Considering new exhaust. Noticeable effect on lag? BMC questions too...
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991.2 GT3 RS Weissach Racing Yellow
991.2 Turbo S GT Silver
991.2 GT3 Chalk (Manual)
2022 Cayenne White
former 1972 911T white, 1984 911 3.2 Targa black, 993 cab white, 993TT arena red, 993TT silver, 996TT speed yellow, 991.1 GT3 white
www.speedtechexhausts.com
info@speedtechexhausts.com
Testimonials facebook SpeedTech Exhaust Videos
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I like a good discussion, so don't take my response as anything other than my take on the issue off the top of my head.
This distinction seems semantic to me. If I understand, someone is making a distinction between the lag associated with overcoming the inertia of the turbo impeller and the lag associated with the time it takes a spinning impeller to compress the air to maximum boost. The VTG's address the first, but not the second. In fact, it seems possible that they may add to the second, given that the impeller blades have to open up, though this may happen very quickly. Please correct me if I've mischaracterized.
In any case, it seems the throttle response is non-linear due to the turbos. Whether or not you call the initial hesitation "turbo lag" is a decision concerning how one defines turbo lag, but it doesn't change the fact that there is an initial amount of acceleration upon opening the throttle at lower rpms, followed by a fairly abrupt increase in acceleration, and this phenomenon is turbo-related--as far as I know.
I guess it's possible with today's drive-by-wire systems that the initial hesitation is caused by the computer trying to decide if you really want to go fast. It wouldn't surprise me at all if that is some of the lag.
I would like to read what Bbywu has to say about it. I'll search around.
LP
This distinction seems semantic to me. If I understand, someone is making a distinction between the lag associated with overcoming the inertia of the turbo impeller and the lag associated with the time it takes a spinning impeller to compress the air to maximum boost. The VTG's address the first, but not the second. In fact, it seems possible that they may add to the second, given that the impeller blades have to open up, though this may happen very quickly. Please correct me if I've mischaracterized.
In any case, it seems the throttle response is non-linear due to the turbos. Whether or not you call the initial hesitation "turbo lag" is a decision concerning how one defines turbo lag, but it doesn't change the fact that there is an initial amount of acceleration upon opening the throttle at lower rpms, followed by a fairly abrupt increase in acceleration, and this phenomenon is turbo-related--as far as I know.
I guess it's possible with today's drive-by-wire systems that the initial hesitation is caused by the computer trying to decide if you really want to go fast. It wouldn't surprise me at all if that is some of the lag.
I would like to read what Bbywu has to say about it. I'll search around.
LP
Here's a good description http://www.mechanicalengineeringblog...-geometry-vtg/
Last edited by TTdude; Apr 22, 2012 at 12:34 PM.
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I like a good discussion, so don't take my response as anything other than my take on the issue off the top of my head.
This distinction seems semantic to me. If I understand, someone is making a distinction between the lag associated with overcoming the inertia of the turbo impeller and the lag associated with the time it takes a spinning impeller to compress the air to maximum boost. The VTG's address the first, but not the second. In fact, it seems possible that they may add to the second, given that the impeller blades have to open up, though this may happen very quickly. Please correct me if I've mischaracterized.
In any case, it seems the throttle response is non-linear due to the turbos. Whether or not you call the initial hesitation "turbo lag" is a decision concerning how one defines turbo lag, but it doesn't change the fact that there is an initial amount of acceleration upon opening the throttle at lower rpms, followed by a fairly abrupt increase in acceleration, and this phenomenon is turbo-related--as far as I know.
I guess it's possible with today's drive-by-wire systems that the initial hesitation is caused by the computer trying to decide if you really want to go fast. It wouldn't surprise me at all if that is some of the lag.
I would like to read what Bbywu has to say about it. I'll search around.
LP
This distinction seems semantic to me. If I understand, someone is making a distinction between the lag associated with overcoming the inertia of the turbo impeller and the lag associated with the time it takes a spinning impeller to compress the air to maximum boost. The VTG's address the first, but not the second. In fact, it seems possible that they may add to the second, given that the impeller blades have to open up, though this may happen very quickly. Please correct me if I've mischaracterized.
In any case, it seems the throttle response is non-linear due to the turbos. Whether or not you call the initial hesitation "turbo lag" is a decision concerning how one defines turbo lag, but it doesn't change the fact that there is an initial amount of acceleration upon opening the throttle at lower rpms, followed by a fairly abrupt increase in acceleration, and this phenomenon is turbo-related--as far as I know.
I guess it's possible with today's drive-by-wire systems that the initial hesitation is caused by the computer trying to decide if you really want to go fast. It wouldn't surprise me at all if that is some of the lag.
I would like to read what Bbywu has to say about it. I'll search around.
LP
If you change to a high flow exhaust, you will improve your lag. Will it be noticeable? Hard to say. But boost availability is dependent on the back pressure created by the exhaust system. The better flow in the exhaust (cat less, larger diameter) the more available boost.
An exhaust system's back pressure has the biggest influence on the pressure ratio across the turbine - the turbine needs to be able to do the most amount of work possible with the air coming into the inlet. For a given inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible back pressure.
The available boost is essentially inlet pressure minus back pressure.
Dave truthfully has more knowledge of this with his background and his hands on experience tooling his engine.
Last edited by bbywu; Apr 26, 2012 at 09:33 PM.
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Our cars were not blessed with a cool, exotic sound, period. Some exhausts may make it sound slightly better. If you want the sound to blow you away and put a smile on your face every time, then you will have to run straight pipes or dumps. It will change the sound of the car drastically.
This post will help illustrate an easy fix of how you can use a Fabspeed system and make your car scream. There are photos and videos of outside and inside the car...enjoy. I suggest you get the Fabspeed so that you can have 2 different exhaust systems...
https://www.6speedonline.com/forums/...treatment.html
Last edited by TAILWAG; Apr 27, 2012 at 07:38 AM.
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Got my car back from getting modded a couple of weeks ago. installed Tubi, no cats + much more. Sounds incredible. No comparison to stock. It is still CPO, 2 years left. Champion did the work. If Porsche does not cover damage (should it occur), Champion will.
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