Modern Vespa

For more air in you can simply take out the hose it will become a Stage 2 airfilter then a K&N cone is a Stage 3






the hose could be attached to your airbox cover the pic's i'm showing are from a MP3, so there could be some differents with a GTS 250 and with a 300 airbox

This is the airbox that most of us are familiar with. It doesn't have the intermediary pipe:

Okay, let's assume for now there is no risk of unfiltered air getting in the cylinder with this modification.

Let's also assume that the piston can now suck in air more easily, resulting in it having to pull less hard than before, resulting in more power output.

But what is getting into the cylinder now? More O2? Same amount of gas or more gas?

If same amount of gas with more O2= leaner burn = more heat strain (the GTS is already getting very hot from lean burn)

If more gas = worse fuel economy

We're not dealing with a perpetuum mobile, so more accelerating power needs to be coming from somewhere. Where is it coming from, then?

And again: if it is really that simple and has no negative side effects, why didn't the Piaggio engineers do it? I would want to believe they know the tricks. They should be motivated to give their product as much power as possible, particularly, if it comes for free, no?

Restricted pollution norms for european market !?

Windbreaker, where did you get the idea that they designed this engine? The GTS250 and GTS300 both use a cylinder head/valves designed for a 125cc!

In the case of the air filter, it looks as if they just grabbed one that was lying around, threw out the inner bit of pipe, and that was it! Its the same filter that was designed for the GT200 carburetted engine.

Regarding the mixture entering the engine, you are forgetting that there is an EFI there monitoring the situation all the time and adjusting the mixture to suit. Admittedly, it sets the mixture a bit weak, so there is scope for aftermarket gadgets to override it, but there is no reason to think the mixture wil get more weak with this mod. Have you never noticed that your scooter runs better just after it has rained? When the barometric pressure is up and the air density is up the engine breathes better. My mod also helps the engine breathe better.

I wish some others would try this mod and report back. But it is very difficult to test, because anyone opening their air filter box to make the mod would inevitably sieze the opportunity to clean the air filter element at the same time, and that by itself could lead to a performance improvement. It takes a lot of will power and time to just change one thing at a time when tuning!

Mike

nearly all performance mods result in worse fuel economy, because that's where the extra power comes from, the chemical energy of the fuel. We are assuming that this type of mod will not draw so much air as to go beyond the enrichment capabilities of the factory injection system (assuming no aftermarket mods in that area) but we can't know for sure unless we use a wideband O2 sensor with readout.

Maksor, I took the cover off my air filter and looked at the air path. If this hose is removed the air totally bypasses the filter. The filth I find on my filter would go straight to the engine. Did you add a filter when you removed the hose? If not trash is getting to the engine and it won't last long.

Nowhere! I said they designed "this marvel", meaning the scooter. So they just take parts lying around somewhere, and as long as they can fit it under the cowls, that's it? Wow! Now I have even more respect for them, making this little scooter work as reliably and powerfully as it does, and all just by pure coincidence...

BTW, I am not doubting your genius. I am only trying to understand it better (your invention, that is).

Duh, I don't need no stinking balloon...

To give your mod a bit more significance (if that is at all possible), I realized that I don't need a balloon to figure this out. We have the displacement (of 249 cc).

At an average RPM of 6000 (probably ~60mph/100kph) we have 3000 air-intakes...of ~249cc each. That's an impressive 12.5 liter per second! For comparison, an average human lung holds between 5 and 6 liter. To breathe in a full lung in one half of one second, I need a decent mouth opening. The nose alone can't do it.

I don't know how big, in comparison, the stock orifice in the air box is. Would you happen to know, Mike, after you've been operating in there?

All that said, at idle and acceleration from a stop, the PRMs are quite below 6K. So there, the situation is not as demanding, which would suggest that the benefit of a larger orifice is not as significant there.

I'm not going to open it up again to measure, but the pipe is about 2" diameter (5 cm to the metricated). I agree, that's a lot of air to get through per second at 6000rpm. And 50% more at 9000 rpm. When I cruise at a steady 60-80 kph the engine is doing 6000 rpm, and it is when accelerating from this sort of speed that I notice the difference.

Regarding Piaggio using bits that are lying around, remember that the GTS300 uses a cylinder head that was designed to fit a GT125 - less than half the size, and the air filter box probably has the same history. Look at the reports on the K&N filter to see the results of letting the engine breate!

