Air box modification

[2Whlsrollin]

My buddy has an "06" Venture as do I. We took a 350 mile trip together today and he got noticable better gas mileage that I. One tank we had 139 miles and I put in 9/10 of a gallon more that he did. He was telling me about how he modified his air box making the air intake hole larger. Also he took off the cones in the back of both tail pipes and drilled four holes in the baffell on each side. Will both these things increase your gas mileage and why?? Are there any posts here regarding both of these modifications. He was saying less back pressure from the modification on the pipes increases gas mileage and the carbs beathing easier from more air helps. Both kind of make sence to me, but I bow to the infinate knowledge of those here that live and breath this stuff.

 

Thanks in advace for the responce.

[Monsta]

Not RSV specific but I believe reducing pumping losses can increase fuel efficiency...to a degree. Pumping loss is the energy consumed to actually suck in the air and blow it back out. However, doing it "too" much will cause mixture problems. Inevitably a lean condition. That means you gotta add more gas. More gas = more power but not necessarily more MPG. Those two increases are typically mutually exclusive.

 

Opening up the air-boxes are said to help. (Mine were already opened up so I cannot comment specifically about the RSV.) This will allow more air to be able to pass though but doesn't mean the plenum and the engine can injest it. It typically means that the intake air velocity is reduced at low RPM and increased a bit at higher RPM. This can be detrimental to performance in some cases as well.

 

All motorcycles must meet noise emissions. Most have smallish intake holes to help reduce intake noise. Increasing the size can usually give the engine a bit more power the way the engineers originally intended.

 

Same for exhaust but don't fall into the "backpresure" myth. There is no such thing. What most call backpressure should be called exhaust velocity. And even then they say it in reverse. Opening it up, again, in most cases, will increase the exhaust velocity at higher RPM. And again, it can be detrimental at lower RPM in some applications.

 

Until someone dynos the homebrewed mods and shows me real-world differences and not just sky-high RPM increases I'll just leave well enough alone on my RSV. I can hear the music better that way. I opened up the intake and exhaust on my 03 Suzuki SV1000 by removing the intake snorkel and drilling the cans. Many guys had dynoed before and after and showed a 8hp average increase over the entire rev range with a 10-12 increase way up top. MPG didn't change because I was too busy exploring the new found power and drive-ability.

[2Whlsrollin]

Ken,

 

Thank you for taking the time for this detailed responce to both issues.

 

Jerry

[venturejockey]

Think of the intake hole to the airbox as a 1/8th inch long tube. Enlarging this tube isn't going to help much unless you enlarge the tube leading from the airbox to the plenum.

 

Also the engine is drawing from both airboxes at a time but only one carb at a time. The carbs arn't any larger than one of the intakes. So you have plenty of air getting to the carb.

 

Lastly, if you modify the airbox you may void the warrenty, and will be inviolation of federal law.

 

My two cents.

 

By the way if you really want to breath freely just clamp a K&N onto each of the carbs.

[Spud]

I've experimented with opening the air box before. The usual result with carbs is that when you hit half throttle you lose power. The engine can't get enough fuel to mix with the air and the engine bogs down and you lose power. The solution is to richen the mixture which defeats the mpg increase scenario, or to plug the holes back up. I haven't seen any improvement in either direction.

 

The only improvement I've seen it to use the Colortune and Carbtune to properly setup the engine. That said I'm getting 46mpg on a UK gallon with the Voyager kit and 2 up. I get 43 when I add the trailer.

 

If you have an engine with fuel injection and an ECM you can open up the air box and the ECM will compensate for you but as long as you have carbs you're stuck with manual adjustments.