DDK - Die Deutschen Klassiker

Any know where to buy a super quiet exhaust box to fit my '66 swb 911 with SSI heat exchangers ?
I want as much performance as possible but noise is the critical issue. Engine is a 2.0 with a std single outlet notch in the left side of the valance. I'm using a std single outlet stainless (Dansk?) item at the moment but the car is struggling through scrutineering on noise tests. I'm at a loss what to do as I think this is a std exhaust.

Any advice welcome
Regards
Andrew

A std (mild steel) 2-in-1-out silencer will be a bit quieter than a stainless steel equivalent but bear in mind that not all brands are equal.

I think that the std 'silencer' is about as quiet as you're likely to get without resorting to 'add-on' extra muffling.

It might be worth speaking to Robert Barrie about this as he has raced extensively at circuits all over Europe - if you need his contact details pm me.

There's a co-incidence! I've had exactly the same problem with my 65 car. I have a mild steel standard exhaust and was still getting 108 dB from the static noise test. I do have an open induction system and was thinking that was the problem. However I tried one of these:

http://www.demon-tweeks.co.uk/Motorspor ... /1884/5898

and the result was 103 dB! Not pretty but does the job. I've generally found noise testers to be sympathetic to early 911s as the drive-by scores are always much lower than the static test would suggest. However there's always one who goes by the book so this is a useful gadget to have in your kit bag.

PhilipB wrote: http://www.demon-tweeks.co.uk/Motorspor ... /1884/5898

Hi Philip,
my figures are about the same but I'm running a std 2.0T with std airbox.
One problem I have is I can't get it to stop popping in the exhaust when revving under no load. It sends the noise even higher but there is just too much fuel going in under no load.
Do you just put this thing on your tail pipe !!! Do you need to fit a LONG VEHICLE sign as well !!!
I have a SuperTrapp which is shorter and does a similar thing but certainly saps power at higher revs.

Your fuelling issue sounds tricky - however at least you haven't got Solexes so you stand a chance of fixing it!

The additional silencer goes on the end of your tail pipe and yes it does stick out a bit! I'm sure it would be illegal on the road but I've seen some much stranger contraptions at track days that haven't bothered the marshals. Am not sure what a scrutineer would think - but will find out at the GRRC Goodwood test day next week and let you know.

In terms of fitting you need to take your chrome end pipe off if you have one. Easier said than done! Had to resort to professional help. I also had to get the pipe on the additional silencer widened slightly by my local exhaust shop to get it to fit properly.

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On my 2.0 a few years back we failed noise as the car had just come off the trailer. After running it up the road and getting it really warm it passed. Didn't need the exhaust extension but do know that they work. As said, not pretty! On the 3.0 we found it was not the exhaust that causes problems, but the fan noise. We put blankets over the fan in order to pass.
The noise issue is very annoying because on a stage you can hear an Escort from miles away but a 911 creeps up on you! The Escort easily beats the noise limit.

911s and MSA static noise test just don't go hand in hand. On track they can use a drive by test but not really practical on a rally.
I am always sure to get the car warmed up fully before testing. It would be even louder if I didn't.
Options suggested so far -
1) Blanket over engine - quite an obvious one for the scrutineer so only really possible if you have a sympathetic scrutineer to start with. Bit of a nightmare if it gets sucked into the fan !!!
2) stick on device on tailpipe -not elegant, prety obvious if you take it off after scrutineering. Torpedo is big but doesn't sap too much power. SuperTrapp is smaller but probably saps more power.
3) I've heard about repackable exhausts but not found one so far to fit single left side outlet on a SWB valance. Anyone got any advice ?

The more people I talk to the more I realise that no 911s seem to pass static noise test without scrutineers being sympathetic.
Sounds like we really need to get the MSA to modify the test to better represent the actual noise disturbance of the car. eg a drive by or just a lower noise level 3m from the side of the car ?

I have just ordered a twin silencer system from Prepfab. Richard Lepley reckons it gets a 911 well under 100 dB, but it is twin outlet, one either side. This probably helps quite a bit as you are only getting 3 cylinders per outlet.

Custom backbox from turbo thomas. Does fine work, focuses on BHP, and generally tend to be quieter than average

Do a search on his name on impact bumpers - he's got good feedback on there

nick-moss wrote:I have just ordered a twin silencer system from Prepfab. Richard Lepley reckons it gets a 911 well under 100 dB, but it is twin outlet, one either side. This probably helps quite a bit as you are only getting 3 cylinders per outlet.

Hi Nick,
I talked to Prepfab about this one too, but they said it wasn't designed to fit a SWB. I'd be really interested to know what sort of noise reduction you get once you've fitted it. Do you plan to do a noise check to test it out ? What do you plan to fit it to ?
Regards
Andrew

I don't understand why it wouldn't fit a SWB, the bumper at the back and the cross panel are exactly the same shape as a LWB. Mine will be fitted to a 3.5, no comparison as the motor hasn't run yet. The plan is to get it below 100 dB for Castle Combe.

nick-moss wrote:I don't understand why it wouldn't fit a SWB, the bumper at the back and the cross panel are exactly the same shape as a LWB. Mine will be fitted to a 3.5, no comparison as the motor hasn't run yet. The plan is to get it below 100 dB for Castle Combe.

I was told by Prepfab that it was designed for the 3.0 cars and that the outlet positioning might not fit the earlier valance. Not least of which there are 2 outlets rather than 1 but I was told the tailpipe angles are differnet. I'd be happy if I could get below 105dB !

Yes, they will be deigned for the 3 litre motors fitted to the 2.7 RS reps used in post-historic rallying.

Hi Nick,
there doesn't appear to be a picture of the twin outlet system on their website. If you could post some detailed pictures when you get it that would be great plus any advice about fitting to a SWB valance. If the left outlet was the correct angle/etc to match the existing valance cut out I might consider modifying the right side outlet as long as I know the exhaust did the business on the noise reduction.
Thanks
Andrew

Hi Andrew,
Just seen your post having been away.
I suggest you try BTB Exhaust in Daventry.
http://www.btbexhausts.co.uk/exhausts/porsche.asp
I have used them for one off for my previous rally car. They may make the Prefab exhaust? They are certainly capable of modifying an existing design to fit.
My 2.7 is marginal through a noise test and uses a standard silencer. I do know that stainless steel tends to resonate more as it uses thinner material and will be noisier. I wondered about going to a twin outlet as they can only measure one pipe at a time. Pay attention to your inlet filtration as induction noise on the Porsche is in the wrong place. I guess you are on carbs compared to my fuel injection.
All else fails run the engine at reduced revs through scruitineering!!!
Let me know how you get on.
Jerry