• Will opening up an exhaust cause power loss?
  • Will opening up an exhaust cause power loss?
  • Will opening up an exhaust cause power loss?
  • Will opening up an exhaust cause power loss?

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  1. #1
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    Default Will opening up an exhaust cause power loss?

    I am planning on putting exhaust cutouts in my vette right after the resonator. I have talked to many people with experience and their answers contradict each other. Some people say less back pressure = HP, while others say you loose HP????

    Will exhaust cutouts after the resonator cause a power loss or power gain? (Stock 1996 LT1) Why?


    Thanks Everyone!

  2. #2
    Will opening up an exhaust cause power loss? TedC's Avatar
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    dogfish246, I can't answer your specific question, but I did ask my local speed shop (with dyno) what are the common mistakes owners make, and exhaust mods are high on the list. This topic is sure to cause debates, but the bottom line to performance was intake and exhaust air velocity. Air velocity can be adjusted by changing intake and exhaust sizes, which moves the torque and related hp curve up and down the rpm scale. Having no back pressure does not mean maximum velocity. I'll use a ricer example. A Honda Si was dyno'ed with a modified exhaust (larger pipes from engine all the way back), and had actually lost power below 4000 rpm. Peak HP did increase, but it also moved up higher on the rpm scale. A lean condition was also occuring. The exhaust system was out of balance with the veleocity ability of the intake, cam and valves. Specific to a C4 L98, their is some room to improve exhaust velocity, but the intake system was designed for low to medium rpm velocity. So the reason you hear two answers is that it all depends what you are trying to do. For my L98, I need wide band torque for maximum performance because of the automatic and lower reving engine. Adding 10 more HP at 5000 rpm doesn't help me if I drop 10 HP at 2500 rpm. There are experts on this forum who can do a much better job of explaining the science behind all of this.

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    Why do you want cut outs?
    If you were after max Hp gain you would have in front of resonator so as to give same effect as open headers like race cars.
    This of course is assuming you have other mods , headers , cam, heads to support such a idea
    If it is only to make noise save the $$ and put muffler eliminators (straight pipes ) on

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    Member ARKvette02's Avatar
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    Boy....those Manalapan cops are gonna love you rumbling up and down rt.33 he he he. Waving a hand from Bricktown
    Billy

  5. #5
    MBDiagMan
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    A common misconception is that reducing backpressure will result in power loss. What has caused this is in the old days, on carbureted engines, people would open up their exhaust with no other modifications and indeed often lose power. The reason was that the loss in back pressure leans out the mixture.

    To benefit from the opened up exhaust it was necessary to rejet the carburetor. Since this was something beyond many folks, the belief that power would be lost was born.

    On your Corvette, any flow increase is automatically compensated for due to the increased flow through the Mass Air Flow sensor. The increased air flow is compensated for by the ECM resulting in MORE power.

    Open exhaust produces MORE power IF the mixture is compensated for.

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    Quote Originally Posted by ARKvette02 View Post
    Boy....those Manalapan cops are gonna love you rumbling up and down rt.33 he he he. Waving a hand from Bricktown

    Yep! haha, I am also in Brick a lot over the summer (fishing Barnegat Bay, and Ocean Fishing off Pt. Pleasant) Maybe Ill see you on the road!

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    Also, the reason I want cutouts is becasue it is cheaper than a new exhaust system, but has the same effect! Plus, my Vette is an everyday driver so if I want quiet, then I just shut the cutouts! I just want to make sure I wont loose power, but from all of the replys and research, I will probably gain power!

    Thanks Guys!

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    Will opening up an exhaust cause power loss? BigJimZ16's Avatar
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    Quote Originally Posted by dogfish246 View Post
    Yep! haha, I am also in Brick a lot over the summer (fishing Barnegat Bay, and Ocean Fishing off Pt. Pleasant) Maybe Ill see you on the road!

