I had been chasing some tachometer issues the past several times I've driven the car. The tachometer reads a certain percentage higher than my Holley Sniper EFI screen and my Innova timing light. I have verified that the installed (factory?) tachometer is reading high multiple times. The Sniper and factory tach are getting their signal form the same source on the distributor. Tach filter checks out fine. The issue persists whether the filter is inline or taken out. The timing light (clamped on #1 spark plug line) and Sniper are both reading the same amount. So I replaced my tach circuit board a few weeks ago (I'm only able to work on the car in bursts) with a new unit from the Cajun Tach Shop (thanks for the tip @interpon !) and took it for a test drive. The same issue persists: factory tach reading high. Reads about 100 rpm high at idle, 300 rpm high at 2600rpm (what I call cruising speed @ ~70 mph), and 500ish rpm high at 5000rpm. I have reset the needle to be at 0 at engine-off correctly as well. So I'm going to replace the tachometer with a new unit from one of the parts houses since the issue has to be the tach's movement. Which tachometer (caution & redline markings) is correct for a 1980 L48 4-speed car?

This is what is currently installed in the car:

Caution 4500rpm, Redline 5200-5300rpm. Some parts houses (Ecklers, Davies, Mid America) say this is what the 305 California cars have and say that this is correct for an L48 350 as well. To be fair, Mid America lists this tach as being for the '80 305 and doesn't have a listing solely for an '80 L48 350.

Other parts houses (Zip, Corvette Central, Corvette Pacifica) show this as being correct for the '80 L48 350 (as well as the '81 L81 350):

Caution ~5200rpm, Redline 5600rpm.

So do I have an incorrect tachometer face in my 1980 L48 car? Which is the correct tachometer for my car, 5200rpm redline, or 5600rpm redline? Thanks!

 

If you look at the engine specifications for a 1980 L48, maximum HP at 4k, a 5,200 rpm tach is correct.

 

After looking around for a long time yesterday afternoon, I think you are correct. I could only find 1 photo of an 80-81 that had that 5600rpm redline tach. It was an '81 with a manual transmission. No guarantees about that tach being original to that car though.

So my question now becomes, what cars, if any, did that 5600rpm tach come standard in? It has the correct marking style for an '80-'81 (omitting the "15, "25", "35", etc. that 78-79 cars got), but I can't seem to find any documentation to say that any '80-'81s got a higher redline tach, other than the '80 L82 cars which got a 6,000rpm redline. A/C was standard equipment starting in '80, so I don't think that has anything to do with the redline, like it did for previous years.

I'm considering going with the 5600rpm tach anyway because I'll be doing some engine and drivetrain mods that should push my powerband up some over stock (gears, cam, valvetrain, etc). But now I'm curious as to what cars those 5600rpm redline tachs are really for.

 

I went back and did further research using the Chevrolet Parts and Illustration catalog from December 1983. It lists 3 numbers for tachometers in 1980.
5659892 for the 305.
5659842 for the base 350.
5659859 for the L82.
if you Google the numbers you come up with 5200, 5600, and 6000.
So not sure how you currently have a 5200 if it is a L48 and is original.
I guess you are not an NCRS member?

 

Huh. That's nuts. My car still has its original L48 and my VIN and Dealer Invoice confirm it is an L48 350 car. It also wasn't shipped to or sold in CA. But my car and basically every other '80 L48 and '81 L81 car I've seen has the 5200rpm redline tach. I only saw a picture of 1 '81 manual car with the 5600. I believe the tach in my car to be original too. The circuit board I took out showed the same aging as the PCB in the center console and the other circuits in the interior. I'm not doubting your numbers and information, just confused from what I have seen.

I went with the 5600 rpm tach. Since I'll be warming the engine over a bit more in a few months once I get the driveline buttoned up.

I am not an NCRS member. Originality went out the window on this car even before I took ownership of it a year ago. I'm sure my Holley Sniper system wouldn't do very well points-wise either.

 

I only mentioned NCRS since their judging manual may clarify the tach situation.

 

I replaced my factory inaccurate tach with a new ACDelco replacement from Zip. 5600rpm redline to replace the 5200rpm redline original. It looks perfect. Same fonts, same flag emblem, just different caution and redline markings. Bang-on accurate now, confirmed by my Sniper screen and timing light. The new tach needle doesn't "float up" to around 1500-2500rpm at key off like the original did. It sags down below 0 at key-off now (minor annoyance), but it snaps right back to 0 at key on and works flawlessly. Higher redline will be handy for the upcoming engine mods in the Spring.

 

The NCRS 80-82 Judging Manual shows the redlines as follows:

1980
LG4 - 5300
L48 - 5300
L82 - 6000

1981
L81 - 5300

1982
L83 - 5300

I believe the vendors are wrong on their inclusion of a 5600 redline tach for 80-81, I own a 44000 mile 81 and it has a 5300 redline tach. I bought my 81 new, and the tach has never been out of the dash. I'm not sure why the Parts Book shows a 5600 tach, but that may be why K&B did a reproduction with that redline. As an FYI, the redlines came out of the most recent edition of the 80-82 Judging Manual.

I didn't bother to pull out one of my Parts Books to see what they say, but I assume MelWff is correct with what he posted. I don't think I have an 80 Assembly Manual, but it might not help anyway because I think the speedo/tach cluster came to St Louis already assembled into the cluster. If so, only the complete assembly would be listed, and not the individual part number for the tach.