I would say around 45+ minutes. Gear it right, and you won't have any heat issues as well.

Ofna makes an MBX R2 rollerfor $179 http://www2.towerhobbies.com/cgi-bin...?&I=LXAXV2&P=0 If i do a buggy i'll use this

Not a bad deal at all.

I used an older MBX version for my 2nd conversion but one thing I didn't really like is the fact that the MBX is more narrow than like my Hyper 7 for instance. You almost have to put the motor over the diff or get creative somehow. I ended up with the motor on one side and a battery on the other.

Well I have begun racing my 1/8" scale. Have you found an ESC that can handle the heat?? I have a fan on my motor and it stays WAY cooler than my esc (8XL 4s lipo 9920).
Today I could only race 5 to 6 minutes with 13/46 gearing on a hyper 7 then it would thermal. after 5 minutes the esc was 155' f. Speed is where I want but it just gets too hot.

Anyone want to buy a 9920?? I am going to get a Quark 125.

Do you have a fan on the esc? the quark would run just as hot,it just wants a lower gearing and more air cooling.

Trouble is the rpm is too low so to get any kind of performance the gearing is too high.If i was going to replace anything it would be the motor along with an adapter to run a 51T spur.

Well I was looking at the motor it says 2084 KV thats more in the 7XL/6XL range?? Any one know whats up with that?

4s lipos would be over reving??

Gustav, shouldn't the Quark 125 stay cooler than the 9920? It's got an aluminum case with the FETs mounted on it (are all of the FETs mounted to it?), whereas the 9920 only has a heatsink on half of the FETs, and the others get no cooling air. So, that means that the Quark 125 has more surface area to cool, making it run cooler.

I guess so.Or a fan on the 9920 would be cheaper.I just think the money for the quark could be better spent elsewhere rather than masking the problem slightly with a different esc.

Edit;i do take your point about the difference in construction,but do you think it could make such a difference if the 9920 thermals after 5 mins? I s'pose with fans aswell it should but i'd still be more inclined to run some more rpms with a lower gearing.

Well, half of the FETs on the 9920 have no sort of cooling at all, the other half have a heastink (and possibly a fan on the heatsink). I can imagine that the Quark 125 might also have more FETs than the 9920.

The extra money spent on the Quark is money well spent IMO. The Quark has actual programming that the 9920 can't get close to, and it's case design is a million times better.

I'd like to try the quark soon.I expect it will be a good controller.The PWM puts me off a bit though,schulze recommend 9KHz for >8 turn lehners and hackers and that's what i look for since my schulze and MGM seem to do well with my motors at that frequency.They say it's the optimum for controller efficiency with these motors,and to experiment with which frequency heats up the controller the least (since it's adjustable on schulzes).I guess i could just try it at 38KHz and see.

Should i not worry about PWM,i'm really not clued up on this,just wondering what you think about it? At the moment i was thinking my next controller will be another schulze because of it(and the smoothness of the schulze too).

Well, there are many people that are happy with their Quarks that run 2pole motors, so I don't see why it wouldn't work for you. These are also supposed to be very smooth.

I am going to try running a few more RPMS and a fan first and see what I get.

First thing to get is a 5s lipos pack and reduce the gearing.
I am concerned the 8XL will be the weak point with 5s lipos. Should we not be around the 9XL for 5s lipos??
Anyone race with a 8XL or 9XL?? What kind of gearing are you using?

I need to do (3) 5 min heats and (1) 10 min main. So I need to be able to double what I am getting out currently of the controller.

First off i'd try a fan on your current setup and see how it does.The 8xl would be fine on 5s,or you could use the 4s packs you have with a 7xl which would be cheaper than buying good 5s packs.Either setup should do well,the 4s obviously the lighter.they both put you in the 33-35000 rpm area.I'd try an 11/46 or 10/46 gearing and go from there.