    Born and raised in Manasquan, spent a lot of time surf casting on the northside of the inlet... Seems like forever since I've been there. Been out here on Lake Michigan since '74.
    The only thing that you accomplish when you make something idiotproof, is breed a better grade of idiot,

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    My guess is cutouts behind the stock resonator will not gain any more power than putting on a complete low restriciton exhaust system because the gain in restriction you get in bypassing just the mufflers will probably equal that you gain in replacing both the resonator and the mufflers with less restrictive components.

    Also, you might not care for the car's sound with cutouts after the resonator. With the exhaust outlets right below your ears, you may find the loudness and/or the quality of the sound objectionable.
    Hib Halverson

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    Member Cruzen's Avatar
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    Quote Originally Posted by TedC View Post
    dogfish246, I can't answer your specific question, but I did ask my local speed shop (with dyno) what are the common mistakes owners make, and exhaust mods are high on the list. This topic is sure to cause debates, but the bottom line to performance was intake and exhaust air velocity. Air velocity can be adjusted by changing intake and exhaust sizes, which moves the torque and related hp curve up and down the rpm scale. Having no back pressure does not mean maximum velocity. I'll use a ricer example. A Honda Si was dyno'ed with a modified exhaust (larger pipes from engine all the way back), and had actually lost power below 4000 rpm. Peak HP did increase, but it also moved up higher on the rpm scale. A lean condition was also occuring. The exhaust system was out of balance with the veleocity ability of the intake, cam and valves. Specific to a C4 L98, their is some room to improve exhaust velocity, but the intake system was designed for low to medium rpm velocity. So the reason you hear two answers is that it all depends what you are trying to do. For my L98, I need wide band torque for maximum performance because of the automatic and lower reving engine. Adding 10 more HP at 5000 rpm doesn't help me if I drop 10 HP at 2500 rpm. There are experts on this forum who can do a much better job of explaining the science behind all of this.
    I agree with this assessment. Most gains in HP from such changes are not noticed until the engine is up near it's peak RPM. From the late 1960's through the early 1980's I built and tested many Chevy small blocks that went through this same process. Adding headers and larger exhaust does hurt bottom end torque and HP. (The 302's were the worst. ) Many articles written during that time period as well as small block hop up books explain this. The carb does need to be rejetted etc. The HP and torque curves are moved up the scale but the bottom end below 2500-3000 is always hurt. Some people disagree with this and I don't argue with them because I have had experience to the contrary. ( I still have access to several of the cars that were so modified.)

    Some people do not understand the relationship between torque and HP curves. Compare the curves for a 1994-96 LT-1 and an 1998 LS1. While the LS1 does produce more HP at top end, it produces less HP and torque at the bottom end. Which is better depends on your driving style.

    I would imagine that on today's fuel injected and computer controlled engines some puter reprogramming will accomplish the same as rejetting but the bottom end as well as MPG will still be impacted so the question remains the same as I asked customers back in 1970. Do you spend most of your driving time under 3000 or closer to 6000. If your answer is 3000 then get some louder mufflers and pretend you made an improvement. It has the same impact as putting those baseball cards in your bicycle spokes.

    The trip is short,
    enjoy the ride,
    Denny

  11. #11
    Will opening up an exhaust cause power loss? Vettefan87's Avatar
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    If you run straight open exhaust it will be very loud at WOT. After a while it gets to be to much.

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    Member So Bay Vetter's Avatar
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    Attachment 19363

    Muffler eliminators are quiet enough with otherwise stock exhaust (until you put your foot in it!) and much less hassle.

  13. #13
    Member G Winter's Avatar
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    Quote Originally Posted by So Bay Vetter View Post
    Attachment 19363

    Muffler eliminators are quiet enough with otherwise stock exhaust (until you put your foot in it!) and much less hassle.
    Are muffler eliminators chambered pipes ?

    Glenn

  14. #14
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    My Vette is my everyday driver so I dont want to have it loud all of the time, but I want a V8 muscle car rumble too. That is why I am looking into Cutouts.

    Thanks for all of the replys, now I have to make a decision (and some $$$)

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    Quote Originally Posted by G Winter View Post
    Are muffler eliminators chambered pipes ?
    No just pipes bent or made to eliminate the mufflers altogether.
    Cheaper to get local exh shop to do

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