I have put some money asside for my JKU and I'm planning on going with a RIPP supercharger as well as gears. At this point, I can only do one and wait till after the holidays for the other. SO.....

Has anyone supercharged their JKU on stock 3.73 gearing? If so, how did you like it? What type of change in MPG was there and was the power useable? Would you do gears to add to your SC?

If I don't SC soon, I will go with 4.88s for my auto JKU on 34s. I know everyone will tell me 5.13s, but I don't want my jeep to be screaming at 3k RPM @ 75mph.

Thanks for all your input guys.

 

Interesting point about go gears first to see if I still want to supercharge. And I'm still really debating 4.88s over 5.13s. I was just thinking 4.88s to get that little bit of MPG over the 5.13s.

 

I have the Ripp gen 2 S.C. on 5:46 gears with 37 tires and that setup works great,I can also backdown tire size to 33 tires with no problem.

 

With 34's I would avoid 5.13s. I had 5.13 with my 37's and my highway mileage dropped from 17 to 15.5 when I changed from 3.73s. My city mileage went up from about 14 to 15 but highway sucked. That was on 37s and it would only be worse on 34s.

 

That's kinda what I was thinking. I live at sea level and don't tow anything. I just don't think I need the added low end of 5.13s at the cost of top end above 70 mph.

 

Additionally, I'm amazed you were able to get 17mpg on 37s with any gearing.

 

LOL, it's all about the speed. That 17 was at about 70. (3.73, 37s, OD off) Increase it to 75 and it dropped to 15. In the other hand, with the 5.13s at 75, it dropped to 12.5. (5.13, 37s, OD on) Otherwise, 5.13s, with 37s at 65-70 I got 15.5ish

I actually got 22mpg on on road trip with 36s. We were in convoy doing 50-55. Was awesome for mileage but took us forever to get there.

 

Assuming you've got a pre-2012 with an auto, I agree with Planman as to gearing. I don't know what was going with the other guys jeep, but go look at the gearing chart in the FAQ section. You won't be anywhere near 3k RPMs on those tires at highway speeds with 4.88s.

Candidly, if I owned a pre-2012 auto, I'd only consider 4.88s if I was certain I was going to keep the stock tire size forever. Even then I'd probably still want 5.13s unless I spent huge amounts of time on the highway. Keep in mind that a pre-2012 manual trans Rubi turns about 2500 RPMs on stock tires at highway speeds. If you're going to go through the expense of a regear, you want to at least get your jeep to that point.

Now, all that is really just considering a regear. My recollection is that RIPP however tends to recommend a size or more down on gears on account of the extra power. For example, I believe I read on here somewhere that Ripp recommended 4.10s for manual trans pre-2012s. Without a supercharger, you'd probably want 4.88s.

So I'd say call Ripp. They generally advise folks to regear before adding a supercharger, and the answer as to what gears you should get may unfortunately vary based on your supercharger plans.