Bullet inlet tract extension

[ace.cafe]

Maybe you can find some large diamter conduit pipe for electrical purposes, locally.
If not, Ebay usually has almost anything.
Or McMaster-Carr has practically anything too.

Related to right-angle bends, that is not good for sonic waveguide purposes..
They don't like right angle bends. A "sweeping turn" is better, and straight with no bends is best.
But, if you have no other option, it might be better than nothing.
In any case, it can get you the ram air you were wanting, even if the sonic activity gets thwarted with sharp bends.

I need to build an intake pipe to mount to the squarish shaped engine air intake. That iwll have to turn 90 degrees backward, and the turn should occur in less than 3 inches. I'll make a flange to fit the intake, and weld the pipe to it.  After that, I have already built a scoop box which I think will work, I just need to take some pipe and mount a filter in the box. The pipe will enter at the front of the box and turn down so the filter will mount beneath it inside the box.
Once this is done I just need to tie the system together with some rubber hose and a carburetor and bob's your uncle.
I'll post pictures when complete.

Cool!
That's all we can do.
Every application has its own difficulties to overcome, and there are often compromises involved to fit the application.
As long as we know what the ideal is, and then make our compromises to least adversely affect the goal, then we are doing all we can do.
Every engineering problem has these kinds of issues come up.. It's all in the hands of the engineer to get as close to his goal as he can, while still working within the structure that he has to fit into. That's the "art" of engineering.

[geoffbaker]

a search through mcmaster-carr isn't showing any useful tubing - it's all thick steel or it doesn't have a 1.75 ID.

their medium walled electric conduit shows an ID of 1.7, that may be as close as I can come. Where did you get your pipe?

[ace.cafe]

Well, first of all, I selected the 1.75" size based on the size of my inlet of the carb I'm using. If you have a different-sized inlet on your throttle body for your injected engine, then you should use that size. It may be the same, I don't know, but the size is determined by what your inlet throat is, so they match.

I got my tube off Ebay. It's aluminum. $12 plus shipping.
But mine is straight. Elbows might be harder to find.

In fact, I just happened to look at the picture of where your present air-filter is, and you do have a particularly difficult application. I can see now why you need that tight turn.

[Rick Sperko]

Interesting write-up, Ace. It accords with my abortive attempt to install that kind of filter close up on the carb. Even though I had gone up a couple of jet sizes, I found I was getting dreadful just-off-idle to 1/4 throttle response - the mother of all flat spots - so I went back to the stock air filter, reluctantly because I wanted the tool box back for putting tools in!

I might fashion a similar tract extension and see if there is an improvement.

Chas

Chasfield,
Interesting!
Because I too, had a flat spot like that after installing the K&N on the carburetor.
This mod eliminated that problem, and it was the first thing that I monitored to see what effects it would have on that. Problem solved by this, in my case.

This flat spot has me concerned. I was hoping to put a flatside carb and cone filter on before spring, but I would hate to spend the money to find the bike responds poorly. Is there much risk of that?

Thanks,
-Rick

[ace.cafe]

Interesting write-up, Ace. It accords with my abortive attempt to install that kind of filter close up on the carb. Even though I had gone up a couple of jet sizes, I found I was getting dreadful just-off-idle to 1/4 throttle response - the mother of all flat spots - so I went back to the stock air filter, reluctantly because I wanted the tool box back for putting tools in!

I might fashion a similar tract extension and see if there is an improvement.

Chas

Chasfield,
Interesting!
Because I too, had a flat spot like that after installing the K&N on the carburetor.
This mod eliminated that problem, and it was the first thing that I monitored to see what effects it would have on that. Problem solved by this, in my case.

This flat spot has me concerned. I was hoping to put a flatside carb and cone filter on before spring, but I would hate to spend the money to find the bike responds poorly. Is there much risk of that?

