2.78 to 3.55 gears to big of jump for a cruzer?

[70 MONTE]

I have a 70 with a pretty much stock 350/350. It has the BOP 8.2 10 bolt in the back. I have an axel bearing starting to make noise and I thought now is the time to get rid of this 1 wheel peel BS and throw a posi in it since I have the axels out.
 

Being that the motor is pretty much stock I thought I should get deeper gears because it can barely do a 1 wheel peel as it is. The guy I bought the car from said it had 3.31’s in it. Like an idiot I believed him and didn’t check before ordering all the new parts. Popped the cover off and the ring gear is saying it’s a 2.78. 
 

Is going from a 2.78 to a 3.55 too much?  I don’t want to be at 4000 rpm to go 60 mph down the road. Should I buy some 3.31’s instead?  The car is barely driven, usually just around town in the summertime but on the highway every once in a while. 
 

Thanks for your thoughts on this. 

[cbolt]

It would depend upon what you want. To simply spin both tires the 3.55's would certainly do the trick but since you were already doing one wheel burn outs with the 2.73's then you would be able to do the same with the 3.31 gears. Either would suit your needs so the question is do you want lower or higher RPM's driving it. Around town? Highway? 

My car sports the 3.73 gears and I wish I would have gone with the 3.31's, but I could care less about doing burn outs. 

[Montemedic]

It will definitely wake your Monte up and you will feel it as a performance modification. If you are mainly running around town with occasional highway use you will be fine. 

[Dtret]

8.2 is not the best housing to work with. If you’re going to spend a decent amount for a complete rebuild you may want to rethink and move to a 10 bolt Chevy or even a 12( more expensive) 10 bolts an be found pretty reasonable. 

[714024SPEED]

3.31 is a nice ,have them in several of our cars. 3.55 depending on how tall of a tire you are running you may not like in the highway.

[72 Monte Carlo]

I haven't heard of a 2.78 gear in a Monte Carlo yet, just the most common gear ratio 2.73. 

I currently have the 2.73 12 bolt with a factory posi in my 72 Monte, but I have a set of 3.31 GM gears, Yukon posi, and a new full install kit to swap into my 12 bolt once the car is painted here soon. 

I'm running 275/60R15 tires in the rear, so I think 3.31 gears will be just about right for my car. 

It really depends upon how big of a rear tire you're running, transmission, engine and camshaft, to gauge which gear ratio you should get, and if you're driving is 90% around town 10% freeway. 

[Scott S.]

Hey Ken....

I thought Joe had corraled all the long term non-members. LOL

I went through what you're contemplation..... Stepped up from 2.73's to 3.31's. And Yeah, your highway RPM's will jump up to the mid 3000 range 3.55 gears. 

Makes for a nice streetlight to streetlight criuser though.

The way some of us have gotten around that (streetable & highway) is with an overdrive transmission. 

Some like the external two speed, some (if you like manual transmissions) go that way, or there's always the 200r4/700r4 swaps. 

I chose the 200r4 becauce it's basically a "bolt in" replacement for the th350. But I did spend a few bucks to make sure it'd take the abuse.

One thing I'd like to mention.... You probably already caught it, but if you're climbing the gears, remember that the carrier housing is different between 2.73 and 3.55. 

Good luck. Scott 

 

[S.Maug]

Sin City 375 posi rear SS454. I love burnouts. smokes em for blocks. no issues highway driving.  Bloo 402 331 posi, never laid rubber in her, runs out great on highway. 

[S.Maug]

maybe 373, heads not great with figures at this time

[SPLATT71MC]

I have 3.55 gears in mine. For me they are about as far as I'd go and continuously cruise at highway speeds. However I'm going to an overdrive transmission.

[cbolt]

10 hours ago, S.Maug said:

maybe 373, heads not great with figures at this time

I did the same thing. Replying first thing after I wake up has never quite been my forte

[DragCat]

2 minutes ago, cbolt said:

I did the same thing. Replying first thing after I wake up has never quite been my forte

Yea Dennis asked me to consider NOT posting in the am till I finished my 1st cup of coffee 🤣

[Dtret]

1 hour ago, DragCat said:

Yea Dennis asked me to consider NOT posting in the am till I finished my 1st cup of coffee 🤣

Might make it two cups mandatory. 

[Scott S.]

18 hours ago, S.Maug said:

maybe 373, heads not great with figures at this time

To many nurses to distract you ?

[Canuck]

I had 3.73 in my 71 SS454 and wasn’t to my liking since I drive a lot of highway. I had a set of 3.07 gears given to me so I decided to put those in and I’m much happier. Ideally I think a set of the factory 3.31 gears would have been a nice all round compromise.

[TheBMan]

In my opinion, a 3.55 is probably as far as you want to go on the street. You'll love it around town but it'll be a bit wound up at 65mph. I went from a 3.73 to a 3.08 and like it; it's a good compromise between street and highway gearing.

You can use this calculator to determine your vehicle speed at any given RPM. https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

Good luck!

[S.Maug]

Nice. With my math skills Bryan, this calculator will come in handy.  

[Scott S.]

TCI has one that will even tell you which gears to use in your transmission to correct for mis matched parts.

[Chevy Dave]

The Transmission Ratio RPM Calculator from Spicer works great! Thanks for sharing it with us.