Uh... yes?!?! Night and day difference. I had two buddies running LST2's with stock engines and one with a muggy with a stock engine. They were fairly new to the hobby last year when I installed the LRP in my aftershock. I ran about 4 gallons with them with the stock 26SS engine in the aftershock and I wanted more power.
I had to gear up considerably to actually use the LRP or I was on my roof all the time. I did the trans gear flip mod and +1 losi bell. I could run circles around my friends and their trucks. I'd give them 20 yard head starts and overtake them pretty quickly. All the while, my engine is running at a breezy 240F while theirs are getting up in the 270-280 range.
I run standard sized tires which is partly why I geared up, but I recently geared up +3 over stock and the gear flip mod. Still wheelie city on many surfaces with poor grip tires (traxxas chevrons).
I was running the HPI polished savage pipe which is a very "open" pipe that lends itself to high torque low in the RPM's. I switched to an LST2 losi HT pipe and like it much better. Really smoothed out the engine HP range. Put the power curve more from 1/4-3/4 vs 0-1/2. It dropped my temps quite a bit as well and I had to tune it quite a bit more lean which in turn gives me longer run times.
It's also much quieter. I can't even hear mine anymore when I'm bashing with others... but I still overtake them with relative ease.
But if u must, the stock is ok. Upgrading the pipe will give you another huge boost.
you wont be sorry because the LRP is worth it.