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3" y-pipe vrs 2.5" gains?

This is a discussion on 3" y-pipe vrs 2.5" gains? within the External Engine forums, part of the LSx Technical Help Section category; At what h.p. would the "stock" 2.5" exhaust pipe be good til? H.p. wise? Also how much gains could one ...

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    Junior Member smslyguy's Avatar
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    3" y-pipe vrs 2.5" gains?

    At what h.p. would the "stock" 2.5" exhaust pipe be good til? H.p. wise? Also how much gains could one expect to get from a 3" y-pipe when it "merges" to a 3"? Just doesn't make much sense to me as to have a 3" y-pipe that merges to a 3"?

    Wouldn't it make more sense if you were upgrading to a 3" y-pipe to make the merge at least a 4" instead of a slamming all that exhaust into the same size diameter pipe??

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    Member My00Z28's Avatar
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    Quote Originally Posted by smslyguy View Post
    At what h.p. would the "stock" 2.5" exhaust pipe be good til? H.p. wise? Also how much gains could one expect to get from a 3" y-pipe when it "merges" to a 3"? Just doesn't make much sense to me as to have a 3" y-pipe that merges to a 3"?

    Wouldn't it make more sense if you were upgrading to a 3" y-pipe to make the merge at least a 4" instead of a slamming all that exhaust into the same size diameter pipe??
    dont know the HP ranges but going from a 3" y-pipe to a 3" I-pipe will create some back pressure which can help your low end torque. same goes for cats

    throttle response can also be affected by back pressure.
    Last edited by My00Z28; 04-20-2011 at 02:04 PM.

  3. #3
    Quote Originally Posted by smslyguy View Post
    At what h.p. would the "stock" 2.5" exhaust pipe be good til? H.p. wise? Also how much gains could one expect to get from a 3" y-pipe when it "merges" to a 3"? Just doesn't make much sense to me as to have a 3" y-pipe that merges to a 3"?

    Wouldn't it make more sense if you were upgrading to a 3" y-pipe to make the merge at least a 4" instead of a slamming all that exhaust into the same size diameter pipe??
    Stock exhaust is good for about 310bhp (read it in an article on here) I thought the stock y pipe was 2". BBK makes a 2.5" Y pipe but I like the TSP 3" pipes the best. Its 3" then it merges down where the I pipe slides in. To answer your question you wouldnt notice much on a bolt on car.

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    megs 02sunsetorangeZ's Avatar
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    i really dont think going to 4 inch is going to gain anything really worth doing the trouble over. 3 inch is the most common. 2.5 inch will restrict you a bit if you decide to go internally later down the road, heads, cam, etc... i say just get a 3 inch ory pipe if you want. If you your worried about the merging into one pipe then go with 3 inch duals with a x pipe that will be plenty of breathing for her. just a litttle bit more expensive

  5. #5
    Quote Originally Posted by 02sunsetorangeZ View Post
    i really dont think going to 4 inch is going to gain anything really worth doing the trouble over. 3 inch is the most common. 2.5 inch will restrict you a bit if you decide to go internally later down the road, heads, cam, etc... i say just get a 3 inch ory pipe if you want. If you your worried about the merging into one pipe then go with 3 inch duals with a x pipe that will be plenty of breathing for her. just a litttle bit more expensive
    This or 3" w/cut out would be fine.

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by smslyguy View Post
    At what h.p. would the "stock" 2.5" exhaust pipe be good til? H.p. wise? Also how much gains could one expect to get from a 3" y-pipe when it "merges" to a 3"? Just doesn't make much sense to me as to have a 3" y-pipe that merges to a 3"?

    Wouldn't it make more sense if you were upgrading to a 3" y-pipe to make the merge at least a 4" instead of a slamming all that exhaust into the same size diameter pipe??
    The factory Y is 2 1/4 I believe.

    And yes you are right, it makes more sense to merge a 3" Y into a 4" I-pipe. Going from a 3" Y to a 3" I-pipe does create a bottle neck.

    We ran several 3" catbacks on one particular car, keeping the headers and Y the same. Switched to a Mufflex 4" catback and the car picked up nearly 3 tenths and 3-4 mph.
    Bottom line, trying to funnel 400 HP through a single 3" exhaust system is actually quite restrictive. You are better off either running a true dual system of some form,,,,or jumping to at least the Mufflex 3 1/2 inch catback.

  7. #7
    Quote Originally Posted by Firebirdjones View Post
    The factory Y is 2 1/4 I believe.

