IF that is the case can you replace the entire diff with the 4x4?

Not sure. I just THINK that I read the internals are replaceable between the two and it was supposed to provide better diff action with the 4wd internals. Just going off of memory though. Was looking for some real world experience. Tired of rebuilding Ball Diffs!

Anyone reccomend a gearing combo for 17.5 blinky? medium/small track

I would like to see what everyone is running?
I was running 75/28 little hot for me 5/6 mins about 160 degrees. Now I'm running 75/26 with little timing on end bell motor 5/6 mins 150 degrees just as much torque faster top end. Next time might take a little timing out bring temps down.

Servo Horn
 

I've looked everywhere for the right answer....What is the correct servo horn for an XP 1313....I was running a j horn and I believe it stripped...or is not the right one...

It's the F horn
Futuba, Savox, Xp 25t servos

J Horn I'm not quite sure I've heard Jr has different sizes

I'm running a D3 at 26/84 with 1.5+ notches on the motor and around 40deg of boost, sorry forget the range it kicks in. Comes off after a main around 145deg

It's got plenty of low end, but I need to squeeze a little more top end out of it.

How were you able to fit 75/28? I run 75/26 with my D3 and I can't fit anymore.. I run full can timing and blinky from a Tekin and it's good for our med/large track but I'd like to try just a bit more but could t fit a 27 or 28.

Using spacer to widen rear 2mm without stripping wheels
 

I have a bunch of tires mounted on regular offset hex wheels. In the front I can use a 2mm spacer and by using a serrated nut it will not come off. But in the back its another story, adding 2 mm spacer is asking for a stripped wheel.
So I tested using 2- 1mm spacers, one on the inside and one on the outside of the hex and can say they have held up very well.

Running a Reedy 7.5 on a med-high bite clay track with big jumps.

I run Orion vortex pro stock 17.5 I have room for 75/30

Counter sink M3 Metric motor screws with those counter sink washers or button head screws in motor then you will have more room for larger pinions, I have run 75/29 could prob even go bigger. 6mm screws are what you want for button heads, and 8mm for the counter sink ones as they measure the head and all with counter sink screws.

I Prefer the counter sinks with counter sink flat washer

.

would a 75/28 spur/pinion combo work on a novak ballistic 8.5 motor?

I would start with 20/84.

I am currently trying to dial in that same setup. I started with a 22/78 (way too low) and have worked my way up to 28/78 which I was running yesterday and the highest temperature reading I could get was 123 degrees running full packs back to back. I have a 30 tooth pinion and a 75 tooth spur to try out next time I am at the track.

I am using a Novak Ballistic 17.5 with a Mamba Max Pro set to use "Smart Sense" with normal timing. The physical timing on the motor is as it came from the factory.

-Chocula