Bullet inlet tract extension

[Blltrdr]

 Keep us all informed of your testing. It is very interesting! What is the target RPM's you are trying to achieve with your mod?

[ace.cafe]

Keep us all informed of your testing. It is very interesting! What is the target RPM's you are trying to achieve with your mod?

With this long extension, I worked it out for 3500rpm target at the estimated torque peak..
It is always an approximation, because of variations in temperature, and the fact that I didn't measure my inlet tract to the exact millimeter and stuff like that.
So, it was actually pretty close to what I targeted, by getting some results around 3300 rpm.
I'm figuring my torque peak to be in that neighborhood of 3300-3700 rpms somewhere.

Without a dyno, it's all estimation. So, I'm just playing around with it, and seeing what I can do to tune it in by observing what it's doing and making changes from there.

The long extension pipe is pretty unusual looking, for sure. I'm not sure if I can get used to something like this, from an appearance viewpoint.

But, whether I end up using it permanently or not, I'm having fun with the learning experience and experimentation. I like doing this kind of stuff.

[Blltrdr]

Keep us all informed of your testing. It is very interesting! What is the target RPM's you are trying to achieve with your mod?

With this long extension, I worked it out for 3500rpm target at the estimated torque peak..
It is always an approximation, because of variations in temperature, and the fact that I didn't measure my inlet tract to the exact millimeter and stuff like that.
So, it was actually pretty close to what I targeted, by getting some results around 3300 rpm.
I'm figuring my torque peak to be in that neighborhood of 3300-3700 rpms somewhere.

Without a dyno, it's all estimation. So, I'm just playing around with it, and seeing what I can do to tune it in by observing what it's doing and making changes from there.

The long extension pipe is pretty unusual looking, for sure. I'm not sure if I can get used to something like this, from an appearance viewpoint.

But, whether I end up using it permanently or not, I'm having fun with the learning experience and experimentation. I like doing this kind of stuff.

 I was thinking yesterday you could run your extension out then down between the gearbox and swingarm. Maybe configure some kind of scoop. I'm not sure how the bends in the tube would effect your tuning? It would give you some length and some stealthiness! I was picturing the end of a auto carpet cleaning attachment as the scoop. Maybe with a gauze face plate. Just an idea.

[ace.cafe]

Keep us all informed of your testing. It is very interesting! What is the target RPM's you are trying to achieve with your mod?

With this long extension, I worked it out for 3500rpm target at the estimated torque peak..
It is always an approximation, because of variations in temperature, and the fact that I didn't measure my inlet tract to the exact millimeter and stuff like that.
So, it was actually pretty close to what I targeted, by getting some results around 3300 rpm.
I'm figuring my torque peak to be in that neighborhood of 3300-3700 rpms somewhere.

Without a dyno, it's all estimation. So, I'm just playing around with it, and seeing what I can do to tune it in by observing what it's doing and making changes from there.

The long extension pipe is pretty unusual looking, for sure. I'm not sure if I can get used to something like this, from an appearance viewpoint.

But, whether I end up using it permanently or not, I'm having fun with the learning experience and experimentation. I like doing this kind of stuff.

 I was thinking yesterday you could run your extension out then down between the gearbox and swingarm. Maybe configure some kind of scoop. I'm not sure how the bends in the tube would effect your tuning? It would give you some length and some stealthiness! I was picturing the end of a auto carpet cleaning attachment as the scoop. Maybe with a gauze face plate. Just an idea.

Yes, I had the same thought!
And it could just barely fit down there. I tried it.
But after looking at it, I sort of liked it better going toward the back of the bike.
It looks odd anywhere you put it.
Nobody is accustomed to seeing an 18 inch long pipe coming off the carb, with a K&N on the ehd,  No matter which direction you run it.

[Jon]

A friend of my son rigged up a fan from a computer between the filter and the
carb on one of those BMW/Rotax singles and claimed beneficial results wonder
if that might work?

[ace.cafe]

A friend of my son rigged up a fan from a computer between the filter and the
carb on one of those BMW/Rotax singles and claimed beneficial results wonder
if that might work?

I really can't see something like that working, Jon.
The air pumping ability of the engine itself far exceeds any of those fans.
As soon as the intake valve opened, the fan wouldn't be able to keep up with demand, and it would act as an impediment to the flow under those circumstances.
It sounds like it should work, but the peak demands of the engine would over-run the ability of the fan to keep up.

