3.90's worth about 2 cars

**RealLiveMD** · 05-20-2010, 08:28 PM

After installing the 3.90's, I thought that it would be helpful for others to know what they feel like. They feel like a 50 shot of nitrous. I have a buddy with a 300 which is generally dead even or he nudges me by a nose in the quarter. With the 3.90s its an easy 1.5 cars my way. I hope this helps.

**corvet786c** · 05-20-2010, 08:33 PM

Hows the fuel economy? Also would you think 4:10's are better?

**Tyler_LS1** · 05-20-2010, 10:53 PM

i love my 3.90s deff. made a difference

**Knight** · 05-21-2010, 05:08 AM

If the car is a A4, 3.73s or 3.90s are a good gear choice. 4.10s are good for a M6. My opinion, but many seem to agree.

**RealLiveMD** · 05-21-2010, 09:45 AM

Originally Posted by corvet786c

Hows the fuel economy? Also would you think 4:10's are better?

Hadn't notice a change in fuel economy. I mostly run on the street so 3.90s are almost too much. 4.10s would simply spin. it depends on hp level. If you are stock with LT's to about 400rwhp get 4.10s If you make 400-550, 3.90's, above that you're probably boosted and need 3.42s. Just my opinion for the street.

**Knight** · 05-21-2010, 10:07 AM

Originally Posted by RealLiveMD

Hadn't notice a change in fuel economy. I mostly run on the street so 3.90s are almost too much. 4.10s would simply spin. it depends on hp level. If you are stock with LT's to about 400rwhp get 4.10s If you make 400-550, 3.90's, above that you're probably boosted and need 3.42s. Just my opinion for the street.

I'm around 450 rwhp and I run 4.10s on the street, but I'm a m6 coupled with Mickey Thompson ETs so I don't really notice any problems with spinning to much. It would be too much for an A4 though IMO.

**RealLiveMD** · 05-21-2010, 10:20 AM

Originally Posted by Knight

I'm around 450 rwhp and I run 4.10s on the street, but I'm a m6 coupled with Mickey Thompson ETs so I don't really notice any problems with spinning to much. It would be too much for an A4 though IMO.

My bad. I should have clarified. If you are on 4.10s with MTs you are probably ok especially if you have a big cam with less grunt in the lower rpms.