Modern Vespa

Rev. B.

Completely cut out center divider, grid both sides, and half of the external snorkle. Bellmouthed the outer edge of external snorkle. Fabbed a bridge for air filter support to replace divider.

It works. Primary concern, injection is able to adapt. Currently running a Malossi O2 emulator but confidant it would be fine without. Also have a slightly larger injector to swap in to try. Suspect it will be very lean open loop.

Sound: better than expected. Not too loud, throaty with a bit of honk when snapped wide open.

Performance: I think it's faster, hard to tell as roads are wet and I can feel it fishtailing as the tire spins. Will need a dry day for proper evaluation. Don't normally ride in the rain but couldn't wait to try it.

How it was done: Xacto knife and Dremel. Cut the grid into small pieces, scored at the base, then bent back and forth with pliers to break off. Cleaned up with Dremel grinding stone. Very time intensive, estimate I have 20 hours in it at least.

No pics, was in a hurry. Will get some pics when I take it back off.

Pics of rev. A, slight mod to divider, bellmouthed snorkle, and grid cut out of outer half.

what's the dimensions of the square hole at the entrance? also what is the size of the exit of that long sqaure tube?

Haven't yet, but if I did the math I think area is the same or close to that of the rubber tube. And it does have a slight taper. Ideally would make it larger but not easily done. I did cut half of it out for the latest revision.

Managed to get a couple runs in today.

Baseline was lightly modded airbox, Malossi emulator, stock pipe.

First run configuration now completely gutted airbox, Malossi emulator, stock pipe. Noticeably quicker off the line than baseline. Acceleration strong up to about 80 (speedo) on the freeway. Very hot though coming in off the freeway, worried about popping a head gasket or scoring the cylinder.

Second run swapped in the bigger injector. Closed loop pretty much the same, O2 sensor apparently easily able to compensate for the injector. Acceleration now strong to 85, still hot though, but good to know I added a but of safety margin. Zero difference in driveability, can't tell the bigger injector is in there other than more power up top.

Injector size is 166 cc/min up from 158 cc/min stock, might do a separate thread on this.

Bottom line, no downside, unqualified success. Biggest bang for the buck, more power everywhere for the price of an injector.

Things I still want to try: a better radiused bellmouth for the end of the rubber tube and possibly an even larger injector.

Will also be reinstalling the Akra, hope to be able to bounce it off the rev limiter on the freeway.

Note on the emulator, probably not necessary. Only affects closed loop and no really noticeable power increase. But it does seem to work as advertised, you can feel a difference. I'm guessing it drops air fuel ratio into the 13s, like the larger injector provides a bit of safety margin with only a minor mpg hit. Will probably test without it at some point.

And another guy owes me a beer. Will have to do a trip around the world someday to collect.

Glad you got some positive results. I also messed arounds with injectors until I flooded the engine completely. I liked the IWP158 at 170 cc/min. Now have a collection of injectors that I will discard. No use on my 2023 model that uses an IPE085, for which I cannot find any specs. It seems to be unique to the Vespa GTS300.

I definitely owe you a beer.

Have been reading your posts on here, AF1, and even the German forum. Your experience gave me the confidence to give this a try.

Bellmouth came in.

Took it back apart for the install and took pics of fully gutted back half.

I think the sound is a little different with the new bellmouth but additional power if any is marginal. May try more of a velocity stack style.

Pics of Rev. B, fully gutted box and Rev. C, bellmouth added.

Update. Put the Akra back on.

No longer using the emulator as it's not needed with the bigger injector. Was running it a couple weeks with gutted box, bigger injector, and stock pipe. Power better every where, pulled really strong up to about 70 then tapered off up into the 80s. Did get a hard check engine light after about a week. Was about to to troubleshoot by swapping the stock injector back in but did the pipe first. Light's off. Go figure, maybe Akra is just enough leaner or maybe I had a leak at the headpipe. MPG dropped from 50ish to 40ish.

Still a little dip in power on the bottom with the Akra but barely noticeable. Pulls strong all the way into the 80s, found the rev limiter at 85, first time for that. Lofted the front wheel for the first time as well. There's an elevated train crossing that I used to fly the S190 over, could usually get about 10 feet of air. The GTS didn't fly, but did get the front wheel in the air. Headpipe is a nice bronze color, not the purple I was getting with stock injector.

