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Thread: Installed wrong muffler could damage my 240z?

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    Default Installed wrong muffler could damage my 240z?

    As per my previous post, last week i removed the following muffler which has 2" inlet and 2"outlet from my car due to its size and fitment besides the gas tank:Click image for larger version. 

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    Anyway, i swap this muffler for a smaller 14" long muffler with 1 3/4 inlet and outlet 1 3/4:
    Click image for larger version. 

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    When driving the car home i noticed the car had lost power and you could hear explosions under the car. I decided to park the car for a couple of days until i could take it to another shop where i found a Dynomax Super Turbo 2" inlet and 2" Outlet muffler. The car now gain strenght but according to my mechainic was running in 3 cylinders only with random explosion noise after shifting to 2nd gear.

    My question is Could driving the car in these conditions have damaged something in the engine, require new tuning of the carbs and new timing adjustment?

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    1 3/4" inlet/outlet is pretty close to what the OEM muffler is - so unless there was something inside that second muffler that had collapsed.. or was shutting the exhaust flow off almost completely - - it is very doubtful anything would be harmed at the engine.

    FWIW,
    Carl B.

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    Carbs may be out of balance

    What do each of the 6 plugs look like starting with #1 (near radiator) to #6 (near firewall)
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    I would like to know more about the "internal explosions" taking place in the engine that you are talking about. Our engines by their very nature have internal explosions to run a they are internal combustion engines. I agree with Carl that unless there was an issue with the muffler itself you should not have any issues. I wonder if you mean "pinging" is what you heard by the internal explosions. If so, this would happen at higher RPMs and could be due to many factors such as incorrect timing, lack of fuel, or using low octane gas to name a few. Just looking at the pictures above, the 90 degree elbow at the inlet of the muffler was definitely hurting flow and performance but should not make an engine run on only 3 cylinders.
    08/1970 240z Series-1 #8011 - Silver, black int., 2.4L I-6, 5spd, 90% restored.
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    sounds to me like it was backfiring - restricted exhaust does richen up the mixture and if the offending muffler has significantly less flow, coupled with perhaps already poorly tuned carbs and suspect ignition timing, and you get fouled plugs, hence "running on 3"...

    following his threads i'm not sure the car is correctly tuned to start with.
    '78 280z - Daily driver/work in progress...

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    Quote Originally Posted by rossiz View Post
    sounds to me like it was backfiring - restricted exhaust does richen up the mixture and if the offending muffler has significantly less flow, coupled with perhaps already poorly tuned carbs and suspect ignition timing, and you get fouled plugs, hence "running on 3"...

    following his threads i'm not sure the car is correctly tuned to start with.
    This is the advice i was looking for!!!! The carburetors may have gotten out of tune. Can i do the ignition timing perfectly without the ignition timing tab installed:

    Datsun 240Z 280z Timing Indicator Tab | eBay

    Please confirm!

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    Quote Originally Posted by rossiz View Post
    sounds to me like it was backfiring - restricted exhaust does richen up the mixture and if the offending muffler has significantly less flow, coupled with perhaps already poorly tuned carbs and suspect ignition timing, and you get fouled plugs, hence "running on 3"...

    following his threads i'm not sure the car is correctly tuned to start with.
    Ok. The car is already tuned up and three spark plugs have been replaced. The car lacks strenght anyhow. Will the Dynomax Super Turbo muffler work fine for this car? something in the exhaust may be causing the power restriction.

    Dynomax 17730 Dynomax Super Turbo Mufflers - Free Shipping on All Orders @ JEGS

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    Disconnect the muffler entirely and see what happens. It will be loud but you should be able to tell if it's down on power.
    1976 280Z, with some minor modifications

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    Rather than relying on the manufacturer's claims, unless you have personal knowledge, I would rely on my local muffler shop to choose a muffler that won't restrict flow, and won't be too loud. They should have plenty of experience as to how a particular muffler will sound, perform and fit. Also, there are some good threads on this site about specific muffler and exhaust pipe combinations, but what someone else thinks is perfect might be too loud for you (and your local PD).

    I've heard to use 2 1/4' exhaust pipe for 240Z engine, 2 1/2" exhaust for 280Z. From your previous posts, you have a built engine with a cam that works better in a higher rpm range. That means if you're driving 30 mph in high gear, performance might not be great.
    If you choke it off with a muffler or exhaust pipe that's too small, performance will be even worst. Your experiment may have confirmed that.

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    I think that his muffler shop created the abomination in the first post. Some of his other posts imply that he doesn't have many good shops to go to. He's in a tough spot.
    1976 280Z, with some minor modifications

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    HAHAHA! The mechanic tuned the car carbs again and changed 3 of the spark plugs that got damaged due to backfiring. The car was tested and had lost power. Thinking that the loss of power could be due to the bad muffler installation, he chopped down the exhaust and discovered it was the electric fuel pump that was failing. What Brand and type of Electric fuel pump can i order for my 240z which has a Far 311 race cam and 5 speed transmission from a 280z? I need a reliable and powerfull one.

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    Quote Originally Posted by jalexquijano View Post
    I need a reliable and powerfull one.
    You just need reliable, not powerful. The cam and the transmission don't mean anything as far as the fuel pump goes. Get a stock pump, or try the Mazda pump (search around the internet for model).

    If your mechanic did all of that work just to find a weak fuel pump, you might still need a new mechanic. By now, using this forum and the internet, you should know more about your car than any of the mechanics you've used. And spark plugs don't get damaged from back-firing.
    1976 280Z, with some minor modifications

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    Well, Just to let all of you know that my car is finally is running smooth with no backfire. It has a Master branded electric fuel pump and a Dynomax Super Turbo 2 inlet and 2 outlet installed. Thanks for your great help!

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