Boss 302 engine rattle or rapping type sound

[Grabber]

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.

[Gr8snkbite]

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...

[Darkside]

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.

[mustang loco]

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....:iagree:

[Tommy Gun]

I'd just turn up the radio.

[CH53Driver]

It's hard to hear rattles and rapping when you're at WOT 99% of the time. :shades:

[Birdman]

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......:shades: there are two TDC's you know.....

[Tommy Gun]

What about TDC between exhaust and intake stroke......:shades: there are two TDC's you know.....


Keith only knows 2 stroke motors. :popcorn:

.

[68fastback]

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.

[Birdman]

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.

[Little Debbie]

Interesting. Dan, what is PWTA/stray-bore? Not familiar with this.

[Birdman]

Interesting. Dan, what is PWTA/stray-bore? Not familiar with this.

Plasma wire transfer arc ...spray bore technology that Ford has pattened first used in the 2011 GT500 block.



The all-new 5.4-liter all-aluminum engine is also 102 pounds lighter than the previous cast-iron engine and due to it’s “SprayBore” Ford-patented plasma transfer-wire arc coating technology (PTWA). It has better cooling efficiency due to it’s superior wear resistance and reduced cylinder wall to piston friction.
http://i189.photobucket.com/albums/z234/svtbird91/news%20info/2011_GT500-Engine06_HR-1.jpg

[Carnut]

Perhaps the Boss motor uses a little shorter piston skirt, certainly would account for cold engine piston slap. The skirt keeps the piston from rocking and the shorter the skirt the more the piston can move about the wrist pin. Just a guess.

[Little Debbie]

isn't some amount of piston slap in any combustion engine normal? it is only when it is excessive that it would ultimately be of concern, correct? at that point, one would then worry if the clearance between the piston and cylinder were just too much, or the pistons and/or bores were mismatched.

aluminum does have a higher coefficient of expansion than does steel, so using a shorter skirt (if that is what they do) would seem to make sense from the standpoint that more clearance would be needed, no? which would also explain that once it warms up, the noise goes away. so long as the clearance isn't too great initially, there would be no worries about tilted pistons.

[Little Debbie]

Plasma wire transfer arc ...spray bore technology that Ford has pattened first used in the 2011 GT500 block.



The all-new 5.4-liter all-aluminum engine is also 102 pounds lighter than the previous cast-iron engine and due to it’s “SprayBore” Ford-patented plasma transfer-wire arc coating technology (PTWA). It has better cooling efficiency due to it’s superior wear resistance and reduced cylinder wall to piston friction.
http://i189.photobucket.com/albums/z234/svtbird91/news%20info/2011_GT500-Engine06_HR-1.jpg

:tiphat2:

[68fastback]

LD, here's a little more on PWTA (a.k.a spray-bore) that might be of interest:

Ford media overview (http://media.ford.com/images/10031/2011_GT500_Engine.pdf)

SAE Article (http://www.sae.org/mags/aei/MANUF/7624)

[Little Debbie]

:tiphat2:

so the Boss does not have PTWA (odd), and may have a hand-built vs. automated build alloy engine, and possibly a shorter piston skirt. ok.

[Gr8snkbite]

Though all engines exhibit a certain amount of "normal" engine slap during start up, below indicates otherwise.

Excessive piston slap occurs when the clearance between the piston and the cylinder bore is too great. The piston to cylinder bore clearance becomes too great either through wear, mismatched pistons and cylinder bores at manufacturing or, a combination of both. The audible noise associated with excessive piston slap is due to the perpendicular impact of the piston against the wall of the cylinder bore. Audible piston slap is typically loudest when the engine is first started up. The pistons then expand with heat reducing the piston to cylinder bore clearance thus, reducing the perpendicular impact of the piston against the cylinder wall and its resulting noise.

i agree with carnut in that the shorter skirt (if applied to the Boss could be the cause)

i still dont see how CNC'd ports have any affect on this. What is the bore of the Boss compared to the 5.4? Though i've not heard this, so can't relate, it certainly isn't existent (to the point of a notice from Ford) in my 11'. Spray bore could be preventing this as well, given the clearance is built up then honed down to fit the piston better. But you still have req'd tolerances to maintain.

edit....

Boss:
3.63 x 3.65 bore/stroke
intake valve 37mm @ 12mm lift
exh valve 31mm @11mm lift

GT500:
3.55 x 4.165 bore/stroke
intake valve 37mm
exh valve 32mm

[Birdman]

Though all engines exhibit a certain amount of "normal" engine slap during start up, below indicates otherwise.

