Got a new 914!, Post 2011 Evil Tranny Clinic update: Options

[Tom_T]

In reality the errors are close for both units on these old school gear driven speedos & odos, since they're not the new tech electronic types. The degradation you described Valy will be more or less the same for both as well - even if not far off.

Just ask Tod914 how his 195/65R15 tires racked upmore than actual miles on the odo & he lost value on the sale due to that (IIRC it was the L80E 75 2.0 that he had before his current red 73 2L).

I put a couple of notes in red italics below.

There are 2 speedos calibration out there: for 155r14 and 165r14. check the part number in the PET to findout what tires it was calibrated for.

IIRC there were 4-5 gear sets applicable to the 914 - 165R14 for 914-6 with the Fuchs wheels/tires in 165, 175, 185; and 155R15 & 165R15 - some of whcih are still available.

Bottom line is that the ODO is usually pretty accurate for the tire size it was designed while the speedo will be off with time. Also the speedo is no linear and DMV rules mandate them to never be pessimistic (never show less speed than reality)

Our 914s & other 35-40 year old cars were built to standards which allowed +/-5% speedo error either way. They are not subject to newer standards, which in fact still have an allowable error either way. Remember that when CHP or local cops pull you over. I don't recall the statute, but it's in the Vehicle Code - I had to cite it in traffic court once!

[Root_Werks]

Good speedo and odo talk guys, thanks for all the great input!

Mine is what it is. Pretty easy to calculate the %# off from actual given the tires, factory speedo settings etc. etc.

I will say a few weeks back after putting the Evil Tranny back in, I went and clocked my speed up north using the mile markers around the Mt. Vernon area on I-5. Those who know the area know the markers I'm talking about. There are.....6 miles worth total I believe? I did 4.

In the past I've used the "Your speed is" radar signs to gauge my %# off from actual. I'm now under the impression those signs might give a slight and false sense of speed. I calcualted an 8% variance from my speedo to a couple of different radar speed signs locally. Figured that was good enough, used a few different speeds and a few different signs so it must be correct.

Using the timed mile marker method, my speedo is only about 4% off. Which would mean I would have to go back and re-calc all my mpg figures. So my last posted mpg figure of 29.3 would actually be 30.5mpg and my last fill up just last weekend would reflect an average of 30.7mpg.

So thanks to the advice of many, I found another method of testing MY 914's speedo accuracy. Which is cool!

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Next on the list of things to do hopefully this week is adjust the valves and install my recently aqucired 1.7 rocker arms and elephant foot adjusters.

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I'll also replace the push rod tube seals and pop in a set of WR8DTC's to see if that helps the mpg numbers.

More to come. (IMG:style_emoticons/default/smile.gif)