For all of you who think backpressure is important!
02-15-2005, 04:35 PM
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For all of you who think backpressure is important!
02-15-2005, 05:39 PM
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thanks for posting that.
A couple of things it mentioned that I think are worth repeating here for those that won't read the entire article.
A 1.5L engine should be a 2" pipe unless forced induction is used. anything larger will rob power.
The Cat's in today's imports flow so well that replacing them usually won't see any gains and gutting them will most def. see losses.
If you put on a "big ___ tip" you will get pulled over and end up on beaterz.com.
Finally, when using a proper straight threw pipe, length doesn't rob power. So, use as long as possible to keep the noise down.
A couple of things it mentioned that I think are worth repeating here for those that won't read the entire article.
A 1.5L engine should be a 2" pipe unless forced induction is used. anything larger will rob power.
The Cat's in today's imports flow so well that replacing them usually won't see any gains and gutting them will most def. see losses.
If you put on a "big ___ tip" you will get pulled over and end up on beaterz.com.
Finally, when using a proper straight threw pipe, length doesn't rob power. So, use as long as possible to keep the noise down.
02-15-2005, 07:13 PM
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that link is filled with so much miss information. 18 PSI of back pressue would blow your muffler off. Too funny and you need some backpressure in any non-WOT type of driving where all street cars spend 99.9999% of the time. You get a 5-10 HP at max from a Scion due to a better exhaust with current cams NA, and more of course forced induced. Don't believe me just unbolt your exhaust after the factory header and let me know how "drivable" your ride is with .5 PSI less backpressure....
02-15-2005, 07:31 PM
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Originally Posted by oldman
that link is filled with so much miss information. 18 PSI of back pressue would blow your muffler off. Too funny and you need some backpressure in any non-WOT type of driving where all street cars spend 99.9999% of the time. You get a 5-10 HP at max from a Scion due to a better exhaust with current cams NA, and more of course forced induced. Don't believe me just unbolt your exhaust after the factory header and let me know how "drivable" your ride is with .5 PSI less backpressure....
02-15-2005, 07:41 PM
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Originally Posted by oldman
that link is filled with so much miss information. 18 PSI of back pressue would blow your muffler off. Too funny and you need some backpressure in any non-WOT type of driving where all street cars spend 99.9999% of the time. You get a 5-10 HP at max from a Scion due to a better exhaust with current cams NA, and more of course forced induced. Don't believe me just unbolt your exhaust after the factory header and let me know how "drivable" your ride is with .5 PSI less backpressure....
+++++++++++++++++++++++++++++++++++++
"An old hot-rodder's tall tale: Engines need some backpressure to work properly and make torque. That is not true. What engines need is low backpressure, but high exhaust stream velocity. A fast-moving but free-flowing gas column in the exhaust helps create a rarefaction or a negative pressure wave behind the exhaust valve as it opens. This vacuum helps scavenge the cylinder of exhaust gas faster and more thoroughly with less pumping losses. An exhaust pipe that is too big in diameter has low backpressure but lower velocity. The low velocity reduces the effectiveness of this scavenging effect, which has the greatest impact on low-end torque."
+++++++++++++++++++++++++++++++++++++
Makes sense to me.
02-15-2005, 07:43 PM
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Originally Posted by Lonely Raven
Why aftermarket exhaust systems are good!
Produced by, and sponsored by- An aftermarket exhaust manufacturer!
Produced by, and sponsored by- An aftermarket exhaust manufacturer!
uh.... the article is about building your own exhaust system?
02-15-2005, 07:57 PM
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Originally Posted by bbcrud
Originally Posted by oldman
that link is filled with so much miss information. 18 PSI of back pressue would blow your muffler off. Too funny and you need some backpressure in any non-WOT type of driving where all street cars spend 99.9999% of the time. You get a 5-10 HP at max from a Scion due to a better exhaust with current cams NA, and more of course forced induced. Don't believe me just unbolt your exhaust after the factory header and let me know how "drivable" your ride is with .5 PSI less backpressure....
