airbox intake mod

marvin

I question how much air will actually flow into the airbox given the restriction of those small filters and the internal resistance of those tubes.

jr60

You're probably right Marvin but it will prob not flow any more or less than the std setup - at least the tubes are going directly to the airbox and not half way around the bike before so!

It will feed cold air into the airbox - which is what they are meant to do - but not under pressure - thats all the org tubes were - cold air feeds.

One criticism Robert - why blue 😄

Johnny

marvin

jr60 wroteYou're probably right Marvin but it will prob not flow any more or less than the std setup - at least the tubes are going directly to the airbox and not half way around the bike before so! It will feed cold air into the airbox - which is what they are meant to do - but not under pressure - thats all the org tubes were - cold air feeds. One criticism Robert - why blue 😄 Johnny

I'm guessing that because of the restriction of the small filters that it will actually provide less cool air to the intake than the standard setup. Just my guess, no factual information here!

got2dv8

Well, since I cannot provide a road test I did at least use my air gun to blow air into the front intakes to test the setup. The air comes out very nicely from each filter. These are high-flow filters similar to the K&N and although they are small, they provide more area than the hose face opening so the only thing impeding flow is the air passing through the filter media. They basically act as defusers. Insted of the air blasting straight into the airbox, it is spread out as it hits the filter roof and comes out 360°. I may at some point try some foam sock filters shortened and zip-tied to the air hose to see if they offer more flow.

Robert

Mr.R

Well I think Robert's job looks very neat 'n' tidy.
... and I think with these new shorter/more direct feeds, the top removed it's got flow more air than the OEM set up IMO.

Wether it actually needs this extra/modified feed is another matter?

Steve R

jr60

Hey Robert, looks like your in good company with your design - see these pics I found from another thread of a SP4S - I presume this was the org setup on the SPS as the pics are from a restoration that has been carried out to the last detail (except for the the blue hoses!) ?

Johnny

AJV

Nice detailed photo's showing the SPS set-up. I've just been looking at that Japanese sit as well..

Without airfiltration I wonder how long the top end would last - any high milage SPS's out there I wonder?

The Desmoquattro Performance Book by Faloon is well worth a read on airbox mods. Neil Spalding of Sigma Performance contributed an excellent article. The main restriction is the volume of the airbox, not how you get the air in. It gets quite technical as air resonance comes into play so best read the article for yourselves.

Best performance mod albeit for very little gain is the Corsa airbox (bigger volume) but this also presents a problem of what to do about air filtration.

Andy

sp2 boy

AJV wroteThe main restriction is the volume of the airbox, not how you get the air in. It gets quite technical as air resonance comes into play so best read the article for yourselves. Andy

Air resonance...I am sure that Griff was making noises about that subject a while back...last I heard of Griff was that he was clearing his garden trying to avoid the snakes!

Anybody know if he's still breathing?

Mr.R

Well here's my thoughts on it...
I've seen several SP(4)S and SP4's with this intake mod, lets face it the SP(4)S's were intended to go racing so they weren't worried about worn out topends.

Now here's my personal experience...
The seal on the front of my OEM '92 aibox with it's cut down lid wasn't that great at the front and crap (I found sand inside the airbox 😯 ) got into it, this crap wore the front bore in particular fairly badly, badly enough for me to put another new bore and rings into the motor the last time I freshened it up.
...and it had only covered several thousand miles.

I wouldn't expect any 851/888 using this style of unfiltered intake to last very long before it was FUCKED!

On another note...
The airbox's on most off these 851,888,926 and AMA 955's bikes aren't a sealed/pressurised unit, (certainly not on the SP's and Corsa's) so resonance makes cock all difference and it isn't too small/a restriction to making very healthy power...
A fact I think I've well proven with my old 851/916cc "Bitsa", this mildly tuned old nail makes 128rwbhp at 9,200rpm on pump petrol, this's only 7 rwbhp short of what Troy Corser's AMA winning 888/955 made at a lot more revs.
...and I don't think his bike used a fully pressurised system.

Steve R

AJV

Steve - cant say I agree with on this... back in the early 90's the benefits of a sealed airbox and correct air resonance wer'nt fully understood by motorcycle technicians. Ducati cottoned onto the benefits along with the Japanese hence the 916's sealed airbox and all later ducati models. It's a fair assumption to say had these principles been understood the 851/888 & Corsa models would have run sealed airboxes.

