I have been thinking again....

[Ivan]

Has there ever been some sort of ram air setup for the XS11? I was watching a documentary on the history of Yamaha which apparently never made anything but the R1, and they said the R1 gets something like a 50 HP boost at 80 mph from the ram air system.

I have seen people who have made plenums out of PVC with pod filters on the end, why not make a tube that maybe comes out just under the front of the tank or somewhere not to overly gaudy to preserve the looks?

Anyone have any ideas on something like that?

[trbig]

Don't you think that would have to have a brain and fuel injection to allow for more air pressure and such? Something to allow to change the mix?


Tod

[Montreux_Blue]

I have kind of thought about it a few times. Here are a couple articles about ram air on sport bikes with theories, formulas and pressurized air intake dyno tests.

http://www.sportrider.com/tech/146_9910_ram/index.html

http://www.sportrider.com/tech/146_9912_ram/index.html

[Ivan]

So, not worth a gazillion HP, but maybe worth 5-10% gain?

Tod, I don't think it would take a whole bunch more tuning. Since the carbs operate off the amount of air flowing through them, they should be able to handle the extra. Maybe a bit of rejetting on the high end. I would definitely say that the bowl vents need to be hooked up to the pressurized plenum as well, or it may push the fuel back out.

All in all, it looks like, from Jeremy's links, the most pressure we could possibly get is about .4 psi above ambient. That is just enough to overcome the restriction of the airbox. I may have to start figuring something out on this...

[XJOK2PLAY]

Ever checked into the specs of the VMax & their ram air setup?

Be cool if one could find a salvage one, and score that setup for the 11.

Ohhh wait, you said 'not gaudy...'

(Personally, I love the look of those shiny, chromed intakes...)

[Ivan]

Uhhhhhh

The V Max didn't use those functionally until the 09 revamp. Before that they were horn covers.

[Montreux_Blue]

I seem to remember someone swapping carbs from a Kawasaki (?) crotch rocket and putting them on a XS11. I remember them saying that the spacing was almost spot on so maybe the air box from that bike with it's ram air tubes may work very easily.

[Montreux_Blue]

It was the ZRX, which doesn't have ram air.....

[WMarshy]

theory

I've been working on some tuned intake analysis stuff. Here is a link that will give you some background on acustic tuning of intakes... If your interested.

http://etd.ohiolink.edu/etd/send-pdf.cgi/Eberhard%20Walter%20Wayne.pdf?acc_num=osu1116358910

[Guy_b_g]

Just remember you have to pressurize the float bowls of each of the carbs to the same value that the ram air is pressurized or they will not work properly. Also you have to find the high pressure zone at the front of the bike to get much benefit, they do a lot of wind tunnel work to get it right on modern bikes.

[WMarshy]

There is also a natural harmonic resonance that every intake has (yes even the XS11) that generates ram-air charging at a specific RPM. This resonance can be modeled via Helmholtz theory or Engelman's electrical analogy. These theories are usually good up to about 8000 RPM and every RPM has an optimal length in which the ram-charging happens. Kinda cool stuff. I know this isnt the exact same as what they are covering the articles but relevent none the less.

[Guy_b_g]

and every RPM has an optimal length in which the ram-charging happens

I think it was TopCatGr58 who had the right idea extending the intake tubes to replace the loss of effective intake length when going to pod filters. Others have mounted the pods at the end of the old (modified) plastic stacks from the airbox.

On my Guzzi I replaced the airbox with pods and ended up with a bad midrange flat spot that was corrected with a set of custom machined aluminum velocity stacks, they were about 5" long on that bike and tuned for that purpose, (worked perfectly).

The intake length can be altered before or after the carbs to get essentially the same effect.

[TomRodgers]

My Vmax had some work done on it to make the scoops functional. i had to relocate some plumbing and the temp. sensor. Drilled out the fake scoop front covers and fabbed some fiberglass inserts to direct the air where it needed to go. Stocker carbs got ditched and replaced with flat slides. Bike didnt do so good at idle..but once it cleared its throat, you better have a good grip!!! So much in fact that i ended up installing and air shifter on the damn thing cuz it pulled so hard that i didnt want to release my left hand at all!!!

[81xsproject]

Tom, while I question the 'family-oriented-appropriateness' of your avatar, I often find myself locked onto it; almost hypnotized by it.

The ram air idea is indeed intriguing. As far as bowl pressurization, 80's carbs would need no additional details as they vent directly into the intake as one of the 4 holes in the inlet bell. With the 70's, you would simply need to plumb in the bowl vent hoses.

[WMarshy]

Conservation of energy now has a new meaning!