zzrpowerd-locost
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| posted on 6/12/05 at 04:16 PM |
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One for you boffins!
Right then!
Two engines both making lets say 90 dB
Is the total noise output 90dB, 180dB, or something in between??
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emsfactory
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| posted on 6/12/05 at 04:26 PM |
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It is not 180.
In general a rise of ten decibels will double your sound level so two at 90 should be 100 in total. In theory.
[Edited on 6/12/05 by emsfactory]
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David Jenkins
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| posted on 6/12/05 at 04:34 PM |
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In practical terms, 2 engines would be a real bar-steward to test with the SVA sound meter - if you set the microphone right for one exhaust,
you're probably wrong for the other!
So, you might get 90dB from one exhaust, or way over 100dB if the mic ends up too close to the other exhaust.
If you put the exhausts on each side of the car, it will be little more than 90dB on each side, presuming that the car itself screens most of the
noise from the other one - the mic is put quite close to the exhaust on a single engined car (1 metre away, at an angle of 30 degrees, I think).
Just to confuddle the issue...
David
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flak monkey
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| posted on 6/12/05 at 04:34 PM |
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Depends if they are in phase or out of phase 
But no it wont be 180dB...if it was, you would be very deaf!
It should still be around 90dB mark, but will be slightly higher.
David
[Edited on 6/12/05 by flak monkey]
Sera
http://www.motosera.com
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emsfactory
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| posted on 6/12/05 at 05:22 PM |
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I think 150 dB will stop your heart!
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MikeRJ
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| posted on 6/12/05 at 05:26 PM |
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Doubling sound power raises the SPL by 3dB, so your total would be 93dB.
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wilkingj
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| posted on 6/12/05 at 05:48 PM |
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quote:
Originally posted by MikeRJ
Doubling sound power raises the SPL by 3dB, so your total would be 93dB.
Agreed.. +3dB is Double, and -3dB is Half.
+10db is x10, and -10dB is divide by 10.
These are the 4 main figures for working out Decibels. Which are a Logarithmic Ratio and have NO fixed values.
ie going from 10 to 20 units (of whatever) is a +3db gain, however, so is going form 1 to 2 units (the same gain ie +3dB).
They are a relative Ratio measured on a Logarithmic scale.
There are special annotations ie
say... 20dBm which in radio terms is 20dB gain relative to 1 Milliwatt ie what the "m" is stating the reference is 1Milliwatt (1/1000 of a
watt).
ie 1mW x 10 x10 = 0.1 Watt (1/10 watt)
30dBm would be equivalent to 1 Watt. (three lots of 10db's)
Hope this starts to explain.
90dB is meaningless unless you know what it is relative to. I am sure that there is a reference level for sound (SPL).
I do know that Concorde was 125DbA. Sound is usually noted as dBA.
The "A" being simmilar to the "m" Milliwatt reference, but I dont know what the reference level figures for sound are.. its
not my Dept!...
I am a Leccy Teccy, not a sound engineer
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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britishtrident
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| posted on 6/12/05 at 06:11 PM |
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Provided the exhaust outlets weren't close together about 92 db --
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zzrpowerd-locost
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| posted on 6/12/05 at 06:35 PM |
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looking like one either side
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Guinness
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| posted on 6/12/05 at 08:47 PM |
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From the draft SVA manual
"NOTE: If the exhaust has several outlets which are not more than 300mm apart and which are connected to the same silencer, the microphone must
face the outlet closest to the vehicle contour or the highest above the ground. In all other cases, separate measurements must be taken, the highest
recorded being the test value."
So two seperate exhausts systems would see Mr SVA Tester measure twice and take the Highest one as the measure.
HTH
Mike
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zzrpowerd-locost
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| posted on 7/12/05 at 01:35 PM |
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quote:
Originally posted by Guinness
From the draft SVA manual
"NOTE: If the exhaust has several outlets which are not more than 300mm apart and which are connected to the same silencer, the microphone must
face the outlet closest to the vehicle contour or the highest above the ground. In all other cases, separate measurements must be taken, the highest
recorded being the test value."
So two seperate exhausts systems would see Mr SVA Tester measure twice and take the Highest one as the measure.
HTH
Mike
Cheers for that mike!
BTW
Found a way to keep my user name, if i cant find a 1100 or 1200 when im ready.
zzr600 engines are dirt cheap
So zzr600 x2 = 200bhp and 95 ft lb of torque
LOL
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ChrisGamlin
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| posted on 7/12/05 at 02:26 PM |
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Trust me, the "dirt cheap" aspect of the 600's will be more than swallowed up once you start trying to connect them together to
drive the car along!
