The 808 uses a 43/10 ratio on the pinion/ring gear, so you may need to re-run your speed calculations. The 42T spur gear is stock, and you also have a 41T and 43T as optional gears that will drop right in.

It is also possible to use the center diff mounts from the XT8 truggy to accommodate larger spur gears, but there are a couple things to consider. First, raising the center diff will case the center drive shafts to get very close to the chassis braces. The braces are composite so it is easy to remove a bit of material, but just keep that in mind.

Second, raising the center will also increase the angle of operation of the center shafts so you will probably see a drop in efficiency there and a bit faster wear of the cv joint pins. Again, not a big issue, just something to watch. You will want to watch and maintain those center cv joints anyways; a bit of mantainance there wil allow the pinion, driveshaft and coupling to last a long time.

I also agree with JHautz assessment of the weight balance of the 808. I preferred the handling of the 808 when I placed the battery towards the rear of the chassis. Some weight measurements put the F to R bias nearly identical to the nitro counterpart with the battery to the rear and the ESC over the rear drive shaft. The nitro 808 handles fantastic in most smooth or rough track conditions, so it was my goal to duplicate those characteristics. With my 4S 5000 packs and 1512 motor, my vehicle weight was within an ounce or so of the nitro chassis, so little change from out teams' setups was necessary.

I have used two different methods to mount an esc over the rear shaft. I made a new center diff top plate from carbon fiber that extends back over the rear shaft, similar to what you see on some of the conversion pictures. I also made a 'pedestal' the straddled the driveshaft. i like the pedestal because it sat a bit lower and also did not require removal of the esc do service the center diff. I used a couple top deck posts from the XRAY T2 sedan as posts for the pedestal, but you could also look at the fuel tank mounting posts that will come in your 808 kit.

Bryan
RC America