Highest horsepower with stock exhaust?
#16
06-12-2014 | 08:46 AM
Thread Starter
|
Registered User
Joined: Jun 2014
Posts: 63
From: Chicago
Rep Power: 13
Central repository of actual data?
Hey Guys,
Sorry my last message was a little garbled. I was dictating it to speech recognition on my phone. Further questions:
1) Is there any central place where actual before and after data is available for any of the mod parts, like before and after backpressure and horsepower from cat changes, exhaust changes, before and after power runs with intercoolers with temps, etc. I've seen some good scattered data, but it doesn't seem like anyone has pulled it all together anywhere.
2) Assuming you can get the charge cool enough, you should be able to run more boost with more backpressure to get the same charge density with only a small penalty in extra work for the turbocharger. So, if the backpressure limits horsepower by limiting cylinder emptying and filling, then just crank up the boost a bit more to get to the same cylinder charge. In other words, the engine should have the same power and cylinder charge and propensity to detonate at 1.4 bar with at some higher backpressure than at 1.2 bar with some lower backpressure, with the exception of a little lost work to the backpressure. Again, terms like "letting it breathe" are really imprecise, it all comes down to the physics.
Sorry my last message was a little garbled. I was dictating it to speech recognition on my phone. Further questions:
1) Is there any central place where actual before and after data is available for any of the mod parts, like before and after backpressure and horsepower from cat changes, exhaust changes, before and after power runs with intercoolers with temps, etc. I've seen some good scattered data, but it doesn't seem like anyone has pulled it all together anywhere.
2) Assuming you can get the charge cool enough, you should be able to run more boost with more backpressure to get the same charge density with only a small penalty in extra work for the turbocharger. So, if the backpressure limits horsepower by limiting cylinder emptying and filling, then just crank up the boost a bit more to get to the same cylinder charge. In other words, the engine should have the same power and cylinder charge and propensity to detonate at 1.4 bar with at some higher backpressure than at 1.2 bar with some lower backpressure, with the exception of a little lost work to the backpressure. Again, terms like "letting it breathe" are really imprecise, it all comes down to the physics.
#17
06-12-2014 | 08:55 AM
I see what you're saying. I get the engineering aspect of it, but you probably won't get all your answers here because none of us care that much.
Sure some like quieter exhausts, some like it loud, but it is just so easy to replace the exhaust and deal with a bit more sound.
Basically what it sounds like is you're trying to redo what Porsche already did. Balance flow with sound.
If you want it quiet, europipe or mod the stock exhaust like markski said.
Sure some like quieter exhausts, some like it loud, but it is just so easy to replace the exhaust and deal with a bit more sound.
Basically what it sounds like is you're trying to redo what Porsche already did. Balance flow with sound.
If you want it quiet, europipe or mod the stock exhaust like markski said.
#18
06-12-2014 | 11:28 AM
I'm not sure this is going to help, because the wastegates dump the exhaust before the turbo. If you're flowing enough exhaust to spin the turbine wheel to produce 1.3 bar of boost, then the stock cat/muffler will not flow as much exhaust as the turbo, still creating back pressure.
Later, Steve
Later, Steve
You're right though. Having too big of a turbo on the stock exhaust can cause what is similar to compressor surge...
I suppose you could just make an extremely quiet 3" exhaust.
#19
06-12-2014 | 12:16 PM
Former Vendor
Joined: Feb 2010
Posts: 356
From: Belgium
Rep Power: 0
Count the cells, all stock cats have 300 cells.
#20
06-12-2014 | 12:20 PM
Former Vendor
Joined: Feb 2010
Posts: 356
From: Belgium
Rep Power: 0
A stock sized 2 3/8 inch (60mm) exhaust can be less restrictive than a 3 inch exhaust.
So don't focus on the tube size, focus on the amount of backpressure.
#21
06-12-2014 | 12:34 PM
Registered User
Joined: Feb 2011
Posts: 1,075
From: Lewisville, NC
Rep Power: 108
Hey Guys,
Sorry my last message was a little garbled. I was dictating it to speech recognition on my phone. Further questions:
1) Is there any central place where actual before and after data is available for any of the mod parts, like before and after backpressure and horsepower from cat changes, exhaust changes, before and after power runs with intercoolers with temps, etc. I've seen some good scattered data, but it doesn't seem like anyone has pulled it all together anywhere.
