good day...what is a possible replacement engine for tamiya nitro thunder?

I dropped an OS 18TM last year, i needed to make some modifications in order to fit in, but a huge difference over the stock engine. Also i have dropped a Tmaxx resonator pipe a month ago with huge improvement all over engines powerband. My only concern now is how the drivetrain will handle the extra power

thanks for the info....what are the mods that you did specifically?

when i got the engine i noticed that the crankshaft is not compatible with the existing clutch system so i inserted the crankshaft from an OS 18TZ. in the picture the left one is the stock crankshaft and the right one is from an OS 18TZ. I highly recommended to install the 2 speed transmission as the power that this little engine producing is amazing.
Also you will need to buy a air filter and a pull start to start for the engine. (I have bought RDLogics starter and i'm using HPI roto start system)

Also another option is to get a 18 CVR-X motor with the correct crankshaft ( i think is Standard Shaft) and a slide carburetor but you will need to install a side exhaust system. maybe one from an HPI RS4, you have to make sure that the lenght of the exhaust system fits between the rear and the front tires.
http://www.osengines.com/engines/osmg2102.html

You can try also the SH engines, i hear they have a big selection on engines and you may found one for direct fit in.