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Our LS400's use plastic (blow-molded?).ductwork from the ram air box that sits astride the radiator, air cleaner assembly and, intake noise damper box atop valve cover to throttle body conduit.
Lexus made a real effort attenuating intake induced noise but left room for improvement.
The air cleaner assembly (on 1999 LS400) and throttle body conduit incorporate metal plates and straps to increase mass....for reduction of intake induced sound energy
The ram air assembly over radiator is noisy to the author's ears. It is plastic and soundings suggest it does little to dampen noise finding its way out from the engine...so I filled the hollow sections behing with 3/4 pound of lead. Now a solid thud instead of a very hollow reflecting sound.
Also filled the bottom of noisy air flow sensor housing bracket with 1/4 pound of lead.
Finally smoothed sharp transitions and plastic mold seams inside section of air cleaner box/MAF housing.
The application made a difference to my ears.
If anyone wants test results, feel free to acquire equipment for before and after testing.
Lead has a fairly low melting point, so it is not necessary to boil the lead...just enough to melt and pour so not as to overheat the plastic parts.
Top view of ram air inlet on 1998-2000 LS400. Earlier models similar. Bottom side of ram air inlet depicted...Lead added to guide vanes to increase mass and dampen noise... Bottom side of air cleaner/ mass airflow sensor housing depicted...very noisy at this point due to velocity of airflow through and around body of tubular MAF sensor 1/4 pound of lead in the pockets..... The entire back half of air cleaner box/ MAF housing tube. Notice the sharp 90 degree transition...lots of turbulence induced noise and restriction here...and in the throat there are sharp molding seams... Plastic seams and sharp transition deep inside throat visible here. Radiused transition from housing to throat and removed plastic molding seams from throat. Just enough to radius sharp edge...careful not to remove more..
I will use plastic polish or wet sand with fine grit to remove latent roughness in tube.
I was thinking you could also use Dynamat and tape it to the bottom of the plastic surfboard of an intake path. Audio guys use it a lot to take care of the trunk rattles so I presume it would have the same effect.
I was thinking of Dynamat too, if it would be able to withstand the engine bay temps (hotter after shutting things down, where there is no air flow to keep cool).
On the test equipment, I have not tried it myself, but I've heard there are app's you can get for the iPhone that use the microphone to make a sound meter. (not exactly rocket science)
wow most people I know would rather get MORE intake noise than less. this is very interesting! this begs the question...isn't lead toxic?
The transition from Air cleaner box to MAF passage leaves much to be desired....turbulence induced noise from plastic mold seams and 90 degree sharp edges...whether you prefer increased noise or not, eliminating this will improve engine performance...or power is exactly the same but quieter.
To some increased intake noise equates to increased power....but in this instance airflow turbulence suggests decreased power....
Lead is not toxic...unless of course you ingest it....and as for the car, it has not keeled over yet.
I have used it in other areas of the LS400 with good results and no ill effects...Check out those postings. "Lead Foot"
It would be better to add a comparison chart something like this below showing the level of before and after. So that we can understand how you are getting a good result.
It would be better to add a comparison chart something like this below showing the level of before and after. So that we can understand how you are getting a good result.
I agree with before and after results presented in chart form.
I invite(d) anyone with appropriate test equipment to perform these minor modifications to present before and after results.
To my listening device at these components there is discernibly less noise suggesting improvement.
If an intake manifold design with such sharp 90 degree transitions was produced....the fix would be to radius it...so belive the. decision to modify "sound".
09-18-17, 04:21 PM
1990-2000 ls400 intake noise reduction