Thanks,
-Rick

Rick,
No, not a big deal.
With a different carburetor like the flat slide, you might not even get any flat spot.
The stock Mikarb comes set up lean from the factory. Many times there is no problem just up-jetting with satisfactory results. But in some circumstances, there is this nagging flat spot right at the transition throttle-position from the pilot jet to the needle.
That spot is around the 1/4-throttle position, and is governed by the throttle slide cutaway.
So, of course I ordered the richer throttle slide, but that was in early August, and it's been back-ordered since then, and I have no idea when it's coming in. So I've been limping along. If it takes much longer, I'm just going to buy a 32mm Mikuni  flatslide and put it on, and tune that one in instead..

[Chasfield]

Regarding possible raw material for inlet extension:

The outside diameter of my Bullet's exhaust front pipe is 1.75 inches. If that was going to be near enough then cut six inches out of an old one (plenty of those about, I reckon) and you would have a nice chromed induction tract. A curved section might offer even more possibilities but the pipe seems to be waisted in wherever it bends.

Also, best put a wire brush down the inside to clean out the grunge.

[Rick Sperko]

Wouldn't a long round K&N (6-10 inches) provide the same functionality? It seems like there could be even more volume and quicker recharge because it is all filter.

-Rick

[ace.cafe]

Wouldn't a long round K&N (6-10 inches) provide the same functionality? It seems like there could be even more volume and quicker recharge because it is all filter.

-Rick

It would provide the necessary volume of air inside the filter barrier. Yes.

But it wouldn't do anything for ramcharging effect on intake mixture speeds or wave tuning at all.

[Blltrdr]

 Ace, your mod is very inexpensive and could be fun to tinker with for a while. But is there any way to test these tubes on the bike to generate some data to see if the effort is worthy? Maybe hook up a vacuum gauge and take some readings? Maybe add a fan to simulate a forced air condition, then compare it to stock figures and so on? Having data to prove the value of something is half the fun of the chase to improve something.

[ace.cafe]

Ace, your mod is very inexpensive and could be fun to tinker with for a while. But is there any way to test these tubes on the bike to generate some data to see if the effort is worthy? Maybe hook up a vacuum gauge and take some readings? Maybe add a fan to simulate a forced air condition, then compare it to stock figures and so on? Having data to prove the value of something is half the fun of the chase to improve something.

Well, we start off by doing some calculations.
Here are some of the basic formula calcs
Pulse in these calcs is the same as reflected wave.

Intake Tract Tuning for RPM = (1100 x Half Intake Cam Duration x 0.960)/Length = 2nd Pulse
(1100 x Half Intake Cam Duration x 0.705)/Length = 3rd Pulse
(1100 x Half Intake Cam Duration x 0.538)/Length = 4th Pulse

Intake Tract Tuning for Length = (1100 x Half Intake Cam Duration x 0.960)/RPM = 2nd Pulse
(1100 x Half Intake Cam Duration x 0.705)/RPM = 3rd Pulse
(1100 x Half Intake Cam Duration x 0.538)/RPM = 4th Pulse

The earlier pulses like 2nd pulse are strongest, and then get progressively weaker as they increase to 3rd pulse, 4th pulse, and so on.
Nascar tunes to 3rd pulse.

This gets you some intake tract lengths to look at for starting points, and the challenge is to try to find where you are going to put all that intake length once you figure out how long it's going to be. And it IS gonna be long. the lower the rpm that you target, the longer the tube must be. And they get real long at the low rpms that we're targeting.
So, then we just probably try to get 4th pulse if we can, and there's realy not enough room for anything that looks relatively "normal" for that length either, so we "could" just try for as long as we can fit. That's what I did.

I do have a full-length 4th pulse tube here that I'm going to strap on the bike and see what it gets me. Just to see. Just so you know what it is for a 4th pulse on the Bullet at 3500 rpms, the inlet tract(this length includes everything from the  back of the valve head all the way to the tube air inlet opening) is 22.3" for the half of 264 duration calc,

Anyway, our goal for the Bullet would be to tune the pipe for the torque peak, which is somwhere between 3250 rpm and 4000 rpm, depending on what the mods on your motor are. For a Bullet equipped with performance exhaust and 28mm Mikarb, it's probably going to be around 3500 rpms for torque peak. Larger carb will have higher torque peak.
The other kind of goal is to tune at higher rpm for the horsepower peak. That's a shorter pipe. But it's only good at your rpm at peak hp.
So, you make the call. I think boosting torque peak is better for us, because with higher torque peak, all the hp figures above torque peak also get boosted. Downside is a real long tube.

