Full exhaust, how much HP?
07-14-2005, 08:26 AM
#31
Originally posted by Initial Daniel
As far as 3" exhausts are concerned, I believe that you're just losing hp if you're N/A. 2.5 is even pushing it N/A, unless you're making decent power, lets say over 200whp.
In properly sized exhaust system, the backpressure is minimized as much as possible while allowing exhaust pulses to line up nicely and provide a good trade-off between both low and high-end power. For most N/A applications this pipe size would be 2.25" in diameter. A common mistake sometimes talked about in "tuner" magazines is that you need some backpressure for the system to flow properly. This is a myth created by amateur testing methods. For an N/A car, a 2.25 exhaust will get the best performance out of any other sizes, bigger or smaller. So because it outperforms the bigger exhaust people just assume that backpressure was the key to success here. I'm telling you right now, they are wrong. The reason the exhaust performed the best was because the exhaust pulses were perfectly in line and able to draw each other out of the exhaust at the highest velocity possible.
I'd really go only 3" if you are turbo.
Another thing is...an exhaust system is just that. A SYSTEM. It works well only when other parts in the system work with it. Having a stock header might help to stop reversion, but WHY choke power from your system? All parts should be equal in diameter for optimum performance.
This makes me wonder why ANYONE would use a stock header, unless they couldn't afford something better? The restrictions of that header might help with reversion, but you're really choking the flow of exhaust gasses.
There are TWO goals of an exhaust SYSTEM (Yes, it's called a system for a reason)
a) to efficiently remove as much of the combusted inert exhaust gases out of the cylinder.
and
b) to keep the velocity or speed of the exhaust gas leaving very high.
Hope this helps you guys and clears up some things...
As far as 3" exhausts are concerned, I believe that you're just losing hp if you're N/A. 2.5 is even pushing it N/A, unless you're making decent power, lets say over 200whp.
In properly sized exhaust system, the backpressure is minimized as much as possible while allowing exhaust pulses to line up nicely and provide a good trade-off between both low and high-end power. For most N/A applications this pipe size would be 2.25" in diameter. A common mistake sometimes talked about in "tuner" magazines is that you need some backpressure for the system to flow properly. This is a myth created by amateur testing methods. For an N/A car, a 2.25 exhaust will get the best performance out of any other sizes, bigger or smaller. So because it outperforms the bigger exhaust people just assume that backpressure was the key to success here. I'm telling you right now, they are wrong. The reason the exhaust performed the best was because the exhaust pulses were perfectly in line and able to draw each other out of the exhaust at the highest velocity possible.
I'd really go only 3" if you are turbo.
Another thing is...an exhaust system is just that. A SYSTEM. It works well only when other parts in the system work with it. Having a stock header might help to stop reversion, but WHY choke power from your system? All parts should be equal in diameter for optimum performance.
This makes me wonder why ANYONE would use a stock header, unless they couldn't afford something better? The restrictions of that header might help with reversion, but you're really choking the flow of exhaust gasses.
There are TWO goals of an exhaust SYSTEM (Yes, it's called a system for a reason)
a) to efficiently remove as much of the combusted inert exhaust gases out of the cylinder.
and
b) to keep the velocity or speed of the exhaust gas leaving very high.
Hope this helps you guys and clears up some things...
I wish I knew the terms a bit better to write it up like that, but what Initial Daniel said was the point I was trying to bring across..
Back pressure doesn't matter it's the rate of velocity traveled through the pipe.
The other thing I always wonderd is if the tuner magazine guys are such pros, why do they always use back pressure as a means of achieving HP and torque, I just don't get that part to well.
Thanx for correcting the Myth on Back Pressure it seems to be talked about in the N/A sticky, that has rambled on forever......
Last edited by BigVinnie; 07-14-2005 at 08:36 AM.
07-14-2005, 08:37 AM
#32
Contributing Member
Join Date: Sep 2002
Location: Massachusetts
Posts: 680
Completely depends on the application. There certanly are applications where a 3" pipe would be perfect for n/a. Heck, there are bound to be applications where a 3" pipe would be too damn small.
There are reasons for this.... and the reasons have nothing to do with magically adding power to the compression stroke through backpressure.
