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Thread: Odd Sound on Decel

  1. #1
    Member rwantin's Avatar
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    Odd Sound on Decel

    Hi, please lend me your ears if you would.

    It may or may not be a big deal, but wanted to bounce this off of some more experienced (probably most of you) than myself.

    I have a Mark IV with an Engine Factory 393 (351 Windsor) with Edelbrock Performer heads and intake. It's my second Roadster, and reluctant to admit it is bought not built. I do all my own work (I guess you could say I am Advanced Shadetree), and have been sorting things, but having a tough time pinning this down.

    On decel or off-throttle, both static and driving, there is sort of a gravelly, almost rattle from the exhaust. I don't think it is physically something with the pipes themselves, and it is even on both sides. The car runs great, and again, maybe this isn't anything, but if it IS something I can fine tune out, I'd love to try. Someone that heard it mentioned cam overlap? In any event, I have no idea. I went through the paperwork, not much there in terms of specs (and I didn't consign this engine).

    I hope this link works, if not, I'll try uploading to Youtube or something.

    https://share.icloud.com/photos/0S-t...ItDqlAOhuYnDKA

    Thanks (in advance) for your time.

    -Robert

  2. #2
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    My 393w, carburetted - has a funny "rattle" on decel too - only when its running "perfect" otherwise.

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  4. #3
    Member rwantin's Avatar
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    Quote Originally Posted by mike223 View Post
    My 393w, carburetted - has a funny "rattle" on decel too - only when its running "perfect" otherwise.
    Thanks much for the reply, it is possible my Vehicular OCD is getting the best of me. That definitely helps.

  5. #4
    Seasoned Citizen NAZ's Avatar
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    People spend a lot of $$ to get that sound on your video.
    Dart Little M 406" SBC 800 HP N/A & 1,100 HP on nitrous, 2-spd Powerglide with trans brake, 6,000 RPM stall converter, narrowed Moser 88 3.90:1 spool with 35-spline gun-drilled axles & Torino bearings, custom parallel four-link, custom tube chassis & roll cage NHRA certified for 8.5-sec (only two FFR Hot Rods have this cert).

    33 Hot Rod Super Pro Drag Racer Build: 33 HR NHRA Cert Roll Cage Build

  6. #5
    Member rwantin's Avatar
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    Quote Originally Posted by NAZ View Post
    People spend a lot of $$ to get that sound on your video.
    And someone assuredly did just that. Thanks, appreciate it. It DOES sound great, just on decel does it seem a bit odd. I should just enjoy the thing.

  7. #6
    Senior Member frankb's Avatar
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    A really looong time ago during my motorcycle days, I installed a 4 into 1 exhaust system on my motorcycle and I noticed a similar sound during engine deceleration. One night during a tuning session, I placed my open hand close to the exhaust outlet and revved the engine a couple times and noticed that the exhaust developed a vacuum (pulled my open hand against the outlet) during engine deceleration. It is this vacuum that was causing the sound change. After that I didn't think about it any more until I read your question above!
    FFR MK4 #8317, 393 Cleveland, Lunati VooDoo solid roller, CHI 3V heads and intake, TKO 600, Std roadster seats, 8.8 3.55 diff, 17" Halibrand replica wheels, Ford "Magnetic Metallic", silver ghost stripe. (Sold 10/16/21)

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  9. #7
    Seasoned Citizen NAZ's Avatar
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    Yes, enjoy the sound. But if you're still worried, ship the car to me and I'll drive it around for a couple weeks and let you know what I think.
    Dart Little M 406" SBC 800 HP N/A & 1,100 HP on nitrous, 2-spd Powerglide with trans brake, 6,000 RPM stall converter, narrowed Moser 88 3.90:1 spool with 35-spline gun-drilled axles & Torino bearings, custom parallel four-link, custom tube chassis & roll cage NHRA certified for 8.5-sec (only two FFR Hot Rods have this cert).

    33 Hot Rod Super Pro Drag Racer Build: 33 HR NHRA Cert Roll Cage Build

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  11. #8
    Papa's Avatar
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    Burble, not rattle. Sounds fantastic to me.

    Dave
    My Build Thread: http://thefactoryfiveforum.com/showt...ter-Build-9754
    (Most viewed Roadster build thread on this forum!)

    Delivered: 6/17/2017
    First Start: 12/30/2017
    Completed: 12/7/2019
    Legal: 1/30/2020

    Member of the Mile-Hi Cobra Club
    Dave's Cobra YouTube Channel: https://www.youtube.com/channel/UCbk...npK1UZHj4R-bYQ
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  13. #9
    Member rwantin's Avatar
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    Thanks a ton guys. Puts my mind at ease. It seems really hard to hear in the video, very subtle on the back end, but it is there. It is far more pronounced on the road, but hey, it runs great.

    And again, many thanks!

  14. #10
    RBachman's Avatar
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    These engines have a history of noises like this. Do a Google search and you'll find a lot of stuff on it. There was even a tech bulletin on it at one time, but that also failed to fix it and I didn't find a resolution when I searched. Some have said reprogramming the EFI helped. Seems to be non-issue, but do your research.
    FFR MKIV ordered 12 July 2019. IRS, Wilwood Brakes, 18" Wheels w/MT tires, power steering, EFI, Heat. 347 Dart w/TKO-600 by Mike Forte, Holley FI, MSD coil and CD box. All new, no donor build.

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