240km/h Speedos

[dguy]

Don't stripes make you go faster?

[JAYGT]

hi guys i think all this can be avoided.   i have a 87 trans am speedo.  it goes up to 140 miles hour.   its electrical not cable.   im going to try to jam it in the stock speedo location.   will it work i have no idea.  has anyone tried this?  i have the tack as well.   check out the pic of the guages on my websight.

http://community.webshots.com/user/redcivicblackhood

[dguy]

hi guys i think all this can be avoided.   i have a 87 trans am speedo.  it goes up to 140 miles hour.   its electrical not cable.   im going to try to jam it in the stock speedo location.   will it work i have no idea.  has anyone tried this?

Whether or not it will work depends upon what type of signal the Trans AM speedo is expecting.  The original Fiero VSS provides a low voltage square wave to the speedometer (4,000 pulses per mile IIRC).  Circuitry in the (original) speedometer then modifies that signal slightly before passing it on to the ECM.

I don't know what type of signal the Trans AM speedo expects....

In the manual transmission cars, the ECM uses the speed signal (in conjunction with others) to operate the shift light.  With an automatic, the speed signal contributes to the decision to lock up the TCC or not.  The speed signal to the ECM may affect other functions--I can't remember at the moment.

So if the Trans AM speedo does not pass the signal on to the ECM correctly, you may experience some entertainment.  


That, and the style of the Trans AM gauge faces isn't quite what I'm looking for at the moment.  I may modernize it some day, but at the moment I want to keep the original look and feel of the instrument panel.

[2ML67]

Soldered in what I believe is a 7.37 mhz crystal into Brian's 140km/h speedo, made a few marks on it compared to one displayed under this topic as 150 mph speedo then test drove. Now I know this is not exactly accurate here I am just checking to see if it is at  least close. I compared it at 50 mph and 60 mph two main speed limits. Found to be pretty close was doing 50 by where my tach would suggest I was doing 50 and speedo sat on 50 mph marker same as at 60. Now needs to be checked more accurately but definetely looks promising to me. Brian where did you buy the crystal I want one, don't need the face plate just the crystal.  

[dguy]

Interesting...  so perhaps by doubling the frequency the thing will still work within reason.  Which I like, 'cause I have yet to find a 3.56MHz crystal in anyone's catalogs.  

Dan I'm surprised that you haven't razzed me yet for wanting a speedo with a higher limit coupled with my paltry little 2.8.    Oh hang on, you hit the big four-oh earlier this month, didn't you?  Must be an over-the-hill thing.  

Brian can probably answer your question regarding where his crystal came from best, but I think I remember him saying that his crystal & face was a favour from a non-OFC friend a few messages back.

I've been buying my little electronic bits 'n pieces from Digi-Key Corporation.  Quick shipping, Canadian prices (rare for an online retailer!), and a damn good variety of components.  Just be patient while their catalog index loads, especially if you're on dial-up.

edit:  Dan, if you're not in a hurry for the Crystal I will be placing an order to Digi-Key in the next month or so.  They place a surcharge on orders under $32.something, so I usually wait until I need a small handful of pieces before buying from them.  LMK...

[GoFast85]

Will get another chrysal today for you Dan. Active on Marival should have 1.

[GoFast85]

Active has a chrystal that is real close. At $1.45 each + tax they are a steal.

[SideCar]

Hi Guys,
I'm a newbie to this forum and I too wanted to change my speedo to a higher max scale speed.
Well I took my 140 km/h / 85 mp/h speedo apart I discovered that the crystal frequency is realy 4.194304 mHz the marking on the crystal that is 6331 is a lot number and not the frequency as is noted previously in this forum thread.

Using this crystal frequency I have recalculated the factors for both km/h and mp/h that will give you the correct crystal frequency to adjust the scale of the speedo.

587/kmh= crystal in mHz

356.5/mph= crystal in mHz

I have not proven these in practice yet but they seem to work in theory.

I hope this helps anybody who is trying to do the same to their speedo.

Oh ya almost forgot.
I have an 85 SE 2M6 that is still going strong and has never been abused.
Happy motoring all

Cheers

SideCar

[SideCar]

Well like most times, I was a little off when i took my first crack at the calculations.
Below are the correct calculations.. I think lol, I can never be sure.
I am be real interested in any feedback. I am going to go out and get the crystal for the 190 km/h / 120 mp/h scale speedo on the 9th and I'll let you all know if it works.

587.2/kmh= crystal in mHz

361.5/mph= crystal in mHz

4.1943 mHz for 140 km/h /  85 mp/h fullscale deflection
3.0905 mHz for 190 km/h / 120 mp/h fullscale deflection
2.4100 mHz for 240 km/h / 150 mp/h fullscale deflection


Cheers,

SideCar

[my-fiero]

It's a 300km/hr




if you want to see how i dit't look here

http://www.my-fiero.com/pictures/my-fiero/pictures/speedometer/index.html

Stan

[GoFast88]

4.1943 mHz for 140 km/h /  85 mp/h fullscale deflection
3.0905 mHz for 190 km/h / 120 mp/h fullscale deflection
2.4100 mHz for 240 km/h / 150 mp/h fullscale deflection


Cheers,

SideCar

To reiterate --  on my machine, the 140 KPH speedo was changed to a 140 MPH one (same graduations) with the addition of a 7.37 crystal. Athough I have not checked it up against the GPS, at 60 mph, I am doing the same as the 100 kph traffic.

[2ML67]

I did Brian's the same as mine, with the 7.37MHZ crystal the 140km/h now reads accurately 140mph as checked with a GPS at 30, 40, 50, 60, 80, 120, and 140mph in my car. Now this crystal value is only for cars with the 4T65E tranny swap in which its PCM is looking for 225/60-16 tires where we are running 225/60-15 tires. So a stock Fiero would need a slightly different value as the tire differences on our cars would put it off by a -3.8% to start with. Dan

[SideCar]

Ok guys, Thanks for the input.

My speedo is from an 85 SE 2m6. Automatic. P195/70/R14 tires.

The 120 mph speedo shown in the post has a very different size PCB compared to mine. ie. Different revision, my guess is 87-88 maybe. I am sure of the crystal frequency in my original speedo. I have a speedo that displays km/h only and it goes to 140 km/h. I am trying to convert it to 190 km/h and I don't want to go any faster and so far all the info I have got from you guys does not answer my question.

The formula that is posted for calculating the crystal value is based on a 6.331 mHz frequency. I have a crystal of 4.194304 mHz in my stock came with the car speedo, so I think the formula factor of 534 is not corrrect. I am still inclined to think I'm right, at least  for the base crystal frequency and the revision of speedo I have in my SE. I'll let ya know if it works. Since I don't have a GPS. I will have to use the, ok where is my tach at on a flat road method. I have emailed the guys at the OSG which is where the formula is from. I'll let you know if they get back to me.

Thanks and Regards,

SideCar

[GoFast88]

I have a GPS and am in Bells Corners. We could meet for coffee one evening and put it through 'er paces. 

[GoFast88]

Did I feel a little bit of a chill down your spine