Ducati Monster Forum

Hi All

Recently enlarged my carbed bike's open airbox. Measuring it I found it now has at least an extra liter capacity under the filter.
I had a chopped airbox lid that only had the very top removed rather than being cut right down, so I put a spare K&N filter there and stuck it there with silicon sealant (rough prototype) ;D. A mate of mine is looking into sourcing a schmick carbon version.

I had previously shortened the velocity stacks by about 20mm. This gave me a couple of ponies thru the range at most and a fatter torque curve. The bigger airbox with higher filter required me to open the IMS half a turn, go up one size on the slow fuel jet and raise the needle a notch, evidence to me of flowing more air, but the dyno will tell for sure. I will dyno test it sometime to ascertain if I need bigger main jets. The 165 main jets work well but richen up over the last 2000 rpm on the dyno/EGA so I'm not worried. I can feel a stronger midrange surge on the butt dyno.

With the shorter V stacks I came to the conlusion that they improved air flow in the airbox by giving them more room from the air filter (by 20mm), and the raised filter/bigger airbox gains another 30mm of space between the stacks and the filter. The stock set up has about a 30mm gap from the stacks to the filter but my set up has about 80mm. The goal was to allow the stacks more free airbox space and still air to draw on under the filter. Normally shorter stacks improve top end and longer help midrange (simplisticly), but when the shorter stacks gave more torque right thru the rev range I figured it was not about stack length but airbox size and configuration. Probably due to the very compromised airbox design on a carbed two valver. Also the inlet manifolds are so long a shorter stack wasn't going to hurt midrange, which was proved correct on the dyno. The shorter stacks helped everywhere, which I was not expecting.

I have seen examples of larger airboxes in Europe. Anyone else tried this, or know someone who has in the States?

No input, but I will be watching this thread.  Are you running an airbox or pods presently?

+1 on watching this.  Pics?

I can only think of two people that might have.

Bruce Meyers or Doug Lofgren.

I'm running the airbox with the short stacks and raised filter, so a litre more capacity.  There's a nice area of space above the velocity stacks.  I think it will utilize the volume of the front of the airbox more effectively.
I'm having trouble posting pics but I can email some picks. Feel free to post them.

Thanks, I might email Doug.

I emailed you some photos Howie.

Thanks for the info DP.

Thanks Howie. [thumbsup]

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Hmmm...  Interesting! 

Got any dyno sheets before & after?

I have dynoed the short and long stacks, and pods Vs airbox.  The short stacks worked best. The ega reading showed more airflow at full throttle. It wasn't much but it was enough to justify whittling down the stacks. But every pony counts when there aren't many. I'll photograph a dyno sheet and send it to you if you like.

The side effect of the short stacks was to make airbox removal and refitting easier. It's even easier now because I removed the annoying (and sharp) filter support struts and relocated them under the raised filter.

I will dyno the airbox soon (when there is a break in the weather). I wanted to tune it a bit street riding locally brtween the rain. Not sure yet if the main jets will change.

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Did I get all of them?

Oops on the first one.  Rotate your computers folks!

Thanks heaps mate.
Cheers. I owe you a beer.

You can see in the pic a hint of the orange gasket/seal of a gutted, used oem filter. This seals the lid with it's "integrated" K&N filter. Although the filter is raised, there's still plenty of room under the tank for airflow for the open airbox.
If the dyno test is positive, it's a mod you can do for the price of jetting, a used oem filter and a tube of sealant. All you need is a sharp knife and good whittlin' skills to shorten and radius the rubber velocity stacks (worth 1-2 hp and ft/lbs thru the rev range).

So, when a e you coming to Bar Matchless in Brooklyn to buy me that beer?

Since you have an extra liter I wonder what effect closing the air box a little might create.

I haven't been to the States since '91, but look forward to getting back there. You might get that beer yet. ;D

Maybe I could test with some duct tape.

Very interesting....  easy to do i think...

i believe freezing the rubber helps.  i might try that at some point.  have you tried the blue fcr stacks as a comparison?

I have tuned a 900 that came with hacked blueys, but since I couldn't get them to seal properly in  the airbox I ruled out their use. I wanted to use them, but the air jets were still exposed to the elements, the airbox didn't seal properly and the cut down blueys were shoved into the standard rubber velocity stacks anyway. The air jets got affected by road grime leading to rough running.

