curiousity has dumbfounded me...

[r@+5un620]

im like a lot of us here hoping for a tach to come along .... so last night i got to thinking. the 280 z tach looks alot like the 620 besides the bezel. so i was browsing ebay and i spotted those white bezel kits. im curious as to if the z tach needle is close to if not the same in position to the 620 i attempted to measue this on my phone but pictures can be decieving and im not the greatest math wiz. i am really hopeful on this bc it would make it look semi stock instead of aftermarket and not to mention last longer as every one ive ever bought has lasted no longer than a couple years

thanks for any insight, kyle

[K_trip]

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[r@+5un620]

no i didnt know that and its a question, why wouldnt it work i apologize for my ignorance

[q-tip]

It wouldn't work because there are two less cylinders so the rotation of the crank is a different speed in relation to the ignition.

[K_trip]

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[datsunaholic]

Actually, a 4-cyl tach "divides" the pulse by 2, since you only get 2 sparks per revolution, and a 6-cyl by 3.  That's because the cam (and distributor) turn at 1/2 crankshaft speed.

 

However, to use a stock 6-cyl tach,  you could just replace the face with a label.  2000 RPM would become 3000, 4000 would become 6000, etc, 6000 would become 9000, etc.  You'd multiply the 6-cyl labels by 1.5.

  

But, that being said, the 280Z tach is physically larger than the 620 tach.

[K_trip]

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[datzenmike]

The 1200 tach is an exact match into the 620 dash, screws right it. I found one in a truck. The only difference is the 1200 has a flat face while the 620 is cone shaped with nipple. I had an old dash and just cut a cone from it and 'made it work'

[r@+5un620]

@ mike- your genius is not bound by anything

from what ive been reading these last few months on here ive learned more than ive learned in 16 years of schooling thanks guys

[r@+5un620]

okay... so basically ive come to the conclusion that going stock is unfeasable and semi stock near that for me... so im just gonna get a retro side sweeping tach... is the tach the rarest of parts?

[datzenmike]

There was also a clock option but the tach is more useful. The clock may be more rare than a tach but...... (shrug) so what?

 

Rare? '79 light brown dash?

[Eagle_Adam]

Rare? '79 light brown dash?

 

Like the one hanging in my garage :P 

[Eagle_Adam]

or any one of the 3 620 tach's i have ;)

[K_trip]

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[bgmk106]

what does the diameter of the aftermarket tach have to be to fit in the stock bezel?

[Z-train]

God,i'm having "Sun flashbacks".

[datzenmike]

Geez I had a Sun Super tach in my new '70 Dart.

[GarrettCuston]

Brainstorming here, someone who is a lot smarter on electrical stuff than I am should  be able to rewire the tach to work with a 4cyl instead of a 6 cyl that it originally came with.  When you buy a new tach sunpro autometer etc you have to dial in 4, 6 or 8 cyl on the back.

 

Roger

[datsunaholic]

Aftermarket tachs have the electronics for all 3 settings, and only use the logic for the ones selected.  Some have a loop wire you cut- that changes the logic as well.  Factory tachs don't have this.  You could, if you were an electronics engineer, alter the circutry with different ordering/types of transistors and logic gates/counter chips, or you could do it with a pulse converter (convert 4 pulses in to 6 out) with a 2 to 3 pulse multiplier.

 

But you still have to deal with the tach being physically larger than the hole in the dash.  There are many, many other 4-cyl tachs that would fit easier. 

[red76datsun]

I had a 1200 tach and a stock 620 tach and as mike said they are the same except the 1200 is flat. (I sold them.... I hate beig 15 haha need money for other datsun parts!)

[Llittle_Llama]

Just go aftermarket, save the time and $$. When you run across an OEM one just swap it in and hand off the old one to another Ratsuner ;)