9XL on 16 cells..what sort of performance?

[Rtsbasic]

Hi guys, I'm purchasing a new setup for my Emaxx - a 9920, with a 9XL, UBEC and RC-Monster heatsink. I'm purchasing it off a friend along with a few other bits off his Emaxx :)

My question is..what sort of performance can I expect from this setup on 16 cells? The previous owner ran 20 NIMH cells/6S lipo on it, he reckoned it was good for over 50mph with very long (30 min) runtimes. And what sort of gearing would you recommend? I'm switching to mod-1 gears with a strobe setup. Infact is there some sort of gearing chart of excel sheet to work out the final drive ratio for the emaxx when using the strobe?

Finally..as part of the deal I'm getting some new diff's for the front and rear (UE ones, not sure if they're the 6 or 8 spyder gear ones), some cvds for the corners (already have center cvds), and as previously mentioned a strobe slipper with some mod-1 pinions. Is there anything else I'm likely to break with this level of power? I'm hoping to get a pair of steel idlers off Mike before I run it on the full 16 cells.

Thanks.

[coolhandcountry]

The steel idlers are needed. If running the 14mm plastic rims the hexes will likely get rounded out. I like the 9xl on 16 cells. Depends on what you going to try for I think the 16 51 worked out well but can run more.

[Rtsbasic]

I'm still using stock wheels/tyres, do you think the RPM nylon 14mm wheels will hold out? I was planning to purchase some of these as they make the truck a bit wider and are pretty impact resistant.

What sort of speed would I be hitting on 16/51? I think I'm getting a pair of 18t and pair of 20t pinions, would either of these work okay on 16 cells?

[studysession]

The stock wheels and hubs will hold. It is the plastic shafts and suspension bits that can't handle the power.

I have an 8L on 12 cells in mine. It would be insance to run on 16 or more cells. Would love to see a video.

[Sylvester]

They should hold up fine, but if they ever do get rounded out, theres always 23mm, and if you do go 23mm, do get dace adaptors, they are much better and are worth the extra bit of money!

[coolhandcountry]

I ran mine with 16 to 20 tooth pinions. It works out pretty good depends on the run time, cells, and tires size.

[Rtsbasic]

Okay so from the sound of it the only other thing I need to pick up are some steel idlers :) If I get any problems with the wheels I'll switch to a larger hex but for the min if it ain't broke I'd rather not fix it.

coolhandcountry, do you know what the final drive ratio when using them pinions would be? I don't even know what the emaxx's tranny ratio is or if its going to change with my new diff's.

studysession, I'll hopefully get a video down the local BMX track when its done, should be a good testing ground for the new power.

[Gustav]

The centre tranny ratio of E-maxx 2nd gear is 1.72:1.So if those diffs are 3.3:1 then on 16/51 your final drive would be 3.1875(51/16) x 1.72 x 3.3 =18:1

[Rtsbasic]

Gustav, nice one, thanks for explaining that. So if I gear it 20/51 (with the 3.3:1 diff's) it should be around 14.5 FDR, which on 16 cells will give me approx 40mph top speed and hopefully still 10-15 mins of runtime on 3700's. Does this sound reasonable from this setup?

[Gustav]

Sounds reasonable to me,i've been using this speed calculator that Brian G made http://www.scriptasylum.com/rc_speed.html.
I normally just put in the nominal voltage and the non-ballooning tyre size (on the basis that they cancel each other out a bit) to get a rough guestimate.

[Rtsbasic]

Thats a great speed calc, thanks for the link mate. Glad to see the website arrives at the same top speed as me.