Modern Vespa

I'm thinking about putting an exhaust and high flow filter on my GTS 300, but I wonder if that will have a negative effect on performance.

I did that with my Honda Civic a long time ago and hated the result. The engine may have made a little more power at very high rpm, but it also lost what low end torque it had. In other words, increasing the air flow just had the affect of shifting the power curve from lower rpm to much higher rpm.

And I'm wondering if making air flow mods to the Vespa will have the same effect. I really like the low end of the GTS 300; I wouldn't want to lose that just to gain 1/2 a hp on the high end.

I've read on this forum adding an exhaust likely won't do much to make the bike perform better. But my question is has anyone who has done it noticed any negative effect, like losing low end torque?

You'd be better off changing aerodynamics for top end speed.

I modified my airbox and went with a malossi filter on my 300. The engine seems to breathe a little better and has a quicker response to the throttle. Doubt I got any significant gains from it otherwise.

What do you expect to gain from a new exhaust other than more noise? I suggest you watch and understand this first:

https://www.youtube.com/watch?v=RWTARjxiqlo

Which Malossi filter? Dual element or red sponge?

I'm looking for quicker response and more top end speed.

Will the exhaust give me more of both, or is there a trade off, or will I get neither?

The PM Tuning exhaust was dynoed and showed a modest bump in power. I did install this pipe and the low end was not impacted, but mid range seemed to have the most benefit. I also installed the Malossi red filter at the same time.

Changing the roller weights in the variator can also yield some improvement. Lighter weights will give you better acceleration but you lose a smidge of top end. With Heavier weights, you can decrease RPMs at higher speeds, but you won't gain very much on the top end.

You can also go with the Malossi piston and V4 head that can give more power as well.

The Malossi air filter does allow the bike to breathe better. We are at sea level, and when the new filter came out we had to rejet the 50s to run better. With a bigger engine, you don't notice the effect as much, but it's there.

Aftermarket pipes look and sound better, and are engineered to take advantage of other modifications you might do in the future.

Big Bore Kit
Variator and
Exhaust
in that order are the three things that will give you the most bang for the buck in performance on a scooter. After that, it's a little bit here and there.

The reason your Honda lost low end torque was that the ECU was not fueling the engine "correctly" at the lower RPMs. Increasing flow with intake/exhaust is almost always better for (4-stroke) performance at all RPMs, unless you can't fuel it correctly.

Also, I think that CVT scooter tuning is a whole different theory than something with a geared transmission. For example, consider the effects of losing 1/2 ft/lb of torque in the lowest 2000 RPM by trading it for 1/2 ft/lb gained in the upper 2000 RPM. A properly tuned clutch & CVT would move quickly through the lower RPM zone, and stay at the higher RPMs for the majority of acceleration, right where the more torque is.

As an example EJK piggyback fuel controller basically has three zones.

Cruise
Acceleration
Full throttle

For CVT scooter tuning there is essentially no "acceleration" mode . This being lower rpm full throttle. As the CVT automatically shifts to a lower gear thus avoiding the "acceleration" mode.

Of course it is not that simple but the basic premise holds.

I also em paranoid about overheating and the electrical stuff