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Author Topic: Quieter power needed.  (Read 6513 times)
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dougdee123
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« on: November 03, 2010, 12:38:03 PM »

I have a 1981 Beta 2000 coupe with a tuned engine. The last time it was on the rolling road it was developing 155 bhp. It has, among other things, an exhaust that was custom made for it some years ago and has a 4-2-1 downpipe with a middle box and rear box that are unidentified but non standard.

At the time the company that did the rebuild subcontracted the exhaust sytem and when it arrived it was much louder than expected. It passed the MOT test and so I accepted it. However it later failed at a couple of MOT stations and in recent years I have had to take it to sympathetic garages where they also prepare rally cars. I am not quite seeking out deaf MOT testers but it is heading that way.

So what with that and also the fact that it is a bit wearing to drive for a long time I want to identify silencers that are quieter but don't kill the performance..

How do you tell what to buy? Or even who to get to update the system on the car at present. The technical discussions I have seen are all geared towards absolute performance and don't even consider how to meet the noise levels that are now required for tracks.

I see that there is a betaboyz range. Are these comparable with the OEM in noise reduction? What is known about how  well they go with tuned engines?

Alternatively, can anyone suggest some alternatives that will do the job?

Thanks for any help in this. I live in Cambridge if that affects any suggestions.

Doug
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HFStuart
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« Reply #1 on: November 03, 2010, 04:13:57 PM »

Hi Doug,

I haven't tried the Betabozy exhausts so I can't comment on their noise but I do know that the Ansa 4-2-1 that I had (now on Marcus' HPE) fitted straight to the standard system - jointing at the sleeve joint somewhere under the handbrake.

The other option is to find yourself a powerflow dealer. They'll do a custom exahuast for you that isn't restrictive and can be tunned from wisper quite to Saxo loud. We have a dealer in Bury St Eds  - Formula 1 Autocentre which is your closest or there's ISC (was Warrior) in Ipswich who have a good reputation.

Stuart

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dougdee123
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« Reply #2 on: November 03, 2010, 09:13:58 PM »

Hi Stuart,

Thanks very much for your suggestion about Formula 1 Auto Centre. I'll give them a call and see what they say about it.

As I said, the thing that stops me attacking this myself is the absence of any information. But this would be an easier option if a bit more expensive.

Doug
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WestonE
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« Reply #3 on: November 05, 2010, 05:53:07 PM »

Doug

All exhausts are a compromise between noise and power robbing back pressure. But they also get louder as the silencing material is over time both pulled out of the silencer casings and coated in carbon. Generally straight through silencers give the best power, but they need to be long enough and with enough capacity to get reasonable silencing. I have seen a CSC casing on a Montecarlo half full after 10 years on a Montecarlo.

If you can make it I recommend talking to all the custom exhaust makers at the NEC show and bare in mind the CSC downpipes we see for Beta's are more appropriately sized for 1600s than 2000s. You can also get a lot of good information from Guy Croft's book if you want the car to continue producing strong power and be free reving.

I will have to get a 4-1 system made for my VX, but that will not be soon.

Eric 
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dougdee123
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« Reply #4 on: November 08, 2010, 03:28:08 PM »

Eric,

I do understand what you are saying and I have spoken to people who have had the same experience where the noise level rises over time because the wadding etc blown away. However, what I am asking about is slightly different.

I do have a copy of Guy Croft's book although it is in storage and I can't get to it at present. However the principle of design for a low or no loss exhaust is simple although the implementation is less so. See this article by David Vizard. http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/index.html. Even though he is talking about V8s clearly the principles are the same. He says 'design for flow' and select silencers (mufflers in America speak) that do not restrict. These ideally should be the same diameter as the termination of the single pipe after the manifold if you have arrived at that by the outline calculations stated. If you do that then the best power output will result. So, if we live in the real world and need to pass MOT tests, we can go and find a rear box and tail box that have that same diameter entry and exit pipe and the perforated pipe that is hidden from view and expect the best performance but understand that the extent of difference will reduce it.

