, fuel pump & injectors, etc.
Thanks,
Jay
Last edited by Evo J; Aug 3, 2009 at 02:12 PM.
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Joined: May 2008
Posts: 697
Likes: 1
From: Mitchigan
27lbs is A LOT on pump, especially with no meth/water/alcohol injection..look into those to attain that kind of boost on pump
do you have e85 in your area, I imagine you do, e85 iirc is about 105 effective octane.
ext wastegates allow you to hold boost more solidy and it's a simple ball and spring type operation in the manual boost controller which equates to your car just going for boost the quickest way and some say the most dangerous also as the ecu has no control, you are physically just going to hit target boost no matter what..even if you are knocking all to hell
it's a lengthy explanation, but I wanted you to know what/how the mbc does what it does...it's very simple and why people say it's the best for spool
do you have e85 in your area, I imagine you do, e85 iirc is about 105 effective octane.
ext wastegates allow you to hold boost more solidy and it's a simple ball and spring type operation in the manual boost controller which equates to your car just going for boost the quickest way and some say the most dangerous also as the ecu has no control, you are physically just going to hit target boost no matter what..even if you are knocking all to hell
it's a lengthy explanation, but I wanted you to know what/how the mbc does what it does...it's very simple and why people say it's the best for spool
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Joined: Jul 2009
Posts: 24
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From: SFL
Thanks MOREPSiTEHBETT4.
Just got this off another evo forum, apparently it's from a cobb tuning website. Seems like a downpipe with an 02 dump will work best.
"Post Turbo Exhaust
The main performance goal of a post turbo exhaust is to create the least amount of backpressure possible. There are a lot of factors that affect this.
Turbulence is one main factor. If the gasses are all stagnating and/or running into protrusions or running into each other it creates more backpressure than a well designed system. The more laminar (smooth and straight) the gas flow, the more the system can flow for a given pipe diameter. Steep angles and abrupt pipe diameter chances should be avoided.
The methods of collecting the outlet gasses and the wastegate gasses add another part of the equation to change. It would be optimal not to join the outlet from the turbo and the wastegate together, but the real world messes with our fun. Just dumping the wastegate to atmosphere is great for a racecar, but not a street car. So a street exhaust should combine them to get all of the gasses through the same cat and muffler system.
Some of the turbo outlet designs include: flanges with a simple pipe, bell mouths, divorced wastegate, and split bell mouths You also have castings and formed piping to choose from. Which one works best is also determined by quite a few different factors and how well they are designed and manufactured.
Flange w/Simple Pipe - The only advantages to this design are cost and simplicity. The pipe does not have to be formed and the flange is simple therefore reducing cost. The labor to weld the pipe to the flange is easy and therefore less costly as well. That is the main factor that make it desirable to the factory and why it is used on the stock exhaust. The wastegate gasses joining the turbo gasses right at the turbo outlet does create turbulence in the worst spot post turbo and reduces flow, thus not making it as desirable for performance as other designs.
BellMouth - This method is much closer to optimal for joining the gasses from the outlets. There is more room for them to join and if the transition is done properly it can flow very well into the main piping. It packages very well and does not have a lot of complexity, making for less to break. We have gotten the best results from this type of downpipe so far. Boost response has been the best out of the outlet designs we have tuned on, it is easy to put a wideband oxygen sensor bung into. We have also had the fewest problems with this design.
Split Bell Mouth - This design separates the gasses in the beginning of the turbo outlet and joins them at the rear of the bell mouth section. It works well and has some of the advantages of the bell mouth and some of the advantages of the divorced wastegate designs. The main deterrent for this is the cost and complexity of adding the splitter. I am a fan of keeping things as simple as possible while still making the product work well.
Divorced Wastegate - Keeping the gasses from the turbo outlet and wastegate separate until farther back in the system is an attempt to combine the advantages of not collecting the gasses and the real world. Combining them far back is closer to optimal than collecting them closer to the outlets. It is also critical to power production and spool-up to join the pipes smoothly and avoid turbulence. The disadvantages are that you add a lot of cost and complexity. You have big temperature differences on each pipe and that makes for a system that can crack. Putting in flex or expansion joints helps, but adds even further complexity and yet another part to fail. With all of the exhaust systems we have tuned with on the dyno we have seen that it is generally harder to bring boost on as quickly with these types of systems as compared to the bell mouth type systems. Perhaps it helps the wastegate function too well. Also, we have had a few situations where the splitter caused problems allowing the wastegate to function properly by not allowing it to open to its full extent, or even open at all. That caused either boost spiking, or no control over boost what so ever. Since the wastegate could not function the turbo ran as if it did even not have one, and the poor turbo just ran whatever boost it could make uncontrolled. The fix was not hard, but the least amount of stuff to go wrong the better. I know that I would not be happy having to pay for someone to install the exhaust only to have another place diagnose the problem, remove the exhaust, repair the part, and re-install the exhaust.
