Very very cool idea, but most likely impossible
 

Imagine installing one of these miniature nitro engines in an XMOD! they are only 2" high and 2" wide so with some serious modifying and parts fabrication, this could work on an XMOD. You would, of course, need to be a real pro with the tiny cars and figure everything else out (where to mount the fuel tank, etc.) Come to think of it, this is pretty much a completely impossible thing to do, but you have to admit, it would be cool!
Cox micro internal combustion engine

It would almost be possible, but not without the use of a transmission. That cox motor does not run backwards.

Most nitro cars don't have reverse anyway. I already thought about doing this on a custom chassis, but there's no way I'd be able to put 4 batteries and a fuel tank under one of the bodies. That motor also doesn't have a throttle, so you'd start it and it'd go right to it's rev limit and sit there until you turned it off or it ran out of fuel.

Heh haven't seen one of those in YEARS! lol anyways yeah that would totlay blow some minds for shure! be cool if you did it, but you might need to go to like 1/24th just to fudge in some extra room!

One more thing, it doesn't have a clutch either, so you'd have to have one of those made.

i have one of these, much older tho, and i cant find any glo-plugs for it :\, to make a xmod a gas powered car, well there would be enough mods to make it not an xmod anymore. first, get a li-ion/poly batt then, figure out a clutch for starters, because you at least need digital control over it(maybe you might be able to slip it a little to go slowish). then real brakes for the amazing speed that you will need to slow down from. now, where are you gonna put that engine? i think someone that has experience with TTTT might be able to pull this off, but a 15 year old on a weekend, very doubtful.(not doubting that someone could do it on a weekend, but do it and sleep/eat and such....) the brakes and clutch are very needed, and also the hardest to do... i doubt there is anything this size right now, so it would have to be totally custom

Most nitro cars use a centrifugal clutch. The way this works is there are three or four little clutch shoes that swing out and grab onto the clutch bell when you accelerate.

Here's a link I found. It's for a chainsaw, but nitro cars work the exact same way.
http://home.howstuffworks.com/chainsaw4.htm

That wont work it probley needs a speed control and needs more torque. Hey isn't COX a model airplane engine anyways. I had a nitro airboat that went off a cox engine( they need model airplane engines). I know all this stuff because I have a nitro car (traxxas nitro sport) and a airboat(name lost in time bought off ebay with no info except gas powered airboat).

You could just strap an airplane engine with a prop to your roof:D . Really, it may be quite effective. Better have good brakes.

The cox .010 is a much smaller motor and more suited for this sort of car.

I actually saw some of those tiny motors in a friend's catalog and wondered how hard it would be to do that...