Triumphrat

Calliway · 01-11-2009, 11:02 PM

I took off my air box tonight to put in my Bella Corse ARK.

I found that I didn't have to hack it apart or even remove the rear tire. I just undid all the bolts then removed the left hand side panel. I slid out the left panel then lifted the rear end by the frame and slid out the rest of the air box. Fender off, shocks off and left hand can off.

So we talk about how restrictive the box is and since I had it apart I took some pics to post.

The inside with left hand panel off and air filter out:

The oval that feeds both carbs. All the air has to go through this tiny oval after going through the filter:

dkreidel · 01-11-2009, 11:15 PM

The air that passes through the baffle only has supply one carburetor at a time. I think the area of the baffle "slot" is about 20-25% greater than the area across the venturi of one carburetor. This is not really an accurate comparision, as there are flow (delta P) losses across the "slot" and through the venturi. One doesn't necessarily want laminar flow through an intake; often a flow bench that measures cfm at a given valve lift can be in improved by inducing turbulent flow. There is no doubt the flow through our airbox is turbulent, but it starts to calm down through the intake rubbers. CV carbs don't like turbulent flow; direct operating carbs (flat slides or round slides) aren't bothered too much by turbulent , non-laminar flow.

Dick

Sal Paradise · 01-13-2009, 06:43 AM

Yes, but the air pressure must go down on the inside of that plate as you reach high rpms, don't you think?

Kind of like running an extra 5000 feet above your current altitude.

dkreidel · 01-13-2009, 07:19 AM

Quote:

Originally Posted by Sal Paradise

Yes, but the air pressure must go down on the inside of that plate as you reach high rpms, don't you think?

Kind of like running an extra 5000 feet above your current altitude.

Yes, there are definitley some flow losses. By meauring manifold pressure and seeing how close we are to ~~1092 mm Hg (29.92" hg) at WOT we can really measure how efficient the many intake alternatives really are. It may be very restrictive, or maybe not. If it is indeed like adding 5,000' of altitude the MP will read something like 21 or 22" of MP. The manifold pressure gage doesn't have favorites :>)

Dick

Sal Paradise · 01-13-2009, 08:51 AM

I don't know what the pressure difference would be, but it would be significant. Probably not equivalent of 5000' of elevation. I just made that up.

But that is the reason you need different size jets, isn't it? As you increase the pressure or (decrease the vacum), it pulls less fuel out into the carb and so you increase the jet size.

tribon865 · 01-13-2009, 09:00 AM

hi does anyone no if there is any difference in performance by removal of the airbox on a efi bonnie

propforward · 01-13-2009, 10:14 AM

British customs did it, and got a significant improvement. A remap of the efi is required. Check this dyno chart:

http://www.triumphrat.net/twins-tech...ml#post1149525

They changed pipes as well as removing the airbox.

mikeinva · 01-13-2009, 01:40 PM

The baffle may limit flow but ,I think what hurts flow the most is all the turns the air must go through to go in and out of the box.If you have ever done any flow bench work you know how bad sharp turns kill flow.Little things can mean alot.The 4 valve heads on these bikes want all the air they can get.The better the head flows the more air it takes to make more power.I ran into something on my motor awhile back that blew my mind.When my motor was stock and i put the 42mm carbs on it ,I had the K&N pod filters that came with the air box kit I had on the bike before I put the big carbs on .It ran fine and was easy to get the jets right.When i built the 898 motor with the big valve flowed head on it.It drove me crazy for awhile ,It would go blood rich over 6500 rpm ,If i put smaller jets in it ,it would get so lean at low rpms it didnt want to take off.Later I found the filters I had on it would not flow as much as the rest of the motor would.I changed to a uni all foam filter and the bike picked up like crazy ,jetting worked like it should again.If the type of pod filter can make that much power what do you think the air box could cost you?
I do agree vac slide carbs do some strange things but i never had any trouble getting them right with out the box.I think the problem is that the stock carbs barley work as they should if everything is right no mater what filters you run.

Howl · 01-13-2009, 01:56 PM

Hello
It's good to see another EFI question as I have a 2008 EFI Thrux and have been reading page after page of carb tuning/airbox info. Does anybody know what was used to remap the EFI Bonnie . Power comander or a tune thingy ( name escapes me ). Any body know the cost ,as 15 Hp looks quite a power gain .

propforward · 01-13-2009, 02:01 PM

As I understand the British Customs map can be uploaded to the bike using a tuneboy - I am not at all familiar with how that is done, though from what I have heard it is a simple enough procedure, a bit like transferring a file on a computer. I think Calliway did quite a bit of that kind of thing on his sprint.