[PhilJ]

Ace,

All this about increasing air flow, now let me date myself. years ago it was desirable to use "dead air space" with a large volume to allow the engine to draw what it needed in the manner it was needed.

I'd be interested in hearing (reading) your thoughts or commentson "normal" aspiration.

[ace.cafe]

Ace,

All this about increasing air flow, now let me date myself. years ago it was desirable to use "dead air space" with a large volume to allow the engine to draw what it needed in the manner it was needed.

I'd be interested in hearing (reading) your thoughts or commentson "normal" aspiration.

Good question, Phil.

The dead air space is basically a requirement for throttle responsiveness.

With current technology, this dead air space requirement has been pared-down to approximately double the engine displacement. In a 500cc engine, then we'd be looking for about a liter of dead air space on the engine side of the filter barrier. This includes the air in the port and in the carb, as well as inside the airbox and  filter body itself.
In some cases, this size of dead air space is partially compromised for space to fit it on the bike. Such as Ducati is currently using about 1.3 liters of dead air space in their 999. But, a bit more than that is desired when space permits.

Now, the dead air space, as I understand it, is primarily to allow a big gulp of air on initial throttle openings, for rapid throttle response.
I don't think that it really has much to do with turbulent air in the vicinity of the intake throat.
And there is little(if any) benefit to provide more dead air space than is actually needed for the purpose, Because the dead air space will replenish itself thru the filter by natural movement of the air. It's when the dead air space becomes less than the engine displacement where it can show itself as a flow problem, primarily as lag in throttle response time..

So, current practices would be to use always more than engine displacement volume in the inlet tract on the engine side of the filter barrier. And preferred to provide double the displacement volume if it is practical to do.

Is that sufficient? Or do you want discussion about how to optimize inlet flow in  normally aspirated engines? That's quite a big discussion, in fact there's whole books written just on that alone. But, the wave tuning stuff that I've been discussing on this thread is part of that.

[PhilJ]

That's good, but it does bring up another question. If the dead air space covers the initial big gulp need for throttle response, and the wave tuning for torque (in our application), it doesn't seem practical, space being the limiting factor, to incorporate both methods. So what, in your opinion, would be more important?

[ace.cafe]

That's good, but it does bring up another question. If the dead air space covers the initial big gulp need for throttle response, and the wave tuning for torque (in our application), it doesn't seem practical, space being the limiting factor, to incorporate both methods. So what, in your opinion, would be more important?

The avaliable dead air space on the engine side of the filter is the more practical, and the more important for normal street riding.

I think the wave tuning is more suitable for racers, or maybe hot-rodders. The wave tuning works well, but I think it is too long and unusual looking for most street Bullet applications.

Actually the stock Bullet airbox and inlet system has sufficient dead air space in it as it is.
But when we take that off, and put the short K&N pod filters on the carb, then we change that.

A few inches of tube extension between the K&N and the carb inlet opening should do the  trick to restore enough dead space.
But, it is important to put a support bracket of some type on, to support the carb and filter assembly, or else it is going to hang too much on the rubber inlet hose and make its life even shorter than normal.

[PhilJ]

Thanks Ace.Cafe,

I thought that may be your answer. I'm glad to know that for my application, it's as good as it gets. 

[BigDon]

That's good, but it does bring up another question. If the dead air space covers the initial big gulp need for throttle response, and the wave tuning for torque (in our application), it doesn't seem practical, space being the limiting factor, to incorporate both methods. So what, in your opinion, would be more important?

The available dead air space on the engine side of the filter is the more practical, and the more important for normal street riding.

I think the wave tuning is more suitable for racers, or maybe hot-rodders. The wave tuning works well, but I think it is too long and unusual looking for most street Bullet applications.

Actually the stock Bullet airbox and inlet system has sufficient dead air space in it as it is.
But when we take that off, and put the short K&N pod filters on the carb, then we change that.

A few inches of tube extension between the K&N and the carb inlet opening should do the  trick to restore enough dead space.
But, it is important to put a support bracket of some type on, to support the carb and filter assembly, or else it is going to hang too much on the rubber inlet hose and make its life even shorter than normal.

Ace, that was my thinking after reading all the other posts on the subject and the info from tech articles on "air box volume" and why I opted for the K&N in  the air box route to my bullet mods.

[Chuck D]

Just dusting off some interesting old threads. Enjoy!