New OASIS message for Engine Rattle

OASIS 2888-

Some 2016 GT350 Mustangs might exhibit Piston Rattle from Idle to 3000 RPM

Some 2016 Mustang GT350 equipped with the 5.2L engine may exhibit a rattle or rapping type sound during cold operation at light loads and speeds from idle-3000 rpm. The noise will be most noticeable during light acceleration in the 1500-3000 RPM range and may also be noticeable in the 800-1200 RPM range with neutral throttle blips. This sound is caused by the piston motion in the cylinder bore. This is an inherent characteristic of the forged aluminum pistons utilized in this high performance engine. Once the engine reaches operating temperature the noise will diminish, although it may still be noticeable even when fully warm. There are no durability concerns with this sound.

So piston slap on a fresh factory engine. Only used to be a sign of an engine bored too much for the pistons in it. But guess it's normal now.

The Boss engine was the same way and mine was bullet proof for five years of heavy track use. Voodoo is a little more noticeable, and they probably had enough owners bring them in with concerns to issue this bulletin.

Glenn G said:

So piston slap on a fresh factory engine. Only used to be a sign of an engine bored too much for the pistons in it. But guess it's normal now.

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All forged pistons do this. Its because forged pistons expand and contract more than the standard hypereutectic pistons. If a forged slug was fit tightly into a bore it would scar the shit out of the walls when heated.

Short piston skirts = rattle.

My '01 Bullitt had a ton of piston slap, nothing new.

And it's not just a Ford thing either. LS9's were REALLY clanky.

Embrace the noise! Be happy manufactures are still willing to build bad ass forged engine cars.

Heard one running recently and like I previously suspected, definitely piston slap. My Boss motor will do this a little until it's warmed up as well. Let me dig up the article on it.

Here are Boss and GT350 piston/rod assemblies. Very similar as far as the short skirt:
http://www.mustang6g.com/forums/showpost.php?p=1072914&postcount=50

AMPowerJ posted this link, which explains the reasons behind somewhat intentional piston slap in modern engines:
http://www.mustang6g.com/forums/showpost.php?p=1072956&postcount=51

FYI - the alloy for the boss pistons grows very little at full temp and they are installed TIGHT. .0035 P/W clearance.

Another reason to not warm engine up by idling.
Once CHT hits above 120, you should start driving slowly.

Excellent. That noise always bothered me. I felt a little better when I heard it on the car I drove at the gt350 track attack.

Glad its normal.

I'm glad that they put something out.

I had a hunch that was it. Previous built engines I've had with forged internals would make a similar sound.

Sandoval said:

All forged pistons do this. Its because forged pistons expand and contract more than the standard hypereutectic pistons. If a forged slug was fit tightly into a bore it would scar the shit out of the walls when heated.

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More than scar, know plenty of jdm sti motors that went pop because a piston sticks in the bore. They run tighter clearances than they should to prevent slap. Put on a bigger turbo than stock, run it hard and boom, piston wedging in breaking all the things. US motors run hypereutechnic pistons and so just puke Ringling every so often

Looks like Ford took a page from the GM pickup piston slap playbook.

cloud9 said:

The Boss engine was the same way and mine was bullet proof for five years of heavy track use. Voodoo is a little more noticeable, and they probably had enough owners bring them in with concerns to issue this bulletin.

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Not just that... The four engine fails have likely increased the awareness of the sound to the owners and concern is raised.