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Discussion Starter · #1 ·
At what point in the drivetrain is our tachometer taking its reading? Would there be any value in a dual tachometer taking readings at points such as the flywheel and clutch plate? I realize that rpm matching is a very intense and valuable art. On that note, is it more of something to just learn and burn or would being able to gauge the transitions be of any value?

Just curious...
 

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Discussion Starter · #2 ·
It seems I forgot to type in my other questions.

Regarding the ECU, what factors and functions does it 'learn' as it drives? I've heard mostly mention of the fuel map. If an external fuel computer is in use, does resetting the ECU have any effect?

With water spray kits is there more benefit in cooling while sitting at idle or when in motion/high rpm's? I've heard mention of heat soak and would like someone to give me a little definition of what that means. At this point I understand it to be a heating of the medium (air in IC) reducing its effectiveness. Has anyone measured the differences in pressure and temperature through the stock intercooler and other aftermarket versions?
 

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Re: Re: Dual tachometer

TypeC said:


I don't know specifically where the speed sensor comes from in the WRX, but on most cars (or the ones I've worked on) the speed sensor is a gear driven device that reads off of the differential (or nearby gear). Most stock speedos tend to lose accuracy at higher speeds (well over 100mph), so you should be good to go.
He said tach, not speedo. Anyway, I do not know the answer but I can reference the shop manuals tonight if nobody has answered this.

-Pace
 

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not sure about the rex but most common in modern cars is a Hall effect sensor, it is mounted on the intake cam on my miata. i will look around the engine to see if i can locate the rex's.
 

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Re: Re: Re: Dual tachometer

pace said:


He said tach, not speedo. Anyway, I do not know the answer but I can reference the shop manuals tonight if nobody has answered this.

-Pace
Dope! I didn't read that correctly!
 

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i believe the tach runs of the ignition timing. most aftermarket tachs just run off the coil. basically you connect it to a spark plug and every time it sparks is 1 revolution...pretty simple.


what the ECU learns...most importantly it learns how to avoid detonation diven your driving habits and gas quality.

I'm not sure how effective it would be to run your IC sprayer while not moving simply because what causes heat in the intercooler is the compression of air. At idle, your turbo is not really doing anything so the air isn't being compressed. the turbo itself might be very hot and heating up the air charge, but spraying the IC might not help that....not sure.
 

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blarg said:

I'm not sure how effective it would be to run your IC sprayer while not moving simply because what causes heat in the intercooler is the compression of air. At idle, your turbo is not really doing anything so the air isn't being compressed. the turbo itself might be very hot and heating up the air charge, but spraying the IC might not help that....not sure.
I thought heat soak was the heat from the engine block/transmission/turbo heating up the intercooler. If I pull into my driveway after driving and touch my IC its cool if I let it sit for 10 minutes its warm. I assumed this was because of all the heat dissipating off the engine etc. If this is the case, then sitting at a stop and using the sprayer would be beneficial because you are keeping hte IC cool.
 

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the tach on my car is about 60 rpms too high. I have an safc that gives a reading from the ecu and the stock tack is consistantly off by 40-60. Not enough for me to worry about.
 

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I really doubt the stock tach is off by any amount that would warrent a second tach. Even if its off by 50-100 timing your rev matches and launches or anything like that won't really be effected, to many other variables. The only time I can see someone replacing a tach in a WRX is if they get a new engine in there that can rev over 9k rpms, because thats where the stock one stops counting. If you get one before that, its just rice.

Also regarding IC spray kits, they would be most effective if sprayed right before you start moving from a stop. When you are stopped air does not flow through the IC so it heats up. When you spray the water over it, the IC will cool down and you will be able to get off the line quicker. Once you are going 20 mph or higher the air will provide enough cooling for the IC so that even if you spray it with water, the effect will be very small.
 
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