tomatoto

Hi

My Tachometer doesn't look reliable currently, sometime it looks accurate but sometime it looks really undervalued, or overvalued. So, I don't trust it anymore, and this is pretty embarrassing when you have to break-in a freshly rebuilt engine...

That's why I was looking for a Gear-Speed-RPM table, in order to find out what real RPMs I'm driving at, based on my speed and gear.
I didn't find that, so I managed to create one, thanks to this useful calculator : Top Speed Calculator

And here is what I've got so far :



Does this look accurate to you ? Based on this other thread ( https://www.rx7club.com/3rd-generati...h-gear-652481/ ) , it looks pretty good to me for the high RPMs, but I'm looking for the low RPMs accuracy, because I can't go beyond 4500rpm at the moment
So, I would really appreciate if you can confirm the lower RPMs/speed of your FD in real life .
By the way, these are concerning a STOCK FD with stock gear ratios.

And/Or, if such a table already exists, please let me know !

DaleClark

iTrader: (55)

If you are simply trying to keep the RPM's reasonable during a break in it will be pretty obvious if you're driving around at 4,000 RPM or something.

That said the chart is in the ballpark enough to give you a guide to where you are RPM-wise.

Dale

tomatoto

Thanks Dale !

not for me, as this is the first time I drive a FD ever...
actually, I started having doubts on the tacho accuracy when I noticed my 2nd turbo after 3500rpm (when I expected it after 4500)

tomatoto

I managed to log a few values from my last driving session. Like 6 values in different gears.
It appears that my real speed is always lower than it should be, according to this chart above.
For instance, I was at 32kmh instead of 42kmh at 3k rpms in 2nd gear. And at 87kmh instead of 116 in 4th gear at 4k rpms. It wasn't difficult to deduce that for this session, my tachometer was always wrong the same percentage : 133% higher. In other words, my real speed was 75% lower than expected from the values displayed on this tachometer and chart.
it seems that the FD tachometer has 2 adjustable **** behind it, so we can adjust its range. Does Anybody can confirm ?
My problem is that sometime / someday, I believe my tachometer to be wrong in the opposite way... I still need to keep a log when this will happen in order to determine the percentage.

tomatoto

So, I used the car a couple days later, and before I got home I checked my tachometer and it was like perfectly adjusted. All values I recorded were exactly (+/- 1km/h) what I expected from the chart/values in my first post. Great !
But when I took the car yesterday, it was showing me off 133% over-values again... I noticed this right after I started driving it. BUT, after a while (30min maybe) and after I reved it a bit, I noticed that it was right again, perfectly adjusted !
So, as the engine, it may just need to warm up ^^ looks weird anyway...

gmonsen

It seems like you are getting a handle on this, but your math has some issues. Your initial readings show speeds that are 31.25%-33% higher than they actually are (2nd versus 4th gear) or viewed the other way, your speeds are 31.25-33% lower than they were expected to be. All good.