Project Aprilia SR50: 100 mpg Madness Part 1, Basic Bolt on Stuff


Next, we replaced the stock reed valve assembly with a freer flowing Malossi V12 part with carbon fiber reeds. The Malossi reeds are 1.5mm wider than stock and the cage is 3mm wider, Reed valves on a two stroke allow for more radical timing of the transfer ports without getting blow back reversion through the intake at lower rpm. They act like a one way check valve on the intake. The Malossi reeds made a feelable difference with more midrange power with slightly more top end. Now Project SR50 could hit 52 mph under ideal conditions and was relatively zippy up to 50.

Aprilia SR50 malossi and stage 6 delta v reed valves
The Malossi V12 reed valve on the right is much more open and freer flowing than stock.  It had a slight gain in power both in the mid range and top end over the stock reed valve.  The Stage 6 Delta V reed assembly on the right has nearly twice the reed area as the Malossi part.  It had more mid range over the Malossi reed and a very slight gain on the top.

We also tried a Stage 6 Delta V reed from a Minarelli horizontal engine. This engine is sort of like the small block chevy of two stoke scooters and there are a lot of aftermarket parts for it. This engine happens to share the same reed assembly as the Aprilia. The Delta V reed uses two sets of reed petals for effectively twice the reed area as a conventional reed valve. The Delta V reed valve gave us about the same top end but gave us a noticeable boost in mid range power helping our acceleration but giving us about the same top speed.

Aprilia SR50 Port stuffer on intake manifold
These are pictures of the port stuffers.  The Morini stuffer as pictured on the left is the stock stuffer once it was cut off the stock intake manifold.  On the right is the new Malossi part.  The Mallosi part is much more open and free flowing.  Photo courtesy of High-Gain Tuning


Malossi V12 reed valve stuffer
This picture shows the intake manifold with the stock stuffer cut off.  Photo courtesy of High-Gain Tuning
Aprilia SR50 Intake manifold match porting
Before and after pictures of the intake manifold showing match porting for the larger Malossi stuffer.  The black parts of the manifold are plastic so its easy to port.  Picture courtesy of High-Gain Tuning

As the higher flowing reeds had their own stuffer inserts that reduce the reeds internal volume and help maintain intake velocity though the reed,  we had to remove the stock reed stuffer that was built into the intake manifold. The stock intake manifold has a molded in reed stuffer molded in to its mounting flange that we had to cut off.  We simply cut off flush with the flange with a hacksaw and smoothed it out with a file.  To be fancy we ported the intake manifold to match the new stuffer.

Finally we used some indexing washers and indexed our spark plug so the plug gap faced the injector spray. The guys at AF1 have registered up to a ½ hp gain when doing this, a sizeable amount in an engine with only around 6 hp to begin with. This modification is controversial in the SR50 community as conventional wisdom by many respected forum members is to clock the electrode so the ground strap faces the injector. Supposedly clocking the plug so the gap faces the spray causes plug fouling although we have had absolutely no problems in a few thousand miles of riding. Some members claim that clocking the plug like us will cause it to fail almost instantly but we have had no issues. We did feel a good boost of power through the powerband, about the same as the reed valve.

spark plug indexing washers
We used these spark plug indexing washers of various thicknesses so we could point our plugs electrode gap at the injector spray.

The result in our first round of mods is pretty impressive. We have turned Project SR50 from a somewhat sluggish commuter scooter to something with some zip and pep, capable of handling tough urban traffic. Project SR50 can zip up to 50 plus mph and keep up with cars, not having to cower in the bike lane. Our mods have not affected our bikes fuel sipping ways one bit. Stay tuned, in new editions of Project SR50, we will work to give the bike impressive levels of power and improve its handling and brakes further.


AFI Racing


  1. This is awesome, I’ve been wanting to own one since 2010, and I just had a chance to own one, now looking at your build and reading about it, wants me to do that to my sr50… thanks for the right up

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