Years ago I worked on a 900 with Uni filters clamped over the blueys, but I can't remember much about that except I didn't dyno it.

 The shortened rubber stacks are within 5mm or so in length and max diameter of the blueys. The taper looks different though.

Since it's street bikes, the air filtration is important, but I've seen plenty of race bikes running the blueys with no filter. Someone advised me that the blueys would work best, so if one could find a way to use them with a filtered airbox it would be great.

I have accumulated some advice and feedback from some helpful guys Stateside. Thought it would be good to check on the direction of the project in regard to some important characteristics of the carbed, long manifold 900 Desmodue. It's reassuring to hear you are heading in the correct direction.

Among other things (like the need for larger valve area and raised ports, etc), the long manifold 900 has some intake restrictions that are worth dealing with on a "bang for buck" basis. The long manifolds restrict higher rpm torque and therefore peak horsepower, but give a wonderful low end and midrange tractability (see Brad Blacks 2 valve Ducati comparison, Bikeboy.org). However, reducing the overall intake tract length is helpful for more power through the rev range without going through the hassle of split carbs on short manifolds. Reducing the length of the rubber velocity stacks as shown helps this and gives 1-2 hp through the rev range.

The air filter is also quite close the the stacks in the stock configuration, so cutting down the stacks helps with this also, moving them downwards nearly 20mm away from the filter.

The airbox could be bigger so adding to the volume is worthwhile. Raising the filter to the top of the open airbox lid (if you haven't chopped it right down) is helpful. Not only does this add about one litre of airbox volume it moves the filter upwards about another 30mm above the stacks. I also relocated the filter support struts to under the raised filter (not shown in photo, did it later). Now they no longer slash your hands and fingers when manipulating the rubber stacks into the airbox. It all makes servicing easier.

Finally, keeping the open airbox helps deal with some adverse resonance issues caused by the intake tract design.

The power increases are small and incremental, but helpful. When ponies are scarce, every hp helps. When I dyno the bike again (soon), I'll find out if the larger airbox volume helps peak hp or just fattens up the midrange a little. The bottom end and midrange respone on the road have definately improved with the raised airbox/filter, but this did require more fuel, so that should say something about increased airflow. Whether this translates to the higher rev range or not we'll see.

The good thing about these mods is that they involve modifying stock parts and are relaitively low cost. It's just a matter of rearranging things a little. After the dyno test, I should have some jettng recommendations that accompany the mods in regards to the top end mixture.

Cheers.

 [thumbsup]

 [popcorn]

Any thoughts on what this mod might do for a carbed 750?

I honestly don't know if it would be beneficial to a carbed 750. The mods are aimed at overcoming some of the issues peculiar to the carbed 900s.
In theory they might help, but the 750 power characteristics are different. Only one way to find out, if anyone wants to try. I can put the parts on their 750 and test them.

Got back from the dyno and the results were very encouraging and beyond my expectations by quite a margin.

My poor bike got a thrashing, but it was for a good cause. There were five WOT runs in all and the gains in torque and hp were substantial over the stock style open airbox with short stacks. More testing would have ensued but for the float bowls flooding and my bike taking a piss on the nice man's dyno! The flooding on the last run buggered the A/F reading run. The manual tap saved the day.

The best power run showed 86.63 hp and 68.06 ft/lbs (STD). My guess is that the good torque figures were a combination of the increased airbox volume and Brad Black's dialing in the cams to increase cylinder pressure (thanks to Brad Black). I think I lucked it on the airbox volume, velocity stack length and cam specs for a real grunter. I believe that the short stacks and raised airbox top (K&N filter) helped hold the torque. It goes like a 1000DS motor.
The worst was 84.82 (the first run), increasing each time until the fourth run which was the best (86.63) as the bike warmed up. The last run was 85.47 which was good since the float bowls were just starting to flood. Then I had to get home and then do the school run.

The midrange torque increase was substantial, but there was a torque increase nearly all the way through the rev range of 3-6 ft/lbs. The torque, and therefore power was held really well with peak power at 7500 and still showing 80 at 8500. It looked nearly as good as short manifolds (but not quite). It still started to head south after 8000 rpm with 74 at 8800. The power and torque curves towered above the curves for the pod filters with the same jetting. Altough not as pronounced, it still sat above the best power curves of the open stock airbox runs. The higher the revs the more pronounced it became. I was surprised by how much it helped the top end.

