Y-pipe kills your Max supposedly!
Senior Member
Joined: Oct 2002
Posts: 553
Backpressure in all cases is bad. Its not backpressure that's necessary, but HIGH EXHAUST VELOCITY. Unfortunately, in order to achieve high exhaust velocity, backpressure is simply a result of a correctly tuned exhaust *for certain RPM Ranges*. High exhaust velocity uses the momentum of the exhaust to produce a slight vacuum in certain RPM ranges aiding in the elimination of exhaust in the cylinder, and consequently making the engine not work as hard.
Now... the reasons why a 3" exhaust on your Maxima is bad unless you're boosted. The volume of air moving through that exhaust is not large enough to facilitate high exhaust velocity so you actually lose power than if you had a 2.5" or 2.25" exhaust system. Now, the smaller the diameter of exhaust, the lower the RPM range that benefits from the exhaust system, however, the higher RPM range suffers. The larger the exhaust pipe, the higher the RPM range that benefits. If you go to large a pipe, you will eventually go out of the RPM range of the engine altogether and have a compeltely inefficient exhaust system. Our exhaust systems (N/A Maximas) should be tuned to take advantage of the power somewhere between 4k and 5.5k RPM where the torque curve is nice and flat. This is where you want the "boost" in power.
The bottom line is, Backpressure is a necessary evil in order to achieve high exhaust flow. However, any restrictions that cause backpressure that aren't necessary should be eliminated, period.
Here are a few links:
http://home.att.net/~t.vago/faq-exhaust.html#backpres
http://www.autospeed.com/cms/A_1466/article.html
There's one really good article I've posted in the past that is similar to the second link that explains very well the issues of backpressure.
Now... the reasons why a 3" exhaust on your Maxima is bad unless you're boosted. The volume of air moving through that exhaust is not large enough to facilitate high exhaust velocity so you actually lose power than if you had a 2.5" or 2.25" exhaust system. Now, the smaller the diameter of exhaust, the lower the RPM range that benefits from the exhaust system, however, the higher RPM range suffers. The larger the exhaust pipe, the higher the RPM range that benefits. If you go to large a pipe, you will eventually go out of the RPM range of the engine altogether and have a compeltely inefficient exhaust system. Our exhaust systems (N/A Maximas) should be tuned to take advantage of the power somewhere between 4k and 5.5k RPM where the torque curve is nice and flat. This is where you want the "boost" in power.
The bottom line is, Backpressure is a necessary evil in order to achieve high exhaust flow. However, any restrictions that cause backpressure that aren't necessary should be eliminated, period.
Here are a few links:
http://home.att.net/~t.vago/faq-exhaust.html#backpres
http://www.autospeed.com/cms/A_1466/article.html
There's one really good article I've posted in the past that is similar to the second link that explains very well the issues of backpressure.
Member
Joined: Oct 2002
Posts: 170
more articles on back pressure
http://www.nissanperformancemag.com/...fthenerds2.php
http://www.nissanperformancemag.com/...revenge_nerds/
however the post above mine explains this well.
http://www.nissanperformancemag.com/...revenge_nerds/
however the post above mine explains this well.
Member who somehow became The President of The SE-L Club
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Joined: Jun 2001
Posts: 16,024
Originally posted by mzmtg
A free flowing exhaust does not cause burned pistons or valves. This was s symptom of poor tuning on older (usually carbureted) engines.
We know that a free flow exhaust lets the engine move more air. Well, if you dont add more fuel to the more air, the engine runs lean. This can burn things like pistons and valves.
Our cars' computers are more than able to automatically account for the extra air with extra fuel. This prevents the lean condition.
If you read the link in the FAQ, you would see why backpressure is always a bad thing for performance, no matter what the engine speed.
A free flowing exhaust does not cause burned pistons or valves. This was s symptom of poor tuning on older (usually carbureted) engines.
We know that a free flow exhaust lets the engine move more air. Well, if you dont add more fuel to the more air, the engine runs lean. This can burn things like pistons and valves.
Our cars' computers are more than able to automatically account for the extra air with extra fuel. This prevents the lean condition.
If you read the link in the FAQ, you would see why backpressure is always a bad thing for performance, no matter what the engine speed.
Your uncle needs to join the 20th century.
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Posts: n/a
I think I just found something convincing enough (http://www.motorvate.ca/mvp.php/504) and now I wonder if I can achieve the same (or perhaps similar) results in my 99 SE-L. Anyway, thanks for all the responses. I'm definitely getting one! 
1: I and many others have done dynos to prove the Y-pipe increases power.
2: I've had a Y-pipe since 2001 (not too long, but long enough), and I've passed emissions three times including just today. I live outside Philly which has an enhanced emissions test that actually monitors the exhaust output from the tailpipe.
Today's readings WITH Cattman Y-pipe:
CO: 0.08% - Limit 0.44%
HC: 49ppm - Limit 78ppm
NO: 460ppm - Limit 625ppm
3: Aftermarket Y-pipes remove pre-cats, which allow for better air flow. Pre-cats are used as extra filtration for emissions output, so as a design principle they do their purpose. If you look into a stock Y-pipe you'll notice that the area for air to move is much smaller, especially around the O2 sensors which hinders power.
2: I've had a Y-pipe since 2001 (not too long, but long enough), and I've passed emissions three times including just today. I live outside Philly which has an enhanced emissions test that actually monitors the exhaust output from the tailpipe.
Today's readings WITH Cattman Y-pipe:
CO: 0.08% - Limit 0.44%
HC: 49ppm - Limit 78ppm
NO: 460ppm - Limit 625ppm
3: Aftermarket Y-pipes remove pre-cats, which allow for better air flow. Pre-cats are used as extra filtration for emissions output, so as a design principle they do their purpose. If you look into a stock Y-pipe you'll notice that the area for air to move is much smaller, especially around the O2 sensors which hinders power.
...as far as reliability goes, there's a 4th gen Maxima owner up here in the "great white North" who's had a y-pipe on his car for the past 3 years with no engine problems.
His car has 380,000km's (approx. 235,000 miles).
'Nuff said.
His car has 380,000km's (approx. 235,000 miles).
'Nuff said.
Newbie - Just Registered
Joined: Nov 2001
Posts: 13
Originally posted by Smithdogg1
Yeah dont worry about it. I could see worrying about a supercharger or spray reducing reliability. Because it puts a lot more stress on the engine and tranny. But a Y-pipe is nothing to worry about. The only way i could see it being bad for reliability is that it is going to make you want to open up your car more...
Yeah dont worry about it. I could see worrying about a supercharger or spray reducing reliability. Because it puts a lot more stress on the engine and tranny. But a Y-pipe is nothing to worry about. The only way i could see it being bad for reliability is that it is going to make you want to open up your car more...
bolt-ons, like the y-pipe are simply "releasing" horsepower. it's kind of funny to say things like, "my intake gave me ** horsepower", or "my underdrive pulley gave me ** horsepower",
bolt-on's are not giving horsepower, they are freeing up horsepower
turbocharger, supercharger, NOS..........."forcing" more hp into the engine
forcing something to do or take something it was not designed for can never be a "long-lasting good thing"
I know if you were to force me to keep eating and eating pork and beans, I'd eventually $hit my pants!
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