Yes. Lower kv will have higher torque. So you gear it a tooth or so higher. My 13.5 with torque rotor is geared 23/84 while my 10.5 is geared 20/84.
Viper is coming out with a new series motor that will have higher kv. Kv and turns of wire don't alway go hand and hand. The 13 turn means each coil has 13 wraps of wire and more wire gives it more strength for more torque.

Was wondering if anyone had used this servo before?

Its a BlueBird BMS-830DMG+HS High Performance Digital Servo.

I know BlueBird servos have a good reputation in 3D aircraft and this one seems like a good fit for RC Off Road Steering duties.

0.10 Sec at 6.0v and 181oz/in of torque.

Diff Tightness
 

Looking at filling my gear diff with oil for the first time. Have been using black grease but want to try oil. Getting different suggestions on what thickness of oil to use. Should the diff be tighter for a track that has good traction? Thinking to use 5K diff oil even though I already have 3K in my tool box. Thanks.

Most suggestions I have seen have been to use either 5K or 7K for racing applications and change based on temperature/traction.

Diff oil depends on traction. 3k or 5k seems to be about right. Maybe 7 on a super sticky surface.

OK, I am taking the plunge: called my LHS (PRCR) and had them put the FT SC10 kit aside for me, I will build it up using my current SCRD chassis.

I got the below reply on another forum. Does everyone agree?

If it's a lose diff on a low traction track all the power will go to the wheel with the least traction so you want thicker to lay down the power on the wheel with more traction. Also when a car turns the outside wheels spin faster as they have more distance to travel. On a higher traction track you have to lighten it up since the wheels have more traction and won't slide in a turn.

I don't agree. And I replied there too LOL

I have also heard those two conflicting theories expressed bf. :weird::confused:

If your going to get a Hong Kong servo get one of these Power HD 8312MG Metal Gear Digital Servos from Value Hobby. You can find a lot of video reviews of them against Hitec servos and it keeps up with them fine. Heres one in an 8th scale. http://www.youtube.com/watch?v=mhlYx59WCdk

0.10sec/60°at 6.0V
180.44oz/in Torque
http://www.valuehobby.com/radio-syst...tal-servo.html

I disagree.
I thought the same things 20 years ago. I've tried it and it doesn't work. I can't give you the whole physics on why, just my experience. The opposite works better.

Just ordered up a RS brushless for my daughter to TRY and race, along with the RPM front arms and needed hinge pins. Anything else that I should watch out for that could break easy, should stock up on spares? Any durability mods?
I read about running the losi springs, may do that conversion for her too. It would take me 2 months to read the 790 pages as well as wrench on my buggy and her truck.

If this truck is for your daughter to try out the sport, I would recommend that you pick up the RPM Front Bumper and Skid Plate Kit. This will add a lot of durability to the front end of the truck. Another piece that you may want to look at installing is the Factory Team Hinge Pin Brace. Other then those two things, you should be fine for a while. These trucks are surprisingly durable. I wouldn't have even recommended getting the RPM a-arms, as the stock ones are quite durable, but I suppose its too late at this point ;)

As far as the Losi BB conversion is concerned, I wouldn't recommend you do that to your daughters truck AT ALL. If you were to do it, I think you would quickly find that there are many ways that you would have rather spent $50+ on your daughters truck. The Losi BB conversion is often more work then its worth, when it comes to a beginner. I mean, there are advantages of it to people on here who are very serious drivers... but for a beginner, its not worth the money and effort. Just stick with the AE stock springs, they work great. But, hope she enjoys the sport!

Speaking of RPM arms, I have a front and rear set I got and didnt like. They are very low use and have all the hardware with them. If anyone is interested let me know. I let em go for cheap, like half off.

They are the blue ones.

Diff Tightness Confusion
 

Interesting that there are still totally opposite opinions on such an important issue. Some folks say thick diff oil for loose track and some just the opposite. Wondering if there is a source to find the correct answer? I assume that this question should hold true for both gear diff and ball diff- "should a diff be tight or loose for a high traction track". Would like to get the correct answer before having to experiment with different weight oils in my gear diff since it is a hassle to remove diff from sc10. Thanks