2) Assuming you can get the charge cool enough, you should be able to run more boost with more backpressure to get the same charge density with only a small penalty in extra work for the turbocharger. So, if the backpressure limits horsepower by limiting cylinder emptying and filling, then just crank up the boost a bit more to get to the same cylinder charge. In other words, the engine should have the same power and cylinder charge and propensity to detonate at 1.4 bar with at some higher backpressure than at 1.2 bar with some lower backpressure, with the exception of a little lost work to the backpressure. Again, terms like "letting it breathe" are really imprecise, it all comes down to the physics.
Sorry my last message was a little garbled. I was dictating it to speech recognition on my phone. Further questions:
1) Is there any central place where actual before and after data is available for any of the mod parts, like before and after backpressure and horsepower from cat changes, exhaust changes, before and after power runs with intercoolers with temps, etc. I've seen some good scattered data, but it doesn't seem like anyone has pulled it all together anywhere.
2) Assuming you can get the charge cool enough, you should be able to run more boost with more backpressure to get the same charge density with only a small penalty in extra work for the turbocharger. So, if the backpressure limits horsepower by limiting cylinder emptying and filling, then just crank up the boost a bit more to get to the same cylinder charge. In other words, the engine should have the same power and cylinder charge and propensity to detonate at 1.4 bar with at some higher backpressure than at 1.2 bar with some lower backpressure, with the exception of a little lost work to the backpressure. Again, terms like "letting it breathe" are really imprecise, it all comes down to the physics.
Basically just changing boost, intake efficiency or intake charge density will not change the fact that you will need a given amount of fuel/air to make a given amount of power. It simply changes how you get there.
You could definitely lower the boost, and reduce the intake temps and still make the same amount of power, because you effectively supplied the same quantity of air.
But to make 600hp (as an example), you will need the same amount of air/fuel, which means you have the same amount of exhaust gases to expel. You can still make a ton of power through a stock exhaust, you just won't be making it efficiently.
Unfortunately you need a lot of muffler volume (space) to reduce the sound without adding restriction. As an example, my M5 makes 500hp through an exhaust that is as quiet as a Honda Civic. Unfortunately it has 4 catalytic converters (another item where you need volume), 2 resonators and 4 mufflers. I know the stock setup is pretty efficient, because adding an aftermarket exhaust adds less than 4% more power.
Our 911's are at a premium for exhaust space, so there is only so much you can do. Unfortunately as you increase your horsepower and back-pressure gets higher and higher with the stock exhaust, your exhaust gas temps will more than likely climb as well. This will also add more stress to the stock cooling system.
Basically I believe you can make 700hp through a stock exhaust with upgraded turbos, intercoolers, fuel system and probably a water/methanol injection system, but it will be very hard on your motor. You will also have a higher chance of detonation, given the higher exhaust temps.
700hp can be made efficiently through a quiet exhaust, but not on our 911's.
Also remember that the catalytic converters and mufflers are all part of the equation. Possibly, you could eliminate the catalytic converters and install mufflers with more volume and less restriction in their place. This may allow you to replace your stock mufflers with less restrictive units, since more of the noise has been absorbed before getting to the stock mufflers. This is probably your best chance, but will definitely cost time and money.
Sorry for talking in circles.
Later, Steve
#22
06-12-2014 | 12:44 PM
Registered User
Joined: Jul 2012
Posts: 2,382
From: kirkwood pa
Rep Power: 433
I would leave this up to one of the many qualified tuners/venders available here= I'm sure they can fix him up with the best compromise of quiet and performance. Does add for some interesting and informative quarry lol.
#23
06-12-2014 | 12:54 PM
in my opinion he should get the oem exhaust fixed up and it it will suite his needs...
markski
__________________
2001 996TT 3.6L and stock ECU
9.66 seconds @ 147.76 mph 1/4 mile click to view
160 mph @ 9.77 seconds in 1/4 mile click to view
50% OFF ON PORSCHE ECU TUNING BLACK FRIDAY SPECIAL
2001 996TT 3.6L and stock ECU
9.66 seconds @ 147.76 mph 1/4 mile click to view
160 mph @ 9.77 seconds in 1/4 mile click to view
50% OFF ON PORSCHE ECU TUNING BLACK FRIDAY SPECIAL
#25
06-12-2014 | 01:48 PM
Good luck and I hope it works out for you
Markski
#26
06-12-2014 | 04:45 PM
Thread Starter
|
Registered User
Joined: Jun 2014
Posts: 63
From: Chicago
Rep Power: 13
Correct me if I'm wrong, but at the risk of over simplification, you need a certain amount of fuel and air to make a given amount of power. This assumes that you're not increasing the efficiency of the explosion through something like ignition timing or air/fuel ratio changes.
