2.25 or 2.5 y pipe
#1
2.25 or 2.5 y pipe
Ok, so ill make this quick, I need a new front y pipe. I have the option to get it in 2.25 or 2.5, I've read forums that the 2.25 will help with toque, I currently have heddman headers 1 5/8 to a 2" collector, and I have the stock 2.25 front y. My setup is mostly stock, stock heads, stock cam, tpi, ported plenum,base,runners, upgraded valvetrain with springs, seals, roller rockers, retainers.
Id like to keep the 2.25, but my friend has a brand new 2.5 that I can get for 50 bucks.
Can somebody explain the pros and cons of both?
Thank you guys!
Id like to keep the 2.25, but my friend has a brand new 2.5 that I can get for 50 bucks.
Can somebody explain the pros and cons of both?
Thank you guys!
#2
Team Owner
I assume you meant a 3" collector? Guess one thing you have to consider is the fitment from the larger Y-pipe to the main cat; Is that diameter the same on both Y-pipes? Also does the larger one have pre-cats?
The rest of the factory exhaust from the main cat back will be 2-1/4" so it may be that the 2-1/2" Y-pipe may not give you a lot of SOTP improvement. And the larger pipe will require fitting it to the reducers. Is the O2 sensor on the header collector or the reducer?
At this point, I would suggest doing away with the rest of the stock system and going with true duals and an X-pipe located where the main cat is.
The rest of the factory exhaust from the main cat back will be 2-1/4" so it may be that the 2-1/2" Y-pipe may not give you a lot of SOTP improvement. And the larger pipe will require fitting it to the reducers. Is the O2 sensor on the header collector or the reducer?
At this point, I would suggest doing away with the rest of the stock system and going with true duals and an X-pipe located where the main cat is.
#3
I assume you meant a 3" collector? Guess one thing you have to consider is the fitment from the larger Y-pipe to the main cat; Is that diameter the same on both Y-pipes? Also does the larger one have pre-cats?
The rest of the factory exhaust from the main cat back will be 2-1/4" so it may be that the 2-1/2" Y-pipe may not give you a lot of SOTP improvement. And the larger pipe will require fitting it to the reducers. Is the O2 sensor on the header collector or the reducer?
At this point, I would suggest doing away with the rest of the stock system and going with true duals and an X-pipe located where the main cat is.
The rest of the factory exhaust from the main cat back will be 2-1/4" so it may be that the 2-1/2" Y-pipe may not give you a lot of SOTP improvement. And the larger pipe will require fitting it to the reducers. Is the O2 sensor on the header collector or the reducer?
At this point, I would suggest doing away with the rest of the stock system and going with true duals and an X-pipe located where the main cat is.
#4
Race Director
u maybe right about the collector, id like to stick with a y pipe, my cat is a catco cat 2.25 inlet and 2.25 outlet I have magnaflow 2.5 tail pipe & 3.5 outlet to boot. My 02 sensor is currently in the y pipe, when I installed the headders i put the bung in the y pipe
#6
Race Director
Is your friend's $50 2.5" Y-pipe cat-less? I assume your main cat is a stocker?
#7
well his y pipe he's selling is for a 90, but ill have to cut the cats and a few more inches after the cats for my headders, I don't think my main cat is stock, it reads catco with an arrow pointing toward the rear of the vehicle
#8
Le Mans Master
http://www.pineboxonline.com/backpressure.html
Some say that "an engine needs backpressure to work correctly." Is this true?
No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.
The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.
The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.
The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.
Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.
Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.
Original web link: Destroying a Myth
Some say that "an engine needs backpressure to work correctly." Is this true?
No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.
The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.
The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.
The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.
Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.
Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.
Original web link: Destroying a Myth
#9
Race Director
Unless you'll convert to high-flow converters (or go w/o) -- up front -- I'm not sure I see the point. $50 is a good price though...and can't hurt your performance. Keep in mind a setup without front converters is VERY likely to drone. I know because I've tried it...with the 2.5" Y-pipe you're talking about.
OTOH, with headers, a simple Y-splitter and short sections of pipe will work too. I'd hang bullet cats off your headers and run short pipe to a Y-joint. From there, I might be more inclined to install a glass pack to connect you to the rear Y-pipe. Of course stock mufflers in the back-end is also a bad move for best power production. With a glass-pack in the belly...and bullet cats...you could install resonated targa tips and end up about right. (in sound)
With a center cat, the sound will be very tame...almost factory euro. Without a center cat, you'll get more gurgle, growl, and bark.
Bottom line...I'm not sure, even with a good price, that you'll benefit from that $50 y-pipe....mostly because headers...and my recommendation for cats leaves you will little need for a complete Y-pipe. Just get a short splitter. (also known as a y-pipe).
One other thing to consider is two bullet cats in a front 2.5" system will outflow what that center CATCO will allow. That's why I like the front bullets better. I also think center canister mufflers/cats is what can cause drone. (If you get louder than stock)
OTOH, with headers, a simple Y-splitter and short sections of pipe will work too. I'd hang bullet cats off your headers and run short pipe to a Y-joint. From there, I might be more inclined to install a glass pack to connect you to the rear Y-pipe. Of course stock mufflers in the back-end is also a bad move for best power production. With a glass-pack in the belly...and bullet cats...you could install resonated targa tips and end up about right. (in sound)
With a center cat, the sound will be very tame...almost factory euro. Without a center cat, you'll get more gurgle, growl, and bark.
Bottom line...I'm not sure, even with a good price, that you'll benefit from that $50 y-pipe....mostly because headers...and my recommendation for cats leaves you will little need for a complete Y-pipe. Just get a short splitter. (also known as a y-pipe).
One other thing to consider is two bullet cats in a front 2.5" system will outflow what that center CATCO will allow. That's why I like the front bullets better. I also think center canister mufflers/cats is what can cause drone. (If you get louder than stock)
Last edited by GREGGPENN; 06-18-2013 at 05:03 PM.
#10
Le Mans Master
I agree with Greg. I would go even a little further, and if going with bullet cats up front, then just go with a "true dual" with an x-pipe. Of course, depending on emission requirements in your state in terms of registration. However, the reference to cutting cats tells me it may not be an issue so much.
#11
Team Owner
Member Since: Dec 2000
Location: SE NY
Posts: 90,675
Likes: 0
Received 300 Likes
on
274 Posts
Cruise-In II Veteran
Is your current front Y mandrel bent? If not replace with one that is.
Is your friend's front Y mandrel bent? If not, skip it.
A mandrel bent front Y will bring more power. Since you have (FL??) haders there is no need to worry about loss of "back pressure".
In fact anything you can do to reduce back pressure should help power over a stock system. Remember that you need 2.2 cfm of exhaust flow for every 1chp to avoid power loss.
When increasing air flow it's necessary to increase fuel flow to match at WOT. This can be accomplished by increasing fuel pressure.
Is your friend's front Y mandrel bent? If not, skip it.
A mandrel bent front Y will bring more power. Since you have (FL??) haders there is no need to worry about loss of "back pressure".
In fact anything you can do to reduce back pressure should help power over a stock system. Remember that you need 2.2 cfm of exhaust flow for every 1chp to avoid power loss.
When increasing air flow it's necessary to increase fuel flow to match at WOT. This can be accomplished by increasing fuel pressure.