Do I have 2.94 or 3.23 ?

[273]

I just bought a 68 valiant 360/380hp create engine with a manual shift 2800 stall 727.

I'm not a hundred percent if the speedo is accurate but after talking with my dad since he followed me home seems it's close.

Mathematically it works out to 3.23 but since a trans has slippage wouldn't that mean its 2.94 ? Revs 2500 at 59 mph with 245 60r 15. 2.94 would rev about 2250 which i would think theres probably 250 rpms of slippage. All the previous owner knew there they were highway gears.

When I was driving it back you'd have to drop it into 2nd to cruise through towns anything under 35 mph especially 30 mph.

 

[halifaxhops]

Easiest way to be sure jack it up and count the rotation of the driveshaft to one full rotation of the tire, then you will know for sure what the rear is also the spedo gear could be the wrong one also!

 

[abodyjoe]

a 26.5" tire at 2500 in the calculator i used works out to be:

3.23= 61mph
2.94= 67mph

looks like you are closer to 3.23

When I was driving it back you'd have to drop it into 2nd to cruise through towns anything under 35 mph especially 30 mph.

why? couldn't you just basically idle in 3rd gear that slow?

 

[273]

a 26.5" tire at 2500 in the calculator i used works out to be:

3.23= 61mph
2.94= 67mph

looks like you are closer to 3.23




why? couldn't you just basically idle in 3rd gear that slow?

I thought autos had a few hundred rpms of slippage that's why I was thinking 2.94 ?

Either way it needs 3.91

Ya it could drive in 3rd but it would be lugging especially under 30 mph and in 2nd it was barely revving. Most cars when your driving in 2nd feels and sounds like you need to shift not this one until after 35 mph.

 

[tonysrt]

My 74 Duster didn't have a cigar lighter in it. So I bought one, installed it and now I check speedo with my portable GPS. Fortunately it was right on the money.

 

[d55dave]

There is a smartphone app that tells you your mph. As was said, only way to know the ratio for sure is to count turns. Too many other variables...... converter slippage, tire size, speedo gear, speedo inaccuracy, tach inaccuracy.......

 

[273]

There is a smartphone app that tells you your mph. As was said, only way to know the ratio for sure is to count turns. Too many other variables...... converter slippage, tire size, speedo gear, speedo inaccuracy, tach inaccuracy.......

True
I'll probably find out for sure when I swapped them for 3.91 lol

I'm gonna keep them though for long trips
The previous owner said he got about 20 mpg with them.

I live in the Toronto area I don't use the highway much.

But will get that app like to know if the speedo is correct