Modern Vespa

If you look inside your GTS air filter, you will see that the air passes through the filter, then negotiates its way through a U-shaped aperture in a central diaphragm, and finally works its way into the end of the induction pipe, which extends quite far into the filter box. Not very conducive to good breathing!

Being the inveterate fiddler that I am, I atacked the aperture in the diaphragm, opening the curved part of the U by 1/4 inch, then cutting away the corners to make a round-bottomed V shape, more-or-less doubling the size of the aperture.

I did not touch the induction pipe, as the length of this pipe is critical for tuning the engine's torque curve. But it is tempting to remove 1/2". In 15", how much difference can 1/2" make?

Anyway, the result of my fiddling is better acceleration right across the speed range, and my scooter now holds 105-110kph up a nearby steep hill where it was dropping to 95kph!

On the downside, the scooter is a bit more noisy at low speeds - up to about 60kph. Beyond that I don't notice it, and if I had an aftermarket pipe I would not notice it at all. Anyway, a lot of members here like a bit of noise. But under hard acceleration from a low speed, it sounds a bit like a two-stroke, and twice I have tried to change gear when accelerating!

I have discussed this mod with Paul of PM Tuning, and he has offered to try it on the dyno if I send him pictures and measurements. It would be nice to have my seat-of-pants evaluatioon verified by him. watch this space ...

Mike

Last edited by Mike Holland on Sun, 21 Feb 2010 01:39:46 +0000; edited 1 time

Mike,

I was nosing at a thread on one of the OZ forums the other day about the guy who mounted a polini filter onder thae panel. looked interesting but i would be dubious about waterproofing etc. this sounds more like it, keep us posted.

Pictures would be great!

do you have a link to the oz forum???? ta

very, very interested in this, both altering original box and running different filter....

I tried a Malossi filter, but didn't like the noise it made. I see Bunnybash has revived the K & N filter topic, but that one is also very noisy. Beauty of my mod is that it keeps the original Piaggio filter, and air intake is from below the box, and not from the heated air around the engine. Also, it costs nothing.

Admittedly, my idea needs a lot more research. I did one cut-and-try, and liked the results. One could cut a lot more, and maybe get a bit more with a lot more noise. Then one could atttack the end of the induction pipe - a half-inch off there would help gas flow a lot, and half an inch in a length of 15 inches shouldn't make that much difference to the induction tuning, should it?

Will post some pics and dimensions of my mod tomorrow. Busy day today!

Mike

I'm sure there will be a lot of interest in this. 8)
I have my hacksaw at the ready.

http://scootercommunity.com.au/forums/t/12927.aspx

This picture shows the cut-away in the airfilter. I have high-lighted it in white. I didn't measure the original U-shaped aperture, but it is now 10cm wide and 5 cm deep.





I have mixed feelings about the extra noise at low speed. Mostly I like it, but sometimes I prefer my scoot quieter. Under hard acceleration from a standstill, it sounds a bit like a two-stroke. I know that would appeal to some of you. But twice I have tried to change gear when pulling off!! Old reflexes still there!

I do hope one (or several) of you will try this mod, and tell me that I am not dreaming! It is dead easy to do - just remove the filter cover and attack with some tin-snips or shears or even a pocket knife.

Just a reminder - this is a backyard mechanic job, I just hacked and tried it out. Maybe less cut away would reduce the noise but still give the benefits, maybe there are much bigger benefits lurking with a bigger cut.

Mike

Last edited by Mike Holland on Sun, 21 Feb 2010 03:03:16 +0000; edited 1 time

might have to give this a go,

mike, did you reset the ecu afterwards?

No, I didn't. Been thinking about it.
Mike

Puzzled - what now stops air getting past the foam filter, which can 'blow in the wind'?

Jim, air coming up that narrow pipe from underneath the air filter box can only go through the filter. There is no other way. The outer cover of the box also has a central diaphragm which meets up with the one I cut, and which separates the filter area at the back from the manifold area at the front.

Mike

I'll take your word for it.

Personally I'd not fiddle too much with the breathing or the exhaust - I'd not want to muddle the ECU. I'd far rather meddle with the transmission, where real measureable gains can be made.

Hmm - too many 'ddle words there. My Dad would call them 'hole' words.

Fid-hole
Mud-hole
Med-hole.

Hmm..

Maybe when the Malossi V4 head becomes available, you will change your mind!

I understand that the ECU is very versatile, and it would take an awful lot of fiddling to muddle it.

I already have a Polini variator and Malossi clutch springs. Plan to experiment some more with sliders in the Polini, and a Fuzzy washer.

Inveterate fiddler Mike.

I will have to re-evaluate the noise from my mod. I have just discovered that my exhaust is leaking where the two pipes join.

No, this is not the 2007 exhaust recall problem, although my scoot is a 2007 model. This is a result of faulty workmanship when I had a new rear tyre fitted last June. The mechanic tightened the clamp just behind where the slots are in the outer pipe, instead of over the slots.

