Noise levels for a 2.0 L FI set up - interior vs exterior padding Options

[914Toy]

I know this is a subjective topic . . ..

Thanks!

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@TdSkip . Don't take this the wrong way. It is not subjective.

There is a whole field of automotive engineering dedicated to Noise Vibration & Harshness. I've spent a small portion of my career doing this sort of work.

Forget whether you have FI or not. Aircooled engines suck for NVH. They make a lot of valve clattering, rattling, knocking, piston slapping type sounds when they are running perfectly.

Tom,

My focus is to find a good recommendation on reducing the 911 high sound frequency fan whine noise, Suggestions?

Air cooled is not in any way comparable to a water cooled engine that has waterjackets surrounding the cylinders. That is why I absolutely LOVE aircooled. They are different and unique.

So know that whatever you do, you're starting at a HUGE disadvantage from a NVH perspective.

Bottom line, if you want anyting even resembling quiet(ish) you need an exterior engine pad AND a constrained layer damping material (Dynamat) on the interior and I'd still probably put the heavy factory inner pad over the top of that + some thin shoddy on the back of the back pad if I could fit it.

I think there was a whole seperate list in a different thread so I won't rehash that here.

The only thing subjective about it is what one person prefers vs. another but I assure you there is engineering science to use if you want to make it as quiet as it can be.

[rjames]

There are of course loudness safety ratings/guidelines that should be followed if one cares about maintaining their hearing which have nothing to do with the level of noise an individual will tolerate.

Use the pad in the engine compartment. It definitely lessens the amount of noise that gets into the cabin.

[Literati914]

Are you guys that use and suggest using the stock type engine pad, not concerned about it holding water and causing rust eventually?

[Tdskip]

Are you guys that use and suggest using the stock type engine pad, not concerned about it holding water and causing rust eventually?

I believe some of our supporting vendors have closed cell foam options available

[Literati914]

Anyone know if there are any stick-on sound deadening materials that would work in the engine compartment's firewall, that can be painted like the original stuff that was on the floor? I personally don't trust anything that sits somewhat loosely to not encourage rust.

[JamesM]

Havent seen it mentioned yet so ill bring it up...

I have quite a few 914s but the one that has the factory undercoating is by far the most quite/comfortable ride. With or without the engine pad in.

Not a popular option due to the rust potential so a lot of people strip it off, but a noticeably different experience. The car has a much more "high end" feel/sound to it and less like im rolling around in a tin can. Curious if other with intact undercoating have noticed similar?


When i ever get around to stripping another one for paint I want to hit the entire pan of the car, and interior firewall with lizardskin to see if i get similar results.

[ctc911ctc]

In the 70's I drove a '70 1.7 and a 74 2.0 across the country. (IMG:style_emoticons/default/driving.gif) Though I was in my 20's I recall being mentally exhausted from the noise of the car. (IMG:style_emoticons/default/wacko.gif) (IMG:style_emoticons/default/wacko.gif)

For our '74 2.0 build this and last year, we used Dynamat. Everywhere. Inside the cabin, floor, side-longs, and firewall-up-to-the-window. Within the engine compartment, we have Dynamat on the cabin side of the compartment AND the 914Rubber Noise Reduction mat. The original fell apart when we took it out of the car. (IMG:style_emoticons/default/sad.gif)

The car has a unique sound where the engine can be heard but it is not as amplified as other cars without Dynamat. The car is almost silent when the top is off. I did say almost!

Dynamat!

[Rikyrat]

Hi all:

Thought I would weigh in on this. I recently repainted the engine bay on my teener. When I removed the engine pad, and scrubbed it, I was surprised to find that it was green, not black. I guess the years had not been kind, anyways, what I did was put fat mat on the firewall, and on the engine side of the mat. Fat mat would not stick to the oem mat, so I ended using contact cement to get it to adhere.
I am getting ready to reinstall the engine, so I don't know how much of the sound will be absorbed by this setup. But I figured, it could not hurt. I will update later

[bbrock]

Can't hurt but you'd be better off sticking the Fat Mat to the firewall and then adding the factory pad. As @Superhawk996 already mentioned, you need different types of sound deadener to reduce different types of noise. Fat Mat and the equivalent are constrained layers that are designed to attenuate the noise generated by vibrating panels. Tight adhesion to the panel is an essential part of the constrained layer system. The engine bay pad is a different animal that is designed to attenuate airborne sound waves like the drone of an engine. Adding a constrained layer to the factory mat will add mass so probably improve the sound deadening, but it isn't using the Fat Mat to its full advantage.

[Tdskip]

Can't hurt but you'd be better off sticking the Fat Mat to the firewall and then adding the factory pad. As @Superhawk996 already mentioned, you need different types of sound deadener to reduce different types of noise. Fat Mat and the equivalent are constrained layers that are designed to attenuate the noise generated by vibrating panels. Tight adhesion to the panel is an essential part of the constrained layer system. The engine bay pad is a different animal that is designed to attenuate airborne sound waves like the drone of an engine. Adding a constrained layer to the factory mat will add mass so probably improve the sound deadening, but it isn't using the Fat Mat to its full advantage.

Excellent note

[Olympic 914]

I have not tried this. But since the dynamat is a tar type bonded to an aluminum backing, could you paint over the dynamat ? sanding it and treating it as an aluminum panel?

I have the Dynamat all over the interior under the carpet and backpad. nothing on the engine side though.

[bbrock]

I have not tried this. But since the dynamat is a tar type bonded to an aluminum backing, could you paint over the dynamat ? sanding it and treating it as an aluminum panel?

I have the Dynamat all over the interior under the carpet and backpad. nothing on the engine side though.

That is exactly what I did. Not Fat Mat, but Noico. Same thing just less expensive. I etched the aluminum face with phosporic acid then sprayed with reduced epoxy primer and then top coat. The result looks very close to the factory tar. You can read the whole process here: http://www.914world.com/bbs2/index.php?s=&...t&p=2659673

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