GolfGTIforum.co.uk
Model specific boards => Golf mk2 => Topic started by: Silverbullet on 17 July 2009, 17:17
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Hi
This may sound stupid :huh:, but can anybody tell me what speedo reading my standard golf mk2 16v should be, when i'm driving @ 4000rpm's on flat/straight road?
Appreciate
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A little ambiguous...!
Your best bet would be to get/borrow someone's sat nav, and see what the speed is on there.
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Ok, the reason why i want to know is that my car feels a bit weak and something needs to be done, but i dont know what. I've been adjusting my ignition timing, but i cant get the results i expect. What else can i do to check if my stup is correct (how will i know if its my ignition timing / CO settings / something else) before i take it to th professionals.
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Ah I understand now...
Check out this site, if you know your gearbox code, there's a calculator on the right hand side where you can enter the RPM, and various other parameters to give you the speed:
If you don't know your code, try a search. Think it will be a 2y in a 16v but don't quote me on that!
http://www.scirocco.org/gears/
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Thanks a lot. Great calculator
According to the calculator my car should be doing 134kph @ 4000rpm, but i'm only doing 120kph @ 4000rpm. Any suggestions of what could be the problem?
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1) Your speedo is under-reading (they usually over-read)
2) Your rev counter is over-reading - (check against secret mfa rev counter.... or maybe the clutch is slipping a bit)
3) You do not have a standard 2Y gearbox (check the code stamped on the box, even then the internals may not be standard)
4) Your wheels are significantly over-sized (would have to be quite a bit to make 8mph under-read @ 80mph)
5) A combination of 1, 2 & 4
IIRC, both of my standard 16v did 20mph/1000rpm in 5th gear (ish)
Tuning/timing/CO adjustment will not change the speed vs rpm readings that you are getting, they are fixed related to the cars gearing, rev counter, speedo calibration and wheel size.
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have you done a full set up including the CO and the timing with a timing gun?
Theres a guide to doing this on here somewhere by rubjohnny. Its shocking what a difference it makes!
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infact:
http://www.golfgtiforum.co.uk/index.php?topic=56707.0
and
http://www.golfgtiforum.co.uk/index.php?topic=22031.0
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Hi thanks for the good info
Must still do CO settings.
-Tyres 15"
-I did replace the speedo gear that goes into the gearbox though
-I'll check if its the standard 16v gearbox
-Fairly new clutch
#how do i check it aigainst the secret mfa counter?
Appreciate
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15'' tyres OK but what is their aspect ratio? 195/50, 205/45 etc., it makes a difference to the overall tyre diameter. There's a calculator for the + or - error from standard fit somewhere........?
If you replaced the speedo gear like for like then it should not change things.....I think you have to change the gear like for like, I don't see how you can put a gear in there with more or less teeth or they won't mesh properly....? 16v speedos are more likely to err as they squeeze 160 on to the dial vs the 8v 120, so the same needle error gives a higher mph error.
There's a guide in the maintenance section on how to access the secret mfa digital rev counter, just drive the car or rev the engine in this mode and check it against the rev clock reading.......no guarantee that its better but at least there are no springs in the mfa to get tired so it should be more reliable...........?
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15'' tyres OK but what is their aspect ratio? 195/50, 205/45 etc., it makes a difference to the overall tyre diameter. There's a calculator for the + or - error from standard fit somewhere........?
This is my favourite, as it actually shows the tyres change size before your eyes!
http://www.kouki.co.uk/utilities/visual-tyre-size-calculator
There is an opportunity to enter your tyre size in the gear ratio calculator however, so you don't need to do any fancy calculations.
To check the accuracy of the speedo, my first suggestion is now actually useful (!) - compare the speedo reading to that on a sat nav.
Most importantly, as jezza mentioned, make sure you do have a 2y gearbox!
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When comparing the speedo to the satnav, you should find that the speedo reads 10% higher - this is what I've found on every car I've used a satnav in.
(My theory is that car manufacturers by law have to calibrate the speedo to within +/- 10%: they go for as high as possible, to make their cars seem faster to customers, and so they don't get people trying to sue them over speeding tickets...)
... That's what I reckon anyway!