Modern Vespa

Finally the airbox modification is ready to go. I have about 45 days of riding with it. It has been on KennyD's and now on LM15's MP3. He is the proud owner of the first airbox modification.

Essentially all that is done is to replace the restricted air inlet tube with a sheet of plastic that provides the isolation between unfiltered and filtered air. By enlarging the front plate inlet air restrictions are reduced. The net is an apparent performance improvement from a standing start all the way through the speed range. High speed cruising (70+) is easily accomplished with less throttle applied.

My initial observation with my 400 are that WOT speeds from a standing start gained 5-7 MPH in about 100 yds. The same with mid-range acceleration. I am currently riding without the modification and it is back to being somewhat sluggishin the mid-range and very little acceleration over 65 MPH.

I have the plates available for sale seperately or you can send me your airbox and I will modify it for you.

Right now the plates cost $30.00 each. This price will change depending on order size. The plastic is not the expense! It is the setup costs. The plates are cut on a CNC waterjet machine. The setup costs are somewhat variable but will be in the range of $200 per setup. I had eight peices made for the initial run and have three currently available.

If you want me to make the mod for you the cost will be $50.00 for the plate and the mod. I think I deserve something for my time since it takes about two to three hours to complete.

I don't know yet what shipping will cost but I will work that out yet this week.

One thing I do know is that this mod will work on all Master 4/500 cc engine CVT setups. So I guess that would include Piaggio's and the rest that use this engine/tranny combo.

Well, what do you guys think? Interested?


This is what we start with.

The inside of the airbox. Remove the rubber tube and clamp.

The air tube and clamp can be discarded.

Plastic is removed from the front plate restricting airflow into the filter.

CAUTION: do not remove any more plastic from the top of the restrictor plate that is required to remove the top of the fitting for the rubber tube.

This is the isolator plate that seperates filtered from unfiltered air.

The plate is secured with glue and left to cure for 24 hours.

When the job is done, this is what it looks like from the outside.

Does the noise level change?

Very nice. If that plate is made of ABS, You could use black plumbers ABS cement to make a VERY solid connection.

Only slightly louder. Nothing like the noise from the K&N. One other enhancement is to use the Malossi air filter. It is much more open and provides an even greater improvement. You will actually feel the difference again.

Looks good.

What's the plate material, and what glue did you use/recommend?

Gonzo

The plate material is ABS and the the glue is PVC / ABS solvent based adhesive typically used for plumbing pipe. You will want to use a compatible primer before applying adhesive.

change really interesting, well done ..!
simple and effective.

I was the fortunate one who has AirBox mod s/n:00001

PonyDrvr put it on my MP3 500 at The Gathering and I must say this is the "blue pill" for air boxes. I have the Malossi Red air filter installed and althought I was not able to do any base line metrics, I can say that:

This thing sounds great even with the OEM exhaust and runs even better. I rode with it for a day around the mountains and valleys of Tennesse and then did a two ride back to Fort Lauderdale with it.

My impression (remember I rode up to The Gathering and several day rides without it):

Fantastic! Much more throttle response, from standing start to acceleration at speed on the interstate (for passing of course). I believe better gas mileage, but I cannot document that now. Also, much more of a baritone from the standard exhaust. The throttle response is better, acceleration and backing off.

The pictures that PonyDrvr posted do justice to it and very much show what was done to create the modications.

I am open to suggestions for creating a baseline for comparing before and after.

I have received an Akrapovic exhaust, but have not installed it yet.

I have the fuzzy washer, but have not installed it yet (waiting for variator tool I have on backorder from Scooter West)

I am planning on putting in Dr Pulley sliders, 17 grams at the sametime I install the fuzzy washer.

So I could have two tests, one with air box mod/Malossi filter and Ak and an additional one when I install the fuzzy washer and Dr Pulleys.

Any suggestions?

I will go on the record and say that the two most "must have" modifications that one should do first are the UFP/XL and the PonyDrvr Air Box modification. These are relatively inexpensive and provide many more times the "return on investment".

Didn't realize it was that restrictive until I saw you removal of the pipe!

Oh man. I should have checked that out when I met you at the gathering. So you put that divider in and put the air filter back in and that is it? I'm down. Look for my PM soon.

If you can quantify the mpg increase it would be much appreciated. Good job.

Sign me up, but I'm holding off until the weather is less cooperative for riding . It has been stinking gorgeous around here the last few weekends.

With the understanding that individual driving style will influence your results.

For me, prior to the mod my distance traveled on the tank until the warning light came on was 125 to 135 miles. After the mod I was typically at 155 to 170 miles. I did a couple of group rides where top speed was only ~45 mph and the avg speed was 27 mph for a full tank. I went 188 miles before the warning light came on.

