Rearend ratio upgrade???

[Mlehnert623]

Hi all!

I have a 2008 Roush 427R, supercharged 4.6, with 3.55's in the rear. Unfortunately, I have recently discovered that both my rear axles are bent and need to be replaced. Since the dealership will have the rear diff open, do you think its work upgrading from a 3.55s to a 3.73s?

My main activity with the car is local/regional autocross.

Thanks very much in advance!

 

[blacksheep-1]

Not sure why both axles would be bent without bending the housing.
Back in the day, we'd draw a line down the length of the axle, when it twisted 180 degrees, we'd swap sides until it untwisted, then threw those axles away. The only issue I have had with non drag race 8.8 axles is the area that rides on the bearings will degrade. Again, I would question the straightness of the housing if they claim the axles are bent.
FWIW..

diff straightening

OK, so back from the races, as you will recall, I had an 8.8 diff with a little "wang " in it. There are several issues here, one is how to measure the wang, and 2 which side is the wang on.. so here we go. So to determine the amount of wang, we need to create a jig whereby the angle of wang can...

trackmustangsonline.com

 

[xr7]

One thing you want to look at is how close to the rev limit are you running. I have 3.73's and I've been tossing around going to 3.55 or 3.31 to eliminate shifting to third. I currently run 295/40-18's, probably will switch to 315/30-18's when this set is worn out and that will only make the problem worse.

 

[JDee]

One thing you want to look at is how close to the rev limit are you running. I have 3.73's and I've been tossing around going to 3.55 or 3.31 to eliminate shifting to third. I currently run 295/40-18's, probably will switch to 315/30-18's when this set is worn out and that will only make the problem worse.

Me too! On 305/30-19s the car is over 7300 on the back straight in fifth. Meanwhile third gear is too low for some corners and 4th is too high. 3.55s would solve those issues. Stock motor and I want to keep it healthy for a long time, keeping revs down will go a long way towards that.

 

[blacksheep-1]

Xr7 and JDee are both correct, it depends on which tracks you are running and the transmission ratios available to you. If you just autocross, then, generally the more gear the merrier, but you still occasionally get stuck in an "in between" gear because the courses always change. Road courses, may have some different configurations, but for the most parts the straights stay pretty much the same, so you can base your gearing on that.

How to pick the right gear ratio for your needs

There are lots of ways to adjust gearing no matter what kind of motorsports you race in.

grassrootsmotorsports.com

I have found this advantageous, even though you have to input your own gear ratios, they have factory gears listed, but it's all rice burner stuff.

MFactory® Competition Products

www.teammfactory.com

 

[Coz]

If you bent your axles, you may want to consider Moser or Strange axles instead of OEM replacements.