The Ram air question

[Rayme]

I've been doing some research (*and still working on it) about ram air setup on bike. As I understand, the smaller the displacement, the more potential there is as you need less CFM to effectively pressurize the intake box. I also read about some issues with carburators (which also need more research, I read something about needing to pressurize the float boals too?).

Anybody have and input on the matter? If ram air would only be good for 1-2 HP, well, that's pretty good for a 250r!

[dubojr1]

Would this counter an air box delete. I believe we would have to keep the air box and then feed the ram air tubes to it.

Hmm... wonder what HP gain comes from removing the air box?

[Alex]

I don't know if our steed goes fast enough to make a noticeable difference. Every time I've read tests of the ram air effect, it doesn't do anything at all until well into triple-digit speeds. Once over 100+ mph, well-designed ram-air effect can start to be measured, but barely, and at 150+ mph, it can be a 3% - 4% increase in peak power for a bike tuned to take advantage of it.

If we're barely touching the ton already, I'm not sure that it would end up being effective at even getting that 1 or 2 proposed hp... , but for sure.

[Snake]

Here is a previous thread on the subject. http://www.ninjette.org/forums/showthread.php?t=32870

[Alex]

I had forgotten about that one Snake, thx! I think Racer X's links from that one were where I learned about what MPH things started to be noticeable.

[Snake]

Racer X's link seems to indicate the nominal gains are realy not worth the modifications that would be needed.

[HKr1]

Ditch the crap ass CV carbs. That right there is a real nice gain, you know with real carbs

[Snake]

What are you calling real carbs?

[Thrak]

flat slides?

[Rayme]

Well I read more about it and I'm still thinking there might be a slight increase.

I will take a measure of the airbox's pressure at WOT at high speed to start

[Racer x]

Originally Posted by Snake

Racer X's link seems to indicate the nominal gains are realy not worth the modifications that would be needed.

From my playing with my ninja .I could use ram air to an advantage if anyone could,
This is why I have not gone further with Ram air. I need to pick what I can do and budget all my time and limited money .
First question . How to build it This is the money part. I can run a hose from the front to a box . That box can be like the air box with the bowl vents going to it .So the bowl is pressurized as the box is and dose not cause fueling issues we can dispense with at this stage of the thinking.

Or the carbs can be mounted inside a box . It is hard to tune and make throttle cables for that set up . But it can be done.

Next comes the working of it . That is the time consuming part. First you have to figure out how much ram air you have to work with. This is where I don't have time to figure it all out, But I would start with raw data.

Build a box with an opening like you would have for the 250 system. Put a pressure gauge to it from a hose . Hang it outside your car and drive at 55 then 100 mph. See how much pressure you get .

Next measure the air volume . First at 55 then at 100. See if you get anything worth working into a system that will add power below 150 mph . Everyone says you cant .But they are not trying to make power from a 250cc engine. Little bits add up. To a little more

[Rayme]

Originally Posted by Racer x

From my playing with my ninja .I could use ram air to an advantage if anyone could,
This is why I have not gone further with Ram air. I need to pick what I can do and budget all my time and limited money .
First question . How to build it This is the money part. I can run a hose from the front to a box . That box can be like the air box with the bowl vents going to it .So the bowl is pressurized as the box is and dose not cause fueling issues we can dispense with at this stage of the thinking.

Or the carbs can be mounted inside a box . It is hard to tune and make throttle cables for that set up . But it can be done.

Next comes the working of it . That is the time consuming part. First you have to figure out how much ram air you have to work with. This is where I don't have time to figure it all out, But I would start with raw data.

Build a box with an opening like you would have for the 250 system. Put a pressure gauge to it from a hose . Hang it outside your car and drive at 55 then 100 mph. See how much pressure you get .

Next measure the air volume . First at 55 then at 100. See if you get anything worth working into a system that will add power below 150 mph . Everyone says you cant .But they are not trying to make power from a 250cc engine. Little bits add up. To a little more

I'm pretty interested in what my reading will be for the airbox pressure, I wonder if there is any vacuum present at WOT at high RPM...Any type of ram air would effectively remove that vacuum (probably having the same effect of open element filters).

I found an article that represent a bit more theory about it...it makes perfect sense.
No OEM pressurised airbox could manage a single psi of 'boost' even at top speed.
The best ones would max out at less than 0.5 psi, with 0.2 psi more common at around 100mph.

So is THAT it? 0.2psi? big deal

But look carefully and let's see what that is compared to:
A non-ramair airbox breathes from the side or a low-pressure area, which is probably also affected by engine heat.
A ramair box is stuffed with fresh air exactly at ambient temperature. So what's the difference then?

As a rule of thumb, for every 4C that air temp goes up, 1% of power is lost. It's easy to have the airbox temp go up by 4C, sometimes a lot more. A ram-air box is always cooler.
More importantly, a non-pressurised airbox is typically under vacuum, and under load at high revs that is several psi worth of vacuum.
People think that it's atmospheric pressure in there, but it isn't. Just calculate how many liters of air are demanded to flow when the throttle is wide open, and you'll realise that the airbox is empty within milliseconds. It takes time to replenish these reserves, typically almost a second (with the throttle closed). If the throttle is kept wide open, the 'replenishment' rate is far lower than the engine's air consumption, so the airbox remains in deep vacuum all through the acceleration process. The higher the engine speed, the deeper the vacuum.

That's where a RAMair intake comes in. It doesn't pressurise more than a few tenths of a psi during cruise conditions, but when the throttle is whacked open, the vacuum appears a bit later - maybe a second later. That feels like better throttle response, because that's what it is. Even then the vacuum is always lower, because now the replenishment rate is much closer to the engine's consumption rate.
http://www.max-boost.co.uk/max-boost...tory_facts.htm

[Racer x]

.Do you think the 250 ninja can accelerate fast enough to pressurize an air box? If you gear the engine for 100 mph top speed the acceleration rate is slowed. SO for testing purposes should the bike be geared for Max acceleration or max top speed?I will read the article tomorrow.

[Alex]

I think that the acceleration isn't pressurizing the airbox, the speed is pressurizing the airbox. Acceleration is what pulls the vacuum on the airbox, more so than holding a constant throttle. Unless the constant throttle = full throttle, then it's attempting to pull a constant vacuum (while the incoming air is working to fill that vacuum).