Back-pressure
02-17-2010, 05:58 PM
#1
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Back-pressure
I had a quick question regarding back-pressure.
I know that the whole idea of an engine "requiring" back-pressure is a myth, and that the less back-pressure there is, the better.
My question is;
Why does the stock muffler have that "flap" that remains closed during part throttle operation?
If back-pressure was always bad, why would Nissan incorporate a device which creates back-pressure during low pressure circumstances?
(The Cattman 3" exhaust thread inspired me to ask this)
I know that the whole idea of an engine "requiring" back-pressure is a myth, and that the less back-pressure there is, the better.
My question is;
Why does the stock muffler have that "flap" that remains closed during part throttle operation?
If back-pressure was always bad, why would Nissan incorporate a device which creates back-pressure during low pressure circumstances?
(The Cattman 3" exhaust thread inspired me to ask this)
02-17-2010, 06:03 PM
#2
i dont believe when nissan made the car performance was the only thing they intended for, im sure that flap is moreso for sound and MPG, and to not sacrifise power when the owner wants it then....... the flap.... its not a backpressure thing, hence why it opens when at WOT, there's barely if any backpressure at 60mpg and whateer low RPM
EDIT: i dont think people are saying back pressure is bad, its just not needed to make to make power that all, im sure even with the 3" there is still back pressure.......... IMO its best to minimize back pressure without gettn rid of it all as long as exhaust gas flows smoothly, im sure somebody is going to disagree with this and i wont even argue it...
EDIT: i dont think people are saying back pressure is bad, its just not needed to make to make power that all, im sure even with the 3" there is still back pressure.......... IMO its best to minimize back pressure without gettn rid of it all as long as exhaust gas flows smoothly, im sure somebody is going to disagree with this and i wont even argue it...
Last edited by Grand_hustle17; 02-17-2010 at 06:08 PM.
02-17-2010, 06:05 PM
#3
i dont believe when nissan made the car performance was the only thing they intended for, im sure that flap is moreso for sound and MPG, and to not sacrifise power when the owner wants it then....... the flap.... its not a backpressure thing, hence why it opens when at WOT, there barely if any backpressure at 60mpg and whateer low RPM
02-17-2010, 06:08 PM
#5
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I get it. Closed for quiet operation and efficiency, open when the power is required.
Thanks.
Edit:
I remember reading somewhere that the only reason why people don't use like 8 inch exhausts is because after a point, the exhaust gas velocity slows down and the gas cools and becomes more dense, becoming harder to push through the pipe. I don't plan on going any bigger than 3".
I wish my headers had a 3" y pipe
Thanks.
Edit:
I remember reading somewhere that the only reason why people don't use like 8 inch exhausts is because after a point, the exhaust gas velocity slows down and the gas cools and becomes more dense, becoming harder to push through the pipe. I don't plan on going any bigger than 3".
I wish my headers had a 3" y pipe
Last edited by Unklejoe; 02-17-2010 at 06:10 PM.
02-17-2010, 06:13 PM
#6
I get it. Closed for quiet operation and efficiency, open when the power is required.
Thanks.
Edit:
I remember reading somewhere that the only reason why people don't use like 8 inch exhausts is because after a point, the exhaust gas velocity slows down and the gas cools and becomes more dense, becoming harder to push through the pipe. I don't plan on going any bigger than 3".
I wish my headers had a 3" y pipe
Thanks.
Edit:
I remember reading somewhere that the only reason why people don't use like 8 inch exhausts is because after a point, the exhaust gas velocity slows down and the gas cools and becomes more dense, becoming harder to push through the pipe. I don't plan on going any bigger than 3".
I wish my headers had a 3" y pipe
02-17-2010, 06:18 PM
#7
02-17-2010, 06:22 PM
#8
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More work than I wish to do really, but I bet there are some gains to be had.
02-17-2010, 06:50 PM
#12
I'm sorry to hear that.....How long have your had your OBX? As for the exhaust question it's all about gas velocity uncle Bubba!
02-17-2010, 07:07 PM
#13
@ uncle bubba... cmax i think you miss read his reply, he doesnt need a new flex section... he was saying if he was to do a 3" Y then he would need to buy a new flex... little anxious for something i see 
02-17-2010, 07:25 PM
#14
I was at a local exhaust shop which is dealing with f-bodys, mainly 500+ hp ones and the guy was saying how their 500+hp cars run 3" all the way out, However putting a 3" after your headers and y which are 2.5" seemed pointless to him because you already passed the most restrictive areas and "your as wide as your smallest pipping on your exhaust"... Any truth to that? It did kinda make sense..
02-17-2010, 07:30 PM
#15
Glad you and he understand each others writing cause I read it again and his initial question were regarding back pressure and he mentioned:" I'd have to get a new flex pipe welded on my OBX headers, but it could be done. I'd also have to get a new test pipe made."
More work than I wish to do really, but I bet there are some gains to be had
So to me it was general statements, cause I'm not good at reading between lines nor minds......But I am waiting for that ......
More work than I wish to do really, but I bet there are some gains to be had
So to me it was general statements, cause I'm not good at reading between lines nor minds......But I am waiting for that ......
02-17-2010, 08:00 PM
#16
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I was just replying to hustle's question about why I can't have a 3 inch y-pipe lol
And I've had my obx for about 8 months now. No Rust really, they just turned sort of brownish.
And I've had my obx for about 8 months now. No Rust really, they just turned sort of brownish.
02-17-2010, 10:36 PM
#17
Ole' school guys used to spray and wipe their SS exhaust down with WD40 on the Ford GT40's back in the 60's to give it a pretty goldish brown color! It was one of their infamous fads......
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