I've got a different velocity stack on the way will post another update with that install. This is really looking like the way to free up power with minimal cash outlay.

"velocity stack"?

Yeah, apparently best for flow on an intake is a full radius bellmouth like I tried first. But I think in this application the size of it is creating a restriction. I'm going for more of a "trumpet" style next try. The factory rubber tube already has a little flare just going a bit bigger.

You mentioned it was very hot coming off the freeway. Do you have a sense of how hot? Redline?

Hot. Potential engine damage hot.

Wouldn't recommend doing this unless you also increase fuel, bigger injector, remap, or piggyback.

It sounds like even with the larger injector you installed, it's still running hot? Or are you happy with the temperature now that you changed the exhaust?

I'm wondering also whether the adaptive system is sufficient or a dedicated map is necessary. Of course it's all extra fuel, but from what I could see a dyno/map for the GTS will yield additional power without any other changes to the bike - not a huge amount of power, but some.

And thanks for sharing your work!

Yeah, stock pipe has a cat, extra fuel was probably making it hot, better with the Akra.

I'm really happy with how it's running now with the pipe. There is another injector that's slightly larger I could try but don't think it's needed.

Factory map is fine for this, closed loop is able to compensate both for the larger injector and increased air flow and open loop now has extra fuel.

I've run through a couple tank fulls and think mpg will be almost a wash, extra power means I don't need to wring it out as much.

Criminal it didn't come from the factory like this, it's really not that much louder than stock, no excuse for such a restrictive airbox.

I'm really excited by this experimentation you've been doing. There are clearly performance gains to be had without major work on the engine, if anyone is so inclined.

As for the OEM airbox design, it's a tough one. I assume this is driven by Euro 5 which also has noise requirements. A free-er flowing aiflow can also possibly reduce low speed performance due to less even fuel-air mixture. The GTS uses port injection which I think would avoid that problem. I'm guessing the net effect of what you've done would fail Euro 5 - not least due to removing the cat - but in terms of power you've reduced pump loss, increased airflow, and possibly improved scavenging at higher speeds.

Another factor for manufacturing is the ribs can be required during injection to ensure adequate flow and strength. I wonder if, say, in six months time you observe any deformation in your airbox or if your metal rib is enough. I hope so! It's a great mod.

I'd love to see before and after dyno results

Airbox is essentially the same all the way back to GT200, only changes to the rubber tube over the years.

My theory on the ribs is noise suppression rather than structural, keeps the box from resonating.

Dyno's not gonna happen. Akra says the pipe is good for about 1.5 hp so conservative guesstimate is 2-3 hp total.

Hi there

This is my first post, greetings from Germany.

Interesting project.

Inspired, my Airbox now looks like this. Will be connected to the throttle-body via cold-intake metal mainfold.

I would like to ask: where to find fitting injectors?

I have GTS310 und would like to as well get a bigger injector.

Thank you in advance.

Nice. Like what you did with the outer snorkle. I'm cautious to go that far concerned about noise, tried just the open tube and it was way too loud. Have you run it like that, how loud it it?

As far as injectors I understand the Euro 5 motors have different injectors than Euro 4 and earlier. If you can figure out what type and flow rate of the factory injector, search the internet flow rate charts for something with slightly higher flow rate.

Hey man

At the moment I am running the E3 versions intake snorkel, which I shortened on the airbox side, to friction fit a shortened carburetor trumpet.

I definitely have a bass-heavy intake noise due to the opened airbox.

But as it is very bassy, it is not annoying as for example a high reving 600cc engine.

At the moment I am not running the metal pipe intake, as it came out too short for my liking on the final fitment. I did lot like the internal transitions between airbox-pipe and pipe-intake. I want it smooth. Being too short, I could not fit it properly, and I am worried about the turbulences.

Regarding the injectors:
That's my point. Knowing the flow rate is the problem. On no source available to me, I can determine the flow rate of a given injector. Piaggio won't specify/provide them, nor any other parts reseller.

injectionDuration = (fuelFromMap * flowRate / 500) + trimByVoltage.

pic is values from GTS310 CM341002 5835MBAO:

(I can lookup almost all GTS models, feel free to ask)

Update.

Scoot was down for a parts order so took the opportunity to catch up on deferred maintenance. Pulled the intake off to see if I could clean it up a bit. A little handwork with some 80 then 120 grit and it's looking much better.