Cast Outlets - Castings have the advantage of keeping a lot of heat in the exhaust as well as freedom with design. You can basically make it almost any shape you want. The disadvantages are more weight and cost. Cast iron pieces can weigh a ton and that is a valid concern for many people. The casting form that the piece is made in is also very expensive and depending on complexity can range from a couple of thousand dollars to well up in the tens of thousands.
Formed Piping -Forming pipe has almost as much design freedom as a casting with less expense and less weight. The only disadvantage lies in if it is not done properly. Poor forming can look bad and effect flow by having creases and crimped spots. You can also get the piping too thin if you try to stretch the metal too far. If done improperly you can also make the metal brittle and it will usually happen where the metal is the thinnest."
Just got this off another evo forum, apparently it's from a cobb tuning website. Seems like a downpipe with an 02 dump will work best.
"Post Turbo Exhaust
The main performance goal of a post turbo exhaust is to create the least amount of backpressure possible. There are a lot of factors that affect this.
Turbulence is one main factor. If the gasses are all stagnating and/or running into protrusions or running into each other it creates more backpressure than a well designed system. The more laminar (smooth and straight) the gas flow, the more the system can flow for a given pipe diameter. Steep angles and abrupt pipe diameter chances should be avoided.
The methods of collecting the outlet gasses and the wastegate gasses add another part of the equation to change. It would be optimal not to join the outlet from the turbo and the wastegate together, but the real world messes with our fun. Just dumping the wastegate to atmosphere is great for a racecar, but not a street car. So a street exhaust should combine them to get all of the gasses through the same cat and muffler system.
Some of the turbo outlet designs include: flanges with a simple pipe, bell mouths, divorced wastegate, and split bell mouths You also have castings and formed piping to choose from. Which one works best is also determined by quite a few different factors and how well they are designed and manufactured.
Flange w/Simple Pipe - The only advantages to this design are cost and simplicity. The pipe does not have to be formed and the flange is simple therefore reducing cost. The labor to weld the pipe to the flange is easy and therefore less costly as well. That is the main factor that make it desirable to the factory and why it is used on the stock exhaust. The wastegate gasses joining the turbo gasses right at the turbo outlet does create turbulence in the worst spot post turbo and reduces flow, thus not making it as desirable for performance as other designs.
BellMouth - This method is much closer to optimal for joining the gasses from the outlets. There is more room for them to join and if the transition is done properly it can flow very well into the main piping. It packages very well and does not have a lot of complexity, making for less to break. We have gotten the best results from this type of downpipe so far. Boost response has been the best out of the outlet designs we have tuned on, it is easy to put a wideband oxygen sensor bung into. We have also had the fewest problems with this design.
Split Bell Mouth - This design separates the gasses in the beginning of the turbo outlet and joins them at the rear of the bell mouth section. It works well and has some of the advantages of the bell mouth and some of the advantages of the divorced wastegate designs. The main deterrent for this is the cost and complexity of adding the splitter. I am a fan of keeping things as simple as possible while still making the product work well.
Divorced Wastegate - Keeping the gasses from the turbo outlet and wastegate separate until farther back in the system is an attempt to combine the advantages of not collecting the gasses and the real world. Combining them far back is closer to optimal than collecting them closer to the outlets. It is also critical to power production and spool-up to join the pipes smoothly and avoid turbulence. The disadvantages are that you add a lot of cost and complexity. You have big temperature differences on each pipe and that makes for a system that can crack. Putting in flex or expansion joints helps, but adds even further complexity and yet another part to fail. With all of the exhaust systems we have tuned with on the dyno we have seen that it is generally harder to bring boost on as quickly with these types of systems as compared to the bell mouth type systems. Perhaps it helps the wastegate function too well. Also, we have had a few situations where the splitter caused problems allowing the wastegate to function properly by not allowing it to open to its full extent, or even open at all. That caused either boost spiking, or no control over boost what so ever. Since the wastegate could not function the turbo ran as if it did even not have one, and the poor turbo just ran whatever boost it could make uncontrolled. The fix was not hard, but the least amount of stuff to go wrong the better. I know that I would not be happy having to pay for someone to install the exhaust only to have another place diagnose the problem, remove the exhaust, repair the part, and re-install the exhaust.
Cast Outlets - Castings have the advantage of keeping a lot of heat in the exhaust as well as freedom with design. You can basically make it almost any shape you want. The disadvantages are more weight and cost. Cast iron pieces can weigh a ton and that is a valid concern for many people. The casting form that the piece is made in is also very expensive and depending on complexity can range from a couple of thousand dollars to well up in the tens of thousands.
Formed Piping -Forming pipe has almost as much design freedom as a casting with less expense and less weight. The only disadvantage lies in if it is not done properly. Poor forming can look bad and effect flow by having creases and crimped spots. You can also get the piping too thin if you try to stretch the metal too far. If done improperly you can also make the metal brittle and it will usually happen where the metal is the thinnest."