What I'm still not able to discover is a figure of merit that describes the attenuation of the noise that any given product might achieve. In the absence of this I have to use one of three strategies.

(1)  Identify a pair of exhaust boxes that are 'straight through' types with the correct entry and exit pipes. Then select the biggest of their type that will physically fit into the locations. Here power will still be optimal but sound level may not be controlled.

(2)   Ignore the internal architecture of the boxes but still select those that have the correct pipe sizes and again select for the biggest that will fit into the space in the belief that this minimises the back pressure for the baffle type. Here power will or may be be reduced but the sound level will be minimised.

(3)  Go to a specialist exhaust designer and have them fit something from their experience. Here I can say if it is still too loud but it is still likely to be the most expensive option and I still don't really know until I drive away if they have reduced power.

Best Regards,

Doug
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HFStuart
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« Reply #5 on: November 08, 2010, 04:45:13 PM »

(3)  Go to a specialist exhaust designer and have them fit something from their experience. Here I can say if it is still too loud but it is still likely to be the most expensive option and I still don't really know until I drive away if they have reduced power.


I've got a feeling Warrior in Ipswich have a rolling road for a before and after....although that's even more expense

Another option is to post on www.Guy-Croft.com there is a wealth of knowledge on there and Guy posts pretty regularly too.

Stuart
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spud
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« Reply #6 on: November 11, 2010, 11:11:41 AM »

The CSC downpipes we see for Betas are more appropriately sized for 1600s than 2000s. Eric 

Really?? I never knew that. So CSC only made the one type then Eric? I have one on my VX- will it be compromising performance? Surely it must still be better than the standard VX manifold though?

Andrew.
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rossocorsa
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« Reply #7 on: November 11, 2010, 10:32:19 PM »

The CSC downpipes we see for Betas are more appropriately sized for 1600s than 2000s. Eric 

Really?? I never knew that. So CSC only made the one type then Eric? I have one on my VX- will it be compromising performance? Surely it must still be better than the standard VX manifold though?

Andrew.

i thionk the answer is it is better than standard but could be much better still
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WestonE
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« Reply #8 on: November 16, 2010, 03:15:39 PM »

Rossacorsa has it in one. Guy Croft can give you pipe diameters and lengths from dyno and race engine tests and this is also in his new book. I used the info to have an exhaust made for my Monte and i was not disappointed!

Eric
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andybeta
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« Reply #9 on: November 29, 2010, 02:40:00 AM »

Doug,

Don Pembleton of Huthwaite makes custom exhaust systems for all sorts of exotica and also exhaust systems for other exhaust brand "names" which you would think make their own. Wrong.

Anyway he has a pattern for a Beta Coupe Volumex exhaust system as I know two owners who had replacements made by him for their Coupes. The results have been very pleasing (I have heard them - you could hear a butterfly land on the boot) and reasonably priced.

Don also made a full 2.5" exhaust system for my HPE VX including manifold 4-2-1 with 30" primaries and 10-11" secondaries and lamba sensor. I chose to miss out the first silencer instead having just 2 straight through silencers - the transverse one and a much longer and fatter tail box basically using all the available space under the floor of the HPE which the std box does not do. The result has been a louder system but the engine breaths sooooo much better which is what I expected. You really need to try to reduce back pressure with a tuned engine as if you don't it can negate any performance gains on the engine you are trying to make. The new system didn't fail the MOT although I must admit I was nervous. But the tester said it wasn't anywhere near failing. So yours must be very loud or you either have some really pedantic testers or they are just trying to fleece you for a new system which you don't need.

Anyway Don is a very nice chap and will bend over backwards to design what ever you want whilst lending his many years of experience to suggest what will and won't work. I suggest you look in a few classic magazines for his advert and phone number as unfortunately I cannot find it at the moment. But he has made systems of all flavours for the Beta. The quality of his work is excellent. Some might say works of art.

As others have said exhaust systems are a compromise. Race and rally cars have noisy exhausts for a reason. Your average family car/road car has so many other constraints to comply with.

BTW I am not far from Cambridge.

« Last Edit: November 29, 2010, 02:46:59 AM by andybeta » Logged
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