OEM tach with V8???

[airbrushguy]

I'm planning on putting a SBC in my '71 C10 that has an OEM tach and a 250 6cyl.
Will the tach work correctly with the V8?

[70shortfleet]

No, you have to get the v8 tach. If it is a factory 6 cyl tach they are kind of rare!

[airbrushguy]

Yes it is factory according to former owner. Is it something I should trade for or is the 6cyl version worth alot more because of it's rarity?

[70shortfleet]

1st of all you should find out that it is a 6cyl tach. When you remove the cluster from your truck, the tach will have 6cyl or 8cyl on the back of the tach. I have 5 or 6 factory 8cyl tachs and if you decide you want an 8cyl tach I will trade one of them for your 6cyl tach

[airbrushguy]

Thank you.
Since it is working fine with my 6 cyl., right now and there are separate tachs for 6s and 8s, wouldn't you assume it is a six?
Thanks

[jabborabbo]

Originally Posted by airbrushguy

Thank you.
Since it is working fine with my 6 cyl., right now and there are separate tachs for 6s and 8s, wouldn't you assume it is a six?
Thanks

By "working fine" do you mean you've checked it with a separate tach? It will show a value whether it's hooked to a 6 cylinder or an 8 cylinder - for instance, an 8 cylinder tach on a 6 cylinder engine will read 480 rpms when the correct reading should be 640 rpms, since the tach is calibrated to show 1 engine revolution for every 8 firings from the coil - the 6 cylinder tachs are calibrated to show 1 revolution per 6 firings.

If it is a 6 cylinder tach I'd be interested in buying it....

[airbrushguy]

Originally Posted by jabborabbo

By "working fine" do you mean you've checked it with a separate tach? It will show a value whether it's hooked to a 6 cylinder or an 8 cylinder - for instance, an 8 cylinder tach on a 6 cylinder engine will read 480 rpms when the correct reading should be 640 rpms, since the tach is calibrated to show 1 engine revolution for every 8 firings from the coil - the 6 cylinder tachs are calibrated to show 1 revolution per 6 firings.

If it is a 6 cylinder tach I'd be interested in buying it....

Hmmm... Interestingly, I will say that I have set the idle at around 500 and found it struggling to keep running at times. It has a new carb, yet you're saying if it was at 500 it would really be higher??
I'll have to wait until I take it off, but my feelings are that it is running very close to what it reads....but I could be wrong!
Thank you

[jabborabbo]

Originally Posted by airbrushguy

Hmmm... Interestingly, I will say that I have set the idle at around 500 and found it struggling to keep running at times. It has a new carb, yet you're saying if it was at 500 it would really be higher??
I'll have to wait until I take it off, but my feelings are that it is running very close to what it reads....but I could be wrong!
Thank you

If an 8 cylinder tach is reading 500 then the real rpms would be 667 for the 6 cylinder engine.

[leddzepp]

This is not the parts board. Please do not turn this into a for sale thread or it will be locked. Thank you.

[airbrushguy]

Originally Posted by leddzepp

This is not the parts board. Please do not turn this into a for sale thread or it will be locked. Thank you.

My only interest was to find out if I can use the tach I have with a V8. I suppose I got my answer by finding out that the tach is marked on the back and until I take the dash apart, I will not know what I have.

[too much stuff]

If it reads accurate now on your 6 cyl, thats what it should be. You will need to hook up another known accurate tach (hand held maybe) to determine that if you don't want to pull it right now.

[duckdude]

could you use the rpm reading off a dwell meter?

[airbrushguy]

Unfortunately the whole truck is apart right now to replace rockers, corners, supports etc and the tank is out.
I guess I'll have to check back of tach after engine and body work is complete.
I know the engine is not running 667 RPM but I'll confirm everything later.
Thanks

[airbrushguy]

Ok, after a few setbacks, the project is back on.
Took dash cluster out and looked behind tach, there is no indication as to 6 or 8cyl.
There is just a marking of 12 volt.

[LockDoc]

-
As Keith said, It would be stamped in black ink and sometimes it is very hard to see. Here are a couple of threads on 6 Cyl tach values. Just remember these are older threads so value may have increased.

http://67-72chevytrucks.com/vboard/s...d.php?t=511414

http://67-72chevytrucks.com/vboard/s...d.php?t=514671

LockDoc

[TBONE1964]

If you need help with your tach, please let me know. I have a tach calibrator that will not only tell me if your tach is a V8 or a 6 cyl but also calibrate it so that it is right on the money.

One thing to note is that a V-8 factory tach cannot be calibrated to work for a 6 cylinder.

One thing you can also do is find a timing light that reads RPM like a Snap On does and compare it with what you have.

Let me know if I can help. I specialize in complete gauge cluster repair, restoration and parts.

Take care,
Tom

[airbrushguy]

Not really trying to sell it unless I can't use it if it is an original 6cyl. Can't find markings
, I'll try to look harder,

[lolife99]

The marking will be really faint.
Not physically stamped into the back,... more of an ink mark stamp.

[davepl]

Since you really can't read them fine enough to do a proper tuneup, I ordered a low-rpm tach from Amazon. It looks like the old Sunpro units but its super cheap - and made like it. It has scales for 6 cyl and 8 cyl (and 4 too I think) so you'd be able to just compare what it says and see which scale it matches.

If its a 6 cyl you could probably trade it for two 8s, or sell it. Who would have ordered a tach with an inline 6? Truck guys I suppose, surely not a perf concern. But for guys with 6 bangers I imagine the factory tachs are hard to find. And probably not reproduced so far as I remember.

Under $30:
Amazon.com: Actron CP7605...