tachometer question
Thread Starter
Race Director
Joined: Jan 2006
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From: CA
tachometer question
First I must say how different the forum is after Mr Mojo went on his tirade.I'm going to have to agree with him on this one,so fewer locked threads.Times are changing,and people here are changing.
So I'm going to take advantage of these more "gentle times" to ask a stupid question.Do you trust your dash tach?I want to reset my timing back to base.The "good book" in the tool section tells me I need a an impulse hand held tach.I don't have one.I do have an old fashon two wire tach,dwell meter,I understand that the dwell is N/A,but can I still use the tach function?And if I can,what do I clip it to?Can I forget about even using a hand held tach and trust my dash tach?TIA
So I'm going to take advantage of these more "gentle times" to ask a stupid question.Do you trust your dash tach?I want to reset my timing back to base.The "good book" in the tool section tells me I need a an impulse hand held tach.I don't have one.I do have an old fashon two wire tach,dwell meter,I understand that the dwell is N/A,but can I still use the tach function?And if I can,what do I clip it to?Can I forget about even using a hand held tach and trust my dash tach?TIA
Last edited by GIMMESOME; Dec 9, 2006 at 01:32 AM.
Le Mans Master
Joined: Feb 2005
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From: The Motor City
I trust it enough to know were I am at (off +150rpm)and I also have a shift light that is right.(I compared and checked it against many datalogs and scans)
Last edited by mseven; Dec 9, 2006 at 01:04 AM.
Thread Starter
Race Director
Joined: Jan 2006
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From: CA
Ok, so far I heard a descrepancy of between 150 and 300,now back to the question,if I have a reasonably good and accurate for its day,older two wire analog tach,can this be used on an hei distributor?Will it read the wave coming off the tach terminal of the distributor?Or do I have to buy a different hand held tach?And if the two wire analog tach will indeed work,what terminals do I connect to?Can I just hook the red wire to the tach terminal,and the black to any battery ground.I don't want to try it for fear of damaging some obscure component or electronic module.Thanks.
Last edited by GIMMESOME; Dec 9, 2006 at 01:26 AM.
Melting Slicks
Joined: Feb 2006
Posts: 2,753
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From: backwoods upstate ny
compared to my scanner tach function, early c4 digital display tachs are good at idle or constant engine speed, but lag by several hundred rpm's during acceleration....analog tachs (rotating pointer) are often off by 100-200 rpm, and consistant in that error thru their range (but can be ''adjusted'') ...of course during rapid acceleration the digital tach is unreadable anyway as the segments flash on and off to display varying digits
we have tried some ''old'' tachs on HEI's in non-vette applications....some worked, some did nothing, none appeared to damage the HEI...but some of those ''goldie oldie'' tachs were less than ''sophisticated'' in their circuit designs and i would hesitate to experiment on a vette....suggest that you find a small repair shop and ask him to plug in a scanner and note any variation (don't go to a stealership, they will prolly rip you $75 for just a 30 second test)
we have tried some ''old'' tachs on HEI's in non-vette applications....some worked, some did nothing, none appeared to damage the HEI...but some of those ''goldie oldie'' tachs were less than ''sophisticated'' in their circuit designs and i would hesitate to experiment on a vette....suggest that you find a small repair shop and ask him to plug in a scanner and note any variation (don't go to a stealership, they will prolly rip you $75 for just a 30 second test)
Last edited by redrose; Dec 9, 2006 at 01:32 AM.
Le Mans Master
Joined: Feb 2005
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From: The Motor City
Agreed, an option for you might be to download datamaster or tuner pro free software (15 times free I think) and boot it up in your laptop you will need a cable as well.
just read your profile and not sure on 86 w/software
just read your profile and not sure on 86 w/software
Last edited by mseven; Dec 9, 2006 at 01:50 AM.
Thread Starter
Race Director
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From: CA
So far I've read that that these cars have what's called a tach filter to accuratly read the pulses.I don't know if my 86E even has this feature.I don't see anything in the manual refering to this.The wiring diagrams are like looking at a bowl of spagetti and trying to find both ends.Is it built into the cluster?
Le Mans Master
Joined: Feb 2005
Posts: 5,146
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From: The Motor City
Originally Posted by GIMMESOME
So far I've read that that these cars have what's called a tach filter to accuratly read the pulses.I don't know if my 86E even has this feature.I don't see anything in the manual refering to this.The wiring diagrams are like looking at a bowl of spagetti and trying to find both ends.Is it built into the cluster?
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Le Mans Master
Joined: Oct 2003
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From: seattle WA
First-yeah, you have a tach filter, its purpose is to change the signal from a linear signal to a square wave signal, kinda smoothes out the signal to make it less erratic.
Second, the tach in my 87 is within 50 RPMs at idle...according to my scanner. I haven't paid much attention to it while scanning and driving, so it could be off more at higher RPMs as mentioned.
As long as I disconnected the tach in the vette I wouldn't worry about hooking up one to the dist.
Second, the tach in my 87 is within 50 RPMs at idle...according to my scanner. I haven't paid much attention to it while scanning and driving, so it could be off more at higher RPMs as mentioned.
As long as I disconnected the tach in the vette I wouldn't worry about hooking up one to the dist.
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
Originally Posted by mseven
Agreed, an option for you might be to download datamaster or tuner pro free software (15 times free I think) and boot it up in your laptop you will need a cable as well.
just read your profile and not sure on 86 w/software
just read your profile and not sure on 86 w/software
freebie software ''winaldl'' works great on my 86 on an old toshiba laptop....IIRC the cable schematic is on that site also, cost abt $5 if you buy the pieces at raddyshack....still have not found and aldl connector tho, alligator clips work and are not big pita
Last edited by redrose; Dec 9, 2006 at 04:46 PM.
Thread Starter
Race Director
Joined: Jan 2006
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From: CA
Thanks guys,I do have a laptop which I don't use much.Look's like it's time for me and my tools to move into a new century.
I'm gonna lurk on the scan and tune section for awhile,and see what I can learn from listening to the techies.Thanks again.
I'm gonna lurk on the scan and tune section for awhile,and see what I can learn from listening to the techies.Thanks again.