Note that for equivalent SAE numbers you can subtract 1 to 1 1/2 ponies/ft/lbs (maybe 2?). It's the same dyno (and operator) with a locked tamperproof auto correction system to stop cheating. I'd never heard of that.

My Igniteck ignition rev limiter was set at 8500, but it cut in at 8800. Phew! So other users take note.
I used Aussie 98 fuel (BP Ultimate) and my max ignition advance was 34 deg, cutting in from 6000 rpms. With a 944 kit I comsider would running 33 deg max advance.

In summing up it has gone like this:  (dialed cams, JE pistons, FCRs, porting. open airbox and stock velocity stacks) = 80 hp. Short stacks = 81 1/2-82. Bigger airbox/raised filter = 84-85 SAE (or 86.6 STD).

Besides hi comp pistons, dialed cams and FCRs, it's the best performance mod I've made to the old girl.
I didn't test long stacks or standard cam timing with the big airbox. I didn't test bigger fuel or air jets although I took 'em along. I ran out of time. Better give the poor thing a break.

I'll post or email some dyno charts when the kids photograph them. I got photos of the WOT runs, pods Vs big airbox/short stacks and stock size open airbox Vs big airbox/short stacks.

Three dyno charts to follow (thanks GK).

One is the progressive power increase as the bike gets up to its best operating temp and then lost power as it got real hot sitting on the dyno with only a fan. Probably a bell curve type of thing. It survived flooding ok which was probably due to being at WOT (another run after cooling down not shown here).
One is against the worst result which was pods on FCRs (sorry pod lovers).
One was against the second best open airbox run with stock velocity (long) stacks. (I couldn't find the best run which had short stacks, but was about 82hp). But it is the best run in previous pictures (I think). Couldnt find it on the dyno so only my old paper copy.

I have taken the old girl to this dyno on six occasions in total now. That's enough. It was hot and humid in the dyno room but cool outside as they had left the heater on, bugger! The dyno guy (Dean at Dynoverkes), was impressed.
Remember to subtract a pony or two for SAE hp.

Here you go!

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GK

Nice!

I will be doing this airbox mod to a mates Superlight. It has JE 944 hi comp pistons, ti valves, minor porting, Dyna coils, DP light flywheel, full Vee Two clutch, Igniteck ignition, dialed cams, FCR 39s. He is running pods at present. It is a very strong bike, so I am looking forward to seeing how it runs with a more effective airbox set up.

how much to modify some rubbers for me?

do you think the filter could sit the other way up and fit under the tank?  I'd like to test them, but would like to use my filter for both, just because i've seen different filters of these types give quite different results at times.  so run it, swap lid, fit filter into swapped lid and run again.  or maybe push it up from underneath.  i could drop it though the top, but then it'd be upside down and all the crap could/would get sucked out.  would have to use a new filter, dont think I have any new ones kicking about.  would be simpler though.

how long does to take to swap the rubbers?  i guess if you cut those braces out you could do it from the top.  maybe.  sometimes the downtime between runs can effect the power output, ie, it makes more after being run, sat for a few minutes than run again.

I'll bring some over to swap for stockers, then I'll  have a pair for Luke's SL.
 I'll also bring some airbox parts  to play with.

Yeah, I ended up chopping out the filter brace and moving it up under the new filter location, so changing rubber stacks should be easier.

It would be interesting to see what filter works best. I used the K&N because they are commonly used. Another test would be the effect short stacks or a bigger airbox have on stock motors without porting or high compression. Also curious as to the result with stock and FCR carbs.

Something I was thinking about was that you get more control of the dyno you use, but I dont, and have to explain to the operators what I want. I really need one for Christmas. It would be good to have the tests replicated on another dyno. The numbers won't matter, but the difference in numbers does. The change in the shape of the power curves is what was significant so I would be looking for that.

I really thought that the bigger airbox would boost low end and midrange power, but it was from the midrange up that got the boost. It is as if the small stock airbox has as much to do with killing top end torque as the long manifolds. The gain from raising the filter was more peak torque and holding it longer, reducing the torque drop off with these motors. I'm guessing it might have worked well with the porting (and your cam specs). You can feel the spike in peak torque when you roll it on up a hill! Not bad for a 900.

