Right then!

Two engines both making lets say 90 dB

Is the total noise output 90dB, 180dB, or something in between??

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]

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

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]

I think 150 dB will stop your heart!

Doubling sound power raises the SPL by 3dB, so your total would be 93dB.

quote:

---

Originally posted by MikeRJ
Doubling sound power raises the SPL by 3dB, so your total would be 93dB.

---

Provided the exhaust outlets weren't close together about 92 db --

looking like one either side

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

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

---

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!

yeah i had thought of that

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.

Go on then!

Ive e-mailed him to see what he says, but in the mean time have a gander at his website

NICE!!!

Would be interesting to see whats in the transfer box?

I aint bothered about reverse either!

And whats the oil pump for???

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.

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!!

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.

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.

---

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!

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.

---

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

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

I know it looks simple but a few decent engineering minds have put a fair amount of effort into making these boxes reliable, so to plan a homebrew with the intention of it being much cheaper and for it to work first time without problems or needing significant development is going to be a bit of a risk. Having said that, like you say if you're prepared to forsake reverse it does make it simpler.

David - It doesnt matter when they are in different gears, the box links the two output shafts together so they can only rotate at the same speed as each other, so if one engine is in a lower gear it will just be revving higher than the other engine, you do need to be careful not to over-rev the one in the lower gear though, because the other engine could push it up past its rev limit if you're not careful.

Im not so sure what happens when the other engine is switched off though, I guess just put it in neutral and let the output shaft be turned by the other engine.

[Edited on 8/12/05 by ChrisGamlin]

Also, do a bit of maths on power / weight before you embark, dont forget that a 600cc engine weighs hardly any less than most 1000cc engines (R6 is about 4kgs lighter than an R1 for example), so add in the extra engine weight, the transfer box, two sets of exhausts, extra bracing / plumbing etc and you'll probably end up with no higher power to weight than a single R1 install, that won't handle as well because of the additional weight.

[Edited on 8/12/05 by ChrisGamlin]

quote:

---

Originally posted by David Jenkins
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

---

I think one of the hardest bits is to get the clutches, throttle openings and gear linkages all set perfectly so they work in unison, otherwise you end up doing things like pulling away effectively on one engine (with the lower clutch bite point) only shifting one engine on occasions, and only have one engine at 100% throttle opening.

quote:

---

Originally posted by zzrpowerd-locost
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

---

Looking at it simply, surely the 600 arnt that much cheaper than the 1200. Like has been said the weights are very similar. If you are going to twin engine and spending around 10k you might as well spend a couple more K and use two 1200 engines.

Slightly O/T but this thread did start off discussing it.

If you were at a trackday and your car was registering 98dB, does this mean you would have to half the noise to get it down to 95dB? What was said at the beginning of the thread really confused me, I understand logarithmic scales but this sounds a bit different. I guess it depends what the dB is comparitive to as someone said. Going to have to do some net research.

[Edited on 8/12/05 by greggors84]

to reduce by 3dB means halving the SPL. Noise is a very complex process to understand fully. So many factors affect it. At SVA i was careful to make sure the exhaust wasnt pointing at anything solid (like another car, wall etc).
Unless you have studied it in detail it will be hard to pick up all that is needed to be known to design something to allow you to pass track tests. Trial and error is about the only method we can normally use.

I was happy with 93dB at 3,900 revs. Hopefully this wont rise too much at full chat.

quote:

---

Originally posted by greggors84
If you were at a trackday and your car was registering 98dB, does this mean you would have to half the noise to get it down to 95dB? What was said at the beginning of the thread really confused me, I understand logarithmic scales but this sounds a bit different. I guess it depends what the dB is comparitive to as someone said. Going to have to do some net research.

---

quote:

---

Originally posted by greggors84
Looking at it simply, surely the 600 arnt that much cheaper than the 1200. Like has been said the weights are very similar. If you are going to twin engine and spending around 10k you might as well spend a couple more K and use two 1200 engines.

Slightly O/T but this thread did start off discussing it.

If you were at a trackday and your car was registering 98dB, does this mean you would have to half the noise to get it down to 95dB? What was said at the beginning of the thread really confused me, I understand logarithmic scales but this sounds a bit different. I guess it depends what the dB is comparitive to as someone said. Going to have to do some net research.

[Edited on 8/12/05 by greggors84]

---

There were a couple of ZX12s advertised recently for around the £1500 mark, something like that or even a £1k R1 is going to be a far better prospect IMHO, even if you can build a dirt cheap transfer box its still going to cost more to do the twin by the time you've factored all the extras the twin needs (two exhausts, two rev counters, extra front prop, extra plumbing etc etc). If you're heart is set on a twin though, why not do it with a couple of ZX9s, at least that way you get the performance benefit and you can pick them up for about £500 each so the extra cost isnt huge compared to the overall cost.

I know Im coming across rather negative and I apologise, its just that apart from the challenge of building it and possibly pose / pub talk value I really can't see many benfits, and can see a shed load of drawbacks. I can understand the desire to have something unique and to explore uncharted territory, but if its going to be at the expense of reliability, useablity and possibly even performance, is it really worth it?

cheers

Chris

[Edited on 8/12/05 by ChrisGamlin]

quote:

---

Originally posted by ChrisGamlin
There were a couple of ZX12s advertised recently for around the £1500 mark, something like that or even a £1k R1 is going to be a far better prospect IMHO, even if you can build a dirt cheap transfer box its still going to cost more to do the twin by the time you've factored all the extras the twin needs (two exhausts, two rev counters, extra front prop, extra plumbing etc etc). If you're heart is set on a twin though, why not do it with a couple of ZX9s, at least that way you get the performance benefit and you can pick them up for about £500 each so the extra cost isnt huge compared to the overall cost.

I know Im coming across rather negative and I apologise, its just that apart from the challenge of building it and possibly pose / pub talk value I really can't see many benfits, and can see a shed load of drawbacks. I can understand the desire to have something unique and to explore uncharted territory, but if its going to be at the expense of reliability, useablity and possibly even performance, is it really worth it?

cheers

Chris

[Edited on 8/12/05 by ChrisGamlin]

---

As long as you know what you're getting yourself into then who am I to complain

quote:

---

Originally posted by ChrisGamlin
As long as you know what you're getting yourself into then who am I to complain

---

Rescued attachment swaprk1.jpg