Enlarged Airbox (and other Airbox Mods) for Carbed Monster

[koko64]

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.

[He Man]

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.

[koko64]

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.

[koko64]

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.

[koko64]

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.

[MotoPsycho]

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

[koko64]

 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.

[MotoPsycho]

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.

[koko64]

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.

[ducatiz]

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.

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.

[koko64]

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  . 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.

[Raux]

94hp and 72 ft/lb

winner takes the bike 

[koko64]

We have a lottery!      
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.

[koko64]

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!

[koko64]

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.