Nissan GT-R Forum banner
1 - 20 of 26 Posts

·
MAJJ
ALPHA 9
Joined
·
1,934 Posts
Discussion Starter · #1 ·
Just sharing the sounds of my Piston Slaps from my rebuild. I went with the AMS Race 3.8 Short Block which has the Alpha Spec Extreme-duty Manley Pistons.

Noticeable sounds:
-Loud crank sounds on cold-start
-Loud slaps on idle (hood open - like the video below)
-Minor "Chittering" sounds while driving (faster chitters , as I increase speed and vice versa).

I know forged pistons are louder due to more clearance… I've never heard one in-person so I'm not sure if it's supposed to be THAT loud or not. Is it?

 

·
Registered
Joined
·
2,631 Posts
In my experience on other platforms with forged "street" motors, having audible piston slap isn't normal. My current 2.15L EVO forged motor (3rd forged motor I've had) is very quiet even on cold start and dynoed [email protected] on Shell 93 pump. However, you purchased a "Race" short block so likely the clearance are much looser to account for piston CTE at the projected power level the engine was designed to handle. If the noise is indeed "piston slap" then either the piston-bore clearances are too loose or you aren't getting the pistons up to temp. Does it make that noise after you've been banging on it at high HP?
 

·
MAJJ
ALPHA 9
Joined
·
1,934 Posts
Discussion Starter · #5 ·
Whats going on with all the mismatched silicone hoses and couplers? Looks like a hot mess under that hood.
Temporary until I replace the upper ic pipes. These hoses are a little thicker than OEM


Sent from my iPhone using Tapatalk
 

·
MAJJ
ALPHA 9
Joined
·
1,934 Posts
Discussion Starter · #7 ·
In my experience on other platforms with forged "street" motors, having audible piston slap isn't normal. My current 2.15L EVO forged motor (3rd forged motor I've had) is very quiet even on cold start and dynoed [email protected] on Shell 93 pump. However, you purchased a "Race" short block so likely the clearance are much looser to account for piston CTE at the projected power level the engine was designed to handle. If the noise is indeed "piston slap" then either the piston-bore clearances are too loose or you aren't getting the pistons up to temp. Does it make that noise after you've been banging on it at high HP?
Same noise with the hood popped? I’ll check and see.. but yes while driving i do hear them.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
2,631 Posts
Same noise with the hood popped? I’ll check and see.. but yes while driving i do hear them.
Sent from my iPhone using Tapatalk
Assuming the noise is audible when driving, does the noise go away after you have been jamming on the motor at full hp? Also, are you certain the noise is "piston slap" and not simply valvetrain noise?
 

·
Registered
Joined
·
333 Posts
The answer is that it depends. A forged engine with high P2W clearance and heavy duty 2618 pistons for a big power build will slap like crazy in street use. Otherwise when operating at max power the pistons will lose all clearance and cause a lot of damage. If your engine was built for light power, not much more than stock bottom-end with tight rings and low clearance for relatively brittle forged pistons then the sounds you're hearing should go away within a minute of driving tops.
 

·
Premium Member
Joined
·
2,006 Posts
I had a built motor on a different platform in the past with CP pistons and a sleeved block. They slapped when cold but went away after a few minutes of warmup. Nothing crazy sounding just a different tone of noise when cold. It wasn't as loud as what I hear in the video but you could tell it was not stock.
 

·
MAJJ
ALPHA 9
Joined
·
1,934 Posts
Discussion Starter · #11 ·
The answer is that it depends. A forged engine with high P2W clearance and heavy duty 2618 pistons for a big power build will slap like crazy in street use. Otherwise when operating at max power the pistons will lose all clearance and cause a lot of damage. If your engine was built for light power, not much more than stock bottom-end with tight rings and low clearance for relatively brittle forged pistons then the sounds you're hearing should go away within a minute of driving tops.
so mine is built to handle 860-900whp , and for the motor as mentioned the Alpha race, with the Alpha/manley pistons (which i hear that Manleys sound loud)
 

·
MAJJ
ALPHA 9
Joined
·
1,934 Posts
Discussion Starter · #12 ·
here's a video i just took in the morning.. you need to listen closely headphone or ear on phone lol.. you can hear the light "chitters" (slow and higher on higher speed).

 

·
Registered
Joined
·
333 Posts
so mine is built to handle 860-900whp , and for the motor as mentioned the Alpha race, with the Alpha/manley pistons (which i hear that Manleys sound loud)
I would ask AMS if those noises are normal. It's possible that your engine has normal but high P2W clearance due to the intended use case, it's possible that your engine has excessive P2W clearance, it's possible that your engine has something else going on. I really couldn't tell you what's going on there.
 

·
MAJJ
ALPHA 9
Joined
·
1,934 Posts
Discussion Starter · #14 ·
I might do that yeah.

Any of you got idle videos with the hood open (built short block)


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
2,631 Posts

·
MAJJ
ALPHA 9
Joined
·
1,934 Posts
Discussion Starter · #20 ·
1 - 20 of 26 Posts
Top