Cabin sound insulation

[Simon]

OK, I've done a search on this and I'm not even sure I'm posting in the right area but here goes.
The sound level in the cabin of my GTD is just too much. I'm running a solid lifter 302 which I guess doesn't help matters, but I took it today for the longest run I've been on so far. It was only 25 miles or so but the general noise was driving me mad and certainly spoiling my enjoyment of the car. I'm not intending to enter any competitions with the car, so weight is not an issue but any advice on making it a bit quieter would be greatly appreciated. With a dirty great 302 sitting just behind my ear, I'm not expecting it to be super quiet, but It's giving me an almighty headache after just ten minutes.
Simon

[Mark Worthington]

Well, if you searched I'm sure you found threads where I've talked about Cool & Quiet thermal and acoustical insulation. This stuff isn't terribly heavy (total added weight to my car is probably between 10 and 15 pounds). I've put it on the engine access panel (foil facing engine), inside the pipe tunnel and E-brake panels, behind my wheel-well panels, along my side-sill panels, and I plan to use it underneath my interior carpet. This stuff can reduce noise directly from both the engine bay and from drumming of panels. It will also insulate the cockpit from heat. I also plan to have a muffler fabricated that will be more effective than the simple resonator I have now.

[Ron Earp]

Search for "Sound Insulation". Make sure "And" is selected in the operator box. Make sure to "Search All Posts", not just the ones in the last week. You'll get a lot.

[Paul Thompson 'Hooligan']

Hi Simon -

Try wearing ear-plugs.... In-car we always wear them, on and off track and with or without crash helmets.

You can still hold a conversation and it cuts out a load of the irritating background noise. They also enable you to detect 'mechanical issues', for want of better words more easily.

Finally, on track they can be worth a couple of seconds per lap - sounds daft I know, but many a club member has instantly knocked a couple of seconds their lap times after wearing them. A fact I mentioned to a friend who races at national level on 600cc bikes. In disbelief he tried it and reported that he too found a 1 to 2 second improvement!! [img]/ubbthreads/images/graemlins/grin.gif[/img]

[Simon]

Thanks guys,

Paul, I was going to take some today but forgot. I think I will be using them from now on. I ride a bike so wear plugs all the time. (still desn't stop my wife calling me a deaf old g*t though!)
Simon

[DaveWharran]

Simon,
I used some products from b-quiet during construction.
They have various products for sound dampning and absorbing at reasonable prices.

http://www.b-quiet.com/

For heat insulation of the center console and firewall, 1/8" ceramic blanket from McMasterCarr.com. Not particularily cheap, but good insulating value and not too thick.

Dave

[Kalun D]

Aircraft Spruce has a small booklet on insulating aircraft, the stuff it covers is applicable to cars. Best of all it's free. They also carry a complete line of insulating materials. Their regular catalog is a wealth of information including a page on cutting and drilling plexiglass.

BOOKLET

[JOSEPH]

This letter was written to me by a GT-40 Buddy. Joe
[img]/ubbthreads/images/graemlins/laugh.gif[/img] [img]/ubbthreads/images/graemlins/laugh.gif[/img] [img]/ubbthreads/images/graemlins/laugh.gif[/img]
Noise level is a big problem with a GT40, stereo or not. Most GT40 cars are in the high 90db range but I have measured one street car with 103 db in 5th at 45mph. A sustained level of 85db is routinely used by OSHA as the cut off for safe and anything above that is classified as producing some degree of hearing damage. Virtually all the new super high performance street cars are at 80 db or below in routine operation.

Fixing the cockpit sound level is a little like Sears with good, better, and best. You don't have to do everything, just a few items will make a big difference. I could only come up with 5 reasonable (practical) ways to improve the sound level in the car. (1) Muffler, (2) air intake, (3) insulation, (4) tire noise, and (5) engine rpm. Obviously a quieter muffler is an option but I will only do that as my last option. After all I still want the car to sound mean. Carb air intake is very noisy on cars with velocity stacks and that is mainly why I opted for a singe 4 barrel. If necessary I will use an air box and a duct to draw air to the carb from the back end of the car like almost all new mid-engine car designs. But I actually do not what to have to do this either because I like the look of the carb under the rear window glass.

