Life with a longer diff

[adam quantrill]

My "new" diff has been in now for a few months and is much "longer", resulting in lower revs when cruising at a given speed.

I've found that sometimes 5th just isn't good enough for acceleration and have to "drop a cog" or even two for some fun. Max revs in thirs is now around 90 I calculate.

On the other hand my mpg has improved by about 20%, which saves some juice for a bit of fun now and again, at no extra cost!

[adam quantrill]

I went from a 3.31 to a 2.88.

I haven't changed the speedo drive yet but have a few different coloured drive cogs to play with.

Yeah the Jag weighs 1825kg and the wedge 1100kg so quite a difference if you look at it that way!
Even the SDi weighed in at a (claimed) 1440kg.

[adam quantrill]

I have heard this rumour from time to time but never had it substantiated. (That is, what is the law that would be broken? If you can cite the statute that would be useful)

It went through the MoT just recently with no complaints (at least, no complaints about the speedo ;^).

[adam quantrill]

OK you seem to be thinking of "The Motor Vehicles (Approval) Regulations 2001"

My car was manufactured and type approved in 1989 so that legislation hardly applies.

As a case in point "the noise measured at 0.5
metres from the exhaust outlet
at 45 degrees to the axis of the
outlet pipe in a horizonatal
plane, shall not exceed
101db(A)."

Good luck with that! My inlet noise alone is 110dB(A)!!

The relevant one for us Wedgers is the 1980 statute: http://www.legislation.gov.uk/uksi/1980/1182/pdfs/...

This does not mention the speedo, nor the exhaust.

Edited by adam quantrill on Tuesday 4th December 23:04

[adam quantrill]

In my case I started with 4l but that irresponsible chap Dave Haughin slapped on a supercharger without changing the gearing.

So I have more torques but les revs (as the blower is now dictating the rev limit).

The gearing was a bit on the low side for the package, it probably works a lot better now.

[adam quantrill]

magpies said:

"The Road Vehicles (Construction and Use) Regulations 1986, as amended, allows the use of speedometers that meet the requirements of EC Community Directive 75/443(97/39) or ECE Regulation 39.....

So - when was the amendment made? The original 1986 statute states:

"Speedometers

35.—(1) Save as provided in paragraphs (2) and (3), every motor vehicle shall be fitted with a speedometer which, if the vehicle is first used on or after 1st April 1984, shall be capable of indicating speed in both miles per hour and kilometres per hour, either simultaneously or, by the operation of a switch, separately.

(2) Paragraph (1) does not apply to—

(a)a vehicle having a maximum speed not exceeding 25 mph;

(b)a vehicle which it is at all times unlawful to drive at more than 25 mph;

(c)an agricultural motor vehicle which is not driven at more than 20 mph;

(d)a motor cycle first used before 1st April 1984 the engine of which has a cylinder capacity not exceeding 100 cc;

(e)an invalid carriage first used before 1st April 1984;

(f)a works truck first used before 1st April 1984;

(g)a vehicle first used before 1st October 1937; or

(h)a vehicle equipped with recording equipment marked with a marking designated as an approval mark by regulation 5 of the Approval Marks Regulations and shown at item 3 in Schedule 4 to those Regulations (whether or not the vehicle is required to be equipped with that equipment) and which, as regards the visual indications given by that equipment of the speed of the vehicle, complies with the requirements relating to the said indications and installations specified in the Community Recording Equipment Regulation.

(3) Instead of complying with paragraph (1) a vehicle may comply with Community Directive 75/443 or with ECE Regulation 39. "

Stil no mention of the "under-reading" rule.

[adam quantrill]

magpies said:

you could ask on the https://www.pistonheads.com/gassing/forum/speed, plod and the law page

I have, and so far I haven't got any sense there, either ;^)