TOPIC:

I got this strange idea tonight about an DIY intake modification for a 4 carb bike.

Here it is simple terms so I don't lose your attention with my insanity.

What if you ran (correct diameter for your model of carb) plastic piping off of each carb and collected all four into a tight bunch (consisting of a conservative length of pipe using L bends) approximately 65-70mm in diamter?

Fabrication would be necassary along with some plastic cement. The finished product would be an intake manifold for a motorcycle. Simply stick on an air filter (similar to the kind in an airbox) and get the jetting right and you're good to go.

I know the manifold sounds redundant since pods or other filters are readily available, but does anyone think this could be a feasible alternative? Would this allow even more breathability or can the intake diameter be TOO large? I'm not sure if this one is too "left field" for you WG but I'd be interested to hear your opinion.

Post edited by: nfswift, at: 2006/03/15 02:29

I don't see that there would be any advantage to such a manifold other than the use of one filter. There's no way your manifold would flow more than the stock air box.

KZCSI

Isn't your description what a stock airbox essentially is?

The Milkman did pretty much what you are asking about, only he replaced the original carbs with a single Stromberg. Check out this thread from tha archives:
kzrider.com/forum/viewthread.php?tid=23259

oldcoldankles... I think you missed the point this nfswift was trying to make. Milkman used a single carb to replace a multicarb set up. nfswift wants to use his four carbs but make intake runners out of PVC that would be fed by a single air cleaner.

First, a stock airbox will generally try and use four equal length runners most of the time. I suspect four equal length runners allows easier tuning as unequal length runners would cause tuning challenges.

There is not reason this could not be done. If you wanted to get silly, you could make four tubes into one and use some flex tubing and make a ram air up front with a filter in between somewhere. Trying to jet a system like this would be a challenge but it might actually add some power... RAM AIR! I have never gotten the urge to do this type mod so my opinion probably isn't any better than anyone elses. You just don't know how something will work till you try it. PVC is cheap... go for it.

Wow, that single carb conversion is really something... I'd stick to individual carbs myself for performance purposes though.

WG brought up an interesting extension of the idea though, to essentially create a homemade RAM air system to force a little more air into those carbs when your getting on the throttle. In response to KZCSI, I believe the only real advantage over the stock airbox would be the possibility of better breathing from the carbs; or if you put a RAM type setup on... considerably more?

A possible drawback, though, if I chose to make it sit under the seat (non-RAM) would be the chance that a wide pipe "slows" the air in the intake charge too much, which would not be good for CV carbs which rely on that fast air moving through to keep the intake charge well mixed.

This has got me really intruigued about the performance gains of using a RAM style intake/manifold.

Hmm, I just need to find out the shortest way to route the filter to the runners and to keep the runners as close to equal in length as I can...

Home made RAM? Can it be done?
We will see...

I think the multi carb to single carb mod done by Milkman wasn't really due to the reasons that might first seem obvious. I am thinking he had either a KZ400 or KZ440 using the twin Keihins (memory?) and those carbs are nasty to find parts for and work on. Most anything is an improve over those carburetors. It would actually be pretty simple to use a single Mikuni round slide carb w/pod air filter attached for filtering and make a two into one manifold out of PVC which could be connected to the Mikuni VM series carb with a rubber connector you could probably get from a home improvement store. The single VM Mikuni allows the cable to directly pull the slide and the choke is mounted on the carb.

nfswift wrote:

Home made RAM? Can it be done?
We will see...

The gain will probably be less than anticipated. In the April 2006 issue of Cycle World's Service column, CW's engineering guru Kevin Cameron addresses ram air. He claims a very low return at street speeds on the order of less than 1% at 80 MPH, rising to around 3% at 160-170 MPH, and around 14% at 350 MPH. Only about 75% of these figures can be achieved.

He does allow that an airbox that "...is designed to resonate (it's pressure rising and falling 180 degrees out of step with the engine intake events), there can be a gain from the airbox alone, and no forward-facing intakes are necessary for this gain. Power is increased because each cylinder's intake occurs at maximum box pressure, with the box refilling between intake strokes. The gain can be substantial. 10-15 percent if done properly. The bigger the engine's individual cylinders, the bigger the airbox has to be, so it's hard to have enough box volume on a Twin, but that's not the case with smaller cylinders."

