finding the right gear ratio ?

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purplescamper

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i have a 73 scamp with a small block, 4 speed trans, 3:91 sure grip rear and im running 245/60/15 tires on the rear. its quick ff the line but when im on the highway im doing 4000 rpm ay 60 miles an hour.
what ratio would be good off the line and decent on the highway ?
 
purplescamper said:
i have a 73 scamp with a small block, 4 speed trans, 3:91 sure grip rear and im running 245/60/15 tires on the rear. its quick ff the line but when im on the highway im doing 4000 rpm ay 60 miles an hour.
what ratio would be good off the line and decent on the highway ?
Click to expand...

with a 4 speed and 3.91s and about a 26" tire there is no way your doing 4k at 60.

you should be at about 2800 rpm.

i have an auto with 4500 rpm stall. 4.10 gears and 27" tall tires. im doing 2900 at 60.
 
I'll bet when your speedo says 60 your passing everything on the road. Probably has the wrong speedo gear in the trans.
 
SGBARRACUDA said:
I'll bet when your speedo says 60 your passing everything on the road. Probably has the wrong speedo gear in the trans.
Click to expand...

I have the same problem with the speedo in my 71 Dart. 14 to 15 inch conversion. How do I find which is the correct gear and where can I get one???
Thanks
 
pyrojim said:
I have the same problem with the speedo in my 71 Dart. 14 to 15 inch conversion. How do I find which is the correct gear and where can I get one???
Thanks
Click to expand...

This link should help you figure out which gear you need.
I have a few gears let me know which gear it is you need after looking at the list.

http://www.mymopar.com/speedometer.htm
 
67Dart273 said:
X2

An online calulator says 3000 is 61 mph
Click to expand...

can't his timing have something to do with it too?
after my engine was rebuilt the shop had set my timing really screwy
my engine would SCREEEAM at 60mph
I just knew it had more in it
took it by 1wildandcrazyguys house one day and he fixed me up
on the way back to my place i was flying by porsches doing 75
like i knew i could
 
Nope. RPM is RPM, and speed in high gear is speed in high gear.

One of the best ways I know (that's both cheap and accurate) to check your speedo is to use a GPS. I don't use "mobile devices," LOL (I use a CELL PHONE) but I understand "there's an app for that"
 
vexer.com/automotive-tools/speed-rpm-calculator‎

Around 3k @ desired speed.
 
purplescamper said:
i have a 73 scamp with a small block, 4 speed trans, 3:91 sure grip rear and im running 245/60/15 tires on the rear. its quick ff the line but when im on the highway im doing 4000 rpm ay 60 miles an hour.
what ratio would be good off the line and decent on the highway ?
Click to expand...

I had the same combo in my Dart, 360, 4 gear, 3.91's, and the same tire. At 60, I was at 3100 rpms. I went to 3.55's and droped the rpm at 60 to 2700 rpms.
 
..i used to run 3.91 and 60 mph was 3000 rpm,74 mph was 4000 rpm...too high!
..now to answer the original post,i think 3.23 is the best 'all round' gear'
 
This is why you should retro to a 5 speed ;-)

I know i'm gonna catch **** for saying this lol!
 
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