JDM imports - km/h to mph conversion - odo adjustment

[Hallsy01]

Hi all, been a long time since I had an import (or a Subaru for that matter!), so a bit out of the loop now!

Considering a Twin Scroll BP5 Legacy, and wanted to get a bit more info around how they are typically converted when imported.

If the speedo has been adjusted to read in mph (so same clock, but a bit of tape over the k and a converter behind the dash), does this mean the odometer will also read in miles or is that a separate conversion?

If the converters convert both speedo and odometer at the same time, would standard practice be to adjust the odo from km to miles (i.e. adjust 100k km to 62k miles) or does it depend on the importer/individual?

I imagine this is a case of 'it depends' but got anyone who is more familiar with imports of this era what would you say is typical?

Just trying to understand if a car with say 100,000km on the clock is likely to be on 100,000 miles, 62,000 miles, or anywhere in between!

Thanks

[vxr2010]

I have a solder in chip in all three of mine , can be wired in behind the dash or off the gearbox speed sensor , the chips are around 40£ or so and come with instructions , ebay job as that's were I bought mine from , once it's plumbed in the speedo and odometer will read in miles from then on , and in effect the speed limiter of 112 mph is effectively cancelled out as you would have to go at 180 mph for it to cut in , clearly a non realistic speed , the clocks can be changed to show mph reading say if it was 100 k kph then it can be changed to 60 k miles , but I have never done that , I just write the kph down as the time it was changed

[TwoBobBit]

Just jumping in on the side - I have a JDM Legacy BP5 twinscroll, that has been converted (don't know how though). Does anyone know if there is any fine adjustment available, as my speedo reads 5/6mph too fast (according to GPS). Reading too fast is good as it helps me to not get caught by the rozzers, but i'd rather it was slightly more accurate

Edited by TwoBobBit on Friday 19th April 08:42

[vxr2010]

Probably had a chip fitted , there is no adjustment as it's a sealed unit , mine are all the same , which I take as one of those things , you can always change your tyre size or wheels as one of my imports is on 19 inch rims so speedo is more accurate , but that's a bit dramatic for speedo accuracy , but I like the idea I am reading under , but just need to remember how much under I am but on faster roads I tend to trust the gps which can itself could be a bit out

[Hallsy01]

vxr2010 said:

I have a solder in chip in all three of mine , can be wired in behind the dash or off the gearbox speed sensor , the chips are around 40£ or so and come with instructions , ebay job as that's were I bought mine from , once it's plumbed in the speedo and odometer will read in miles from then on , and in effect the speed limiter of 112 mph is effectively cancelled out as you would have to go at 180 mph for it to cut in , clearly a non realistic speed , the clocks can be changed to show mph reading say if it was 100 k kph then it can be changed to 60 k miles , but I have never done that , I just write the kph down as the time it was changed

Thanks for the info - I guess unless you have the auction/import documentation, then it will always be a bit of an unknown.

[vxr2010]

The older scoobies ie classics could have a device plug not wire into the bash of the speedo that changed it to mph , on some cars the Ecu can be re programmed to work in mph , im not sure on the scooby on that , Richard at FB tuning could advise , but cost and easy fitting wise the chip wins out and I expect most have the chip fitted , it's either behind the speedo clocks or wired into the gearbox sender , both fairly easy to spot , if you ever went on a track the jdm limiter of 112 mph would get in the way

[TwoBobBit]

vxr2010 said:

Probably had a chip fitted , there is no adjustment as it's a sealed unit , mine are all the same , which I take as one of those things , you can always change your tyre size or wheels as one of my imports is on 19 inch rims so speedo is more accurate , but that's a bit dramatic for speedo accuracy , but I like the idea I am reading under , but just need to remember how much under I am but on faster roads I tend to trust the gps which can itself could be a bit out

Thanks for the info vxr2010, as with older cars I guess we just have to accept a few foibles as extra character!

[vxr2010]

Fully agree , I like my monaro but the Forster sti is also full of character and does every thing well , fast , economy , load carrying , 4 wheel drive , fun to drive , good sound track lol

[Konan]

Hallsy01 said:

If the speedo has been adjusted to read in mph (so same clock, but a bit of tape over the k and a converter behind the dash), does this mean the odometer will also read in miles or is that a separate conversion?

It's two different things. Changing the ODO involves changing the stored value on memory in the clocks. So opening them up and putting a reader on the appropriate chip. It's the modern equivalent of clocking.

Typically, the kmh/mph conversions done by most importers are a box that sits before the clocks. I think there are a couple of companies that sell them in the UK.

On a BP5, a speedo converter has to perform 2 functions. It has to rewrite the speed value on the CANBUS as it's fed to the clocks and it has to change the pulse that drives the speedo needle. You'll actually find the little trip computer thing is getting fed miles now, so the DTE is in miles. These don't adjust the road speed as far as the rest of the car is concerned, be that from the gearbox or wheel speed sensors.

The ECU doesn't 'think' in KPH or MPH, it's just 16 bit integers for speed (IIRC). They might happen to match KPH, I've never looked! If you've just adjusted the clocks but want to change other speed based limits (cruise control being the infuriating one!) then you just change the value in the map itself.

TwoBobBit said:

Just jumping in on the side - I have a JDM Legacy BP5 twinscroll, that has been converted (don't know how though). Does anyone know if there is any fine adjustment available, as my speedo reads 5/6mph too fast (according to GPS). Reading too fast is good as it helps me to not get caught by the rozzers, but i'd rather it was slightly more

Been there, suffered that. Mine reads 70mph at 60, even with bigger tires. Too far out to ignore. Again, this is with a converter in line with the clocks.

The box is a digital unit and just applies a *0.62 conversion to the figures. I spoke one supplier years ago and they can adjust the programing on it to calibrate it, but wanted £200 and to have the car to do it. I really didn't have time to take a day off.

In the end, I fitted a GPS unit to drive the speedo. Has it's pros and cons, but it means it's self adjusting!