Trimmed more off the external snorkel. Noise is a bit more aggressive but still not that much louder than stock, can't hear it at speed.

Removal of the posts that supported the filter sponge is a non-issue. Most of these weren't fully formed during the molding process and weren't in contact with the sponge anyway. Have several thousand miles on it like this with no evidence of filter sealing issues upon disassembly.

Velocity stack is from Weber 48 DCOE carb, just need to trim off the flange. Factory tube is 48mm ID so stack is friction fit in the rubber tube, no clamp needed. A bit more radius than stock.

Current fueling is the 5% greater flow injector and Malossi O2 emulator. Went back and forth on the emulator, small mpg penalty but it's better with, Euro4 factory map in closed loop is just too lean. Pretty happy with throttle response and power, only apparent issue is a slight bog off the line I think can be fixed with stiffer clutch springs.

This is final configuration, if I take it any further will try open filter. Will probably do another post with more detail on the injector.

wont chopping all the supports behind the filter out of the back half cause it to flop and either then giving gaps for air that won't filter or simply block somewhat? originally there are thin stalks for exactly this reason. since you've removed those stalks I'd add a couple of horizontal thin braces

(yes poorly explained)

"only apparent issue is a slight bog off the line".

Very interesting, I was watching out for your review. I wondered if keeping the OEM snorkel but using a shorter external snorkel was a good balance to improve power overall.

I saw when others have removed the air box end of the snorkel and replaced the main snorkel with a larger diametre one they lose power at the start of the range, but gain flow which is useful at higher revs. This was proven on the dyno and is typical. A german workshop has some videos on this and they sell a larger diametre snorkel.

Basically, the short/larger diametre snorkel and opened up airbox benefited if someone wants to improve power over 90kph/55mph. The cost is loss of power around 40kph/25mph.

I'm wonder if this is what you're feeling off the line. Basically, the smaller longer diametre snorkel provides superior velocity at lower revs, but the airflow is restricted at higher revs. Of course it could still be a matter of optimising the fueling. I hope so.

Yeah, I was originally concerned about this as well.

As I was cutting out the grid noticed that most of these supports weren't even touching the sponge, in the molding process they hadn't fully formed. After I trimmed these out there were only couple left so decided to cut them all.

Have a couple thousand miles on it like this and have had it apart a couple times. The edges and center are clamped tightly between the halves, no leakage of unfiltered air. Filter element itself may be flexing a bit but it's pretty robust. As long as I swap it out for new every couple years should be okay.

I think it's fueling, rich just off idle because of the larger injector.

I was under the impression that open loop is only high rpm/load but SteelBytes, our MIU Guru, posted a chart in one of my other threads that shows ecu is open loop at idle to just off idle. Who has a tach on their 300 (pre HPE)?

I think raising clutch engagement rpm should fix this. Had Malossi yellow clutch springs on my last scoot and liked them, slightly higher rpm than stock but not too racy, was going to install them anyway.

are you're thinking about the cells around 2500 for 3.8, 5? you'll pretty much never be in that range as to get rpm to 2500ish would require the tps to be open a bit so not normal idle.

No, idle. Think your chart shows and pretty sure I read on the German forum that scoot is actually open loop at idle.

When I crack the throttle off the line the clutch engages then I get a slight rpm drop or bog before it takes off, not ASR as I always shut it off. I'm thinking it's too rich right off idle from the injector.

nope. the lambda o2 feedback loop is active during idle. see the cells for tps 3.8 at rpm 1600/2000 at Who has a tach on their 300 (pre HPE)? (Post 2718162)

Hello everyone!
Here's what my airbox modification looks like.
This mod provided a very noticeable improvement in acceleration after 70 km/h.

• First run – 13.47 s (before any upgrades), with 130/70/12 and 140/70/12 tires and the Prodigy variator.
• Second run – 12.47 s after the ECU remap ("chip tuning").
• Third run – 11.18 s after installing the throttle body funnel.

where did you get that bellmouth? looks a nice size ...

https://www.ebay.com/itm/293918851068

that looks like the 2nd one you used, not the first red one?

Red one. Had to extensively modify to fit. ID was 48mm.

https://www.amazon.ca/SEADEAR-Carburetor-Connector-Motorcycle-Accessories/dp/B0B35YXVWK