My scooter was very noisy, and backfiring whenever I throttled down. When I got home today I found some plastic melted off a set of cables near the exhaust. I have moved the clamp to where it should be, and tied the cables up out of the way, so my scoot should be alright for tomorrow's Vespa club ride, but I shall be going back to the dealer for a new gasket on Monday.

Mike

Very interesting. Going to take a look at my airbox. Was wondering like JimC, if some air doesn't by-pass the filter.

I've got to take the cover off my airbox to see and understand what you are describing. Right now I tend to side with JimC regarding bypassing air, but I don't know what I'm talking about.
I always tend to believe that the engineers who designed this marvel know what they do, and if it were so easy to get more oomph out of it, they would have done it.

That said, how much air does this little piston breathe anyway? If I had a balloon, I'd inflate it with my exhaust to see.

Please do take the cover off your air filter. Then you will see that the air enters through a narrow pipe from underneath, then passes through the filter to enter the main chamber. There is no other passage.

Then take note of the circuitous route the air has to take to pass through the small U-shaped aperature to get from the rear half of the box to the front half, and how it then it has to work its way around to the end of the induction pipe.

Once you have seen this for yourself, you will share my dismay at the possibility of ever getting a smooth flow of air into the engine. You might also want to start cutting away at the obstacles.

Mike

I did take the airbox apart and Mike you're right.....there is no way the air can get by the filter, when modified . Had to really look at it a while, because it's a bit confusing (when apart) how the air moves through the box & filter.

And you put it back together without doing anything about it?
MIke

...........I'm thinking........I'm thinking about it..........and probably will after we get back from Bike Week in Daytona.

haha i was the guy doing the pod filter work here in australia... i think you will find that the noise isn't as bad as you think... it's more like adding an aftermarket pipe...

Ok all this sounds good but what are the gains.. I'm confused... I don't thinking that little bit of a cut away will make any kind of performance gains.. In my opinion probably will just mess with air fuel mixer and give u problems.. Just my opinion

There is certainly some unfiltered air passing through. I understand your reasoning behind cutting the wall that separates the halves of the airbox, but the same lip/wall that travels around the perimeter of the filter element is what holds it in place, and also seals its edges. The location of your cut would allow the filter to dip inward from the vacuum pressure, allowing air to slip by on the other side, where the outer cover would meet your cut area.

If you want to cut that area down, leave at least a cm (probably two) of the material at the top edge to retain the filter, and cut a hole rather than a slice.

Something more like this:


(orange lines indicate edges)

Mike, I had my air filter out yesterday to clean it, so I thought I'd get the Stanley knife out.
I didn't cut out as much as you have, it does seem to pull a bit better.
While I had the knife in my hand I thought I would see if there was anything else that needed some attention.

Aha, whats this I've found?

(I'll post pic's in bit, can't find my card adapter.)

Tease

Conform copy of the gts300 spare parts manual pdf's.

There is a différene with the 250's one ? That's it ?

The hole is a native intention for the 300.

Last edited by PhiliP190 on Fri, 05 Mar 2010 19:22:59 +0000; edited 2 times

Sussed it.
(Sorry for the wait glover.)




Don't cut too low or you risk water getting in.

They look the same to me.

There is this hole in the 250 ?

The 1st bit I cut.

Where does the tube, wich is under the air box on the image that i sent, fit in the air box.

I didn't see it in my air box. Normal ?

That's the tube in the middle, it's the one that goes to the throttle body.

The tube in the middle of you photo is this one in yellow, isn't it ?.

Is the other (in green) inside your air box ??

Yeah, you're right it is the yellow one.

It looks like the one that your talking about slots into the piece that we've cut out, which would reduce the air flow even more.

Exactly. I do not remember having seeing it (The green) in my air box. Did you have one in your's ?

Anyway, i do not see how to fit it starting to the hole that we were speaking about...

Mine didn't have one, but if you look closely at the pic. the bit on the end is slotted so that it can be slide into position, then when you put on the outer cover it would be held in place.

I can't imagine what that worm-shaped thing in the middle is. Never seen one!

It is certainly designed to slot into the U cutaway, but then what? The inlet manifold prortudes too far into the box for that thing to bend around and fit on the end of it. Chop 3 inches off the manifold and that might work.

The mystery deepens!

In answer to Drewteague's concern, my filter fits snugly into the cover, and when I have opened the box there has been no sign of it having been sucked out leaving a gap. Anyway, that partition that I cut lines up with the corresponding partition in the cover, so it would play no part in holding the filter in position. I am quite happy that no air bypasses the filter.

Having replaced my exhaust bush, I now find that there is no extra noise associated with my mod, just a slight change in tone at low speed. So how much benefit does this mod give? I think that there is an improvement in acceleration, but it would be nice if PM Tuning could fit it into their schedule and come up with some figures. My feeling has always been that anything which promotes smooth flow can only be good.

Mike

Last edited by Mike Holland on Sat, 06 Mar 2010 09:08:20 +0000; edited 1 time

A smooth flow of air/fuel is definitely the way to go.