RPMs

[Mercury Mike]

What kind of rpms are you guys getting on your 200s at like 65 mph? I have one of those hand tachs that you can use to set the idle, and I'm thinking about running a long couple of wires through the firewall, 1 to ground and 1 to coil, and leaving this tach in the cabin. I don't really have the money for a mountable tachometer yet, but I will get one eventually. Just wondering what kind of RPM I should expect at highway...

 

[2v XLE]

If you know your final drive, then you should be able to work it out here:

http://www.bgsoflex.com/auto.html

Just go down to "RPM & MPH Correlation"

Then bookmark the site - VERY handy

 

[Mercury Mike]

Maybe you can help me out.

I have the stock '65 Mustang differential, don't know the ratio.
I have a C4 automatic tranny (green dot), don't know the ratio.

Know what they are?

Also, I have the 14" hubcaps, but I don't know what the actual diameter of the tire is.

 

[2v XLE]

Sorry I cant help you with the diff ratio, but i think (dont quote me) the C4 might have a final drive of 1:1.

In regards to tyre diameter, if you know the size of the tyre eg. 235/45R17, use this one:

http://www.s-series.org/htm/calc/tiresizeconv.htm

I'm not the best with the maths side of things myself, but a quick search in gogle brought this up. Good luck.

 

[Mercury Mike]

Thanks.

 

[MustangSix]

A C4 has a 1:1 final drive, but you can add 500-600 rpm due to torque converter slippage at highway speeds.

 

[mugsy]

To find the ratio, there is typically a small metal tag attached to one of the bolts on the differential housing cover. It should have a bunch of letters and numbers on it; look for the three digit code with a period. The ratios used were typically 2.54, 2.83, 3.00, 3.25, 3.50, 3.89 and 4.11:1. As far as I know there was no "standard" or "typical" ratio. The ratio is what the ratio is...

When you go under the car to look for the tag bring some carb or brake cleaner, rags and maybe sandpaper. The tag is usually covered with oil/grease/road dirt, rust, etc.

tanx,
Mugsy

 

[CZLN6]

Howdy Back All:

65mustang200- FYI- Look for a Vehicle Warrenty Plate located on the rear face (Lock Face) of the left (driver's side) door. The second figure, may be a number or a letter, from the left is the axle ratio, if it is OEM.

A number indicates a non-locking differential. A letter indicates an Equa-lock differential.

Most common on a '65 200 with an auto trans would be-
1 or A - 3.00:1
3 or C - 3.20:1
4 or D - 3.25:1
6 or F - 2.80:1

Adios, David

 

[Mercury Mike]

Great info thanks!

 

[Anonymous]

65 mph = around 4000-4200 rpms.

Somewhere in that area

Doug

 

[JackFish]

With a 3.08 rear I'm about 3100rpm at 60mph. But then it comes on a bit, at 3300 I'm at 75. C4 trans and PR185/75R14 tires. Revs up to almost 5000rpm in first gear. Stock, except for an FSPP chain in at 4* advance.

 

[mraley]

I've got a T-5 with a 3:00 rearend

5th gear 65 is 2200 and 75 is about 2350

4th gear would be a 1:1 ratio and 65 is about 2900

Hope that helps!

 

[kirkallen143]

With my 33" tires, the 3.03 tranny runs the engine to about 2700 rpms at 65 mph.

Kirk

 

[Funky Cricket]

with a stock '80 7.5 rear and a performance rebuilt c4 i would cruise at 70 right @ 3100.