Printable Version of Topic

Posted by: horizontally-opposed Oct 21 2020, 09:16 AM

Noticed that this 914 build had a thicker rear window made, and it got me to thinking about whether that might help with noise in a six-cylinder car when the top's on?

http://www.914world.com/bbs2/index.php?showtopic=335596&pid=2681087&st=0&

Anyone have any experience with this. Is the 914's rear window truly flat, and therefore easy for an automotive glass shop to duplicate?

Posted by: 914werke Oct 21 2020, 10:28 AM

Yes it is truly flat so if you could get a glass shop to cut you a piece of tempered glass
"slightly" thicker should be fine. Too thick you may run afoul of keeping it in place

Posted by: Mark Henry Oct 21 2020, 11:11 AM

I don't think it will do much.
But do make sure the window is sealing, one of the jobs I have to do this winter. I already have the mastic tape from 914rubber.

It's the firewall insulation in cab and bay that will deaden the most sound. I have the factory insulation, modified for my hatch, in my /6 with Webers and at cruise my noise level is totally acceptable. Sure at full song the Webers are loud, but at 3-4k rpm you can carry on a conversation. Any single plenum system or a weber stock filter assembly will be quieter than open filter/rain hats.

Posted by: burton73 Oct 21 2020, 01:25 PM

Like duel pane windows in a home. It cuts down on sound coming through the window. 2 pieces with a small space in-between. Ck the rest of things like bad sealing at window.
Seems like more work to try this. Thicker glass, I do not think so. It is the space in-between that does it. Triple glass with space? Try all the other things from the factory.

Bob B

Posted by: Superhawk996 Oct 21 2020, 01:35 PM

@http://www.914world.com/bbs2/index.php?showuser=2058

I think you're aiming at NVH reduction previously discussed in the other thred. The common modern NVH solution is to use laminated side glass to reduce NVH into the cabin. The laminated glass is another form of constrained layer solution that decouples the two panes without the vastly increased thickness of two pane glass and it is more effective to boot.

Posted by: horizontally-opposed Oct 21 2020, 02:02 PM

Yup, I was, and now we're talking.

I suspect glass per your description + the right modern interior firewall matting + some sort of sound pad on the bottom of the painted section of the engine lid + the factory engine side firewall (mine is still there) would make a nice difference when the top is on, with little to no detriment to when the top is off. Was also wondering about the dual-pane stuff the German manufacturers make, but that might be a big job unless there's a way to add a second stock window spaced from the first and then mod the interior pieces to account for the added thickness? Downsides are weight and modding interior parts as well as figuring out how to add and support it to the existing window. And seal it.

I wouldn't say my engine noise is awful by any means, as I've got the stock airbox on a 2.2 with carbs, but I wouldn't mind cutting the interior engine noise (and it's mainly engine/fan/cam/chain noise I think?) when the top is on. My car was much nicer on the freeway as a four. A 5% to 15% cut would be fabulous, but I'd settle for just a bit of the edge off. Would make the car a lot nicer for long hauls with the top on.

Posted by: SKL1 Oct 21 2020, 10:45 PM

I thought we all loved the 914-6 BECAUSE of the engine noise!

Posted by: sixnotfour Oct 22 2020, 12:19 AM

DAN ROOT Did it yrs ago @http://www.914world.com/bbs2/index.php?showuser=2105

Posted by: Mikey914 Oct 22 2020, 09:26 AM

The noise reduction is minimal at best. The glass does a very good job of deflecting the sound waves. The only problem with thicker glass is that you run into spacing issues if you go too thick as the roll bar pad has to be able to seat into place and there is not much of a gap there.

Posted by: Root_Werks Oct 22 2020, 11:07 AM

Yup, it was the 914 I bought from you (Wish I still had that one). Had a shop cut tinted glass for me. It was laminated and a little thicker. It was just fine.

Posted by: Root_Werks Oct 22 2020, 11:15 AM

It was this 914:

http://www.914world.com/bbs2/index.php?showtopic=88222&st=0

I tried to buy it back from the owner years ago, he said "nah".

I think on page 5 there is an okay picture of the tinted lam glass.

Posted by: Mikey914 Oct 22 2020, 11:28 AM

Why not 1st try applying a film? Perhaps the additional layer will have some effect.