Adjustable speed converter / delimiter

I'm planning to fit a hybrid gearbox to my NA-T but I will need to fix the speedo error. Right now I have a 4.083 LSD and the speedo conversion has already been done using a fixed ratio converter but the speed sensor setup in the JDM turbo autobox I will be using is (as far as I can see) designed for a 3.769 diff.

I think that this will produce a significant speedo error of about +8.3% or in other words at a true road speed of 60 mph the speed will indicate 65 mph. I understand that this is within the legal limit of +10% but does anyone know of an adjustabe speed converter / delimiter that I can fit to bring the speedo back in line with the true speed?

I know the Thor converter/delimiter has a small potentiometer inside it for fine tuning. I don't know if it allows as big a changes as you require though.

Im running the same box. Thor don't seem to make these anymore but as mention above the potentiometer may not adjust that far. One way is to run the rear tyres on a slightly thicker profile.

Chris Wilson might make speed converters these days. I think I've read a thread on it here. If he does, you could ask if he could make you one with a bigger adjustment range. It's possible I'm thinking of fuel cut defenders though.

Just been out to check what I have currently against the Sat Nav (which isn't normally in this car) and got a surprise. With the current speed converter, diff, wheel, tyre setup (275/35/18) the speedo is reading low. At 60 mph per the speedo the Sat Nav is switching between 61 and 62, at 30 the Sat Nav is a solid 31. My read on this is that the Sat Nav would be somewhere around 30.75 at 30 on the speedo, with double that it makes 61.5 which causes the switching at an indicated 60.

This should reduce the error to around 5.7% which is indicated 63 at a true 60, I guess I can live with that if I have to. But the question is, how accurate is the speed indication of the Sat Nav going to be?

Like Dazzi said, the rolling circumference can be tweaked with different profile tyres and or wheel size.

See Homers thread. http://www.mkivsupra.net/vbb/showthread.php?225050-Supra-specific-gear-diff-ratio-and-tyre-size-calculator

When you have settled on the decision above, pop off the speedo needle, drive at 70mph with satnav and pop it back on at 70, then you know it is correct at the naughty line and any error at lower speed will be less.

I'm planning to fit a hybrid gearbox to my NA-T but I will need to fix the speedo error. Right now I have a 4.083 LSD and the speedo conversion has already been done using a fixed ratio converter but the speed sensor setup in the JDM turbo autobox I will be using is (as far as I can see) designed for a 3.769 diff.

 

I think that this will produce a significant speedo error of about +8.3% or in other words at a true road speed of 60 mph the speed will indicate 65 mph. I understand that this is within the legal limit of +10% but does anyone know of an adjustabe speed converter / delimiter that I can fit to bring the speedo back in line with the true speed?

I have used this company before for some stuff and everything that i have had works great. and they have this convertor for very low cost. just bear in mind that it's an australian company and instructions are upside down, but it's easy to sort, just hold instructions up to a bright light.

http://www.jaycar.co.uk/productView.asp?ID=AA0376&form=CAT2&SUBCATID=965#11

regards chris.

ps let us know how it works.

Like Dazzi said, the rolling circumference can be tweaked with different profile tyres and or wheel size.

 

See Homers thread. http://www.mkivsupra.net/vbb/showthread.php?225050-Supra-specific-gear-diff-ratio-and-tyre-size-calculator

 

When you have settled on the decision above, pop off the speedo needle, drive at 70mph with satnav and pop it back on at 70, then you know it is correct at the naughty line and any error at lower speed will be less.

Thanks David, but what's this needle you're talking about?

The Speedometer needle, it pulls off, if it is tight use a pair of teaspoons to prise it off.

Chris88, what car is that? It's not a supra, I know that much.

Thanks David, but what's this needle you're talking about?

 

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Oops just seen your pic, I'm not familiar with Soarer gauges.

Chris88, what car is that? It's not a supra, I know that much.

It's a 1995 JZZ31 Soarer, same engine, gearbox and lots more as the MkIV Supra NA. This is my project car. It already has UK Supra brakes and aftermarket Supra suspension, will soon have the Supra gearbox and Whifbitz Supra NA-T kit.