Cam duration for the intake cam on a Bullet is 264 degrees at .012" lash, or about 230 degrees at .040" lash(which is where the valve curtain is unshrouded). Some people design one way, and other people use the other figure. It's up to you.

So, that gets you somewhere in the neighborhood.
You can't use a flow bench for this, because we're not increasing flow. We're making wave tuning modifications to extend flow longer after BDC which doesn't show up on a static flow bench.
And unless you have a dyno, you have to use the "seat of the pants dyno".
If it's working, you'll know it, beause you'll have more torque, and everything above the torque peak(hp) will be stronger.

A fan won't help with anything. It's all based on engine filling during the intake period.
Vacuum gauge won't help anything either.

If you really want hard numbers, you have to do it on a dyno.


This is well-proven technology. All serious racers do it.
Most racers use high-revving engines, so their tubes don't need to be that long.
Our difficulties come from our low target rpms, and not having alot of room to put the tube. It can be curved gracefully with shallow radius curves, if that helps any.
I think we need to make a compromise between what we can get for length that fits into the appearance of the bike.
But, it's fun to experiment!

Any inlet length increase is going to be picking up some wave reflection at some rpm. It just depends on what it happens to be. 7" inlet tract, which is what we have from vavle to carb mouth, is too short for any wave pulse  to be strong enough to really do anything for us at our low rpm range. It's just too short. So, anything "could" possibly be a help at some rpm. The longer, the better. You'll run out of room to put the tube before you hit the optimal lengths. But it's worth a try to get something.
A BSA Gold Star racer I know uses a 15" length pipe on his Gold Star carb. With a big fat K&N filter on the end. He has a support bracket for it coming off his rear shock mount. It goes that far back!

[Blltrdr]

 Ace, can you use a cone shaped tract to get more volume instead of a long cylinder? Or is it necessary to have a tube like your using?

[ace.cafe]

Ace, can you use a cone shaped tract to get more volume instead of a long cylinder? Or is it necessary to have a tube like your using?

Yes, for certain purposes you could do that. That would handle the needed volume on the engine side of the filter barrier. That is a different matter.
But, not for the purpose that we're talking about here.
For wave functions, the length is the key. The reason is that we're timing that wave reflection to coincide with our air intake charge. The length directly determines the timing of that sound wave, and we can't get around that. So, we need to have the correct length if we want to get this effect.

[Blltrdr]

 I have the PWK. If you think about it there is plenty of room, look at the spacing from the head to the carb on a stock bike. Shouldn't be a problem with the PWK.

[ace.cafe]

I have the PWK. If you think about it there is plenty of room, look at the spacing from the head to the carb on a stock bike. Shouldn't be a problem with the PWK.

I can't think of any downsides to having it, then.

[ace.cafe]

Ace, your mod is very inexpensive and could be fun to tinker with for a while. But is there any way to test these tubes on the bike to generate some data to see if the effort is worthy? Maybe hook up a vacuum gauge and take some readings? Maybe add a fan to simulate a forced air condition, then compare it to stock figures and so on? Having data to prove the value of something is half the fun of the chase to improve something.

Well, we start off by doing some calculations.
Here are some of the basic formula calcs
Pulse in these calcs is the same as reflected wave.

Intake Tract Tuning for RPM = (1100 x Half Intake Cam Duration x 0.960)/Length = 2nd Pulse
(1100 x Half Intake Cam Duration x 0.705)/Length = 3rd Pulse
(1100 x Half Intake Cam Duration x 0.538)/Length = 4th Pulse

Intake Tract Tuning for Length = (1100 x Half Intake Cam Duration x 0.960)/RPM = 2nd Pulse
(1100 x Half Intake Cam Duration x 0.705)/RPM = 3rd Pulse
(1100 x Half Intake Cam Duration x 0.538)/RPM = 4th Pulse

The earlier pulses like 2nd pulse are strongest, and then get progressively weaker as they increase to 3rd pulse, 4th pulse, and so on.
Nascar tunes to 3rd pulse.