+++++++++++++++++++++++++++++++++++++
"An old hot-rodder's tall tale: Engines need some backpressure to work properly and make torque. That is not true. What engines need is low backpressure, but high exhaust stream velocity. A fast-moving but free-flowing gas column in the exhaust helps create a rarefaction or a negative pressure wave behind the exhaust valve as it opens. This vacuum helps scavenge the cylinder of exhaust gas faster and more thoroughly with less pumping losses. An exhaust pipe that is too big in diameter has low backpressure but lower velocity. The low velocity reduces the effectiveness of this scavenging effect, which has the greatest impact on low-end torque."
+++++++++++++++++++++++++++++++++++++
Makes sense to me.
It makes perfect sense because the information is factual and accurate,unlike the information that some self proclaimed experts here in this forum spew.
02-15-2005, 08:05 PM
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I've been thinking lately of running a larger diameter exhaust system. I have the Borla axleback but I want to get headers and run custom tubing from the headers to the Borla axleback. Am I going to have to worry about my sensors freaking out and dash lights coming on?
02-15-2005, 09:40 PM
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It makes perfect sense because the information is factual and accurate,unlike the information that some self proclaimed experts here in this forum spew.
Yeh here is the quote:
“Some stock mufflers and exhaust systems have up to 18psi of choking, power-robbing backpressure. In direct contrast, a well-designed, high-performance street exhaust system typically has about 2 to 6 psi of backpressure. “
How much is 18 PSI? Well lets see um stock muffler is say 1 foot in diameter cylinder, 2 feet long, Area is PI x Diameter x length = 905 sq inches x 18 PSI = 16290 lbs of pressure pushing out of the case or a little more then 8 TONS. Want me to calculate the CFM flow through the engine to pressurize the exhaust system to that? I think not. Oh and how much backpressure is the “guru” talking about if say I put my hand in back of the exhaust system? 2.25 / 2 sqaued x PI x 18 PSI = 72 pounds of pressure, that is what this “guru” is saying is being run in the pipe and cause of the gas law this is through the whole pipe – some small pressure drop needed to actually flow this from source to sing. LOL too funny!
You want me to calculate the amount of HP loss to 18 PSI of back pressure or how about torque? OK Torque lets see 18 PSI means the piston has to force 18 PSI out the exhaust so um that is
3.48 bore / 2 squared x18 PSI = Force on piston top x moment arm of crank which is idealized as ˝ of 3.78 = torque needed to drive piston up the bore against 18 PSI of backpressure or => or 26 ft-lbs. We are not talking torque gain because of better cylinder savaging which most headers and exhaust systems do, we are talking direct pumping loss. I personally think I’d notice +26 ft-lbs across the entire range, but please unbolt your head pipe and drive around for a few days and let us know if you find +26 ft –lbs across the torque range which is 26 HP @ 5250 or 52 HP @ 2700 RPM or 104 HP @1350 RPM BTW. Spanking.
Here is a working model feel free to play with it:
http://www.maxcooper.com/rx7/how-to/...ystem/why.html
Yes I see that the author probably over exaggerated the restrictions, but this is a much older turbo RX7 TURBO which can use and does need a bigger exhaust.
Um and I’ve used this type of performance gauge and it goes upto 8 PSI!
http://shop.store.yahoo.com/bradysto...aprgaotc7.html
Oh and my old favorite is David Vizard here!
http://www.installuniversity.com/ins...k_pressure.htm
street/race car should be at or below 2.2 psi of exhaust backpressure. At anytime if the cumulative back pressure is above 5 psi, the exhaust system needs serious modification.
Like I said in the first post any street legal after cat exhaust system normally aspirated with current cams will show at best .5 PSI Well I did not say it that way but I should have. Point being 18 PSI is completely and totally laughable, which I did say.
02-15-2005, 09:46 PM
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Um yes with turbo you should look into something and really I'd start from scratch and do a 3" depending on the turbo and what you are going to do, even at 2.5 (2.75 pipe is not common) you would be butting heads with the exhaust, 3" you would be good to some crazy levels of power. Just my thoughs I've had 2.5 on turbo 4 bangers before most much smaller then 2.4 liters and each time the performace was much better uncapped after the down pipe.
Supercharger to sane levels say 250 BHP, header, 2.5 mandrel is good enough.
For me if I supercharger I want quite, so stock exhaust for me or maybe that cool header with the CAT, but really I don't want anybody knowing I'm packing under the hood. good upto say 225 BHP, after which the exhaust should be address stem to stern.
Supercharger to sane levels say 250 BHP, header, 2.5 mandrel is good enough.
