Best sound deadening for type 26 with a hard top.

[Davidb]

I am in a similar situation to you with a 26 mostly modified to 26R spec. I fitted flooring spec closed cell foam over the centre tunnel part of the chassis before fitting the body. I think that the diff area needs more attention though-there is only 1/8" fiber glass between you and the diff! I put insulating foam above and below the rear "Y" area. The boot floor seems to transmit a lot of noise so I have lined that with 1/2 inch Dynomat-I don't carry a spare and that may reduce my sound deadening. I covered the whole bulkhead with thin sound deadening foam since both diff, wheel and exhaust noise comes through there. I have yet to figure out what to do about the hard top! I drive for 8-10 hours a time in the car at high speeds and the noise is tolerable. The seats need to be in good shape for that - get them right and they are very comfortable.

[Frogelan]

Interesting subject and there are possibly some solutions to reduce NVH. I have not got beyond the rolling chassis for the time-being, but here are my ideas.

It is not essential to use the "hardest" full race bushes / competition mounts (engine and gearbox). Selective use of nylon / rubber washers (interior of the bulkhead heat shield, dashboard mounts) might all contribute to reduce noise and vibration to start with.

The idea of dynamat on the subframe spine seems to be coherent. The extra weight will be centred and lowered and it should absorb NVH from the drive train before it is echoed into the interior. Whilst I know that this heavy, for endurance events it makes sense not to be exhausted by the sound levels.

Why not make up an underfelt / carpet set that can be removed at race meetings just prior to each race?

Lastly, a number of sound absorbing materials are not necessarily heavy. Frustrated by the poor availbility of the standard S2 dash top (FIA requirement) and unconvinced by the original door panels, I plan to make my own from Banova (balsa plywood) which has the added advantage of burning more slowly than the original injected foam.

No doubt my final remark will shock the 26R warriors who prefer the interior of their cars to look totally stripped out, lose 5kg oneself...

[nmauduit]

Unfortunately, sound reduction performance decreases when adding lightness (-6dB if halving a panel mass), and I believe the lower the frequency the more energy it takes to dampen it, so I don't see any trick to get around that : a light racing car will be noisy.
Though it is still worth making sure that there are not added resonances from panels etc. that would convert a vibration into an other sound source inside.

[Elan Peter]

Thank you very much to every one who has kindly given time to tell me how sound deadening works and who makes the best.
To answer the above comment about my car and to clarify, my car will not be an out-and-out race car (well not really), I am building it to exacting specifications of a 26R as it would have left the factory (bar a new rollover bar).
If you take a look at the photo attached, you will see the fully carpeted interior, bucket seats and lined roof. I have also had a lot of help from a mr Bruce Ward who has owned an original 26R form new and he has shown me the exact specifications of a factory-fresh car.

[rgh0]

mmmmmmm...... how does the FIA specs for 26R and replicas that they allow align with these photos ?

[Elan Peter]

In my opinion, they should all look like this but I am sure that the race winners wouldn't agree.
Best regards, P

[elj221c]

mmmmmmm...... how does the FIA specs for 26R and replicas that they allow align with these photos ?

Not at all, Rohan. Not at all.
Another generation of 26R experts.....?

[Davidb]

Elan Peter: That isn't a fully carpeted interior-it is rubber matting! Not much help in the noise department...

[Elan Peter]

I wasn't 100% sure if it was matting ore carpet. Thanks for the reassurance.
I will probably still put sound deadening material under the mat.
Best regards, P

[theelanman]