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Old 08-19-2012, 01:07 AM   #1
OC_Nooby
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Default How accurate is your tach compared to RomRaider logger

Hey Guys,

I'm just curious to know how accurate your tach is. I ask because my redline rev limit is set to 6900 "on" and "off" at 6700 in RomRaider but with the logger my measured redline is 7200. That's also where I shift around.

So I want to put my stock 2.5L redline at 7000.

So the settings would be "on" at 7000 and "off" at 6900 (stock 05 sti map). I'm just worried that it would now record the redline at 7300-7400rpm. Not sure if the tach is really reading correctly.

Could my tires cause this confusion? 225/50/16 (unsure of the stock 2003 wrx rim/tires). Its an STI swap in a WRX.

Any help would be nice!
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Old 08-19-2012, 12:27 PM   #2
lukeskywrx
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Trust the ECU, the RPM is detremined by the engine the wheels and tires have nothing to do with it. The error comes in when the signal must be converted to a gauge needle position for the tach display.

There is no accuracy expectation on the stock tach, they are usually within +- 200 RPM. When I spin out to ~8K on the tach datalogs usually show ~7800. so mine reads a little high, but who cares.
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Old 08-19-2012, 02:37 PM   #3
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I have a blue printed 10mm oil pump so I don't think I'll have any issues but what your saying is trust the ECU and put back the STOCK STI redline rev limit back? I think I will and record to see what it goes to then.
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Old 08-19-2012, 04:49 PM   #4
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RomRaider lags back around 150-200 rpm as you have to give time for the data to transfer from ECU to laptop. This has been focussed before if you would have searched. The tach is a calculated measurment made by the ECU, etc.
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Old 08-19-2012, 05:41 PM   #5
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I tried to search via google and typing nasioc at the end of my search. Usually I have great success like that, not so much in this case.
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Old 08-19-2012, 07:37 PM   #6
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Quote:
Originally Posted by OC_Nooby
I tried to search via google and typing nasioc at the end of my search. Usually I have great success like that, not so much in this case.
You are 1 of few haha. But as I've stated already go off the tach not RR and remember that it does lag behind. Do a few logs and take some quick glances and you'll see that it shows if the evidence isn't enough by your logs now. Don't want you to blow the car up cause of over revving
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Old 08-19-2012, 07:55 PM   #7
OC_Nooby
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Tach shows roughly 7200, RR shows the same. Ecu programmed for 6900. Lowered value compared to what it should be 7000 stock. Maybe I'll just put it back up to stock. I'm using a WRX tach with an STI swap. Doubt it matters but no need to be paranoid.
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Old 08-19-2012, 08:05 PM   #8
lukeskywrx
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Quote:
Originally Posted by ppayer38 View Post
RomRaider lags back around 150-200 rpm as you have to give time for the data to transfer from ECU to laptop. This has been focussed before if you would have searched. The tach is a calculated measurment made by the ECU, etc.
Electrons do not work that way!


The O2 sensors lag slightly depending on position because it takes a little bit for the exhaust gasses to move. The crank trigger has to be extremely precise to deliver fuel and spark on time and that is where RPM comes from. The data to romraider is just a snapshot taken of the values several times per second.

The tach is just an approximation for the driver to use, DO NOT trust it over the values you are programming into the ECU.
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Old 08-19-2012, 08:17 PM   #9
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Quote:
Originally Posted by lukeskywrx View Post
Electrons do not work that way!


The O2 sensors lag slightly depending on position because it takes a little bit for the exhaust gasses to move. The crank trigger has to be extremely precise to deliver fuel and spark on time and that is where RPM comes from. The data to romraider is just a snapshot taken of the values several times per second.

The tach is just an approximation for the driver to use, DO NOT trust it over the values you are programming into the ECU.
Would you trust the values RR provide you then? or just program her back to 7k and be done with it, I think I'm too paranoid
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Old 08-19-2012, 09:33 PM   #10
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Luke and ppayer both have points.

If you're logging with RR and you have a TON of parameters, expect the maximum RPM reading to be inaccurate in the lower gears (1st, 2nd, maybe 3rd on a 6MT) due to the poor sampling rate. However, if you take an RPM-only log, that's as accurate you're going to get aside from logging a CAN car with the OpenPort + CAN logger patch.

In any case, both are more accurate than the tach.
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Old 08-20-2012, 09:17 AM   #11
ride5000
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Quote:
Originally Posted by OC_Nooby View Post
Would you trust the values RR provide you then? or just program her back to 7k and be done with it, I think I'm too paranoid
put it this way:

i've been running an 8k redline for nearly 10 years on an ej205.

do i play up there often? no. but i have, and i will on occasion.
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Old 08-20-2012, 11:01 AM   #12
lukeskywrx
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Quote:
Originally Posted by ride5000 View Post
put it this way:

i've been running an 8k redline for nearly 10 years on an ej205.

do i play up there often? no. but i have, and i will on occasion.
It is not terrible on a car with shimless buckets, although the 205 valve springs are softer than the 207 springs made to spin that fast. Even on my 207 I rarely take it past 7K because the torque is just not there.
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Old 08-20-2012, 04:17 PM   #13
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^^agreed. it's basically only touched during "no-time-to-shift-right-now" moments in the low gears.
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Old 08-20-2012, 08:48 PM   #14
lukeskywrx
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Quote:
Originally Posted by ride5000 View Post
^^agreed. it's basically only touched during "no-time-to-shift-right-now" moments in the low gears.
LOL, "I WILL make this light!"
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