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Thread: exhaust cutout

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    Better than that "other" place Not Verified Feedback Score 2 (100%) x2xtreme360's Avatar
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    exhaust cutout

    Eventually, I will be custom welding an exhaust cutout to my downpipe before the main cat. I am wondering here, if the cutout outlet is at an angle, will the exhaust have an easy flow out or will it still attempt to go down the straight path of the exhaust?



    This is just an example. If the cutout "Y's" off away from the straight flow of exhaust, would this cause turbulance in the exhaust system or would the excess pressure still find its way out just fine?

    I'm looking at this to get rid of ALL backpressure in the exhaust system while keeping the catback completely stock. It saves money and does exactly what I want it to do.

    Vacuum reduction, Powdercoated misc, cruise relocate, Evo9 BOV, Custom catch cans, Russell fuel filter, SS braided fuel lines, High flow fuel loop, Autogage fuel gauge, Catless DP, DNP Y-pipe, Fuel pump hotwire.

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    1st ever COTM and COTY verified Feedback Score 9 (100%) green-lantern's Avatar
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    Get the electric one, vr3.9 has one.

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    Member verified Feedback Score 1 (100%) B-Man's Avatar
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    Yes, it would cause turbulence, but it's so close to the exit, that the backpressure it would cause is negligible.

    I've been toying with the idea of making a vacuum actuated one by just using a wastegate off a stock turbo to open the valve.
    '92 Dodge Stealth RT/TT - Aug. 2012 COTM

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    Better than that "other" place Not Verified Feedback Score 2 (100%) x2xtreme360's Avatar
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    Quote Originally Posted by green-lantern View Post
    Get the electric one, vr3.9 has one.
    Oh, yes... for sure. I'm not going to buy one at IPS though. I can get the cutout for around $150 and weld in a small amount of tubing to branch off the downpipe.

    Quote Originally Posted by B-Man View Post
    Yes, it would cause turbulence, but it's so close to the exit, that the backpressure it would cause is negligible.

    I've been toying with the idea of making a vacuum actuated one by just using a wastegate off a stock turbo to open the valve.
    Thought about it... but I'm not interested in it being on all the time ie: every time I hit boost. I would only use it when I need it.

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    1st ever COTM and COTY verified Feedback Score 9 (100%) green-lantern's Avatar
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    If you were custom building the exhaust you could make the angle side go through the rest of the exhaust and have the straight side open. Not really sure if it would be worth it though.

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    Better than that "other" place Not Verified Feedback Score 2 (100%) x2xtreme360's Avatar
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    Quote Originally Posted by green-lantern View Post
    If you were custom building the exhaust you could make the angle side go through the rest of the exhaust and have the straight side open. Not really sure if it would be worth it though.
    I thought of doing that too. A little more work, but I don't care about the backpressure when it's closed... I only want it eliminated when it's open.

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    The one. The only. verified Feedback Score 11 (100%) stealthee's Avatar
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    You're not going to cause enough backpressure with the angle and no catback to cause a major power difference. Keep the straight side on the normal exhaust, and leave the angled end to the cutout.

    Personally I've had an idea for a cutout I want to do. I love the sound of my car, but the volume gets annoying at times since its my DD. I wanted to get an electric cutout with a 3 way stepper motor. In mode A it would flow through the catback and mufflers at all times. In mode B it would flow through the catback and mufflers until wide open throttle it would switch to an open cutout, and in mode C it would just be an open cutout at all times.

    [06-05, 19:29] OhioSpyderman: Brian, finding a woman is NOT the answer, you need to shop for a good VACUUM

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    Forum User Not Verified Feedback Score 2 (100%) jba3's Avatar
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    I had a cutout setup on my car in that very spot for I guess a year or so. When the cutout is open, it'll flow out both ways. It seems, and just as a guess by sound and standing at different spots, to follow wherever it sees the least resistance AND in it's natural flow path; i.e. it goes mostly straight out the normal path, until it gets "saturated' and it's easier for it to go straight out the cutout opening ... but all happening so quickly, it just has exhaust coming out from every spot.