My next option is insulation. Before my engine is installed I am going to add a product called Dynamat Extreme to the engine side of the bulkhead and to the entire inside of the cockpit. It is a 1/8" thick material with a heavy aluminum foil layer on the outside and a elastomeric butyl barrier+adhesive on the applied side. This product has no petrolum smell like "aluminum backed tar roof matting" and is highly resistant to heat. Under the engine bonnet I am also going to put in a layer of Dynamat Extreme and a heat shield called "Hoodliner" from the same company. All the seams and edges will be covered with aluminum tape. I have talked with the Dynamat engineers for specific recommendations a couple of times. They claim 18 db reduction for a quality application, 15 db very routine, and 12 db easy to achieve even if not all areas are done. The sound insulation and thermal shield will add less than 50 pounds to the car. Their website is "dynamat.com" and is full of information and examples. The part numbers and US$ costs are: Dynamat Xtreme Automotive Bulk Pak, #20455, $250.00, and Hoodliner, #11905, $70.00. PDF spec sheets for each product are attached here.

Tire noise is also a big factor. As a test I changed my Corvette tires from the factory Goodyear run flat tires to Goodyear Eagle F1 GS-D3 285-40-YR-17. Sound level went down 5-6 db which was a huge noticeable improvement. Most car magazine tire tests list these with a group of 10 or 12 other performance tires as # 2 for performance and # 1 for low road noise. "tirerack.com" gives a good comparison chart of all the tires in the maximum summer performance category. Tire rack lists the standardized roadholding performance and road noise scores on all its tires which are in line with the published car magazine tests.

Engine rpm at highway cruise speeds of 60-80 mph can also be lowered to drop cockpit noise. I went with a ZF transaxle so that I could pick the gear ratios. There is more details to the story than I will mention here but I picked a final drive ratio and a 5th gear ratio so that at 75 mph engine rpm would be about 1900 rpm. Try this yourself. Drive at 75 in 5th and notice the sound level then lower your speed down to 1900 rpm and stay in 5th. Again a very significant change.

Also, a minor engine point, I have "under drive pulleys" on my engine so the alternator and the air conditioning compressor will not be spinning as fast as on a standard pully size engine. Most car buffs would do this to up the available hp but for me it address sound. Double bonus.

If I do all of these things I hope to get the cockpit sound level down to new car standards with the only significant sound being the exhaust.

Even though you already have your car done, and do not want to change mechanical things, you could add the cockpit insulation for about $400. Most of the carpet is just held in place with Velcro. Enough of the Dynamat Extreme material for the inside of the car only costs about $250. Each 3db reduction is a 50% improvement so if you got only a very conservative 6db change that would be very noticeable. After I do my car I will send sequential pictures of the job so you can see if you think it would be worth the effort.

[JOSEPH]

Hey Guys, Here is a picture of the sound insulation installed on the engine compartment side of the bulkhead behind the seats. I have a sample of the stuff and it looks like it should work realy good. Joe [img]/ubbthreads/images/graemlins/laugh.gif[/img] [img]/ubbthreads/images/graemlins/laugh.gif[/img] [img]/ubbthreads/images/graemlins/laugh.gif[/img]

[mike_starling]

Dynamat Extreme is often available on e-bay as it is used extensively in automotive sound system installations. It is usually less than 50% of list price.

[Simon]

Theres some Dynamat on Ebay UK http://cgi.ebay.co.uk/ws/eBayISAPI.d...sPageName=WDVW
It's £120 for 36 sq ft. I only want enough to do my bulkhead, does anyone want to go halves with me? (18 sq ft each)
Simon