The external WG will work fine with it plumbed into the main exhaust or as an external dump. You may allow the exhaust to flow a little better at WOT with the external dump but the difference on the stock turbo will likely be minimal at those airflow levels. Keep in mind a GT35 turbo at 20 psi is quite a bit more flow than a stock turbo at 20 psi.
Stock Turbo boost taper is still restricted more by the airflow through the compressor side of the turbo and will likely be the same as before. If it's any better than this curve, by all means report back your findings!
4000 32 psi
4500 30 psi
5000 28 psi
5500 26 psi
6000 24 psi
6500 22 psi
7000 20 psi
7500 19 psi
This is what DG Motors was running and it is possible to tune the car to run crazy boost down low with reduced timing and richer AFR's at those RPM's. In general you are best off tuning for 25-26 psi boost for longevity and from 5500+ the turbo is going to taper without some modifications.
Stock Turbo boost taper is still restricted more by the airflow through the compressor side of the turbo and will likely be the same as before. If it's any better than this curve, by all means report back your findings!
4000 32 psi
4500 30 psi
5000 28 psi
5500 26 psi
6000 24 psi
6500 22 psi
7000 20 psi
7500 19 psi
This is what DG Motors was running and it is possible to tune the car to run crazy boost down low with reduced timing and richer AFR's at those RPM's. In general you are best off tuning for 25-26 psi boost for longevity and from 5500+ the turbo is going to taper without some modifications.
27lbs is A LOT on pump, especially with no meth/water/alcohol injection..look into those to attain that kind of boost on pump
do you have e85 in your area, I imagine you do, e85 iirc is about 105 effective octane.
ext wastegates allow you to hold boost more solidy and it's a simple ball and spring type operation in the manual boost controller which equates to your car just going for boost the quickest way and some say the most dangerous also as the ecu has no control, you are physically just going to hit target boost no matter what..even if you are knocking all to hell
it's a lengthy explanation, but I wanted you to know what/how the mbc does what it does...it's very simple and why people say it's the best for spool
do you have e85 in your area, I imagine you do, e85 iirc is about 105 effective octane.
ext wastegates allow you to hold boost more solidy and it's a simple ball and spring type operation in the manual boost controller which equates to your car just going for boost the quickest way and some say the most dangerous also as the ecu has no control, you are physically just going to hit target boost no matter what..even if you are knocking all to hell
it's a lengthy explanation, but I wanted you to know what/how the mbc does what it does...it's very simple and why people say it's the best for spool
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Joined: May 2008
Posts: 697
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From: Mitchigan
and that's a lot of boost on pump dude...approaching 30lbs of boost on pump, on 91 that is just asking for trouble. I mean I know the 4g63 can put up with a lot, but 27psi on pump with a lot of heat is just asking for it imho.
i am surprised that a ots map if that's what you are talking about that you have is tuned like that...i bet the timing is very low..like 5*
i am surprised that a ots map if that's what you are talking about that you have is tuned like that...i bet the timing is very low..like 5*
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and that's a lot of boost on pump dude...approaching 30lbs of boost on pump, on 91 that is just asking for trouble. I mean I know the 4g63 can put up with a lot, but 27psi on pump with a lot of heat is just asking for it imho.
i am surprised that a ots map if that's what you are talking about that you have is tuned like that...i bet the timing is very low..like 5*
i am surprised that a ots map if that's what you are talking about that you have is tuned like that...i bet the timing is very low..like 5*
The problem with the external wastegate setups i have seen available is that they do not keep the exhaust pulses truely split. How much harm it will do would have to be tested...
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Joined: May 2008
Posts: 697
Likes: 1
From: Mitchigan
^^^i really don't understand what you are saying...why does excess exhaust have anything to do with pulses going to the turbo.. ok are you saying it's making the turbo have the incorrect pulses because the exhaust gas they should get is going out the ewg and should be going to the turbo?
prrease explain your logic ...
prrease explain your logic ...
^^^i really don't understand what you are saying...why does excess exhaust have anything to do with pulses going to the turbo.. ok are you saying it's making the turbo have the incorrect pulses because the exhaust gas they should get is going out the ewg and should be going to the turbo?
prrease explain your logic ...
prrease explain your logic ...
So as you are spooling, will there really be enough flow through one side of the split internal passage to the other to cause problems? Since the WG passage is still closed there should be very little flow into that area and I would think the vast majority of gasses would have a much easier time flowing through the turbo itself. Since I have plenty of data showing 20 psi boost by 3600 in 4th gear then I guess someone needs to test this and see if it's an issue. 
and that's a lot of boost on pump dude...approaching 30lbs of boost on pump, on 91 that is just asking for trouble. I mean I know the 4g63 can put up with a lot, but 27psi on pump with a lot of heat is just asking for it imho.
i am surprised that a ots map if that's what you are talking about that you have is tuned like that...i bet the timing is very low..like 5*
i am surprised that a ots map if that's what you are talking about that you have is tuned like that...i bet the timing is very low..like 5*
As far as the EG. OP why wouldn't you just use a downpipe with a divorced o2 dump?
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