    Fully opened, I noticed a distinct lack of grunt in low to mid range power (lack of backpressure? i dont know), but it didn't have nearly the drop-off in mid to top end power that it usually does. This is on stock 9Bs.

    It didn't pass inspection (need a visual cat, but no sniffer test), but I plan to have it reinstalled in the catback; to have the straight portion be the dump exit, and the offset angle follow where the catback naturally does. So it'll go:

    downpipe > HFC > midpipe > cutout (at the Y, dumping near the rear axle) > mufflers

    Something to think about it exhaust gas recirculation back into the car, if you have an open downpipe. Not an issue at speed, but in traffic or around town, it can get a bit, fragrant.
    1995 VR4 Coupe

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    Better than that "other" place Not Verified Feedback Score 2 (100%) x2xtreme360's Avatar
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    Quote Originally Posted by jba3 View Post
    I had a cutout setup on my car in that very spot for I guess a year or so. When the cutout is open, it'll flow out both ways. It seems, and just as a guess by sound and standing at different spots, to follow wherever it sees the least resistance AND in it's natural flow path; i.e. it goes mostly straight out the normal path, until it gets "saturated' and it's easier for it to go straight out the cutout opening ... but all happening so quickly, it just has exhaust coming out from every spot.

    Fully opened, I noticed a distinct lack of grunt in low to mid range power (lack of backpressure? i dont know), but it didn't have nearly the drop-off in mid to top end power that it usually does. This is on stock 9Bs.

    It didn't pass inspection (need a visual cat, but no sniffer test), but I plan to have it reinstalled in the catback; to have the straight portion be the dump exit, and the offset angle follow where the catback naturally does. So it'll go:

    downpipe > HFC > midpipe > cutout (at the Y, dumping near the rear axle) > mufflers

    Something to think about it exhaust gas recirculation back into the car, if you have an open downpipe. Not an issue at speed, but in traffic or around town, it can get a bit, fragrant.
    Well, the backpressure argument is a myth... and is only applicable with NA engines. In a turbocharged engine, you want ZERO backpressure all the time.

    Also, you failed with the cutout before the cat? I find it incredibly pointless to install the cutout before ALL the restrictive parts of the exhaust... I want it to bypass all that crap for maximum performance.

    As far as the EGR, I don't have EGR... and I wouldn't ever use the cutout in traffic or around town. This would be strictly when needed ie: racing basically

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    Forum User Not Verified Feedback Score 2 (100%) jba3's Avatar
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    Quote Originally Posted by x2xtreme360 View Post
    Well, the backpressure argument is a myth... and is only applicable with NA engines. In a turbocharged engine, you want ZERO backpressure all the time.

    Also, you failed with the cutout before the cat? I find it incredibly pointless to install the cutout before ALL the restrictive parts of the exhaust... I want it to bypass all that crap for maximum performance.

    As far as the EGR, I don't have EGR... and I wouldn't ever use the cutout in traffic or around town. This would be strictly when needed ie: racing basically
    Maybe it was all in my head, since I didn't do logs to verify, but it definitely felt slower at the low end of the stick with the cutout open. Could be since it was so much louder, I subconsciously expect it that much faster? I don't know. My evo was the same way with the cutout; loss of low end, and tradeoff of better top end.

    Actually, I failed with the cutout and no catalytic converter at all. I removed the cutout and put the HFC in there, with plans to relocate the cutout. I'm guessing you meant "pointless NOT to install the cutout before...."?

    I didn't mean exhaust gas recirc as in EGR, what I meant was that with it exiting right underneath the cabin, the exhaust fumes will spread out, if you have your windows down, at a light or in traffic, you can smell the exhaust after sitting still for 10 or so seconds. Not the most pleasant smell, but if you're keeping it shut when not running, it's a non-issue.

    An evo club member posted about running a track day with open downpipe (same way I had my evo cutout set up), and said he had no issues with it. I don't remember having any issues with the cutout after the downpipe in the evo, but it did smell funny with the VR4. Get the 90* turndown piece to minimize it spewing black stuff all over your undercarriage, too. Fitment is tight under there, but it's possible. Let me know if you get stuck with anything or want more info on how I used to have it set up. I used the QTP electric one.

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