For me if I supercharger I want quite, so stock exhaust for me or maybe that cool header with the CAT, but really I don't want anybody knowing I'm packing under the hood. good upto say 225 BHP, after which the exhaust should be address stem to stern.
02-15-2005, 09:54 PM
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Originally Posted by hahaitzskippy
thie means i have to get a new exhaust system when i turbo my car?!?!?!
man...
man...
02-15-2005, 10:05 PM
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Originally Posted by acasanova
Originally Posted by oldman
that link is filled with so much miss information. 18 PSI of back pressue would blow your muffler off. Too funny and you need some backpressure in any non-WOT type of driving where all street cars spend 99.9999% of the time. You get a 5-10 HP at max from a Scion due to a better exhaust with current cams NA, and more of course forced induced. Don't believe me just unbolt your exhaust after the factory header and let me know how "drivable" your ride is with .5 PSI less backpressure....
Now, since you call them EXPERTS, it would be nice to put them (Magnaflow) in contact with TOYOTA so that way they can tell the SCION Engineers in Japan how wrong they were regarding exhaust systems and how little they know about cars design. Probably Toyota will recognize the big mistake they did.
02-15-2005, 10:12 PM
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Originally Posted by oldman
It makes perfect sense because the information is factual and accurate,unlike the information that some self proclaimed experts here in this forum spew.
Yeh here is the quote:
“Some stock mufflers and exhaust systems have up to 18psi of choking, power-robbing backpressure. In direct contrast, a well-designed, high-performance street exhaust system typically has about 2 to 6 psi of backpressure. “
How much is 18 PSI? Well lets see um stock muffler is say 1 foot in diameter cylinder, 2 feet long, Area is PI x Diameter x length = 905 sq inches x 18 PSI = 16290 lbs of pressure pushing out of the case or a little more then 8 TONS. Want me to calculate the CFM flow through the engine to pressurize the exhaust system to that? I think not. Oh and how much backpressure is the “guru” talking about if say I put my hand in back of the exhaust system? 2.25 / 2 sqaued x PI x 18 PSI = 72 pounds of pressure, that is what this “guru” is saying is being run in the pipe and cause of the gas law this is through the whole pipe – some small pressure drop needed to actually flow this from source to sing. LOL too funny!
You want me to calculate the amount of HP loss to 18 PSI of back pressure or how about torque? OK Torque lets see 18 PSI means the piston has to force 18 PSI out the exhaust so um that is
3.48 bore / 2 squared x18 PSI = Force on piston top x moment arm of crank which is idealized as ˝ of 3.78 = torque needed to drive piston up the bore against 18 PSI of backpressure or => or 26 ft-lbs. We are not talking torque gain because of better cylinder savaging which most headers and exhaust systems do, we are talking direct pumping loss. I personally think I’d notice +26 ft-lbs across the entire range, but please unbolt your head pipe and drive around for a few days and let us know if you find +26 ft –lbs across the torque range which is 26 HP @ 5250 or 52 HP @ 2700 RPM or 104 HP @1350 RPM BTW. Spanking.
Here is a working model feel free to play with it:
http://www.maxcooper.com/rx7/how-to/...ystem/why.html
Yes I see that the author probably over exaggerated the restrictions, but this is a much older turbo RX7 TURBO which can use and does need a bigger exhaust.
Um and I’ve used this type of performance gauge and it goes upto 8 PSI!
http://shop.store.yahoo.com/bradysto...aprgaotc7.html
Oh and my old favorite is David Vizard here!
http://www.installuniversity.com/ins...k_pressure.htm
street/race car should be at or below 2.2 psi of exhaust backpressure. At anytime if the cumulative back pressure is above 5 psi, the exhaust system needs serious modification.
Like I said in the first post any street legal after cat exhaust system normally aspirated with current cams will show at best .5 PSI Well I did not say it that way but I should have. Point being 18 PSI is completely and totally laughable, which I did say.
Here is another article on the whole backpressure issue. Note this is a naturally aspirated engine unlike you other interactive example which was a turboed engine. The whole issue is backpressure (negative flow) its not necessary ,rather gas velocity and the correlation between pipe size and scanvenging . Thats the key to performance.
Here the link:
http://www.miata.net/garage/KnowYourCar/S4_Back.html.