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Author Topic: Enlarged Airbox (and other Airbox Mods) for Carbed Monster  (Read 18514 times)
koko64
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« Reply #15 on: August 04, 2012, 09:02:25 PM »

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.
« Last Edit: August 04, 2012, 10:38:59 PM by koko64 » Logged

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2013 M1100 Evo    Street
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« Reply #16 on: August 07, 2012, 04:29:33 PM »

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.
« Last Edit: August 08, 2012, 02:23:01 PM by koko64 » Logged

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« Reply #17 on: August 10, 2012, 02:12:28 AM »

 waytogo

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« Reply #18 on: August 12, 2012, 05:12:14 PM »

Any thoughts on what this mod might do for a carbed 750?
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koko64
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« Reply #19 on: August 12, 2012, 06:56:56 PM »

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.
« Last Edit: August 12, 2012, 10:50:13 PM by koko64 » Logged

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« Reply #20 on: August 12, 2012, 11:44:01 PM »

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.


« Last Edit: August 13, 2012, 05:43:07 AM by koko64 » Logged

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« Reply #21 on: August 13, 2012, 05:09:54 PM »

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.
« Last Edit: August 13, 2012, 07:22:43 PM by koko64 » Logged

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« Reply #22 on: August 13, 2012, 07:17:23 PM »

Here you go!





GK
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JE high comp pistons, bit of porting, open airbox with DP filter, PC3 with custom map, CCW matched injectors, Termignoni cf slip ons, 14:39 gearing.

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« Reply #23 on: August 13, 2012, 07:47:05 PM »

Nice!
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koko64
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« Reply #24 on: August 18, 2012, 07:38:17 PM »

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.
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« Reply #25 on: August 18, 2012, 09:59:47 PM »

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.
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koko64
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« Reply #26 on: August 18, 2012, 10:55:10 PM »

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.
« Last Edit: August 23, 2012, 05:34:46 PM by koko64 » Logged

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« Reply #27 on: August 19, 2012, 03:04:11 PM »

Very interesting & impressive result!
And THX f sharing all that info.  waytogo

Now, where is that old airbox...
« Last Edit: August 19, 2012, 03:06:25 PM by greenmonster » Logged

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« Reply #28 on: August 19, 2012, 03:26:41 PM »

Hey gm!
Long time no hear! I was just asking guys where you've been!
 Grin
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« Reply #29 on: August 23, 2012, 05:01:17 AM »

Very interesting & impressive result!
And THX f sharing all that info.  waytogo

Now, where is that old airbox...

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.
« Last Edit: August 23, 2012, 05:08:25 AM by koko64 » Logged

1999 M750.    "Scrambler"
2013 M1100 Evo    Street
2004 GSXR 750     Track
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