What final drive would raise my 3rd gear to equal 4th or 5th gear? Swiss noise testing and import problem, resulting in ban to drive my seven.

[anthony1956]

Here's the deal:

 

I get x rpm in 3rd gear. (6 speed box)

I want x minus as much as possible rpm in 3rd gear

 

To do that a method is to change the diff ratio.

 

So what is the lowest ratio diff I can put in my K series dedion ? And where can I get one?

 

(when I say "lowest ratio" I mean the one that goes furthest with every turn, NOT the one that goes less distance but accelerates faster)

 

If you had to do a test in 3rd gear and needed lowest rpm, what would you do?

It is not about speed or power or any other performance measure.

 

is this genius at work.. especially as it doesn't affect the static test.

 

 

 

Edited by - anthonym on 25 Feb 2011 07:33:08

[DohNut]

 

3.14 is what some bike powered cars use.

That is the propshaft only has to turn 3.14 times for the drive shafts to turn once.

only available on Sierra Diesel pick-up or something silly and very rare

 

Compare with the more usual 3.6 and 3.9 versions

 

On my crossflow I found that at 60mph I had a reduction of noise after making the gearing easier - an accidental side effect of going from 14in to 13 inch wheels

not quite the same I know but..

 

 

[Paul Deslandes]

Assuming that you're planning to reinstate the status quo after you've got the car through its import tests, rather than mess a round with your existing diff you'd be better of trying to borrow a high ratio one and just swap the whole unit over. I've no idea who might have one though but you could try the 'Wanted' section.

 

I can't imagine that a 'K' engined 7 with that ratio would be much fun to drive for the long term.

[Graham King]

Anthony, I'm not clear if this is a temporary fix you are after or a permanent change, why not increase the size of the wheels as it will have the same effect. On the assumption you currently have 175/55 R13, if you changed to a 195/60 R15 it would increase the rolling circ by approx 20% which is roughly the same as reducing the final drive ration from 3.62 to 2.9.

 

I hope I haven't made any major c*ck ups in that calc or misunderstood what you are trying to achieve.

 

Graham.

 

[Stationary M25 Traveller]

Think it is a temporary 'fix' for approval puproses.

[Brian Soper]

I run a 3.67 diff in my 1961 Lotus 7 S2 it has a 1300 A series engine with approx 100bhp and a C/R gearbox using 6000rpm this gives me 40 mph in first 70 mph in second 90 mph in third and 120 in 4th in theory!! but actually a nice cruising revs at 80 to 90 .It is not a town car and needs 3000 revs to be on cam but is fun on the open road

I think a Sierra auto diff would be what you need and is 3.36

Hope that helps

 

Brian

 

Edited by - Brian Soper on 22 Feb 2011 13:15:35

[bstark]

'Tis only a thought, but my car only has 4 speeds - how much do your authorities know about the spec of your car?

 

Wondering if a cheap option is a 4 speed gearknob, and then take off in 3rd (as "first" gear) - especially if you can use a temporary plate to restrict the gearlever so 1st and 2nd aren't accessible.

 

3rd then equals 5th with minimal cost 😶‍🌫️

[Bricol]

I was about to suggest the same!

 

As it's a 6 speed, reverse is up and left, so block off 1st, making 2nd a dogleg 1st - and 4th the new 3rd . . .

 

Bri

[MADMALC]

I have a 'what if' spread sheet, blatmail me if you want it.

[anthony1956]

So many ideas, yes temporary fix, noise test in morning, bigger wheels! So simple.

I have massively reduced the noise.. so now I can hear the intake roar. Great.

Wonder where I can borrow some wheels. Too late i fear, but have decided to proceed because i need data, assuming she fails, need to understand the extent of the problem.

 

Thanks for all ideas, yes they have the car spec, no of gears etc.

 

 

[Jason Plato]

are you driving for the test ?

add throttle stop to prevent side open throttle and use 5 th gear instead of third ?

[rj]

Dave,

 

 

Which gear to be used is not the choice of the driver. It's given by the regs.

 

Anthony,

 

You'll struggle to find anything lower than 3.14:1, currently you have 3.62:1.

 

There's a chance that I'll soon have a 3.14 diff on the shelf for (one of) my next project(s)

[anthony1956]

Did not succeed on this occasion.

 

Tested result 95DBa

 

Required result 75DBa

 

(Inc 1db allowance)

 

So.

