Engine "Rattle"

[stanglife]

It could be piston slap. Some Coyote and Boss engines do it a little until they are warmed up. Good reason to let it warm up a few minutes before you drive it.

I'd have to hear it. Where in South Florida are you? I'm in Tampa area.

Ahem. . This happens to be audible when cold (on my boss motor, which shares a similar piston design) but all cars with forged pistons experience a bit of growth. The alloy on these expands a little less than some so the pistons are installed pretty tight...but they still do it. It definitely doesn't mean it's worn out. Now, if you start hearing it even after the engine is warm, that will turn into a problem.

Warm em up first!

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[Bossing]

Yes my car was completely cold when they compared to the one in the showroom.

 

[chopsui]

Ahem. . This happens to be audible when cold (on my boss motor, which shares a similar piston design) but all cars with forged pistons experience a bit of growth. The alloy on these expands a little less than some so the pistons are installed pretty tight...but they still do it. It definitely doesn't mean it's worn out. Now, if you start hearing it even after the engine is warm, that will turn into a problem.

Warm em up first!

It happens even when the engine is warm.

 

[stanglife]

It happens even when the engine is warm.

"It" needs to be verified. I've seen a ton of "my car is making this sound" threads over the years and it seems like there are usually at least two different things that people are confusing as the same sound.

I hope they aren't slapping when warmed up - that would certainly lead to diminishing performance and premature failure... So what I'm saying, is I hope you're sound is something else! :cheers:

 

[stanglife]

Without them in my hands to measure, it's hard to be exact but the dimensions and skirt look very similar to the Boss - which a lot of them slap when cold.

Here's the piston/rod from my Boss build:

http://93coupe.com/boss-302-engine-build-crankshaft-rods-and-pistons/

and from the GT350:

http://www.*******************/2015/06/04/tech-2015-shelby-gt350-5-2-engine/

^Seriously???

This is getting to be a pain in the ass. I cant link over there but I can save the picture and post it.....

 

[AMpowerJ]

Here's a good read from a GM engineer supposedly on piston slap:

http://ls1tech.com/forums/generatio...791-piston-slap-explaination-gm-engineer.html

 

[stanglife]

Here's a good read from a GM engineer supposedly on piston slap:

http://ls1tech.com/forums/generatio...791-piston-slap-explaination-gm-engineer.html

Good read!

 

[Hack]

I was driving around the other day and thought I should mention something. The Voodoo engine has relatively small, light weight pistons in order to keep the rotating mass low. With the Voodoo engine design you should be careful not to lug the engine. Also, the car is geared very high, so 6th gear should really only be used at 70 mph and above and on very flat highways. 6th should never be used to accelerate.

What this means is don't open the throttle a lot at low RPM, especially in higher gears (4-6) and when the engine isn't warm. If you hear a rumbling sound, that is indicative of lugging the engine. This is not good at all for the engine and should always be avoided.

You really want to be at least at 2,500 RPM and preferably over 3,000 RPM when you step on it even in 1st through 3rd gears.

Maybe too late for some of you who are hearing piston slap now, but I hope for newer owners this might help some of you.

 

[stanglife]

I was driving around the other day and thought I should mention something. The Voodoo engine has relatively small, light weight pistons in order to keep the rotating mass low. With the Voodoo engine design you should be careful not to lug the engine. Also, the car is geared very high, so 6th gear should really only be used at 70 mph and above and on very flat highways. 6th should never be used to accelerate.

What this means is don't open the throttle a lot at low RPM, especially in higher gears (4-6) and when the engine isn't warm. If you hear a rumbling sound, that is indicative of lugging the engine. This is not good at all for the engine and should always be avoided.

You really want to be at least at 2,500 RPM and preferably over 3,000 RPM when you step on it even in 1st through 3rd gears.

Maybe too late for some of you who are hearing piston slap now, but I hope for newer owners this might help some of you.

I agree on make an extra effort to make sure you're in the right gear on this motor and not ride out a gear at a low RPM because you don't want to downshift.

Are you suggesting that lugging the engine might have caused some piston slap for some people? The way I understand it, these pistons just need a little room to grown, considering their short skirts - and they just need to be warmed up.

 

[kgschrader]

I was driving around the other day and thought I should mention something. The Voodoo engine has relatively small, light weight pistons in order to keep the rotating mass low. With the Voodoo engine design you should be careful not to lug the engine. Also, the car is geared very high, so 6th gear should really only be used at 70 mph and above and on very flat highways. 6th should never be used to accelerate.

What this means is don't open the throttle a lot at low RPM, especially in higher gears (4-6) and when the engine isn't warm. If you hear a rumbling sound, that is indicative of lugging the engine. This is not good at all for the engine and should always be avoided.

You really want to be at least at 2,500 RPM and preferably over 3,000 RPM when you step on it even in 1st through 3rd gears.

Maybe too late for some of you who are hearing piston slap now, but I hope for newer owners this might help some of you.

This is certainly not what's happening with mine.
Easiest way to hear it...
Start the engine in the morning and head down your driveway or the street and VERY gradually ease into the throttle. No lugging at all. You're VERY carefully ease the throttle further, it will keep rattling until about 3000rpm.

As it warms up, you will see the start of the rattling rpm move up until it's probably at 2500 or so, but it is always there. Even with the the motor warmed up and having driven 40 miles.

I use my car to commute to work.

A slight increase in throttle will make it go away, a slight decrease in throttle will make it go away. I can make it rattle at will.

FWIW,
Kirby

 

[Hack]

I agree on make an extra effort to make sure you're in the right gear on this motor and not ride out a gear at a low RPM because you don't want to downshift.

Are you suggesting that lugging the engine might have caused some piston slap for some people? The way I understand it, these pistons just need a little room to grown, considering their short skirts - and they just need to be warmed up.

Yes. I'm saying that this issue might have been exacerbated by lugging the engine, especially if it isn't warm. When the piston is cold it can rock in the bore more and if you floor it at low RPM in a high gear that's when you are more likely to do damage.

Once you've done it the engine is going to make more noise for the rest of its life.

 

[chopsui]

This is certainly not what's happening with mine.
Easiest way to hear it...
Start the engine in the morning and head down your driveway or the street and VERY gradually ease into the throttle. No lugging at all. You're VERY carefully ease the throttle further, it will keep rattling until about 3000rpm.

As it warms up, you will see the start of the rattling rpm move up until it's probably at 2500 or so, but it is always there. Even with the the motor warmed up and having driven 40 miles.

I use my car to commute to work.

A slight increase in throttle will make it go away, a slight decrease in throttle will make it go away. I can make it rattle at will.

FWIW,
Kirby

This is a great description of the issue.

I just got back from East Texas. The rattle was still there at the end of that 200 mile drive. The thing that concerns me most is that the RPM range that the noise occurs in is right in the cruising range for the car. No matter what it is - piston slap, clutch, etc. It just can't be good for something like that to be happening constantly for such a long time. It's really hard to track down because I can't get it to happen for longer than a split second when the car is stationary. It would be great if someone with access to a dyno could take a look.

 

[CANTWN4LSN]

I would think if it was something intrinsic to the engine it would be happening to every vehicle. Is this the case, or are there people out there who don't have this occurring? Assuming good hearing or hearing aids.

 

[Patio208]

I definently have experienced what's being described here. I just took it to be "normal" for this car.

 

[RoadRacer]

Mine has the rattle since day one. I'm not concerned as I believe it's just a characteristic of the voodoo. I'm skeptical of the claim that low RPM engine loads can cause or accelerate this condition.

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