Just finished whittlin' a pair of stacks. Finished Luke's airbox lid. The rest of the airbox is coming from Motowheels.

Very interesting & impressive result!
And THX f sharing all that info.  [thumbsup]

Now, where is that old airbox...

Hey gm!
Long time no hear! I was just asking guys where you've been!
 ;D

If you do it and test it, it would be great to see some dyno charts. Seeing the performance gains (or not) for different bikes with different mods on different dynos would be interesting.

I've just finished some velocity stacks for Brad to test and I have nearly finished another airbox lid. I hope to contact someone who has made an extended airbox lid comercially so I can test it. Mine certainly have a prototype look about them.

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 [beer]

I'm with you... [thumbsup]

I've emailed you some photos and jetting info. Cutting down and porting the rubber velocity stacks is a pain in the arse and raising the air filter less so. I think both are important as the whole might be more than the sum of the parts.

As I said to Brad the other day, it's mitigatng a design characteristic with these motors, the inlet tracts could be shorter and the airbox bigger.

I'm looking for someone to make a nice carbon airbox lid with integral filter. Then I can give up cuttng and gooping. I'm not that crafty.

Got them...thanks.

Hmmm...c/f lid?

A mate of mine knows someone who used to make them. Got to convince the guy to start making them. I don't even know what they look like yet. Using the stock parts only costs a couple of hours time and a tube of goop, but "porting" the stacks takes patience and concentration.

Visited Brad today and showed him a finished enlarged airbox (for a customer) and swapped him some "ported" stacks to test. We discussed ways of acheiving a better airbox, etc (really better done over a beer than me distracting him at work) ;D

Brad will test the "ported" stacks against stockers on his 750 engined M600. I should also have an enlarged airbox lid for him when it's time to test. So there should be some answers for you 750 guys. The motors have different power characteristics and issues so it will be interesting to see how the mods apply to that motor.

Curious as to why cutting the stacks is difficult. What am I missing?

just a thought, but since the stock match up and it's a funnel, cutting it would cause a mismatch. Whereas starting with a different size funnel and cutting it down to match would make sense?

If you check out the pictures on page 1,  you can see that it is possible get a good radius and fit.

So you get a sharp knife, cut them down and then carefully scrape or whittle away material, then sand down or scrape the angles to get a nice radius. Take off too much material and they're ruined. Got a price for new stacks at the dealer  $50 a piece! Used ones half that.

It really is porting in a sense as you have to carve and shape a good radius to promote airflow. It is a difficult material to work with and requires patience.

Cutting the stacks down to where they enter and join the airbox works well. They end up about 18mm shorter and the widest part of the funnel is 5mm greater in diameter than when in stock configuration.

Hard to explain, but when you have a go at doing it you know very quickly!

what about using a dremel and a cutting stone to whittle it down?

Worth a try for sure, maybe with a fine sand mop to finish. But thats after cutting the extension off with a scissors/knife.
I was cautious using static tools because it was like tattooing, the medium wasn't very firm and you can't clamp it. Its holding it in one hand and the tool in the other. I found foam sand pads great to get the tactile feedback and not go too far, to avoid ruining it.

Brad suggested freezing the stacks, that could help before using the dremel. I put mine in hot water first and them cut them down with sharp scissors. Then peeled the first angle of the radius with a sharp filleting knife, then some good ol' fashioned whittlin', then finished by sanding for the "porting" .

I reckon at least half an hour to an hour on each stack for the last set, but the first set were done in half that time and looked better. The rubber carved real easy.

Strangely, each pair of stacks has been different to work with, maybe due to heat cycles, age, rubber batch, etc.

Edit: I am porting another pair now and are using different sand paper to finish it off. It is coming along quite easily now that I'm game enough to use some heavier sand paper before finishing off with a fine foam backed sand paper.

The airbox mods definately flow more air.

With the extra airflow, I also needed to increase the slow fuel jets another step with 55s. I needed to open the slow air screws a quarter of a turn to 1 3/4. I have the IMS at 1/2 a turn. Really needed a richer needle root diameter, but slow jets are cheap. Low speed tuning is often best done with test riding than on a dyno. It's important to test for ridability and feel at small throttle openings rather than theoretically correct numbers on the dyno.

