Exhaust diameter

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  • Exhaust diameter

    Bigwhite, what can you tell my about the diameter of the exhaust for my car? For example, the bigger, the better, or the other way? I heard a lot of oppinions, but I think that, on a N/A engine, it's not so good to have very large exhaust, because the engine might loose some of the low and mid-rpm torque and gain insignifiant horsepower. Am I wrong?

    And another question: if you have an unrestricted exhaust, it's better to have some restrictors at the end of the exhaust? Does it help the engine to keep a good torque curve or it doesn't help at all?

  • #2
    Re: Exhaust diameter

    it is a controversial topic.

    Let me explain my experiences;

    One of friends Type-R, we had taken out the original exhaust system, including the cat, the resonator whatever it is in the system (loud). We have installed a 60mm diameter custom fabricated steel exhaust.

    We, slightly lost the feel of "torque". on the other hand, the top rev-ability was increased definately (after Hondata and our program, whole characteristic has changed, it became a rev-monster, each gear-each rev, it was powerful).

    Before the exhaust modification, everything standart, we had a dyno result of 197hp.

    We replaced the exhaust (remove all the unnecessary cats-resonator etc), but a Hondata, adjust the fuel and the timing (+vtc off course) we had 221 hp (95 Octane). This gain is a conglomerate gain of exhaust+hondata tune.

    In a City like Bucarest, where you dont have smooth roads and flowing traffic, you need the down-low torque. Therefore, even a slight decrease in down-low can make you feel slower with the standard engine (mak you unhappy). However, if you are planning to update the engine and/or ECU, my advise is to replace it with one bigger size (not to the biggest available.) Otherwise, dont do anything on your standart system.

    What do you expect from your car? To win a drag race? to have a drivable characteristic? To be drivable in noise point of view? First you have to decide on the exact route to go.

    Assuming that you are a daily driver, in Bucharest, you need a drivable but marginally faster Type-R. If I were you, I would get rid of any unnecessary weights in my car, including the spare tire (buy a repair kit instead), including the music system. (I had taken out even the A/C, the stability bars, the safety bars in my Civic Vti! when I had that car).

    Then I would buy a Hondata (not reflash but an ECU). I would try to adjust it on a dyno with a wideband oxygen sensor. (and increase the rev-limit 500rev/min higher).

    Standard 197ps-1400 kg with driver = 7.1kg/ps
    After slight mod (100 octane fuel) 225ps-1350 kg = 6kg/ps.

    This a huge gain. I would go for it.

    If, you want something further, It would be a topic for another discussion

    PS: The answer of your last question is yes in theory. In practice, there are differences that you can slightly feel. More than this, you would have the noise concern.

    Originally posted by BogdanCTR
    Bigwhite, what can you tell my about the diameter of the exhaust for my car? For example, the bigger, the better, or the other way? I heard a lot of oppinions, but I think that, on a N/A engine, it's not so good to have very large exhaust, because the engine might loose some of the low and mid-rpm torque and gain insignifiant horsepower. Am I wrong?

    And another question: if you have an unrestricted exhaust, it's better to have some restrictors at the end of the exhaust? Does it help the engine to keep a good torque curve or it doesn't help at all?

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    • #3
      Thanks a lot for de advice.
      I'm not that really interested in winning drag races, but pushing the engine to its 'safe' limits. I also hate to have a very loud exhaust, I rather have a performant one than a loud one. My goal is to increase the VTEC 'zone', from a lower than stock to a higher than stock rpm, to make it more aggressive in the VTEC 'area' and, in the same time, to keep the torque curve somewhat unchanged.
      For example, maybe I can do that with a K-pro and an ice box (cold air intake is better, I know, but city traffic condition and all that dust and water makes me a little scared), but I'm a little confused about the right diameter of the exhaust. Should I keep it a little bit restricted or just let it flow?

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      • #4
        Originally posted by BogdanCTR
        Thanks a lot for de advice.
        I'm not that really interested in winning drag races, but pushing the engine to its 'safe' limits. I also hate to have a very loud exhaust, I rather have a performant one than a loud one. My goal is to increase the VTEC 'zone', from a lower than stock to a higher than stock rpm, to make it more aggressive in the VTEC 'area' and, in the same time, to keep the torque curve somewhat unchanged.
        For example, maybe I can do that with a K-pro and an ice box (cold air intake is better, I know, but city traffic condition and all that dust and water makes me a little scared), but I'm a little confused about the right diameter of the exhaust. Should I keep it a little bit restricted or just let it flow?
        K20safe limits are really high; don't have any question mark in your mind on safety point of view. They are quite capable, and safe. Your style of exhaust is "Mugen". It has the best design, comparatively low sound (very good sound), but unrestricitive.

        related to CAI vs short vs icebox matter, CAI is, in my opinion, am uncessary marketing thing. The longer the pipe, the longer time to get it full; i.e. the later the power to come. It is a reality of fluid dynamics. Also, I have seen same test results, showing that CAI's are less cabaple in higher rpm's than the Short ones. Related to the under hood temperatures issue, I have connected a Service Diagnosis Device, went in the traffic. When you get stuck in the traffic, the underhood temp. is going high like +30 of ambient temp. As soon as the car moves; it drops drastically. Within 5 sec or so, it equals the ambient temperature. That is why I dont consider it as a positive thing. Buy a short ram.

        K-Pro may be a little overkill in your situation, especially if you dont have anybody to tune it. (is there anybody in Bucharest by the way?). It is a bitch to tune (especially the VTC thing). If you have the tuner here, just buy and enjoy.

        After your statements above, my opinion is not to enlarge the exhaust pipe, but to put a test pipe, a good final exhaust like Mugen. That would keep the noise down and with the help of K-pro, it would give you what you want.

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