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Thread: Boss 302 engine rattle or rapping type sound

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    Boss 302 engine rattle or rapping type sound

    3219 - boss 302 engine rattle or rapping type sound.
    some 2012 boss 302 mustangs might exhibit a rattle or rapping type sound during cold engine temperature operation at light loads and speeds from 1000 - 3500 rpm. This sound is caused by the piston moving from one side of the bore to the other at tdc. This is an inherent characteristic of the forged aluminum pistons and the combustion dynamics caused by the high flow cnc intake ports. Once the engine reaches operating temperature the sound will no longer be audible. There are no durability concerns with this sound.

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    Re: Boss 302 engine rattle or rapping type sound

    Thanks Rob, but i ain't buying it....there's plenty of high end horsepower engines out there w/alum pistons that aren't doing this.....At tdc your at your power stroke and inertia forces would prevent this...
    Failure is simply the opportunity to begin again more intelligently....

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    Re: Boss 302 engine rattle or rapping type sound

    Quote Originally Posted by Gr8snkbite View Post
    Thanks Rob, but i ain't buying it....there's plenty of high end horsepower engines out there w/alum pistons that aren't doing this.....At tdc your at your power stroke and inertia forces would prevent this...
    Whoa there MC, you went total engineer on us for a second there at the end of that. Say again last calling station.......in English this time.
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    Re: Boss 302 engine rattle or rapping type sound

    Quote Originally Posted by Darkside View Post
    Whoa there MC, you went total engineer on us for a second there at the end of that. Say again last calling station.......in English this time.
    lol....
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    Re: Boss 302 engine rattle or rapping type sound

    I'd just turn up the radio.

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    Re: Boss 302 engine rattle or rapping type sound

    It's hard to hear rattles and rapping when you're at WOT 99% of the time.
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    Re: Boss 302 engine rattle or rapping type sound

    Quote Originally Posted by Gr8snkbite View Post
    Thanks Rob, but i ain't buying it....there's plenty of high end horsepower engines out there w/alum pistons that aren't doing this.....At tdc your at your power stroke and inertia forces would prevent this...
    What about TDC between exhaust and intake stroke...... there are two TDC's you know.....

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    Re: Boss 302 engine rattle or rapping type sound

    Quote Originally Posted by Birdman View Post
    What about TDC between exhaust and intake stroke...... there are two TDC's you know.....

    Keith only knows 2 stroke motors.

    .

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    Re: Boss 302 engine rattle or rapping type sound

    Interesting!! Almost sounds like cold-rattle piston slap.

    The BOSS has different pistons (forged alloy) than the base 5.0 (hypereutectic alloy) so that might account for it doing it cold at TDC, since the hypereutectics change size during initial warm-up much more closely synchronized to sleeve/bore size change than do forged alloys. This permits hypereutectics to be fitted much more closely to bore size without binding on warm-up. But why doesn't the '11 GT500 (alloy block with forged alloy pistons) have this problem? Possibly because of PWTA/stray-bore (dunno) since the only other modular Ford V8 with forged alloy pistons in a sleeved alloy block in recent memory is the 1999/2001 Cobra (the SOHC 3V is sleeved alloy but has hypereutectics, not forged) and some 1999/2001 Cobras also occasionally experience a barely-audible slap on cold start (as well as an annoying valve-train tick which only lasts several seconds on cold start). Neither seem to incur any durability issues.

    But the 1999/2001 Cobra, unlike the 5.0, is a hand-built motor (Romeo niche) and, like the GT500, has components indexed/matched based on production size variations (semi-blueprinted), so may account for why the sound is uncommon and slight. My understanding is the 5.0 is essentially an automated build, but I don't know if the BOSS is similar or hand-built/semi-blueprinted. If it is, I don't know where that's happening since it's not at Romeo as far as I know and I'm unaware of any niche build line at Windsor, so this *may* account for the cold TDC slap. If so, I'm thinking it will be only on some percentage of units give small size variations ...we shall see.
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    Re: Boss 302 engine rattle or rapping type sound

    Yes this is indeed common in these mod engines especially when equipped with ported heads , higher lift cams and forged pistons for the combination of reasons given in the explaination. Many 4.6 3v owners who have swapped cams have experienced this phenomenon as well.

    I believe given the piston/bore clearence with the forged pistons being more when the engine is cold does indeed make some sound but that sound is amplified because of the increased bore size of the CNC'd intake ports coupled with the more agressive cam profile magnify's this combustion dynamic. This is probably occuring when the piston is at TDC on the intake stroke when the valves are open.

    I would also agree with Ford's assertion that there are no concerns about excessive engine wear or durrability issues in fact IMO if anything this engine is even more durrable than the generic 5.0 GT engine which itself is a very well engineered engine to begin with.

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