• mufflers...to be or not to be...
  • mufflers...to be or not to be...
  • mufflers...to be or not to be...
  • mufflers...to be or not to be...

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  1. #16
    mufflers...to be or not to be... TedC's Avatar
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    At WOT, the ECM runs in power mode. If the exhaust is too big, the stock ECM will run lean, and you are kissing power goodbye. Just connect a scanner and drop the rear y-pipe and mufflers and watch the results. You want a scavenging effect in the exhaust system, which is maximized when exhaust air velocity remains high with minimal back pressure. Zero back pressure reduces power below the torque peak. There is room for improvement with the stock exhaust, but the L98 is plugged up on the intake side, so don't go crazy and end up reducing low end power.

  2. #17
    MBDiagMan
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    POWER MODE? That's a new one on me. The system is either running in closed loop mode or open loop mode. I will assume that you are referring to open loop mode.

    There is little or no scavenging effect with a stock L98 exhaust system. Scavenging is an effect that takes place with full length headers. It is almost nil with short tubes such as the stock units.

  3. #18
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    Quote Originally Posted by TedC View Post
    At WOT, the ECM runs in power mode. If the exhaust is too big, the stock ECM will run lean, and you are kissing power goodbye. Just connect a scanner and drop the rear y-pipe and mufflers and watch the results. You want a scavenging effect in the exhaust system, which is maximized when exhaust air velocity remains high with minimal back pressure. Zero back pressure reduces power below the torque peak. There is room for improvement with the stock exhaust, but the L98 is plugged up on the intake side, so don't go crazy and end up reducing low end power.
    All this discussion about L98 engines is irrelevant.

    A 92 doesn't have an L98 engine. It's has the LT1. Additionally, the 92-96 exhaust system is completely different than whats on cars with L98s.

    Also, Doc's comment above about scavenging is correct. Once you bolt an exhaust system (ie: cats, pipes and mufflers) the scavenging effect one gets under certain limited conditions on engines with headers will be extrememly limited or not present at all.

    Finally, when the ECM goes into the power enrichment mode (it will also be in open loop), it is true that reducing exhaust restriction such that flow across the engine increases, the engine may run more lean. If it runs more lean to the extent that power decreases, the solution is to change the ECM calibration and give the engine more fuel.

  4. #19
    Member Cruzen's Avatar
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    Quote Originally Posted by Hib Halverson View Post
    Your best bet is a well-designe, "catback" exhaust system. Flowmaster is a good compromise between performance and price. On a 92 LT1 with a stock or near stock engine, the gain will be 5-7hp and the resonance will not be near as bad.
    I have been wondering about the Flowmasters myself. Since they offer several different chamber designs, have you any preference or recommendations on the one two or three chamber design in relation to the stock sounding exhaust. I am thinking of just a muffler change. I would love for my 94 to have the sound of a small block 64-67. Since the 94 runs at about half the RPM of the C2 small block I am assuming it would need to be just a bit louder. I really miss that sound of that small block coming back over the rear deck of my C2 roadster and if I could recreate that in my C4 roadster I would be happy. You could hear it but it wasn't loud. Driving from Chicago to LA in a day and a half in my 65 coupe with factory side pipes permanently cured me of the need for LOUD!

    The trip is short,
    enjoy the ride,
    Denny

  5. #20
    mufflers...to be or not to be... TedC's Avatar
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    I'm far from being an expert on exhaust tuning, but the comments below match very closely to what my local dyno shop has been sharing with me.

    "High velocities, that don't incur pumping losses are the rule!!! Just changing backpressure is a bogus way of trying to create the "ideal" pressure in the system. The exhaust system should work like a correctly conceived header. It should extract the exhaust from the header, to minimize pumping pressures. The only way to create a system that will serve as an extractor is to properly size the tubing to allow the flow velocity to create a sort of "vacuum" behind it. Just as with headers, creating a system that will provide the best of all worlds at all throttle positions and rpm ranges is impossible. It's all going to be a trade-off. You can tune for the throttle positions and rpm ranges where you desire the greatest performance, but you'll sacrifice performance at the other end of the rpm range."

  6. #21
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    Quote Originally Posted by Cruzen View Post
    I have been wondering about the Flowmasters myself. Since they offer several different chamber designs, have you any preference or recommendations on the one two or three chamber design in relation to the stock sounding exhaust. I am thinking of just a muffler change. I would love for my 94 to have the sound of a small block 64-67. Since the 94 runs at about half the RPM of the C2 small block I am assuming it would need to be just a bit louder. I really miss that sound of that small block coming back over the rear deck of my C2 roadster and if I could recreate that in my C4 roadster I would be happy. You could hear it but it wasn't loud. Driving from Chicago to LA in a day and a half in my 65 coupe with factory side pipes permanently cured me of the need for LOUD!

    The trip is short,
    enjoy the ride,
    Denny
    You're better off with the cat-back because it eliminates the restrictions ahead of the resonator and it replaces the OE resonator with a unit designed for work the flowmaster mufflers.

    But, if you want mufflers only, I'd put 50 Deltas on it.

  7. #22
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    Since this is all about exhaust, maybe this is the place to ask my question. I just bought an 84 4sp std. that has an aftermarket exhaust that I'm trying to figure out what it is. It has no resonators -the only "muffler" is the Cat. The flange behind the cat splits into two, with each tail pipe spliting into twin outlets at the end "framed" with a rectangular SS suround. It has that 70's sound, loud but sweet -anyone have an idea of who made this system?
    Thanks, Glen

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