Since the NSX had a 2 pane rear window I was wondering if it would be worth it for the 914? I know the NSX has a vacuum in between to cut sound transmission that would be hard to create.
The 914 has the room on the "ledge" for 2 and a gap (5mm + 5mm + 5mm).

fire away

I thought about this and never followed up. It would be great for sound deadening. I had some seat time in Jenny's car (which doesn't have a rear window) and it was LOUD. I'm game ($) if we can figure something out.

Any glass shop can get a insulated glass unit made in the thickness you request and in the shape you want if given a pattern to go by. Not sure if it would make any diff in the teen or not. The factory glass is about 5mm or 3/16". probably wouldn't give but 3 or 4mm of vacuum in between.

BTW, better have it tempered. You can also have it made from tinted glass. Should be easy.

It should help with the heat transfer also and make the car cooler.

count me in if it is cost effective.

Bernie

I pay less than $100 bucks for a 4' X 4' insulated glass panel. Two peices of 1/4" plate with 1/2" space in between. Tempered is slightly higher. I have to order some tomorrow. I'll check with my supplier and see if it can be done and the cost.


Curt

Isn't there a slight bend to the shape of the glass?

I don't have one in front of me, but I would think that an insulated glass panel wouldn't flex.

Silly question.... what's special about insulated glass?

Thanks Curt, let us know.

Starting to look like I'm going to have 2 extra windows instread of 0.

The rear glass is flat.

I wondered about that too Karl, but not according to my cabinetmakers straight edges. Apperars to be a flat peice of glass. I have a car without a rear glass, and lots of 1/4" plate we took off a job last week, so I should be able to make a pattern, cut a piece and find out. I can do that tomorrow.

you guys got me thinking now. I'll report back later.

It will also add some weight to the car.

Insulated glass is two plates of glass with a dead air space in between, ie, vaccum. The ouside glass will be hot or cold to the touch. The inside will be room temp. It would also keep the rear window from fogging.

Goddamn, I got to do one now!

Hmmm, one more thought. Chris, do you have one that's out? check the edge and see if it's laminated glass. Two sheets of glass with a thin sheet of plastic in the middle.

I have one on my kitchen table right now, it is flat and not laminated.

BTW good idea.

Thanks Dylan

Until the edge seal fqails then it will fog when water gets in. Insulated galss is not a good application for cars, and it would be difficult to accommodate the thickness of that glass assembly in teh rabbet of the 914 rear window.

A much better idea is laminated glass...it has a higher sound isolation rating than insulated glass and could be made as a direct replacement for the thickness of the stock glass. Its the same stuff used as windshields.

Well, there is one more small problem. I don't think there's enough room between the glass and the backpad, or side trim peices to go any thicker.

If it can be done, it should be tempered so if it breaks there isn't many sharp edges at neck height.

As to the insulated glass, many window builders use argon gas with a reflective heat shield on one of the layers of glass. The two panes (or three)of glass are sealed around the edges with silicone and a needle is inserted between the panes. The air is sucked out and a squirt of argon is put in to displace any moisture. This stops the glass from getting cloudy when it heats up.

If it's not sealed it will fog.

Not practical IMO

Sealing is not the problem. The compund to seal the two sheets of glass is the same compound used to seal the glass to the frame. One shouldn't fail before the other. As long as the unit is professionally made. The thickness, I think, is a problem.

I'd look if I had mine in... maybe that's why it fell out in the first place.

My car is unique in that the V-6 puts alot of heat into the firewall, softened up the roll seal.

My pads can be trimmed since they are getting a cloth covering anyways. Rear pad is now carpet.

I'm still looking for a rubber seal to hold the 2 pieces of glass together. Argon injection may be an issue. Oh, I'm still looking into using factory glass if you haven't guessed yet.

You could use plexiglass instead of Glass. It is much thinner and wont shatter like glass. I think it is also stronger.

Bernie

Thanks to all the people who helped us quickly realize that it can't be done. Actually, now that I think of it you can't put a 928 engine in a 914 and you can't turbo a 4 cylinder motor.




Anyway...
This article claims laminated glass (windshield glass) will reduce sound like glass wice as thick. Might be time to invest in a deciblemeter (?)/sound meter.