With a bit of juggling on the jetting it idles well, has fierce pick up and is smooth at backstreet and cruising speeds.

Edit: (The bike has significant modifications including a light flywheel and portng of the inlet tract so don't take the following statement as being just due to a bigger airbox).

Wheelies. Second or third gear. I don't try them in first gear!

Speaking of airboxes, take a look at the EVR carbon airboxes at Motowheels.
Very impressive. Alas, nothing for the older desmodues.

I'm not aware of anything EVR for a 2V.

There is an impressive looking large airbox with carbon velocity stacks for the Hypermotard 1100. It appears to have a substantially increased volume. I cant figure out what type of filter it uses or where it's located. Not even sure where the air intake is.
Its in the engine intake section. $1500!

Fitted an enlarged/raised airbox with "ported" velocity stacks to a 1992 Superlight today.

Motor is a 944, skimmed head, (correction: checked with builder),  no porting, Ti valves, dialed cams via adjustsble alloy pulleys (by Brad Black), FCR 39s, slip on pipes and modified header cross over, light flywheel, Vee Two clutch, Dyna coils and Igniteck ignition.
Boy it's got some compression! A very punchy engine.

For those of you considering enlarging the airbox on an SS/SL, there is less space and clearance under the rear of the SS tank and at the front of the SS frame. It fits, but it's a tighter fit than on the 888 framed Monster.

Now to tune the carbs and ignition. Looking forward to putting it on the dyno.

did you dial the cams in yourself?

I was thinking about dial in the cams myself, but im unsure of the procedure and can't seem to find it anywhere.

Once i get the bike back im going to do the valve adjustment at ~2,000 miles and dial the cams in then go for a dyno adjustment on the map.

The cams were dialed by Brad Black. I may ask him to put them back to stock because the cranking compression is so high. Maybe he will give me the spec to move them back a notch.
I would suggest talking with the tuner about setting them with your goals in mind. It wouldnt surprise me if the bigger evo cams give a softer midrange, smoothing things out a bit for the dangerous confines of NYC.

Update.
Brad tested long and short stacks on his 750 today. After looking at the chart I would not bother trying short stacks with a 750. There was hardly a difference. This is most likely due to the relative characteristics of the 750 and 900 motors according to some notable tuners. It would be interesting to see if the stock sized airbox is large enough for the 750 capacity. I believe I have demonstrated that it lacks sufficient volume for the 900 capacity, but I wonder about the 750.
I'll discuss the test further with Brad and see if he can post some results when he comes back from his break.

 Edit: For more on this see bikeboy.org which has a link to this thread. The short stacks dont help a 750 like they do a 900, but the 750 is not as badly restricted by the long inlet tract as is the 900.

So if you have a 750, dont bother to shorten the stacks like I would for a 900.

One thing I haven't tested yet is comparing long and short stacks in an enlarged airbox.
Cheers.

For Brad's dyno chart on short stacks for a carbed 750, see the thread "have you dynoed your bike lately"?
The short stacks appear to fill a few dips in the curve, but don't give a significant increase in horsepower. Interestingly, the a/f trace is also richer.

I was just curious if only the modified airbox lid was tested compared to stock instead of the velocity stacks on a 750.

 Brad tested the different length stacks. Next time he can borrow my extended airbox lid. I'm curious to know whether it will help a 750 as much as it did a modified 900.

The dyno charts show that the long manifold 900s start choking at 7000 rpm and the extra airbox volume and modified layout helps mitigate this somewhat. The 750 doesnt choke like this, so I dont know if its a worthwhile mod for 750s. They just dont drop off like the 900s.

Only one way to find out! Try it and let us know.

I'd considered taking it a step farther. Instead of using a stock lid I had considered fabbing my own lid from aluminum with a flange on top and nice trim ring to seal the filter to the flange. Only problem is I have to find access to a box brake to bend the aluminum then somebody to TIG it for me.

Be great to see what you come up with.
If you like I could email you pictures of what I did if it helps with your project.
I'm waiting to see what He Man comes up with for his S2R 1100 evo combo.

Alternatively, just do the box like you describe and make it an extension under the stock cover.  Just 1" increases the volume by like 20-25%

You'd need longer retainers.  Or permanently attach it to the stock lid and add divots for the oem retainers.