That is just me your results may be different. While I don't ride aggresive most of the time, I do like to keep moving quickly. I'm definitely not a Sunday morning cruiser.

I would have thought it would be the other way at first. But then I realized that you are probably going at a higher rpm with more air and the same amount of gas... Good, my excuse will be, "honey, I am going to get better mpg!"

and that will be the truth too. The added benefit is increase performance.

Wow, a 25% increase is huge. Sign me up. Let me know how to pay you.

I like that the sound is not as loud as a K ad N or my Uni. I feel like I have never really even heard my Giannelli pipe, because all I hear is the UNI filter.
The only downside is you still have all those recessed screws with the OEM airbox, such a pain! But nothing is perfect....
I will recommend this to my friend Bob, and might consider it myself!
If there was a small improvement it might be to stretch a prefilter of some sort, like the toe of a pair of hosiery, over the intake hole, just to keep the worst stuff out.

That's not really necessary. As long as you seal off the chamber with the restrictor plate, then the filter (which does a much more thorough job than a K&N/UNI) will do all the filtering that is needed.

This is interesting because I am about ready to scrap my K&N Mod. Loud, and it passes too much oil out the breather, which ends up dripping from the bottom of the filter. (The breather pipe passes through a fuel filter, and then there is a restrictor inside the hose just before it attaches to the intake.)

My parts are ordered for a different approach.

I'm leaving the stock intake tube in place.

Over the recessed area on the outside I'm going to try and install a stainless steel marine clamshell vent cover. It will point down and forward. Under the vent cover I'm going to drill holes.

I believe the intake tube in the stock design is like that for a reason -- most likely to accelerate the air so that dirty air gets deeper into the prefiltered chamber. The mod I'm working on reduces the velocity through that intake tube, but allows air to enter the filter chamber more to the rear. That should distribute the dirty air across the filter.

I'm also getting the Malossi red air filter.

I wish that K&N made a drop-in flat filter element, but you can see it would be a design and manufacturing challenge to seal the edges, seal the center hole, and get the filter to work properly with all those stand-off pins inside the box.

Hard for me to picture what you just wrote. Please post pictures when your done.

What is the clearance between the isolation plate and the slot outlet from the air/oil separator that is in the other half of the air filter box? (This may only be a factor on USA MP3s -- and maybe not all of them.)

I believe that the reason for the routing and mounting of the air inlet tube is to allow air from the breather to enter the filter box on the "filtered" side.

Please note that this mod cannot be done on the 250. The air box is different. So all of us with the small MP3's are out of luck...

I am not sure I follow all this engineering, actually, I am sure I don't!
But others here have mentioned finding quite a bit of junk sucked up into the
airbox, as we found looking in my friends 500s airbox recently. Even though it is filtered, it was still a mess in there. If the air is being sucked in, seems better to keep some of that out to me, just for the sake of not having to clean it now and again. What I was thinking anyway.
I will leave it to better gear heads than me to question whether the stock filter does a signifiantly better job of filtering than the Uni or K & N, but if this setup works and is quieter, then that is an improvement to my way of thinking, enough to consider changing.

Just heard from my friend Bob. and we are in for one. I will PM you fpr details.

Do you have a huger over the rear wheel? That helped keep stuff out for me.

You have no idea - you look into the end of the pipe and it's barely big enough for your pinky.

I had the same thought last night. About a month ago, I bought an extra airbox to experiment with and came up with the exact same idea of removing the pipe and installing a barrier plate. After making a template, I saw that the plate would cut off that vacuum slot in the breather end which would result in the breather tube becoming backed up. I then saw Ponydrvr mention that he came up with an airbox mod that worked really well, so I shelved it until I saw some more details, no sense in reinventing the wheel.

After seeing this post yesterday, I pulled the box and template off the shelf and made a plate with some 7/32 thick ABS plastic that I had on hand, and then remembered why I had shelved it. The slot would get plugged.

Some thoughts I had on this were that you could drill a hole on one of the other faces of the breather end box or you could form the separator plate into a curved surface that would allow the intake flow to still act as a slight vacuum to the breather box slot. The tricky part is to make sure that the oil mist isn't facing the intake air to keep as much of it out of the intake as possible; instead allowing it to collect on the walls in the airbox and move down to the collectors.

The other option is to reroute the breather to an external filter, but having the original plumbing is part of the reason I wanted to keep the airbox on in the first place. That and noise control.

I think once the breather slot is addressed, then this mod will be at 100%.

I considered that approach as well. My goal was to improve airflow into the engine without the noise of the current state of modification with the K&N types. It also allows the bike appearance to remain as designed.

