Gear ratio for A518

[Moespar]

So, I've finally gotten into the rear end of my 73 challenger. 489 case, and 2.76 gears, with a non Sure Grip ( go figure?) I'm going to be giving Dr Diff some of my loot for Sure grip unit and was thinking about gear too. mild built 440 with a A518 transmission. My goal is to get on the highway and road trip, couple hundred miles at least, without busting 3000 RPM. . But also dont want her to be a dog off the line. I've done a bunch of reading here and elsewhere about gears for a similar setup as mine.
would I be safe with the 3.23 or 3.55? which of those two are the better compromise. Or... should I just keep the 2.76? All my planned driving is NOT just road trips but in town type cruising and maybe some tire smoking... ya never know! thanks ya'll

 

[Chryco Psycho]

IMO 3.55 or 3.73 will work great , I used 2.76 with a .71 OD & I could literally idle at 75 MPH in OD

 

[Katfish]

I have 3.73 gears with my 518 and very happy with it.
2500 RPM at 80mph works well for Hwy drives

 

[Steve340]

There is a fairly simple calculation if you know the overdrive gear ratio and the desired cruise RPM.
Let me know I can post it for you.
Another thing you need to be sure of is the converter stall speed. The cruise RPM needs to be a littler higher than this so the torque converter is fully "locked" at cruise RPM.
If not you will toast the transmission.

 

[Katfish]

The cruise RPM needs to be a littler higher than this so the torque converter is fully "locked" at cruise RPM.
If not you will toast the transmission.

Curious what the basis is for that?
Stall is RPM at max torque, almost 99% of street driven miles are under the stall of the converter.

 

[Steve340]

Sorry you are wrong there.
Stall speed is not the point at which the engine is making maximum torque. Max torque of the engine is typically 500-1000 RPM higher than the stall speed. Depending on the engine it may be even higher.
Stall speed of the converter is when the engine RPM rises to a point the converter locks or gives maximum drive.
It is the point of maximum torque multiplication of the converter. You may be confusing this point.
The extra heat generated in the transmission by operating under stall speed for any length of time will cook the trans in a very short time.

 

[Katfish]

OP will have lock up, so no issue.
Everyone do your research a lot of bad info floating around

 

[MAC]

If interested i have a very good 3:55 i would trade you even for the 2:76 if your intrested.....thanks
Mike