Looks like an interesting engineering exercise.

- Nate >>

Post edited by: n0nb, at: 2006/03/15 20:14

There's no way your manifold would flow more than the stock air box.

KZCSI

N0NB wrote:

nfswift wrote:

Home made RAM? Can it be done?
We will see...

The gain will probably be less than anticipated. In the April 2006 issue of Cycle World's Service column, CW's engineering guru Kevin Cameron addresses ram air. He claims a very low return at street speeds on the order of less than 1% at 80 MPH, rising to around 3% at 160-170 MPH, and around 14% at 350 MPH. Only about 75% of these figures can be achieved.

He does allow that an airbox that "...is designed to resonate (it's pressure rising and falling 180 degrees out of step with the engine intake events), there can be a gain from the airbox alone, and no forward-facing intakes are necessary for this gain. Power is increased because each cylinder's intake occurs at maximum box pressure, with the box refilling between intake strokes. The gain can be substantial. 10-15 percent if done properly. The bigger the engine's individual cylinders, the bigger the airbox has to be, so it's hard to have enough box volume on a Twin, but that's not the case with smaller cylinders."

Looks like an interesting engineering exercise.

- Nate >><br><br>Post edited by: n0nb, at: 2006/03/15 20:14

That would be pretty tough to pull off. An airbox of given proportions will have a natural resonant frequency. That frequency will vary some with air temperature, but will be very little variation in normal operating temperature range. That's easy enough to ccalculate, but the frequency of the engine varies with RPM. With that in mind, unless the volume of the airbox changed along with engine RPM you would only see a gain in performance in a small RPM range.

Tarmac wrote:

That would be pretty tough to pull off. An airbox of given proportions will have a natural resonant frequency. That frequency will vary some with air temperature, but will be very little variation in normal operating temperature range. That's easy enough to calculate, but the frequency of the engine varies with RPM. With that in mind, unless the volume of the airbox changed along with engine RPM you would only see a gain in performance in a small RPM range.

Not being an engineer myself, I tend to agree with you. I doubt Mr. Cameron was talking about a street application, but rather something that would be investigated and employed at the MotoGP level. At that level a few percent of gain on the long straights will definitely be an advantage.

I thought it was interesting that this thread came up at about the same time as his commentary in this month's Cycle World. I was surprised at the low percentage of gain ram air seems to deliver. The airbox idea was interesting to me as well.

I do wonder how much engineering went into the stock airboxes on the KZ models. Are they performance tuned (not likely to be as much as today's Ninja models), or just designed from the space available. It's too bad we don't know much about the engineering thought that went into certain aspects of these bikes.

- Nate >>

I can speak to the engineering of the Kaw airbox a bit... Look at the original Z1 airbox. Essentially a soft rubber tub sitting behind the carbs with somewhat different length runners. It is also small and easily fits. The downside to this airbox was noise, low air volume, and the non-equal length runners. You can see the evolution of the VM style airboxes through the 70s to where in 1980, the airbox was MUCH bigger to allow for a much larger still air supply for the carbs and it had equal length runners between it and the carb venturis. The downside to this airbox is that it came in 31 pieces and you had to disassemble the bike to get it out... Ever see a 1980 KZ1000E2 ST airbox? You have to take the bike apart to get the bottom tub out. The other downside to the equal length runners is that they made them out of rubber hose (I guess that is what I would call it) and the stuff gets hard/brittle and makes carb swaps a pain. Kaw did do engineering on the airbox concept but like all applications, each has some good points and each has some bad. I give up the better points for the early Z1 airbox on my carb test bikes as the MAIN characteristics I like about it is that they are small and the rubber remains flexible to this day making them easy to pull and install.

As for Mr. Camerron and his writings, I seldom can follow his reasoning for much of his arcane engineering-speak but find that he addresses issues that are very much of interest but stays on the far-edge of the techno-speak. I have found that many people who can't write or otherwise communicate in plain English on engineering subjects don't really have a grasp of the practicle but since he is about the only writer who writes about tech issues, I like to see what he says. The other bike magazines address tech stuff on the basis of how to tighten your drive chain or how to change grips or other things which hold little interest for someone who has been into bikes for awhile.