I know from experience, that even without a rear wheel hugger, deep water, heavy rain (torrential style) will not keep the filter from doing it's job. I experimented with two forced air induction schemes and found that both tended to cause operational issues causing the motor to lose power and finally quit while riding.

My recommendation of the Malossi filter is a direct result of those trials. Unfortunately, with the forced induction, moisture was able to pass through the Malossi and cause problems. The OEM filter acted like a sponge when absorbing water,and literally chokes off the air resulting in complete engine shutdown.

Some of the folks at the recent SE Gathering witnessed the water run out of my cover when initially removed for discussion. This water caused no operational issues at all. It was from the most recent ride in the rain prior to the gathering. About a week prior.

I trust this gives some insight to the testing done. If you have more questions or comments post here or send a PM.

I have sold all of the initial parts that were made. I will collect orders hopefully for a larger quantity that will allow the cost of the plate to be reduced. A thirty piece order will allow for a $20.00 cost.

The best payment is via the "Personal Payment" on PayPal. My email address for the payment is : ponydrvr@twc.com .

Those of you wanting me to make the mod for you - add the cost of your shipping charges to the payment then your cover will be returned in your container via the same method. If you want it returned on a priority basis.... I will have to look into that..

Last edited by ponydrvr on Thu, 05 Sep 2013 13:15:01 +0000; edited 1 time

I'm curious why you took the path of no return by hogging out the plastic on the inlet. Seems the resulting hole after removing the pipe would be plenty big enough.

Tried that too. Once I found that more opening was needed; in for a dime...in for a dollar! It makes a big difference. Besides I had a spare airbox to work with.

Really, I was trying to get the opening as large as possible yet slightly smaller in area than the inlet hose . This keeps the pressure differentials in the box and inlet system in the proper order for things to work right.

the clearance is 15mm

if you look at the pics ponydrvr post the only thing this mod is doing is removing the restrictive inlet tube and opening the intake hole to 1 and 1/4 inches or little more. it has nothing or does nothing to the oil collection coming from the crankcase. there is more than 15mm of clearance from the plate to the oil collection box.

I'll take another look this evening.

mine shipped today! (yes, I'm geeked about it)

If there is 15mm, that should be plenty. My understanding is that the slot feeds breather air into the filter box. Since the hole that leads from the breather hose to the air/oil separator labyrinth is something like 3mm or 4mm in diameter, 15mm clearance on the other side should be ample.

Were you asking me? Hard to tell from the post. However...

Attached is a quick and dirty shot of the concept.

Shown taped in the approximate position is the first vent cover I considered. This can be had for around $2 if you shop a bit. It is smaller than I wanted (1-3/4 inch Long x 1-5/8 Wide x 7/16 High). I got it on Amazon, but had to pay shipping.

I've ordered the next larger size (2-1/4 inch Long x 2-3/16 inch Wide x 9/16 inch High -- capable of covering a round 1-1/4 inch hole) from Amazon and it's on the way. Cost was $10.31 and "free" Amazon Prime shipping.

Once riveted in place, I'll just cut/drill some holes from the inside.

So either of these could be purchased, shipped, and installed for about $10, plus the cost of three stainless steel or aluminum pop rivets.

The opening will angle towards the front. This is not to drive air into the filter box, but rather to not turn the vent cover into an air eductor sucking air out. Rear facing or down facing (opening parallel with the street) might induce that. The main purpose for the vent cover is to keep water out when parked.


Small clamshell air vent taped over MP3 500 air filter box -- demonstrating the concept. A larger cover will be used in the final version.


Last edited by LJClark on Wed, 28 Sep 2011 10:51:51 +0000; edited 1 time

Thanks LJ! That's a good idea too!
Are you actually going to do the mod?

I took a closer look this evening and you're right, there's some clearance there, and it should be enough to provide a slight vacuum so that the box functions as designed. The way I had made my template, was more along the edge of the cover, which would have left very little to no clearance whatsoever.

This looks like a good mod to me.

LJClark, I like how you've managed to find a scoop that follows the curves. I'd keep it simple and just use a small bolt with SS and neoprene washers and a nylock nut instead of the pop rivets.

Yep.

I also ordered some S/S pop rivets from Amazon and everything should arrive Wednesday or Thursday.

I figure to drill each hole, cut away any plastic bits (such as reinforcing web) that interfere with a flush fit on the back side of the rivet, and then squeeze the rivet over a backing washer.

After the cover is on I'll take a drill, rotary tool, or hot knife tip and cut holes between the reinforcing webs.

I have a Malossi filter element on order from Scooter West, but shipment was held up waiting for the variator tool I ordered at the same time. That will probably show up next week.