Hi comp 944 Superlight is ready to go on the dyno. It has the airbox mods described in this thread. I am hoping the bigger airbox will help the motor hold its torque to give good horsepower numbers.

JE 944 pistons, with full, unskimmed crowns, skimmed heads, advanced cams so it has very high cranking compression which is taxing the poor old starter. Edit: believe it or not, no porting. Considering it has Ti valves, I would have put the money into porting and cleaned up the stockers, or got 44 inlet valves. This was a surprise to me.

I may retard the cams back 7° to stock or will probably get some ST2 or 900ie cams for it  [evil]. Some longer duration cams will ease the low end/midrange corrected compression and cranking compression (hopefully). The hotter cams should not hurt the midrange with the compression it has. This motor in theory, should be able to take more cam.

If my 904 makes 86.6 std hp and 68 ft/lbs, then I think this bike should beat 90hp and 70 ft/lbs on the same dyno.

94hp and 72 ft/lb

winner takes the bike  [evil]

We have a lottery!       [laugh]
Ok 94/72 locked in for Raux.
Oh, to be clear, we will go with sae hp.

On a more serious note.
The owner of the Superlight said that the volume and note of the enlarged airbox sounded good and was an improvement over pods. Not as loud but a much deeper note.

Dyno test for the Superlight is posponed. Owner of the SL is looking for 900ie or ST2 cams. That's the plan.
If anyone has some to sell, let me know.
Bigger cams, some work on the starting system (starter may have burnt out yesterday), then to the dyno..

EDIT:
Starter will be rebuilt and beefed up, possibly with the Monsta 4 pole mod.  Thanks Monsta. I'll see if my sparky can do it.
Sprague to be repaired.
Wiring to be beefed up some more (stage two!)
900IE cams on their way!

Well, I found out that the 944 wasnt ported by the builder (I dont know why considering other expensive mods were done).

Checking the jetting and  baseline power runs it made 80hp and 65 ft/lbs. We were disappointed, but it is what you would expect from an unported hi comp 904/944. The bike is incredibly strong in the lower rev range and stomps mine up to 5000rpm, (no surprise with the compression it has), but from that point my ported 904 is stronger. My enlarged airbox didnt do much either, as greater air availability is only beneficial  to ports that can use it. It didnt ping, so at least I got the timing right.
As many have pointed out, the 900 heads are the bottleneck for horsepower gains in these motors.

900ie cams go in this week, we'll see what it makes next time and if they work in conjunction with the airbox mods. The 900ie has, besides the longer duration cams and shorter more tapered manifolds, a greater airbox capacity, so I'm hopeful. I fear that without porting we may have just traded some midrange for easier starting. The compression being so high should mitigate that happening. We'll know soon enough. I'll ask the dyno guy to overlay some runs to compare.

Who knows, the owner may want the heads ported and maybe go up to FCR41s.

Well the 900ie cams went in (thanks Rowan).
I put in a new sprag bearing, swapped the electric fuel pump for a Monster vacuum pump, tweaked the carbs and beefed up the starter wiring. The rebuilt starter works well without the electric pump drawing power. With only a 300W alternator the absence of an electric fuel pump helps not only starting, but keeping the Shorai battery topped up to 14Volts. It struggled to keep the Li battery at 13.5 Volts.

Bike starts great.

Curious to see how the big cams work with the big airbox. The owner is talking about another dyno run. He's also talking about porting.

Since this relates to a new thread and I had questions asked about this, I thought I'd raise this one from the dead rather than redo pics and info. This goes through the process in more detail of how to "enlarge" the airbox on your carbed 900. It's not really made bigger but rearranged in it's layout to increase the sub filter volume by about a litre and make all the box contribute. If your bike doesn't have porting then its a waste of time. I found the shortened rubber velocity stacks made airbox removal and replacement easier as did relocating the razor sharp filter support struts. Servicing was easier. The AFR for the shortened stacks showed a more stable graph for the 900 allowing bigger main jets to help WOT midrange without going crazy rich at high rpm. The opposite was true when I tested pod filters.

My conclusions and theories to explain the power gains may be better understood, explained and tested by others with a better theoretical framework. My majors were in the social sciences not engineering. I ran out of dyno money pretty quickly trying to learn stuff. It would be great if people test these mods to gain some repeatable data as I am down here in Oz and was testing with Oz fuel on local dynos, using a modified 900.