Motor KV in MBX-5?

[SilentMonster]

So far I have decided I am going 4S, MM. I'm pretty sure I am going with the Lehner line due to the Neu/MM cogging issue. I am a little confused(read a lot confused) with what KV motor I need to run. I am using the motor calculator that BrianG has made. It tells me to run a 1940/8 with a 15/46 gearing. Top speed is at 40MPH. That motor will spin 30543 rpm's at 3.7 volts per cell.
That all makes perfect sense to me except I have read several times I need to shoot for close to 40,000 rpm. If I change the pinion to 12 that puts it right about there but then recommends a 1940/6 which from what I gather is a little to hot of a motor to be running and isn't what I see on other buggies here.
I understand the lower the turn the more efficient it will be but isn't there a point that gearing a lower turn motor will offset the efficiency due to over gearing?
I'm setting this up to race so there is no concern for speed runs. What am I missing? Also would I gain anything besides weight if I went with the 1950 series or is that just over kill for a buggy? Stephen.

[glassdoctor]

1950 is probably overkill, yes... but I recall anyone running a 1950 in one.

The "optimum" 40K rpm is a myth. Don't worry about it. I can run my buggy with it peaking under 25K rpm and it works great.

That's a 1700kv on 4s.... I'm not saying that's what you should run, but it shows what can be done.

[Dafni]

I have a 1950 in my MBX5. It's nice. Tons of power. A 1940 would be more than enough, though. I'd even say a 1930 would get the job done without problems.

[glassdoctor]

Originally Posted by Dafni

I have a 1950 in my MBX5. It's nice. Tons of power. A 1940 would be more than enough, though. I'd even say a 1930 would get the job done without problems.

Ok... time to edit my post, lol

[SilentMonster]

OK so forget the 40,000 rpm thing eh? So given the same speed via different gearing, what motor would be more efficient and run cooler: 1940/8, 1940/9 or 1950/7? Sorry for all the questions. I normally am one who has to figure out every thing in detail by myself but electrical systems have always been quite difficult for me to get a good full grasp on. I've got to admit, that's the main reason I got the Novak system for my G2R because I new it would at least work correctly(except for the snapped motor shaft "YEP") even though I new there was much better stuff. I've only been into this hobby for just over a year so for pete's sake give a guy a break will ya? Sorry bout that kinda got carried away HAHA. Thanks again, Stephen.

[neweuser]

I personally would stick with your first initial thought with the 1940/8 or go with a 1930 as Dafni suggested. With racing, no need to do 40mph IMO.
The nice thing with the 1940/8 though, you ahve more gearing options I would think and torque at hand if it's needed.