Delimiting 112mph - any tips?

[Stickers]

I'm preparing my mk1 Roadster for the track & would appreciate some help on removing the top speed restriction of 112mph.

I have read that a screw needs to be removed from behing the speedo - other than that I'm completely in the dark.......anyone able to point me in the right direction?

Thank you in advance.

[SkinnyBoy]

I would of thought slapping a UKDM ECU in it will sort that problem.

[MX-5 Lazza]

No need to swap ecu. The restriction is taken away by removing a screw from the back of the speedo. I can't help any more than that though but I'm sure if would only take 5 minutes on Google to find out which screw needs to be removed.

[vrooom]

i am in same boat. i only hit over 180kph twice.

[dg45]

1.6 Roadsters (1989-93) are easy to derestrict; take the clocks out, look at the circuit board, speedo side. Where the main bunch of connectors plug in, find the one marked 180 s/w (or something similar). Follow the circuit till you reach the screw. Remove screw, and hey presto, derestricted. If you remove the speedo entirely, you'll see the speed limiter is nothing more than an electrical contact made when the needle reaches 180 kph. Owners who have a UK or US speeo fitted of course have no speed limiter...unless you have a 1.8. The speed limiter on this I believe is wired into the ECU, so no easy solution I know of.

[Stickers]

dg45 you are a top man, I'll have a look at doing the job within the next few weeks and take some images as I go along - might be worth a sticky on here?

Either way - thanks for the descriptive advice, it is very much appreciated.

[OllieWinchester]

How does the speed limiter work out of interest? Haven't gone faster than 112mph anyway I don't think.

[GravelBen]

Is there any point derestricting an otherwise standard 1.6? Mine seems to top out at about 175km/h, never makes it to the limiter.

[OllieWinchester]

I'm sure I've asked this before but no one seemed to know, what speed would a standard 1.6 be doing when it hit the rev limiter?

[MX-5 Lazza]

It should be restricted to 112mph but as it's triggered by the speedo then your actual road speed will likely actually be something like 105mph.

[GravelBen]

I think he's talking about rev-limit rather than speed cut, in which case I'd guesstimate:

Approx 3300rpm @ 100km/h (from memory)
redline @ 7000rpm, limiter maybe 7200?

7200/3300 = 2.1818

2.1818*100 = 218km/h (135mph) theoretical maximum, but you wouldn't even get close with standard 1.6 power.

Edited by GravelBen on Wednesday 10th June 12:50

[MX-5 Lazza]

Oh, right. I'd be surprised if a 1.6 would get past 115mph. It might show more than that on the speedo but it over-reads (as they all have to by law).

[OllieWinchester]

There must be someone out there with a FI'd 1.6 with standard gearing that can slam into the rev limiter in top

[MrV]

OllieWinchester said:

There must be someone out there with a FI'd 1.6 with standard gearing that can slam into the rev limiter in top

I can first car I have ever owned that runs out of gears before the engine runs out of power

It tops out at 133mph on gps.

[insanojackson]

MX-5 Lazza said:

Oh, right. I'd be surprised if a 1.6 would get past 115mph. It might show more than that on the speedo but it over-reads (as they all have to by law).

wrong most speedos do overead but its not required in law. The law says they have to be accurate to +/- 10%

[bluetone]

^^^^ What he said. Manufacturers protect themselves from law suits by making speedos over-read.

[MX-5 Lazza]

There you go then, I'm wrong again. I thought it was a legal thing. Ah well, the basic fact of over-reading is still true

I think my car is geared to hit around 160mph at the rev limiter. I think it might well get there too. I've seen an indicated 150mph and it was still accelerating strongly. I only stopped there because that's where the speedo stops and I don't have a sat-nav. One day I'll get over to Germany and test it properly

[roverspeed]

I am surprised at people saying they don't even get near the limiter. My eunos only has mild mods and it hits the limiter pretty hard. Scared me a bit first time actually.

Induction, exhaust and cam work can't make that much of a difference!

[GravelBen]

Perhaps the law is different in the UK but most places they have to read between +0-10%, they're not allowed to underread. Most are fairly good though, within about 5%.

[MX-5 Lazza]

According to Wikipedia (not always the most reliable source but easy to find)...

EU:

• The indicated speed must never be less than the actual speed, i.e. it should not be possible to inadvertently speed because of an incorrect speedometer reading.
• The indicated speed must not be more than 110 percent of the true speed plus 4 km/h at specified test speeds. For example, at 80 km/h, the indicated speed must be no more than 92 km/h.

UK:
The amended Road Vehicles (Construction and Use) Regulations 1986 permits the use of speedometers that meet either the requirements of EC Council Directive 75/443 (as amended by Directive 97/39) or UNECE Regulation 39. [12]

The Motor Vehicles (Approval) Regulations 2001[13] permits single vehicles to be approved. As with the UNECE regulation and the EC Directives, the speedometer must never show an indicated speed less than the actual speed. However it differs slightly from them in specifying that for all actual speeds between 25 mph and 70 mph (or the vehicles' maximum speed if it is lower that this), the indicated speed must not exceed 110% of the actual speed, plus 6.25 mph.

For example, if the vehicle is actually travelling at 50 mph, the speedometer must not show more than 61.25 mph or less than 50 mph. There is also the added problem of cars not complying with the United Nations standards, being imported and allowed to be registered, making the situation even more complicated. This needs further investigation.

So I might not have been so wrong after all