-Justin
There are reasons for this.... and the reasons have nothing to do with magically adding power to the compression stroke through backpressure.
-Justin
07-14-2005, 08:57 AM
#33
Contributing Member
Join Date: Oct 2004
Location: Woodbridge
Posts: 886
Hey, Thanks Vin--I knew what you were trying to get across though, I figured that I'd help clear it up a bit.
It is true that dependant on what kind of setup you're running that you MAY need 3", but again stock N/A cars won't effectively utilize that much exhaust flow. I wasn't getting at the fact that a 2.25 sized exhaust system is the only way to go, but on a STOCK N/A car, it is perfect. On more heavily modified N/A cars, it's okay to go bigger to compensate for the increased air/fuel and power!
I mean, if you are letting water out of a garden hose to water your garden, thats fine, but hooking your garden hose to drain Hoover Dam is just stupid. The reverse side is hooking up a fire hose to your house to water your garden...there just isn't enough pressure is there? I hope you understand what I'm getting at.
Right now we are looking at the opposite end of the spectrum from advice commonly given by "tuner" magazines. "The bigger exhaust you have the better it flows and you have no backpressure anymore so you make tons more power." Yeah right. Funny how these "tuner" magazines will say something on one page and then say something opposite on the next. And yeah I keep putting "tuner" in quotes because I'm being sarcastic. I honestly think most of those magazines are a joke.
Anyway in an exhaust system that is too big, the exhaust pulses get disorganized and don't follow each other in line. Some of the pulses will bounce around, causing exhaust gasses to hang around in the exhaust pipe with little forward motion. These gasses are susceptible to being sucked back into the combustion chamber on the piston's intake stroke, diluting the fresh air/fuel mixture and ultimately causing power loss. So while you have minimized backpressure even further with an over-sized pipe, you did so at the price of disorganizing the exhaust pulses. This is why proper exhaust system sizing is IMPORTANT.
Originally posted by Justin.b
Completely depends on the application. There certanly are applications where a 3" pipe would be perfect for n/a. Heck, there are bound to be applications where a 3" pipe would be too damn small.
There are reasons for this.... and the reasons have nothing to do with magically adding power to the compression stroke through backpressure.
-Justin
Completely depends on the application. There certanly are applications where a 3" pipe would be perfect for n/a. Heck, there are bound to be applications where a 3" pipe would be too damn small.
There are reasons for this.... and the reasons have nothing to do with magically adding power to the compression stroke through backpressure.
-Justin
I mean, if you are letting water out of a garden hose to water your garden, thats fine, but hooking your garden hose to drain Hoover Dam is just stupid. The reverse side is hooking up a fire hose to your house to water your garden...there just isn't enough pressure is there? I hope you understand what I'm getting at.
Right now we are looking at the opposite end of the spectrum from advice commonly given by "tuner" magazines. "The bigger exhaust you have the better it flows and you have no backpressure anymore so you make tons more power." Yeah right. Funny how these "tuner" magazines will say something on one page and then say something opposite on the next. And yeah I keep putting "tuner" in quotes because I'm being sarcastic. I honestly think most of those magazines are a joke.
Anyway in an exhaust system that is too big, the exhaust pulses get disorganized and don't follow each other in line. Some of the pulses will bounce around, causing exhaust gasses to hang around in the exhaust pipe with little forward motion. These gasses are susceptible to being sucked back into the combustion chamber on the piston's intake stroke, diluting the fresh air/fuel mixture and ultimately causing power loss. So while you have minimized backpressure even further with an over-sized pipe, you did so at the price of disorganizing the exhaust pulses. This is why proper exhaust system sizing is IMPORTANT.
Last edited by Initial Daniel; 07-14-2005 at 09:07 AM.
07-14-2005, 09:00 AM
#34
Originally posted by Justin.b
Completely depends on the application. There certanly are applications where a 3" pipe would be perfect for n/a. Heck, there are bound to be applications where a 3" pipe would be too damn small.
There are reasons for this.... and the reasons have nothing to do with magically adding power to the compression stroke through backpressure.
-Justin
Completely depends on the application. There certanly are applications where a 3" pipe would be perfect for n/a. Heck, there are bound to be applications where a 3" pipe would be too damn small.