Basically just changing boost, intake efficiency or intake charge density will not change the fact that you will need a given amount of fuel/air to make a given amount of power. It simply changes how you get there.
You could definitely lower the boost, and reduce the intake temps and still make the same amount of power, because you effectively supplied the same quantity of air.
But to make 600hp (as an example), you will need the same amount of air/fuel, which means you have the same amount of exhaust gases to expel. You can still make a ton of power through a stock exhaust, you just won't be making it efficiently.
Unfortunately you need a lot of muffler volume (space) to reduce the sound without adding restriction. As an example, my M5 makes 500hp through an exhaust that is as quiet as a Honda Civic. Unfortunately it has 4 catalytic converters (another item where you need volume), 2 resonators and 4 mufflers. I know the stock setup is pretty efficient, because adding an aftermarket exhaust adds less than 4% more power.
Our 911's are at a premium for exhaust space, so there is only so much you can do. Unfortunately as you increase your horsepower and back-pressure gets higher and higher with the stock exhaust, your exhaust gas temps will more than likely climb as well. This will also add more stress to the stock cooling system.
Basically I believe you can make 700hp through a stock exhaust with upgraded turbos, intercoolers, fuel system and probably a water/methanol injection system, but it will be very hard on your motor. You will also have a higher chance of detonation, given the higher exhaust temps.
700hp can be made efficiently through a quiet exhaust, but not on our 911's.
Also remember that the catalytic converters and mufflers are all part of the equation. Possibly, you could eliminate the catalytic converters and install mufflers with more volume and less restriction in their place. This may allow you to replace your stock mufflers with less restrictive units, since more of the noise has been absorbed before getting to the stock mufflers. This is probably your best chance, but will definitely cost time and money.
Sorry for talking in circles.
Later, Steve
Basically just changing boost, intake efficiency or intake charge density will not change the fact that you will need a given amount of fuel/air to make a given amount of power. It simply changes how you get there.
You could definitely lower the boost, and reduce the intake temps and still make the same amount of power, because you effectively supplied the same quantity of air.
But to make 600hp (as an example), you will need the same amount of air/fuel, which means you have the same amount of exhaust gases to expel. You can still make a ton of power through a stock exhaust, you just won't be making it efficiently.
Unfortunately you need a lot of muffler volume (space) to reduce the sound without adding restriction. As an example, my M5 makes 500hp through an exhaust that is as quiet as a Honda Civic. Unfortunately it has 4 catalytic converters (another item where you need volume), 2 resonators and 4 mufflers. I know the stock setup is pretty efficient, because adding an aftermarket exhaust adds less than 4% more power.
Our 911's are at a premium for exhaust space, so there is only so much you can do. Unfortunately as you increase your horsepower and back-pressure gets higher and higher with the stock exhaust, your exhaust gas temps will more than likely climb as well. This will also add more stress to the stock cooling system.
Basically I believe you can make 700hp through a stock exhaust with upgraded turbos, intercoolers, fuel system and probably a water/methanol injection system, but it will be very hard on your motor. You will also have a higher chance of detonation, given the higher exhaust temps.
700hp can be made efficiently through a quiet exhaust, but not on our 911's.
Also remember that the catalytic converters and mufflers are all part of the equation. Possibly, you could eliminate the catalytic converters and install mufflers with more volume and less restriction in their place. This may allow you to replace your stock mufflers with less restrictive units, since more of the noise has been absorbed before getting to the stock mufflers. This is probably your best chance, but will definitely cost time and money.
Sorry for talking in circles.
Later, Steve
However, I want to just try with just k16s w 1 bar or stiffer wastegate, intercoolers, injectors, tune, and the stock exhaust and see what I get. I can always add the exhaust.
#28
06-12-2014 | 07:14 PM
Mostly agree with you,,
Cat cell ratings, muffler design are all part of the total equation..
I have seen on the dyno on a 550 rear wheel HP car make more HP with a catless 2.5'' system over a 200 cell 3'' system..
#29
06-14-2014 | 03:02 PM
Registered User
Joined: Jun 2012
Posts: 222
From: evil lair
Rep Power: 32
This is the best advice ever. Makes me wonder why we have so many exhaust venders and virtually none post back pressure results, only drag slips.. insane.
I don't have a Europipe but, if I was in the exhaust market, I would look no further.