Excessive piston slap occurs when the clearance between the piston and the cylinder bore is too great. The piston to cylinder bore clearance becomes too great either through wear, mismatched pistons and cylinder bores at manufacturing or, a combination of both. The audible noise associated with excessive piston slap is due to the perpendicular impact of the piston against the wall of the cylinder bore. Audible piston slap is typically loudest when the engine is first started up. The pistons then expand with heat reducing the piston to cylinder bore clearance thus, reducing the perpendicular impact of the piston against the cylinder wall and its resulting noise.

i agree with carnut in that the shorter skirt (if applied to the Boss could be the cause)

i still dont see how CNC'd ports have any affect on this. What is the bore of the Boss compared to the 5.4? Though i've not heard this, so can't relate, it certainly isn't existent (to the point of a notice from Ford) in my 11'. Spray bore could be preventing this as well, given the clearance is built up then honed down to fit the piston better. But you still have req'd tolerances to maintain.

It has to do only with the "combustion dynamics " in that whatever noise the forged piston is producing, especially when the engine is cold (and it may not even be "piston slap") it is magnified by the intake port design and the added air flow those ports enjoy.

[Gr8snkbite]

It has to do only with the "combustion dynamics " in that whatever noise the forged piston is producing, especially when the engine is cold (and it may not even be "piston slap") it is magnified by the intake port design and the added air flow those ports enjoy.

edited my post above....ports are from what i can tell roughly the same...tho i know there are suttle differences. So what are the design differences between the two engines i wonder. i dont see the size having relevance, but maybe the face angle cut dealing with flow, but flow isnt the issue. If not eng slap, what then.

And yes, i know there are two tdc's.....:doh2: in either case, it wouldnt matter....skirt length however has alot to bear....

[68fastback]

Can't see why the BOSS would need a shorter piston skirt than the 5.0 ...same stroke, bore and displacement, tho it may have shorter skirts for some other reason. As I recall, the BOSS does have a 'racing' crankshaft with more refined leading-edges/counterweights, but unless they were larger in diameter (from crank centerline, which implies the 5.0 left some room) there would seem to be no reason for shorter piston skirts, though it's possible. The BOSS does have slightky beefier rods so the crank/RA is necessarily differently balanced than the 5.0 but still seems unlikely shorter piston skirts would be required, however maybe they did it (if they did) to reduce the reciprocating mass for better sustained high rpm operation.

My 460 4x4 Qudravan developed piston slap gradually (when new it did it only briefly on cold-start in cold weather) and by 86K miles it was bad enouggh that the engine had to be replaced. Good thing I documented it early-on (several times) because I got a lot of pushback after it was out of warranty, but it was there on day one and a regular cold-start occurrence way before warranty was up so I wouldn't back off and region rep everntually came around to my view. I mention this because, relatiive to its gigundo bore size, the 460 had rather short piston skirts for a truck engine ...or so I was told. When it got to the point that it didn't go away full-warmed is when I told Ford I'd had enough. Curious thing is that, right from the factory, that 460 had a 3" high light blue script "F" hand-painted on the darkblue air cleaner lid ...and no one at Ford could explain what the heck that was. I contested that Ford accidentally or otherwise put an engine with a possible or known defect in a fleet vehicle and the documented cold-slap -- there since new -- was the reason. Anyhow, just mentioning fwiw.

[68fastback]

It has to do only with the "combustion dynamics " in that whatever noise the forged piston is producing, especially when the engine is cold (and it may not even be "piston slap") it is magnified by the intake port design and the added air flow those ports enjoy.

So Ford is essentially saying the condition is 'normal' but it's just heard more ...due to head design and combustion dynamics? I hope they're right but I'm struggling to understand that.

I notice they do say cold engine temp on light load 1000-3500 rpm ...exactly when piston-slap would be most noticeable. That's also when my 460 did it worst and as load lightened on a lazy 1-2 shift (auto) it was even more noticeable. I am struggleing with the combustion dynamics part tho ...unless that translates as: bigger clearances means bigger shirt gap and therefore more rocking at TDC when cold, but it seems a stretch to call that (or anything at TDC) combustion dynamics vs mechanical dynamics of the rod rocking the piston. Also how high-flow intake ports might augments this isn't clear at all clear to me. Not asying it doesn, just that I'm not getting it.

"...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."

[Little Debbie]

nice thread :popcorn:


:smile:


even if it is "normal" and it does go away once warmed up, it certainly doesn't make for warm fuzzy feelings, does it?