This gets you some intake tract lengths to look at for starting points, and the challenge is to try to find where you are going to put all that intake length once you figure out how long it's going to be. And it IS gonna be long. the lower the rpm that you target, the longer the tube must be. And they get real long at the low rpms that we're targeting.
So, then we just probably try to get 4th pulse if we can, and there's realy not enough room for anything that looks relatively "normal" for that length either, so we "could" just try for as long as we can fit. That's what I did.

I do have a full-length 4th pulse tube here that I'm going to strap on the bike and see what it gets me. Just to see. Just so you know what it is for a 4th pulse on the Bullet at 3500 rpms, the inlet tract(this length includes everything from the  back of the valve head all the way to the tube air inlet opening) is 22.3" for the half of 264 duration calc,

Anyway, our goal for the Bullet would be to tune the pipe for the torque peak, which is somwhere between 3250 rpm and 4000 rpm, depending on what the mods on your motor are. For a Bullet equipped with performance exhaust and 28mm Mikarb, it's probably going to be around 3500 rpms for torque peak. Larger carb will have higher torque peak.
The other kind of goal is to tune at higher rpm for the horsepower peak. That's a shorter pipe. But it's only good at your rpm at peak hp.
So, you make the call. I think boosting torque peak is better for us, because with higher torque peak, all the hp figures above torque peak also get boosted. Downside is a real long tube.

Cam duration for the intake cam on a Bullet is 264 degrees at .012" lash, or about 230 degrees at .040" lash(which is where the valve curtain is unshrouded). Some people design one way, and other people use the other figure. It's up to you.

So, that gets you somewhere in the neighborhood.
You can't use a flow bench for this, because we're not increasing flow. We're making wave tuning modifications to extend flow longer after BDC which doesn't show up on a static flow bench.
And unless you have a dyno, you have to use the "seat of the pants dyno".
If it's working, you'll know it, beause you'll have more torque, and everything above the torque peak(hp) will be stronger.

A fan won't help with anything. It's all based on engine filling during the intake period.
Vacuum gauge won't help anything either.

If you really want hard numbers, you have to do it on a dyno.


This is well-proven technology. All serious racers do it.
Most racers use high-revving engines, so their tubes don't need to be that long.
Our difficulties come from our low target rpms, and not having alot of room to put the tube. It can be curved gracefully with shallow radius curves, if that helps any.
I think we need to make a compromise between what we can get for length that fits into the appearance of the bike.
But, it's fun to experiment!

Any inlet length increase is going to be picking up some wave reflection at some rpm. It just depends on what it happens to be. 7" inlet tract, which is what we have from vavle to carb mouth, is too short for any wave pulse  to be strong enough to really do anything for us at our low rpm range. It's just too short. So, anything "could" possibly be a help at some rpm. The longer, the better. You'll run out of room to put the tube before you hit the optimal lengths. But it's worth a try to get something.
A BSA Gold Star racer I know uses a 15" length pipe on his Gold Star carb. With a big fat K&N filter on the end. He has a support bracket for it coming off his rear shock mount. It goes that far back!

Well, I tried the real long inlet tract extension today.
The full 4th pulse length of about 23", and I had to snake it around the side of the bike and it went back to the rear shock mounting bolt. Very long.

Took it out for a spin, and it apparently began to work at a slightly lower rpm than predicted, but not too far off. Around 3300 rpm.

And here's how I knew where it began to work.
I hit a spot where I couldn't accelerate any further. It got to 3300rpm(approx) and then it started coughing and sputtering because it was going lean.
Couldn't get it to go any faster.
So, then I put on the enrichment lever, and I was able to get a few hundred more rpms before sputtering again.

So, I need to re-jet richer in the main jet.
The effects of this mod are changing the air going into the engine sufficiently to require jetting-up richer on the main jet.
I'm going to order some bigger jets to test this thing further.