    And yes you are right, it makes more sense to merge a 3" Y into a 4" I-pipe. Going from a 3" Y to a 3" I-pipe does create a bottle neck.

    We ran several 3" catbacks on one particular car, keeping the headers and Y the same. Switched to a Mufflex 4" catback and the car picked up nearly 3 tenths and 3-4 mph.
    Bottom line, trying to funnel 400 HP through a single 3" exhaust system is actually quite restrictive. You are better off either running a true dual system of some form,,,,or jumping to at least the Mufflex 3 1/2 inch catback.
    Yeah it cant be 2.5 because the bbk y pipe is 2.5 and you cant run the factory y w/ long tubes. As far as the 3" cat backs go, I have a lm1 on mine and I cant see it being that restrictive. I only have full exhaust and lid though..

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    Moderator Firebirdjones's Avatar
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    It's not so much the muffler choice, it's the size of the piping that we found to make the biggest difference.

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    Junior Member smslyguy's Avatar
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    Quote Originally Posted by Firebirdjones View Post
    The factory Y is 2 1/4 I believe.

    And yes you are right, it makes more sense to merge a 3" Y into a 4" I-pipe. Going from a 3" Y to a 3" I-pipe does create a bottle neck.

    We ran several 3" catbacks on one particular car, keeping the headers and Y the same. Switched to a Mufflex 4" catback and the car picked up nearly 3 tenths and 3-4 mph.
    Bottom line, trying to funnel 400 HP through a single 3" exhaust system is actually quite restrictive. You are better off either running a true dual system of some form,,,,or jumping to at least the Mufflex 3 1/2 inch catback.
    What kind of ground clearance did you have with the mufflex 3" to 4" y-pipe? I was looking at there y-pipe. Very nice merge collector. And also was woundering about there 4" catback for clearance over the axle.

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    Junior Member smslyguy's Avatar
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    Quote Originally Posted by Firebirdjones View Post
    The factory Y is 2 1/4 I believe.

    And yes you are right, it makes more sense to merge a 3" Y into a 4" I-pipe. Going from a 3" Y to a 3" I-pipe does create a bottle neck.

    We ran several 3" catbacks on one particular car, keeping the headers and Y the same. Switched to a Mufflex 4" catback and the car picked up nearly 3 tenths and 3-4 mph.
    Bottom line, trying to funnel 400 HP through a single 3" exhaust system is actually quite restrictive. You are better off either running a true dual system of some form,,,,or jumping to at least the Mufflex 3 1/2 inch catback.

    Any idea's of what the 3 1/2" catback is good for h.p. wise? I have a pretty nice cam and ported and polished heads in my car.

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    Electrical Engineer KMdef9's Avatar
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    Quote Originally Posted by smslyguy View Post
    What kind of ground clearance did you have with the mufflex 3" to 4" y-pipe? I was looking at there y-pipe. Very nice merge collector. And also was woundering about there 4" catback for clearance over the axle.
    You might need the pan hard relocation brackets for extra clearance for that 4".

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by smslyguy View Post
    What kind of ground clearance did you have with the mufflex 3" to 4" y-pipe? I was looking at there y-pipe. Very nice merge collector. And also was woundering about there 4" catback for clearance over the axle.
    Quote Originally Posted by smslyguy View Post
    Any idea's of what the 3 1/2" catback is good for h.p. wise? I have a pretty nice cam and ported and polished heads in my car.
    We used the 4" on a buddies 97 LT1 and it installed without much hassle at all. No ground clearance issues at all, which is the reason we went that route instead of fabbing a dual system.
    Once installed, you couldn't even see it. He used the single hidden tailpipe setup.

    On the 3 1/2" I also chose the single hidden tailpipe. I also went with the Magnaflow muffler that is now optional as well.
    Not sure off hand how much HP this system in particular will support.

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    Junior Member smslyguy's Avatar
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    just wanted to let you guy's know that i went with a 3" y-pipe to a 4" catback with a mufflex muffler. Sounds awesome!! And yes it was a tight fit, but well worth it. It does fit nice with no ground clearance issues. Not even over the axle.

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    Junior Member smslyguy's Avatar
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    Quote Originally Posted by KMdef9 View Post
    You might need the pan hard relocation brackets for extra clearance for that 4".
    DIdn't need them it fit well over the axle...
    2001 camaro z28 ss vert with factory slp upgrade, LT headers with a 4" exhaust airlid,s.s.r.a.,t.c.bypass,ported and polished m.a.f torquer v 2. comp cam with ported and polished heads and a tune with EFI Live Tune.
    Dyno- 399 r.w.h.p.
    384 lbs of torque

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