[Gr8snkbite]

no it doesn't.....

and as Dan said, i to am struggling with the flow dynamic...

another thing that can contribute is the piston pin (attaches the piston to the conn rod)...

[Carnut]

Can't see why the BOSS would need a shorter piston skirt than the 5.0 ...same stroke, bore and displacement, tho it may have shorter skirts for some other reason. As I recall, the BOSS does have a 'racing' crankshaft with more refined leading-edges/counterweights, but unless they were larger in diameter (from crank centerline, which implies the 5.0 left some room) there would seem to be no reason for shorter piston skirts, though it's possible. The BOSS does have slightky beefier rods so the crank/RA is necessarily differently balanced than the 5.0 but still seems unlikely shorter piston skirts would be required, however maybe they did it (if they did) to reduce the reciprocating mass for better sustained high rpm operation.

My 460 4x4 Qudravan developed piston slap gradually (when new it did it only briefly on cold-start in cold weather) and by 86K miles it was bad enouggh that the engine had to be replaced. Good thing I documented it early-on (several times) because I got a lot of pushback after it was out of warranty, but it was there on day one and a regular cold-start occurrence way before warranty was up so I wouldn't back off and region rep everntually came around to my view. I mention this because, relatiive to its gigundo bore size, the 460 had rather short piston skirts for a truck engine ...or so I was told. When it got to the point that it didn't go away full-warmed is when I told Ford I'd had enough. Curious thing is that, right from the factory, that 460 had a 3" high light blue script "F" hand-painted on the darkblue air cleaner lid ...and no one at Ford could explain what the heck that was. I contested that Ford accidentally or otherwise put an engine with a possible or known defect in a fleet vehicle and the documented cold-slap -- there since new -- was the reason. Anyhow, just mentioning fwiw.

Forge aluminum is denser than cast therefore heavier. This is a really hi reving engine so it really is possible they removed some from the skirt to keep its overall weight down.

Piston slap is not a good thing, just a trade off for something else. With all of the testing Ford does, you would think they do have a good handle on the issue though.

[68fastback]

Forge aluminum is denser than cast therefore heavier. This is a really hi reving engine so it really is possible they removed some from the skirt to keep its overall weight down.

Piston slap is not a good thing, just a trade off for something else. With all of the testing Ford does, you would think they do have a good handle on the issue though.

I would hope so too.

Another thing that occurred to me is this is essentially the BOSS-R motor that ran a full season of SCCA Conti Challenge racing first, not to mention subsequent full durability and thermal torture testing. Seems odd this didn't turn up then ...or maybe is only noticed in a nice quiet cockpit with those nice long runners telegraphing the sound up into that alloy intake plenum sitting up on top.

Maybe if we had an opportunity to hear it, it might be clear that its not a real problem ...vs actual piston-slap which surely is a problem.

In a way this TSB is a bit humorous -- in an unintended way:

Customer: my BOSS is rapping on cold light load (lol ...could be a song in there :rofl3:)

Service writer: let me look that up ...oh! ...good news! ....there's TSB on it.

Customer: Really? Great! What's the fix?

Service writer: ...ummm, well ...you need to change your cold light load noise expectations. :giggle:

I think it's good Ford issued the TSB; it just seems a bit ...unusual.

Maybe this is the automotive equivalent of the software world's WAD APAR (Working As Designed Authorized Programming Analysis Report), a.k.a "yup, that's how it's supposed to work -- not a problem" :rofl3:

I bet Blackshelby and GTflyboy both know from WAD APARs :biggrin:

[Grabber]

Dan,

This is not a TSB. It is a Ford Broadcast message to the tech's that work at Ford dealerships.

Just thought I would mention that.

Rob

[68fastback]

That makes a lot of sense ...thanks, Rob :tiphat2:

...a.k.a Techs: don't attempt to fix this; it ain't broke.

[Joe G]

...a.k.a Techs: don't attempt to fix this; it ain't broke.

Mrs G tells me that all the time whenever I attempt to work on my car. :doh2:

[Birdman]

I wouldn't worry about the design or durrability of the new 2012 Boss 302 engine.....just sayin

click on Vid #3 THE BOSS 302 5.0-LITER HI-PO V8 3:02

http://www.ford.com/cars/mustang/gallery/videos-and-demos/boss-302/?intcmp=fv-fv-a1b07c13d000765e14f12g01h14j12k16m4n0p20110329

[68fastback]

...cool vids! ;-)

[Little Debbie]

+1