Anyway, it seems no-one else is brave enough to try this mod, so I won't see any independent support for my results. Pity!

Mike

NB, Thanks for your comment about my genius. It is not often that us geniuses get recognised while still alive. 8)

The GT200 airbox does have that tube in between the two sections of the airbox. If 250 does not have it then there is nothing pinching the filter along that edge and there could be some risk of the filter being pulled into the U and allowing air to flow around it. Given the 250 seems to ship that way I think a few conclusions could be drawn.

1. Piaggio didn't "design the airbox for the 250" they did design it for the 200 and then found that leaving a bit out worked ok on the 250.

2. The width of the standard U is not wide enough to allow the filter to let air by unfiltered. Something to consider when enlarging the passage, may want to go deeper rather than wider.

Keep in mind that the smaller initial intake is working all the time while the carb/throttle body bit is only "intaking" 1/4 of the time. So a small air box opening is not necessarily a restriction that impacts performance, much.

Would you please paraphrase these parts? I don't understand what you mean

Here's a diagram of the GTS and GT200 airbox. When the engine sucks in 200-250cc of air at the left it does so over one stroke of the piston. The airbox then has 3 strokes of the piston to recharge. So the relatively small passage going into the airbox (at the far right) and the U shaped divider in the middle (or short rubber tube in the GT) don't have to be as large to flow the same amount of air over 4 strokes of the piston. That doesn't mean they can't be enlarged, it's just not quite as bad as it first looks.

Patrick, I hadn't thought about that factor, and you are quite correct. But previous table-napkin calculations on the air flow are still as correct, only the engine takes it in in intermittent gulps, which means the air flow has to be four times as fast through that part of the filter box. All the more need for some streamlining.

Results with K&N filters prove that the standard air filter is too restrictive and is throwing some performance down the drain. The problem is to get that performance back while still ensuring good filtering and not too much noise!

But I still don't believe that that central divide does anything to hold the filter element in place. It lines up with the edge of the filter cavity, not with the filter element. Even with it there, the filter is just as likely to be "sucked up" out of place, which is not at all in my opinion. My filter has not ben sucked up at all, and makes a perfect seal all around so there is no air leakage past it.

I have had the filter open several times since making my mod, and the element has not moved. I am thinking about cutting away much more of the partition, but then the law of diminishing returns comes in because of other restrictrions, like the narrow air channel up the back to get into the box.

I remain very happy with my scooters mid-range acceleration and think it is the easiest and cheapest performance mod available.

Too much here. Sorry, I get carried away!

Mike

I don't find it at all carried away, great thread and input from oops and drew!

Thanks, Louis.
Just an afterthought. That 15" long induction pipe would do a lot to smooth the air impulses going through the valves, so what passes through the air filter will be pretty smooth, and not gulps as previously suggested.

Mike

I'll be doing about 300 miles this weekend, so we'll see how it behaves.

Thanks, Baz. I am longing for a independent view on the results, to assure me I am not imagining it.

But I will be away on a weeks beach-side holiday next week, no computer access, so I won't see your comments until a week later!

Mike

Pulled my air filter open today, and found the filter had shifted - but not where I cut the partition away as the sceptics had suggested. It had moved out at the top, where the air inlet is. I concluded that the filter had been blown out by the incoming air because much more air is being sucked in now.

My solution for this is more-or-less Baz's operation, shown in his earlier post -



- except that where he cut a hole in the middle of the air inlet tube, I cut away about 1" at the top. The result will be that the incoming air is directed towards to centre of the filter, instead of the top edge, and this should make better use of the whole filter area.

This latest change is still to be tested, but I remain delighted with my scooter's performance, uphill and accelerating on the straight.

Mike

Yes! It's obvious if you remove a lot of air filters. Looking at them in their dirty, crimped state shows a lot about how they sit in the airbox, and also the directions and intensity of the airflow.

I clicked on that link for the pod filter.. I think that is the way to go that is some serious time cut... As far as the sliders i dont think i wanna do all that.. but the filter is cool..

yeah it's pretty awesome... and waaaaay quicker than all this measuring and stuff... but i gotta pay respect Mike and his tinkering... total badass... love it, and i love the different approaches towards the same end result

It did seem to 'pull' better from stand still and up hill.

