Hey,

I just wanted to see if these numbers seem right to anyone.

First off, my car is basically stock. The only thing that isn't original is the engine, which I bought brand new in the crate.....it was a direct replacement 305.

When I'm going down the highway at 80 miles an hour my RPM's are at the red line. (I think the red line is at 5500 or 6000 RPM's)

Does that sound right for a stock setup?

Here's another example.....going 45 miles an hour, in fifth gear, it runs at 3000 RPM's.

I dunno, I just seems like to many RPM's for the speed I'm going.


Any comments are greatly appreciated.

Bryce

 

Think of that thing in your dash that shows RPMs as a "trim package", not an "instrument".

The tachs in these cars (like most stock gauges) are almost always extremely inaccurate. These usually read high, and as they age, they read higher and higher. Sounds like yours is acting pretty typical.

So, no, those are not right at all, as far as actual indications of reality. But they sound about right for what I'd expect to see if I just got into some one of these cars and drove it.

I have about 3 or 4 factory tachs for these cars hanging around my house. Every one of them reads high. One of them reads almost exactly double the real engine RPM. The one in my car is the most nearly accurate of any of them, and it's only about 3% high, which is pretty good for what it is.

You can have your tach "calibrated" at almost any tune-up shop; that is, see what your dash tach reads when a real tach says the engine is at various RPMs. It's not real practical to fix the indication of one of these tachs because they're controlled by a laser-trimmed surface-mount resistor, whose resistance increases with age (causing the error).

 

Well.

That was much more then I expected......

Thank you for the VERY thorough answer.

 

wow..i didnt realize they could get that bad. thats ridiculous.

 

by shifting at "6800" instead of the actual readline, i dropped .8 in the 1/4.


what i would do is have someone hook up a accurate tach, and run the car to its redline with that tach. then look at the factory tach... where the needle is is your redline...

that will work until it gets so bad that it is just pegged.

 

O.K.

So if your redlining in a stock setup......about how fast should you be going (miles per hour)

roughly......

 

You'd be going a little under 200MPH if everything was stock (T5+3.08 at least). And then you'd wake up because a stock setup doesn't have the power to go that fast.

 

So your saying the car would reach top speed before the engine was redlining?

 

yes, it will run out of power long before you could hit redline in 5th grear. your actualy top speed may even be in 4th gear, depending on gearing, powerband, ect.

 

when my car was stock...
120mph at 3000rpm <-- if the stock rpm reads good
t5 - 3.08.

slowed down because i got wild vibration about 80mph... still dont know what it is, but i might try an other driveshaft.

Could it go faster, yeah i think so.

 

Yeah, yanfoo your tach is pretty accurate.

Also vibration can be tires, of course....

 

Wow.

My tak must be waaaay off.

My tak reads 3000 RPM's when I'm goin 50 mph.....

 

was your car originally a v-6, mine was and when i put the 350 in it, when the tach said 6500, it was only 4500.

 

A stock 305 TBI 5-speed Camaro with stock 3.08 rear gears @ 1500 RPM should be running 60 MPH if you have 235/55/16 tires.

 

Stock '86, 2.77 rear, TH700-R4 in OD and lockup = 1,750 RPM @ 70 MPH. Thank the Maker for precision wirewounds...

 

we put a 383 tpi in an 84 firebird that had the v6. the tach reads double! he didn't beleve me that his tpi was not reving to 7000+rpms and making power and closer to 4500 so we got the wiring hooked up so the tech1 would talk to his ecm. test drove the car and right on the money just like I told him. take the tach to about where 7000 rpms are (no markings that high) and the tech1 showed rpms at 4500