Consider it an early Christmas present!
OK, I'm a nerd... But what do you think re: actual RPMs vs expected
- Thread starter CZ-75
- Start date
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No smiles yet... They said they had trouble getting a part out of the rear end. Sounds like a personal problem to me LOL
Sounds like your mechanics are more "excited" than you are! Hehe..
WOWOWOWOWOW!
OK, just let me say that swapping out my rear end is the single best performance upgrade I've done thus far.
I can also confirm that my car actually did have a 2.75 rear end. I counted the teeth... 44/16 = 2.75.
So, my torque converter must have still been "slipping" at highway speeds, because all indications pointed to a 3.25 gear set.
Let me also say that going to a 3.89 would have been a mistake if I had not upgraded to an overdrive tranny.
With my 2.75, I was getting really low RPMs at cruising speeds, and a reluctance to downshift. But now with the more agressive gear set in the rear, the car behaves like a freakin' beast. I absolutley LOVE the way the drivetrain works together now. All this time, I had it in my head that the existing gears were 3.25, and therefore, was expecting a moderate improvement. BUT DAMN!!!!! going from a 2.75 to a 3.89 is AMAZING! Very streetable... and quite a sleeper now
So, in summary: Wide ratio AOD + 3.89 Trac-Lock = Friggin' AWESOME, even with a EPA neutered 1973 351 2V.
Don expressed some initial concerns, that going with a wide ratio AOD and a 3.89 gear set might be a little too agressive for a street cruiser. I'm happy with it, although. I probably would have been just fine stopping at 3.70 or maybe even 3.5.
Now, off to modify my 10-best performance upgrades in Ken's thread.
OK, just let me say that swapping out my rear end is the single best performance upgrade I've done thus far.
I can also confirm that my car actually did have a 2.75 rear end. I counted the teeth... 44/16 = 2.75.
So, my torque converter must have still been "slipping" at highway speeds, because all indications pointed to a 3.25 gear set.
Let me also say that going to a 3.89 would have been a mistake if I had not upgraded to an overdrive tranny.
With my 2.75, I was getting really low RPMs at cruising speeds, and a reluctance to downshift. But now with the more agressive gear set in the rear, the car behaves like a freakin' beast. I absolutley LOVE the way the drivetrain works together now. All this time, I had it in my head that the existing gears were 3.25, and therefore, was expecting a moderate improvement. BUT DAMN!!!!! going from a 2.75 to a 3.89 is AMAZING! Very streetable... and quite a sleeper now
So, in summary: Wide ratio AOD + 3.89 Trac-Lock = Friggin' AWESOME, even with a EPA neutered 1973 351 2V.
Don expressed some initial concerns, that going with a wide ratio AOD and a 3.89 gear set might be a little too agressive for a street cruiser. I'm happy with it, although. I probably would have been just fine stopping at 3.70 or maybe even 3.5.
Now, off to modify my 10-best performance upgrades in Ken's thread.
Don65Stang
Well-known member
Cool. Very glad to hear your report.
So my spreadsheet gives a theoretical optimum first gear ratio range of 9 to 11 as being optimal. Now that you have this installed I'd like to hear what the rpm and mph shift points are for normal, non-aggressive street driving. Maybe a video even? Big
So my spreadsheet gives a theoretical optimum first gear ratio range of 9 to 11 as being optimal. Now that you have this installed I'd like to hear what the rpm and mph shift points are for normal, non-aggressive street driving. Maybe a video even? Big
I'll try... But it's getting cold up here and there is rain in the forecast...
This thread was full of great info! Nice job guys. I was thinking about going with 3.70s over 3.50s. I'm thinking that 3.89s Are the way to go with my (no bottom end) 4V heads.
If you have a 4-speed (top gear around 0.7:1 or lower), then I would say either 3.7 or 3.89.
One thing to think about, is speedometer gear... I have a 23-tooth speedo gear in mine, and it would be more accurate with a 3.70 gear set. As it is now, the speedo thinks I'm going a little faster than I am... so slightly steeper than 3.89 would tune it right in.
Tire size is another factor when choosing speedo gear.
One thing to think about, is speedometer gear... I have a 23-tooth speedo gear in mine, and it would be more accurate with a 3.70 gear set. As it is now, the speedo thinks I'm going a little faster than I am... so slightly steeper than 3.89 would tune it right in.
Tire size is another factor when choosing speedo gear.