 

I now have to follow alternative idea.

 

Thanks for inputs.

For anyone who has followed this three year saga the underlying matter is two federal departments with different instructions to me.

[rj]

Hmmm

 

 

Sorry to hear that Anthony!

 

Do you by any chance have documents to prove the instructions?

 

If you do, why not contact the Ombudsman?

[Stationary M25 Traveller]

75dBA .... that's like a pigeon farting isn't it ?

 

Was it exhaust noise ? How about an extra rear-exit box under the tank, or a double-decker side exhaust .... there was a thread with pictures a year or two ago.

[anthony1956]

Yes pigeon fart.

A Swiss ombudsman, is there such a person?

 

THEY drove. They removed the bonnet and wired what I expect was a throttle switch at Wide open throttle. I was cringeing , 100 yards away as she hit 4000 an awful vibration always activates and stops when passed that rpm. She, (the car) has always had this feature. It is akin to finding a resonance, but with what has always had me foxed. More recently someone, RJ perhaps, pointed to an engine bay oblique (cross) member that has the engine resting against against it; Actually it may be a water (coolant) pipe. The noise is metallic in character, not of an exhaust or inlet type.

 

Inspiration welcome :-)

[Stationary M25 Traveller]

We hope visiting Sevens are immune to such quietness ....... let us know the address of where THEY live 😬 Sure we can arrange a late night flypast !!

[Bricol]

Sounds like you need an alternative throttle stop rather lower than wide open, or even an alternative throttle assembly (single rather than multiple - standard Rover?)

 

I think you will need to do some serious silencing to drop that low. For SVA here with a Lancia Stratos replica, I used a single downpipe, three silencers, and one outlet, all stacked at the rear of the engine bay. And an enormous, baffled, air inlet filter assembly to reduce inlet noise. Lovely and quiet - easily passed. And of course, as soon as I returned home after passing, the original air filter and twin downpipe, single silencer, twin outlet exhaust went back on . . .

 

I hope your paperwork doesn't have to state what the specification is at time of test, and therefore what it needs to be on the road all the time.

 

 

Bri

[anthony1956]

I have not given up regarding a technical solution, but this is an R500.

The exhaust is listed as Raceco. Roadside police static noise test would, aiui, be at the exhaust exit. The static test data is created when moving test has been passed, being about half a metre from exit, at 75%of max rpm. So that provides direction for attention. The appointment doc requests final drive ratio, but so far as i saw, (literally) the data is neither used nor tested, of course they may do some calcs to check power and speed.

 

I have extensive documentation in two languages. All based around Regulation 51. I'll add some links for enquiring minds. Swiss law is pasted from the UN EU accords we have all signed. I remain unable to find the originating accords or local laws behind the release from noise test obligations implemented in the federal customs clearance of immigrants' household goods process. I have right here a customs doc given to me by a central customs house officer confirming his words that the noise test is NOT reqired.

 

Four years now since I was first told this I also have the federal DVLA dept instructions to testing centres to carry out the tests if they think the car is noisy. I was completely unprepared for any noise evaluation, not least one I later discovered breached the static noise test standard signed by everyone including Switzerland.

 

So there is a flavour. ISO 362 iirc.

 

Typed on my phone....

[anthony1956]

Also wondering if there may be a human rights aspect.

[anthony1956]

Every individual with whom I have had dealings has been polite and even friendly, except the head of the original testing dept who I found polite but dismissive. And who I recall remained in the background but definitely present when the original noise test was conducted. That test was 6500 rpm, stone cold engine, car was trailered there, ubpacked muffler, measured at. 50cm, also 4 month old petrol and oiled up plugs. Basically broke every requirement for static noise tests. They took the car outside and floored it in first, and decided it was noisy. Stone cold having been stored sub zero. I remain not entirely satisfied that procedures were applied as required even by federal regs, as until the issue was forced, in first gear, there were no unpleasant noises.

 

So now you know how the issue arose.

 

My view is that something is afoot, politically.

[rj]

Just the rattling, when it's rolling, of a Seven is close to the 74dB.

[Nifty]

Feck .. I'd better not take mine to Switzerland then ❗

 

[Paul McKenzie]

Can't you get it MOT'd back here and ...feck 'em? ...this law is stupid 😔

 

Paul

[anthony1956]

Oh. Please do visit! Oh yes y 😬 😬