Question: Anyone have a 3.73 Differential?

[adfac]

I currently have a 2.73 rear end installed and have been going back and forth for the last 6 months trying to decide if a 3.73 is worth the expense at Ecklers or Mid-America. They want about 1800 bucks (including core) for the entire assembly and I'm OK with that as long as it gives me the SOP feel I'm looking for. I've also been told that it's probably the best way to add some "pop" to the car without making major modifications to the engine. But what about highway speeds? I was wondering how those with a 3.73 rear end feel about them and how much do you sacrifice in the 70 to 80 mph range or when you hit overdrive? I rarely take my car over 90 but I still want enough power to pass if I have to. My engine turns between 2,000 and 2,200 rpm at 75 mph which I'm told is pretty low (I couldn't get the tach to hold ... it fluctuated). Can anyone tell me what to expect if I put in a 3.73? And also if you like yours or not? Thanks for any thoughts.

 

[boomdriver]

I currently have a 2.73 rear end installed and have been going back and forth for the last 6 months trying to decide if a 3.73 is worth the expense at Ecklers or Mid-America. They want about 1800 bucks (including core) for the entire assembly and I'm OK with that as long as it gives me the SOP feel I'm looking for. I've also been told that it's probably the best way to add some "pop" to the car without making major modifications to the engine. But what about highway speeds? I was wondering how those with a 3.73 rear end feel about them and how much do you sacrifice in the 70 to 80 mph range or when you hit overdrive? I rarely take my car over 90 but I still want enough power to pass if I have to. My engine turns between 2,000 and 2,200 rpm at 75 mph which I'm told is pretty low (I couldn't get the tach to hold ... it fluctuated). Can anyone tell me what to expect if I put in a 3.73? And also if you like yours or not? Thanks for any thoughts.

I don;t have the low gear but I can tell you right up front that you;re adding 1 full rev of the drive shaft out of almost 3 currently...so expect a dramatic increase in pulling power thru the entire range...passing will be like it was in 3rd and not OD....Freeway speed will be like it wants to upshift to OD, but you;re already in OD..

BUT

What was cruise at 2000 will now be 2600 or more. The rpm will go up alot because of the 25% increase in drive shaft speed (eng speed). MPG will drop 2-3mpg..maybe more. It'll jump off the line and get to hiway speed quickly...
and heres the BIG BUT.....

You'll get used to that in weeks and then be searching for the next level of thrill....

So, you might want to consider something inbetween those ratios and maybe do some safe bolt on engine enhancements that won;t ruin mpg or reliability. K&N< open lid, 52mm throttle body, runners, port matching, upgraded exhaust...lots that can be done without much of a sacrifice anywhere. If you drop those gears that much, you're stuck with what you've got and no way to un-do it.

 

[adfac]

I don;t have the low gear but I can tell you right up front that you;re adding 1 full rev of the drive shaft out of almost 3 currently...so expect a dramatic increase in pulling power thru the entire range...passing will be like it was in 3rd and not OD....Freeway speed will be like it wants to upshift to OD, but you;re already in OD..

BUT

What was cruise at 2000 will now be 2600 or more. The rpm will go up alot because of the 25% increase in drive shaft speed (eng speed). MPG will drop 2-3mpg..maybe more. It'll jump off the line and get to hiway speed quickly...
and heres the BIG BUT.....

You'll get used to that in weeks and then be searching for the next level of thrill....

So, you might want to consider something inbetween those ratios and maybe do some safe bolt on engine enhancements that won;t ruin mpg or reliability. K&N< open lid, 52mm throttle body, runners, port matching, upgraded exhaust...lots that can be done without much of a sacrifice anywhere. If you drop those gears that much, you're stuck with what you've got and no way to un-do it.

Great advice. They also offer a 3.55 ratio. After that it goes to a 3.08. I have the open K&N and an upgraded exhaust. Not sure on the throttle body but I'm pretty sure it's stock. So maybe I should consider a 3.55 with some minor engine mods?

 

[boomdriver]

I would..thats just me. I try to keep in kind whats able to be easily un-done if I decide that I don;t love it or what I might be stuck with that will cost a fortune to get rid of.....

I'm just cheap that way...

I'm sure someone thats actually running those gears will see this and give some details on what the rpm is like at 75 mph and so forth...

Right now I'm kinda liking the tall gears...even looked at a 2 speed trans OD unit that gave an extra OD gear....The closer to more MPG I can get right now...the more I'll consider it ! Biggest problem is my foot.....

 

[Hib Halverson]

Going from a 2.73 to a 3.73 the four things you will notice:

1) The car will spin the tires off the line and probably spin a lot
2) Once it hooks, acceleration will be noticeably more robust
3) Fuel mileage will decrease significantly
4) Highway noise level in the interior will increase.

 

[vetteoz]

Going from a 2.73 to a 3.73 the four things you will notice:

1) The car will spin the tires off the line and probably spin a lot
2) Once it hooks, acceleration will be noticeably more robust
3) Fuel mileage will decrease significantly
4) Highway noise level in the interior will increase.

And if you have any form of TPI intake you will run out of revs real fast.
3.73 with ultra low 1st gear of auto becomes almost unusable ; car hardly moves before you shift into 2nd

3.07 is almost universally recommended ratio for stock(ish ) TPI setups
Some analysis reading
http://forums.corvetteforum.com/1568185079-post21.html
http://forums.corvetteforum.com/1568186621-post24.html
http://forums.corvetteforum.com/1568194010-post27.html
http://forums.corvetteforum.com/1568212084-post30.html

I have 3.73's and love them but my 383 spins to 7K; not the 5K max of the TPI

 

[John Robinson]

Here is the formula for figuring the rpm for the different gear ratio

RPM=mph x final drive ratio x gear ratio x 336
________________________________________
26

So lets use the final drive ratio and gear ratio for my 93 for this example

75 x .70 x 2.59 x 336 = 456876 Divided by 26 = 1752 RPM

Now all you have to do is plug in what ever ration you want

Using a 3.73 instead of a 2.59 will have the following results at 75 MPH the RPM will be 2530 or 778 RPM more per mile.

You can simulate this by dropping the trans into a lower gear that puts the rpm in that range at 75 to see if you would like that on the road.

As others have said the MPG and the traction will be big issues but this would give a lot more low end performance without touching the engine.

If the engine has any miles on it this will increase the piston wear factor by about 7% because of the increase in what is called feet per minute.