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zzrpowerd-locost
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| posted on 7/12/05 at 04:23 PM |
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yeah i had thought of that
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ChrisGamlin
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| posted on 7/12/05 at 07:23 PM |
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I can get you some ballpark minimum figures if you like, a mate of mine converted his Westie to twin ZX9's and it cost him a huge amount, and
although you could do it cheaper, you'll find you need to spend quite a bit to make it anywhere near reliable.
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zzrpowerd-locost
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| posted on 7/12/05 at 07:42 PM |
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Go on then!
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ChrisGamlin
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| posted on 7/12/05 at 08:49 PM |
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Ive e-mailed him to see what he says, but in the mean time have a gander at his website
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zzrpowerd-locost
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| posted on 8/12/05 at 11:56 AM |
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NICE!!!
Would be interesting to see whats in the transfer box?
I aint bothered about reverse either!
And whats the oil pump for???
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ChrisGamlin
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| posted on 8/12/05 at 12:08 PM |
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There are pics of inside the transfer box if you go to Modifications - transfer box.
I believe the oil pump is connected to the transfer box to pump oil round a cooler as otherwise it was overheating.
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NS Dev
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| posted on 8/12/05 at 12:11 PM |
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Dunno, but I do know that Geoff Berrisford who owns GBE is an absolute expert, and is one of the few people in motorsport that I have come across that
I can trust totally and have the utmost respect for his work.
There are not many autograss cars in the country without one or another of his parts on, and I have yet to see one break!!
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ChrisGamlin
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| posted on 8/12/05 at 12:27 PM |
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I wasnt suggesting it was just the transfer box that made things more unreliable as the inrerent complexity of the entire install means there's
much more to go wrong than with a single engine'd car, although the transfer box does seem to have required development on both the twin
Caterfields I know of (this one and also the yellow original Tiger Z100) to make it reliable for trackdays etc.
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zzrpowerd-locost
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| posted on 8/12/05 at 12:29 PM |
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quote:
Originally posted by ChrisGamlin
There are pics of inside the transfer box if you go to Modifications - transfer box.
I believe the oil pump is connected to the transfer box to pump oil round a cooler as otherwise it was overheating.
See it now!
If you ignore the reverse thats simple!!!
And the pump just sends oil from the box though cooler and back into the box
[Edited on 8-12-05 by zzrpowerd-locost]
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NS Dev
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| posted on 8/12/05 at 12:30 PM |
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Sorry, I wasn't suggesting that!
Just reference to my satisfied service from GBE over the last few years!
Will shortly be ordering the driveshafts for my 7 from him!
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ChrisGamlin
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| posted on 8/12/05 at 12:33 PM |
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Right, this is what Tim said in his reply:
quote:
Xfer box: £3k
Engines: £600ea
Exhausts: iro £1k
Props: Can't remember, but twice whatever a decent TRT prop costs.
Gearlinkages: depends on application
Tachos: £200min
Radiator: £300
Oilcoolers and pumps etc: £300
Loom: no idea - probably spent 100quid or so on wire, switches and bits
Mods to my chassis were several grand, depending on how much is needed for the specific
chassis/engine combination.
There's also lots of incidental costs which would depend on what he already has.
I saved a bit by using one temp gauge to monitor 3 things by using a rotarty
switch on the inputs. May find that there's no space for existing battery so
smaller one would be needed.
Also he'll need to make up ducting and stuff to make the coolers efficient.
Maybe change diff ratio. etc etc.
Basically unless he can do the chassis welding himself he'll be lucky to get
change from 10k IME.
Also bear in mind that not all engines are suitable for a twin installation
anyway. It's very dependant on where the gearbox outputs are in relation to the
bulk of the engine. ie can you get the short front prop past the back engine to
mate up to the inputs on the xfer box. Xfer box was designed around the ZX9R
engines. GSXR1000s were ok, R1s weren't, for instance.
Obviously this is most relevent assuming you're converting an existing car and planning on using an off-the-shelf transfer box from Z-Cars /
GBE, but it gives you a good idea.
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zzrpowerd-locost
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| posted on 8/12/05 at 12:48 PM |
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Transfer box £3k  Although in some alipcations you dont mind paying for proven and reliable products, but this is locost!
I have had lots of machining exp and know lots of people! Transfer box without reverse shouldnt be to hard??
Have alot of contacts in the agri engineering business so should be easy to get hold of three gears and some bearings that will easily cope with the
150 ft lb of torque! And a small pump
I can do the chassis myself, will be building from new which will be easiler
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David Jenkins
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| posted on 8/12/05 at 12:59 PM |
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Surely one of the problems with designing a transfer box is handling the situation when only 1 engine is running - you have to transfer from one
engine while ignoring the other. Then do the same when the other engine is running and the first is stopped.
Then what do you do when the engines are in different gears...
Aaargh!
David
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