mallie

Just an update to let you know guys (not that you should care that much ) that I actually have a 4.11 and not a 4.56 rear end. Code correct. So I guess my tach is off by 200 or so:

50mphX1X4.11X336/25.6' = 2700rpm but my tach shows 2900rpm at 50mph in 4th...

66since71

I think your problem is bigger than you calculate. Tire size has nothing to do with what the speedometer reads! (Although it obviously affects how fast youre actually going.) The speedo just tells you how fast the half shafts are turning, indicated on a scale that assumes a 27" tall tire. And the accuracy of that is a function of the speedo gear set in the car (I.e. assumes it matches the rear axle).

Taking that into account, I get 2557 for the rpm you should see at an indicated 50 mph!

Harry

Should have run 4.56's it comes out 2840. Bet you have either 4.56's or have a 4.56 speedo gear in the transmission !

65tripleblack

66since71

Was kind of a "duh" moment, wasn't it?
I was just trying to make the point that when comparing speedo and tach readings, adjustment for tire size only screws up the result. And, that's a real common mistake on this forum...

Harry

69z28&ss396

Just to appease me, and a 456 is fun as I have one in my 302 Z28, what color is your 65?

daz_au

I calculated my L76 '64 to have 4.11's measuring speed with GPS (but speedo is not far off). Definitely not a highway cruiser, but is always ready if I need to pass... cant imaging what the 4.56 is like. I would be lucky to be getting 10MPG, probably more like 8.

Even though I like the muncie shifts, I am looking forward to a 5sp swap, most have a lower 1st (will feel like a 4.56) and cut revs by around a 1/3 on the highway.

Kerrmudgeon

I was just going to say that hardly anyone ordered a 4.56 ratio when they were new unless they went straight to the drag strip. Even 4.10s are hard to live with on the highway for cruising. My 62 came with the standard 3.36, but when I chipped a tooth on the ring, I put in a 4.11 I had in the garage. It's fun, but no cruiser. Now I've got a set of 3.36s which will go in soon.
You should keep the original 4.10s and carrier as a unit, and buy a rebuilt ready to go unit in either the 3.70 or even better, a 3.55 ratio. It's a good compromise.

mallie

Glen Green

69z28&ss396

Thanks.. on the lookout for a white 65 l76 my dad restored in the early 90's..

donbayers

Turns out we had a 4:11 gear in our 63 L76. Ha! A few months ago I had no idea what that would have even meant. I've learned a lot in a short time.

I went back with a 3:36 for cruising fun and think it is a great combo.

http://forums.corvetteforum.com/c1-a...rstanding.html

MikeM

If you had a close ratio transmission in your car and the same camshaft the OP has, you might not be so jolly with the gearing combination! That would be miserable in my book.

AZDoug

Why does it have to be an L76?

I had 4.56 posi in my '61 when I had a mildly modified L79 back in the late 1970s.

The motor ran to 7K RPM with zero lashed valves, and with the M21 and a Mr Gasket close throw shifter, it ran like a raped ape. The nitrous made it even more fun. I had a first gear nitrous lockout and used a TH400 carb mounted kickdown switch as the nitrous activator once the main power was turned on so i didn't have to fiddle with manually turning it on or off during a speed contest.

For any freeway driving over 100 miles, I swapped the pumpkin out for a 3.55 Posi setup i had ready to go. 98% of my driving was around town or county roads under 60 MPH.

Doug

mallie

ha ha. was in the same boat not long ago.
now I'm a C2 expert, well almost!
I think most of the L76 came with 3.70 rear end, some with 4.11 and very few (700 or so total) with 4.56. 4.11 is not great for highway driving but it's fun to drive on the streets. I can live with it, not doing much highway driving...

AZDoug

Just remember:

"I never lose with 4.56 gears" Song, Astronauts c. 1964

Doug

00fxd

Doug, do you know what song it is? I googled them but there are quite a few songs. I think that I would like to listen to the one that you mention

65tripleblack

Try this:

Chuck Gongloff

An old "rule of thumb" was that you could double your tach RPM in fourth gear to get the speed with 4.11's. (stock diameter tires)

So, 2500 RPM = 50 MPH, 3000 RPM = 60 MPH, and so on...........

How accurate is your speedometer? In today's world where just about everyone has a GPS/Garmin, etc. you can go cruising and check your GPS speed and compare it to the speedometer speed.

If they're almost the same, you're OK, BUT..........

If they're not, you can calculate a "factor".........

EXAMPLE:

You're going 60 MPH on your GPS, but your speedo shows 50 MPH.

50/60 = .833

Pull the driven gear out of the trans and count the teeth on it.

To speed up your speedo, you need a gear with FEWER teeth.

Let's say you have a 25 tooth gear in there.

.833 x 25 = 20.8 rounded up to 21.....

So, in this made up example, you would need to replace your 25 tooth gear with a 21 tooth gear to correct your speedo reading.

Chuck

00fxd

Good times.....

Ironcross

This is all you need to remember with a 4.1..... Chucks above comment

My 61 315 got 20 MPG at freeway speeds and higher with its 4.1 and the 62 360 with its 4.56 is 16-18 MPG....I dont understand why nearly all of the messages or replies condemn the 4 series gears unless they cant rely on their engines...Hell, the Vettes are built to handle those gears...That's why I drive them, I know mine were...Possibly too many of todays owners think the 'glass in fiberglass relates to them being brittle ....... you know the Chinese didn`t build them..........