I've already got mine planned out (awhile back, and still another reason everyone else is 'driving' their 914's, and mine sits on jack stands ). I've got three rear windows. One of the windows has the defrost heater on it, which will be the outside window. The inside window will be limo-black tinted (to keep head lights from burning out my retina) with a 2mm air space between the two. At first I was going to seal all of the way around the window except for a small area at the top and bottom, but after reading this maybe one could shoot some argon/nitrogen (from a MIG welder?), and then seal the gaps.


Hey, it looks good on paper.....

We have put many Lami units in homes where sound was an issue and had great success. You can get Lami in alot of colors also, green, bronze, and two shades of gray (gry & gry lite 14). Also it comes in two different thickness, 3/16 & 1/4. Never build a unit that has a tint on the inboard lite of glass, heat will build up between them and cause it to break. Been there done that. Also if the inboard lite on a insulated unit is not supported well it will sag and leak. Been there also.

The only part of "can't" I understand is "can't afford to"

Found a rubber seal that can be modified for use. I still need to figure out how to adapt the A/C guages to the argon tank, vacuum, and that needle thing.

You guys are making this complicated

- starting to understand why ricers look like they do, gets boring when all you need to do is drive it

Has anyone tried or made a lexan rear window? The stuff is bullitproof. I does scratch easy however. I am thinking it's the way to go. Thoughts?

Racecars do it all the time. I think it's not very sound proof though.

I thought it might be more soundproof. Based on the comments about laminated glass. It is probably hard to judge as race cars are loud for lots of reasons.

I have to agree here with Jeff Bowlsby. LAMINATED Glass! first of all it will kill the sound, second if you hit it you won't go thru it even if it cracks so its very safe. Also they can cut it to anyshape you want pretty easy. Tempered glass is first cut then sent out to the ovens where it is tempered. Won't stop the sound more than the regular glass.

I have thought of going to laminated glass for a couple of years to kill the sound some more. Just have to finish the other projects...

Your windshield is laminated glass BTW.

Lexan breaks just like glass with sharp pieces.

Glass

Would I be able to get a "local" glass shop to cut laminated glass? Is the windshield tempered and laminated or just laminated? What kind of cost would/should be involved? Thanks

Read the sticker, its laminated. When it breaks it cracks! Tempered glass like the side windows break into little tiny pieces.
I would rather have behind my head a piece of laminated glass like the windshield. It will kill the sound. Yes, any glass shop can cut laminated glass, its a pain but they can do it. Not Home Depot thou.

Be safe not sorry! Lexan is for racing for a reason.

Regular glass even insulated would be very unsafe behind your head.

Geoff

Whats not safe about lexan?

Most glass shops will cut laminated glass but I don't think it's cheap because of breakage. The more complicated the ship the more they will charge.
I was told once that they cut both sides, break it, then pour lighter fluid on it and set on fire to melt the plastic. I don't know if that's true.

Laminated glass is not tempered.

it will break into bigger sharp pieces than say tempered glass. Thats fine racing as you are wearing a helmet. Its very light which it good. In a race car the cage will protect you from the crash impact and the lexan plastic will bend alot before breaking. Glass doesn't bend so the small less than a 1" pieces are great in a crash. The laminated glass takes a huge blow to fail although it cracks . Ever see a rock go through a windshield? Pretty hard to do that


Geoff

Ok, here's the latest from my research with a couple of local glass guy's I work with.

First, they both said that unsupported on the bottom, the inside glass would sag and the seal would fail.

Second (to my surprise), the laminated glass would give almost the same sound and temp insulating qualities as the the insulated unit.

Third, both said they could not make the insulated unit knowing what it was meant for ( implied laibility).

Fourth, the insulated unit would be too damn thick to fit behind the trim panels.

My consensus. Just leave it like it is untill you have to change it.

I guess you cant turbo a 914 then.

So can we make laminated glass from 2 OEM pieces?
or is the OEM tempering prohibit that.

- I've used Lexan in the sign business, it's strong as hell but I wouldn't want to have to polish it after washing the car...

Nope. You can't seal them. moisture will find it's way in between. Just take one of yours to a glass shop and ask them to make one in 1/4" laminated glass. Ask them to look at a sample of ford graylite 12. Nice smoky color.

Just got back fom the glass shop. They could make the rear window in 5mm laminated grey tint for $90.00 or 5mm tempered in grey tint for $40.00. A sheet of grey tint lean 3/16" $168.00. I am not super worried about noise so I may just go with tempered. BTW all prices CDN.