Ram-Air

[ZnsaneRyder]

I notice that when you are going fast on your bike, that around 25-35mph or more the push from the wind against you feels really strong.

It would be nice to use some of that resistance to help you go faster. I've been thinking of using a cone of some sort with a tube to the intake for the Ram-Air.

I figure it may make more HP, and probably will need the carb tuned a bit richer, but that's no problem. I'm also wondering how much it may help MPG.

Also I wonder if it would be as beneficial to a small engine as it is to a large engine.

Has anyone else here considered a forced Ram-Air setup before?

 

[arceeguy]

"Ram-Air" is pretty much a marketing gimmick, I wouldn't waste my time.

For Ram-Air to be the least bit effective, you'd need to be traveling a lot faster than 25mph. (100+ comes to mind)

 

[mabman]

I am thinking one of these would be a nice little add on to try out.


http://cgi.ebay.com/Nitrous-kit-poc...14&_trkparms=72:1205|66:2|65:12|39:1|240:1318

 

[Simonator]

"Ram-Air" is pretty much a marketing gimmick, I wouldn't waste my time.

For Ram-Air to be the least bit effective, you'd need to be traveling a lot faster than 25mph. (100+ comes to mind)

+1

Ram air isn't effective until well over 100mph. Maybe over 200mph. The engine is sucking in air way faster than it can be pushed in. it is effective on a car because it draws in cooler air as opposed to warm air in the engine compartment.

 

[RdKryton]

Let me tell you what happens on a Whizzer when you ride into a strong head wind. The NE5 air filter cover will actually force enough air into the carb to lean it out to the extent that it stalls the engine remove the cover and the problem goes away. These carbs are not able to compensate for the extra air and if you jet them rich you will be way out of tune unless you are at top speed with wide open throttle. It's just not worth the hassle in my opinion. There is a thread about this. http://www.motoredbikes.com/showthread.php?t=9049

 

[arceeguy]

If a Whizzer crapps out in that manner, I suspect that it just has a very sensitive main fuel circuit. Even a slight increase in pressure from the "Ram Air" effect will have the undesirable effect of eliminating the "Venturi Effect" which is how the fuel gets drawn up from the fuel bowl and into the carb throat. (If there is positive pressure in the venturi relative to the fuel bowl, air will get pushed into the fuel bowl) So it isn't so much that the carb cannot compensate for the extra air, it is the extra air pressure essentially shuts off the fuel supply. This is why a carbureted engine with a turbo or supercharger draw air through the carb before boosting it.

 

[RdKryton]

If a Whizzer crapps out in that manner, I suspect that it just has a very sensitive main fuel circuit. Even a slight increase in pressure from the "Ram Air" effect will have the undesirable effect of eliminating the "Venturi Effect" which is how the fuel gets drawn up from the fuel bowl and into the carb throat. (If there is positive pressure in the venturi relative to the fuel bowl, air will get pushed into the fuel bowl) So it isn't so much that the carb cannot compensate for the extra air, it is the extra air pressure essentially shuts off the fuel supply. This is why a carbureted engine with a turbo or supercharger draw air through the carb before boosting it.

I stand corrected in my theory but the result is the same I believe. I just don't believe it will work.

Jim

 

[arceeguy]

Yup - At least you'll know right away if you are actually ramming air down the intake - your engine will cut out!

If the engine were fuel injected, with an air flow sensor, you might just see a small increase in power but nothing really significant until that 100 mph mark.

 

[ZnsaneRyder]

When I removed the airfilter cover off my engine as stock, it gained much more torque and revved quicker, and deeper note with a load on it, similar to how any car engine has been after an intake mod.

With the cover on, it breathes with just two small holes, one near the hot air by the cylinder fins and another small one opposite of that before getting to the air filter. Now with the cover off, the filter is in the open and the engine runs best. Wind blows right by the filter, but not into it. Airflow does make a lot of difference, however I don't want to overdo it.

I see what you mean about the suction needed from the carb, so you can't shove a lot of air down the carb for it to still get gas. I'm just wondering with a slight bit of forced air, but not enough to kill it, if it will increase the velocity of what's already being sucked in to aid with total flow. My engine runs out of peak powerband RPM around 47-49mph, so I have to hold it at full throttle @ 46mph, and it slowly creeps up to 49mph because the revs are high, and it needs to breathe more to go faster, and I'm going to get a better filter to help, but want to reduce what bottlenecks I can to gain a bit more. I'm not going 100mph, and I'm not wanting a ton of air, just enough to make a difference and raise the RPM some.

 

[Honda50]

The way the air stream enters a carb is important. If the air enters the carb as a straight stream, it enters the carb's venturi in a more orderly fashion. It also builds inertia before entering the carb venturi. This will intern provides more concise airflow into the venturi at wide open throttle and more even velocities means even fuel mixing in the main venturi as velocity and pressure remain stable. At wide open throttle, ambient air pressure is pushing the air into an engine. It is not sucked in. Since an engine is an air pump, improving the intake side should be met improving the exhaust side.

Ram air would only benefit engine performance at wide open throttle and high speeds (as mentioned). In four stroke engines, there is a point at which both intake and exhaust valves are open at the same time. This is known as valve overlap and is measured in crankshaft degrees. Since regularly aspirated engines are not 100% volumetrically efficient, meaning that some of the exhaust gases remain in the cylinder, diluting the incoming air-fuel mixture. The idea is to increase the engine's volumetric efficiency. This can be done by finding ways to evacuate as mush inert exhaust gases as possible. The engines camshaft profile and valve timing in relation to piston travel comes into play here. Stock cam profiles are designed to find a middle ground in terms of performance and reliability. Attempting to increase volumetric efficiency without addressing other known 'choke points' will result in possibly lesser performance and upset the balance of the other components working in concert with one another. In some applications, a small width spacer placed between the carb and head will at a certain rpm, will aid in airflow into the valve port. No 'trick' works throughout the entire rpm range.
Now, if you increase volumetric efficiency, the airflow through the engine is more efficient, resulting in more air or denser air. Theoretically we have more air entering and exiting the engine. Suddenly the stock carb does not match the new airflow or remains a major restriction to the improvements just made. See where I'm going?

When squeezing more performance from an engine, it's a trade off game. Every advantage has a disadvantage. It's a fun game to play. It involves a lot of basic physics and math, trail and error. It's a lot of fun just the same.