What size gear ratio should I use with my swapped Mercedes 5cyl turbo diesel? Im leaning towards 4.88's with 31's and will be getting some 33's soon along with a rear locker. But I need some opinions on gear size 1st!

 

whats that engines best cruising rpm?
Find out where it needs to be at 65mph. Wouldn't worry about anything else with a diesel.
You definitely don't won't to high of rpm's.

 

It's very similar to the 3.0 that was in it as far as RPM range and such for cruising and what I could find on what that motor cruises at. But I don't do hardly any Highway driving where I get over 60mph.

 

In that case id definitely go 4.88. As long as that diesel can run at 3,000rpm safely, if you ever did need to go 65mph.

 

oh it'll run the 3k no problem, with that motor it has tons of torque over that 3.0 I had. lol Thanks for the help bud!

 

I run 4.30s in my 4Runner on 33s with the 3.0 5sp and it does fine. I threw them in because I had them already and didn't feel like spending more money for new gears. If money wasn't I factor I would have gone lower of course. Basically what I am saying is on 31s and that power plant I wouldn't be overly worried about your gearing just yet if you have other things on your plate to get the truck done. Gears could easily come later if you happen to have budget issues. Drive it with stock gearing and figure out from there.