The limitations of the small airbox on 851 models has been understood for many years. Lets not forget Neil Spalding is a rather clever 'modern' engineer with access to equipment home mechanics can only dream about. Neil has proven and documented his finding on this matter and progressed to become one of the leading experts on MOTOGP technology.

Airbox design including volume, resonance etc. is a major factor in motorcycle performance tuning - FACT.

Andy

guy851

sealed airbox

Well....from the little that I know the later 888/926's saw a big improvement using a large and sealed airbox and the 916 series really utilised this to big advantage getting rid of the cross brace was phase one and then the SPS/SP5 and indeed the Foggy Rep frames went to great lenghts to make more sealed airbox space

Nobody else in the "modern" age utilises an open airbox they are all sealed calculated spaces

IMO anyway

Guy851

Jasper

Now i used to have this.I didn't know what it was until I sold it!! It was a seled airbox for a 926 that was running in BSB. It was no good to me at the time as a Corsa tank was out of my price range and it didn't fit my standard tank.

sp2 boy

Well the tank letterbox cover air dam would help to settle the air under the tank but what you have shown there Jasper would improve upon that no end. The later tanks were closed at the front and are usually sat with a foam pad around the chassis top tubes in an effort to seal the area, so there was little need for that cover.

Ducati were obviously getting there, the 916 frame did not use the top chassis rails in the same manner as the 888 did for locating the airbox, in fact on the 916 it's tank sat on top of the airbox sealing it with the exception of the air runner inlets on both sides.

Mr.R

AJV wrote

Yes I know this but I was talking about the 851/888's, Ducati with the 916 era bikes then went down the route of fully pressurised airboxes, the unsealed airboxes on the 851/888's were good enough to make in the mid 130's rwbhp.

As for Neil Spalding my personal oppinion is that he's a no nothing boring twat, I came to this conclusion after listening to his drivel on the MotoGP commentary, I think he probably had some clever people working for himi at Sigma though.😉

Steve R

P.S. I generally watch the GP's with some very clever boys who all agree with me.

got2dv8

The truth of the matter is the 851 wasn't designed to utilize a sealed airbox. The frame made sure of that. The 748/916 was designed to do so from the ground up and even then needed to boost the airbox volume at one point by using the Kyalami frame. You could make the 851 faster and more powerful by strapping a rocket to the back too... but like a sealed airbox, it's a moot point.

And for fear of Steve quoting his output figure for the 100th time 😎 , many people and racers using 851/888 have made more than enough hp to be happy and win championships without the aid of a sealed airbox.

Onto earlier posts... Interesting setup on the SPS. Here was my influence for my airbox mods. I would have done it this way buy the airbox sensors took up the space, so I was forced to put one intake in the rubber thingy which in the end I prefer as each intake horn has it's own cold-air source.

Robert

sp2 boy

got2dv8 wroteAnd for fear of Steve quoting his output figure for the 100th time 😎 Robert

😁 😁

I wondered whether it was only Spike and myself that had noticed repeated record playing!

😁

got2Lev8

Well, it only took me 4 years to find an alternative filter for my intake mod. The original Airaid filters which were installed inside the airbox fit in the id of the air intake tube and were pretty restrictive due to a smaller opening than the intake hose. I took a chance and ordered some air filters with a 40mm mouth which fit on the od the the tube(s) and they fit/work quite nicely. Now the front intake charge isn't restricted by a reduced air filter size and opening.

Robert

chris ardern

Air box tubes.

This is my new conversion to get more air into the front of my air box. I kept the old air tubes at the back and redirected them down by the radiator and the new blue tubes come directly from the front faring holes to the front of the air box. I haven't ridden it yet but I hope it works.

tboooe

chris ardern wroteThis is my new conversion to get more air into the front of my air box. I kept the old air tubes at the back and redirected them down by the radiator and the new blue tubes come directly from the front faring holes to the front of the air box. I haven't ridden it yet but I hope it works.

Do you have any pics of the arrangement?

chris ardern

Can't upload from my iPhone.
WhatsApp me on
07823337174
I'll show you what I've done and maybe you could put the pics up for me

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