Tach is at 2500 to 3000 at 55 60 MPH ??

78 C3 Light Corvette Blue · 10-12-2010, 07:58 PM

Is this normal ??? 78 L82 Automatic

Timsride · 10-12-2010, 08:22 PM

It can be if You have gears around 3.55:1 in the rear.

78 C3 Light Corvette Blue · 10-12-2010, 08:51 PM

There is no tag to tell me the gears. I think back then the rpm's ran a bit high. I remeber a 69 Firebird being high. I don't think as high as this Vette.

604 · 10-12-2010, 09:01 PM

My 78 with 3.08 gears turns 2,400 to 2,500 at 60

meinthe73 · 10-12-2010, 10:53 PM

whats your tire height?

78 C3 Light Corvette Blue · 10-12-2010, 11:23 PM

255\60\15

meinthe73 · 10-12-2010, 11:42 PM

Quote:

Originally Posted by 78 C3 Light Corvette Blue

255\60\15

Well assuming you have a th400 with a 3rd gear of 1.1 and 27" tire.

so you must have a 3.55 to a 4.11

wombvette · 10-13-2010, 12:03 AM

Many 78s had 3:70 gears.

phildawg19 · 10-13-2010, 12:31 AM

my 77s tire height is 27.4 and i was at 3000 rpm at 61 mph. and calculated it out to be 3.91 gears in mine so yours are going to be close to mine

fugawi · 10-13-2010, 06:15 AM

my 70 with 3:70 gears tachs at 2500 @ 55 mph in high gear..

stock 27 inch tires..

jb78L-82 · 10-13-2010, 07:08 AM

With stock tire height (255/60/15 or 225/70/15) my L-82 4 speed (all stock) and 3.70 gears should turn exactly 2,860 RPM's at 60 mph which it does. At 70 MPH, my car is turning approximately 3,500 RPM. Now you know the reason so many 4 speed owners convert to 5 speeds with the overdrive. It is normal! One of these days I will do the conversion as well. Hope that helps!

73jst4fun · 10-13-2010, 07:36 AM

Quote:

Originally Posted by wombvette

Many 78s had 3:70 gears.

sounds like 3:55 or 3:70 to me..check the numbers on the underside of the differential housing, there should be the code there...

604 · 10-13-2010, 07:41 AM

Quote:

Originally Posted by meinthe73

Well assuming you have a th400 with a 3rd gear of 1.1 and 27" tire.

so you must have a 3.55 to a 4.11

Were did you find that calculator? That is pretty slick!

karol · 10-13-2010, 08:23 AM

Quote:

Originally Posted by Timsride

It can be if You have gears around 3.55:1 in the rear.

Standard axle ratio for a 78 L82 Auto was 3.55.

L48 standard was 3.36 for 4spd and 3.08 for auto

4spd L82's had the 3.70 as standard.

so it sounds about right.

meinthe73 · 10-13-2010, 09:38 AM

Quote:

Originally Posted by 604

Were did you find that calculator? That is pretty slick!

just google rpm calculator. i think its the first one.

81_vette! · 10-13-2010, 09:54 AM

I recently purchased a 1977. 4 speed manual.

5200 rpm at 65 mph. Tires are 25.7 ".

3500 rpm at 45 mph.

Note: the actual rpm tested with a meter is roughly half of what the gauge shows.

So, what is causing the rpm gauge to read so high?

meinthe73 · 10-13-2010, 10:41 AM

Those are some little tires for a c3

81_vette! · 10-13-2010, 10:55 AM

Quote:

Originally Posted by meinthe73

Those are some little tires for a c3

The car is lowered - so the height of the tires needed to be appropriate.

meinthe73 · 10-13-2010, 11:06 AM

Quote:

Originally Posted by 81_vette!

The car is lowered - so the height of the tires needed to be appropriate.

Nice... I said that was a small tire because that will increase rpm. Looks good, but just my thoughts get a little bigger tire for the rear, but still looks good.

78 C3 Light Corvette Blue · 10-13-2010, 07:05 PM

Thanks Guys
My mechanic was wondering what kind of gears were in there? I thought it was normal. How ever I thought I would ask. Get some feed back with you that own and drive these cars.
Thanks again
I will look for the code. I have to replace a clip on one of the yokes.