Yea i just ordered a pod filter but i cut my box like mike was saying the other night.. so im gonna roll with that for a little and then put the pod on and see if i can tell a differance

I am interested in trying this mod and / or getting the pod filter. Spoke to local Vespa dealer today and he reckons that the ECU WILL compensate for the changes in the ammount of air by adding extra fuel. So no damage to valves but less fuel economy (and who cares about that )

yeah we did all the tests up at a scooter mechanics place when i did it all and he had the testing equipment out etc... and i have put around 7000km on mine since doing it and a mate has put 20,000 on his since doing his... so yeah... we thought we should finally do a scientific test though, and the results that the mechanic told us with a surprised look "that is running 100% perfectly still" that was under load and everything too... we were pretty pleased to hear that from a licensed mechanic not just from our own seat of the pants experience!!

So i put my pod filter on i think mikes way is better not as much noise.. also i was wondering what do u do with the other hose that connects to the airbox just let it dangle..

ahh yeah that is another 15 dollar part you can get, just get a small pod filter... really small one, it fits right on...

I used a crank case filter from the parts store..$3


Its the orange thing in the pic.

I have just done this. Both mods. I cut an inch hole at the top of the air inlet. Mod two, I left the top opening on the filtered air side the same, but enlarged the hole beneath as Drew suggested.

Impressions? Noisier, when full throttle but in a nice way. Definitely torquier, even from standstill. I like it. A lot.

Now this will compliment today's shopping. A PM exhaust and a 9 roller variator. Goody-goody.

Thanks for the report, Doug. It's nice to know I am not imagining it.

That's two who have reported good results with my mod. Any more takers? Its the cheapest mod available, all you need is a pocket knife! (and a screwdriver).

My GTS now accelerates strongly up to 120kph (indicated) up a long steep hill. Top speed is unchanged, but power definitely improved.

Mike

Mike:
Thinking about doing your mod . . .
Question: If you had it to do over again, would you do it the same way, or would you opt for Drew's suggested mod, which is to cut a hole instead, and why?

If you look at the pictures of the unadulterated filter housing you will see a U shaped cutout. Mike has changed the shape of the U to a wide V.

The air filter lies across the top of the U. It is possible to leave the top of the U which contacts the air filter intact and widen the bottom. This will make sure that the air filter doesn't shift out of position while giving greater airflow.

Judging by Jess's recent report on the Malossi V4 head, the ECU doesn't have any problems compensating for either air or fuel changes....

thinking of using this method on a Scarabeo 500ie...

Stinky, I have not seen any signs of the air filter shifting out where the cutout is. Contrary to Doug, I see the partition that I cut lining up perfectly with the corresponding partition at the side of the filter, so that it does not play any part in keeping the filter in place. All those protruding pins hold the filter in place.

I only had a problem with the filter shifting out at the top, resulting in my second mod which has fixed that.

So if I did it again, I would do exactly the same, but if you have any concerns leave the top of the U alone and open up below it. Shouldn't make any difference. Just anything to give the air an easier passage.

Mike

Mike and Doug:

Thanks for the feedback--my warranty expires in April, so i think i will pull it apart and do this mod at that point--probably in the manner in which doug described--just because . . . well, just because i'm a skeptic.

12.5 liters per second . . . that's a lot! I'm assuming this filter box is a little like a restrictor plate (NASCAR)?

Interesting that the UK forum has done a bit of the "nah it won't work leave it alone" stuff. It does actually seem to make a difference and the length of the intake which is responsible for torque, hasn't actually changed.

Mike Holland,
It is now 40 days since you published your mod. You must have refilled your tank at least a few times since then.

So, what are your findings for fuel economy?

I am considering this mod if I can find a way to reverse it in case I'm not satisfied. If I do it, I will do a before-and-after side-by-side comparison with Salima's GTS to see if it is all just a placebo in our brain or reality on the tarmac.

Stay tuned, and let's hear your fuel consumption data.

Fuel consumption? What's that? I fill my tank and I ride!

I measured my fuel consumption once, and got about 30k per litre. But fuel consumption depends mainly on how you ride, and I enjoy accelerating hard.

I am more interested in how many smiles per gallon than how many miles per gallon.
l
If you are worried about economy, then don't do any modding. Just cruise everywhere at half throttle.

Mike