There are reasons for this.... and the reasons have nothing to do with magically adding power to the compression stroke through backpressure.
-Justin
But it wasn't magical it's an equal balance between all pistons and there masses in the chamber. After all we are dealing with 4 stroke engines that consume 4X before dumping on ignition. Lets say you wanted to do the 248/248 91-94 HOT cam set up using 2 exhaust cams, unless the exhaust cam is retarded the engine will only lose power, unlike the 248/232 set up that actually pulls pretty decent HP numbers.
Fact is I'm not going to tell some guy that bought 3" pipe and has done NO other modifying that it is reasonable. I would of said to modify the header atleast 1st if no engine mods have been done.
Take myself for example I focused on other means of dropping degredation for larger HP numbers, such as intake, Fidanza Flywheel, removal of the secondary butterflys, an aluminum pulley, and an APEXI SAFC "which actually increased CHP by shifting the TTP.
I decided to mod the engine abit before increasing the diameter of my exhaust, with the 2.5" pacesetter exhaust.
Then you still have to account for the CATYLITIC converter, I still have the stock converter, and plan on recieving a Random Technology in the near future along with my DC sport header.
A new set of cams, a 11.1:1 wiseco forged CR kit, and sr370cc injectors will be dropped in hopefully within the month, now there is some power where I may think to consider a 3", but more than likely not, I like the torque that the 2.5" exhaust provides.
07-14-2005, 09:14 AM
#35
Contributing Member
Join Date: Oct 2004
Location: Woodbridge
Posts: 886
Originally posted by BigVinnie
Fact is I'm not going to tell some guy that bought 3" pipe and has done NO other modifying that it is reasonable. I would of said to modify the header atleast 1st if no engine mods have been done.
Fact is I'm not going to tell some guy that bought 3" pipe and has done NO other modifying that it is reasonable. I would of said to modify the header atleast 1st if no engine mods have been done.
When you buy stuff for your car, you should definitely decide what kind of setup you want to run or at least come to some kind of HP goal so you are able to choose which exhaust system will benefit you, and build your setup towards that goal.
Like...Big V probably knows what kind of power he wants to make, and he builds around that idea to cater to what his car needs to achive that goal, which is the reasoning behind his choice of cams, exhaust sizing, compression ratio, etc.
Last edited by Initial Daniel; 07-14-2005 at 09:17 AM.
07-14-2005, 09:22 AM
#36
Originally posted by Initial Daniel
Exactly.
When you buy stuff for your car, you should definitely decide what kind of setup you want to run or at least come to some kind of HP goal so you are able to choose which exhaust system will benefit you, and build your setup towards that goal.
Like...Big V probably knows what kind of power he wants to make, and he builds around that idea to cater to what his car needs to achive that goal, which is the reasoning behind his choice of cams, exhaust sizing, compression ratio, etc.
Exactly.
When you buy stuff for your car, you should definitely decide what kind of setup you want to run or at least come to some kind of HP goal so you are able to choose which exhaust system will benefit you, and build your setup towards that goal.
Like...Big V probably knows what kind of power he wants to make, and he builds around that idea to cater to what his car needs to achive that goal, which is the reasoning behind his choice of cams, exhaust sizing, compression ratio, etc.
07-14-2005, 10:31 AM
#39
Contributing Member
Join Date: Sep 2002
Location: Massachusetts
Posts: 680
Vinnie,
Unless Random Tech has switched to using a thick welded flange for their cats, you will probably be better off going with a catco with custom flanges like the ones they sell at www.enjukuracing.com or www.heavythrottle.com .
-Justin
Unless Random Tech has switched to using a thick welded flange for their cats, you will probably be better off going with a catco with custom flanges like the ones they sell at www.enjukuracing.com or www.heavythrottle.com .
-Justin
07-14-2005, 12:25 PM
#40
Originally posted by Justin.b
Vinnie,
Unless Random Tech has switched to using a thick welded flange for their cats, you will probably be better off going with a catco with custom flanges like the ones they sell at www.enjukuracing.com or www.heavythrottle.com .
-Justin
Vinnie,
Unless Random Tech has switched to using a thick welded flange for their cats, you will probably be better off going with a catco with custom flanges like the ones they sell at www.enjukuracing.com or www.heavythrottle.com .
-Justin