Exhausting stuff.

[macdonald.dm]

Chust in case it's not being seen due to peeps not clicking the 'show only new posts' button, I'd really appreciate advice on my new exhaust system - see post below for full details.

Basically, has anyone tried a motorbike can? Or does anyone know of a really quiet 'standard' car 'box?

Thanks.

I said 'THANKS!'

I said - oh, wait a minute 'til I shut the engine off...

[danny_nelson]

Re: Exhausting stuff.

Supatrap works well and of course has adjustment by adding or taking out discs.

[macdonald.dm]

Re: Exhausting stuff.

Cheers, Danny.

Supertrapp is a new one on me - never heard of them before. Looks like they'd do the trick ok, but I wonder how it would compare with a standard large bike muffler?

[jon_cox]

Re: Exhausting stuff.

Donnie,
There is a simple rule to follow with a silencer. The larger the volume of the silencer the more noise that gets absorbed. Add to this the total surface area of the pipe within the box. Straight through pipe has less surface area than a box with a dogleg pipe or S or Y shape pipe running through it. Also, the larger the pipe bore the louder it will be although this is only a small % of overall db. Bike cans are good for low rev noise but they usually have a valve that opens when airflow increases which then makes them extremely loud. The valve drastically reduces air flow which reduces engine performance but as bikes rev to twice that of a car with there power band coming in at 6-12000 rpm this is seen as an acceptable compromise. Not good for a car!! I also read that you have attached the exhaust to the fibreglass wing. This will create a great amount of 'drone' as the whole body will now act as a sound box. Before spending money on a new silencer get a good heavy gauge bracket welded direct to the chassis and use good quality exhaust bobbins to isolate the NVH of the exhaust. This will make a difference. If the exhaust is attached anywhere else then you need to sought that too. I also notice from your picture that the pipe exits are pointing down to the floor. This again will increase the booming effecting as the noise bounces off the floor and echoes around the rear of the car. Turn them so they exit out the side. You may need to stagger them as you say there are twin rear pipes. Again, if the inner exit pipe does not reach to the outside of the car then extend it so that it exits level with the wing edge.
Hope this helps.

[jon_cox]

Re: Exhausting stuff.

Donnie,
Remember never to 'hang' the exhaust using the bobbins. They will just split apart. The exhaust should always 'sit' on bobbins. I have attached some pictures. One is of the roadster bracket and the others are of mounting.

[jon_cox]

Re: Exhausting stuff.

Donnie,
Here is a picture of a Cabrio with side exhaust. This actually uses 2 silencers. I believe this car belongs the Richard Becker who lives down your way.

[macdonald.dm]

Re: Exhausting stuff.

Hi Jon. That's really useful stuff - as always!

No risk of the box falling off as the bolts pass right through the metal strap and the running board, with a rubber sandwich in-between. Hmm, I bet that doesn't help the nvh!

Lots of stuff to go on - I'll give it some serious thought. Many thanks.

[daniels917]

Re: Exhausting stuff.

Hi All, I dont usually comment on here as mine is a roadster, but i just aquired an aston martin tailbox off Ebay, 30 inch long, 2inch boar, stainless sounds great on my 2L pinto, not too loud, and a good bark, hope this helps. Merv

[macdonald.dm]

Re: Exhausting stuff.

Interesting, Merv!

Obviously subjective, but how loud do you find it when cruising? Also, is it side-exit?

Thanks.