Air Box and exhaust mod.

[FZ6771]

I really opened up the box this time, and it runs great!!!!!

 

[FZ6771]

I really opened up the box this time, and it runs great!!!!!

Excuse the First post....

 

[RJ2112]

Pic #1 is the 'after' shot, right? #2 shows the wrap on the pipe that replaced the cat?

Good work.

 

[Geoff]

I iz afraid to do the airbox mod, Im sure Surdyke Yamaha has a reason for its design.

 

[CrazyBiker]

Opening the airbox helps smoothening the throttle response as the stock snorkel really chokes the bike. It also reduces the engine braking a bit as a result - maybe good or bad for some.

 

[RJ2112]

I iz afraid to do the airbox mod, Im sure Surdyke Yamaha has a reason for its design.

The only reason I can think of, for that 'snorkle' is to prevent certain tones from exiting the bike via the intake.

I'm pretty sure it's a 'hi pass' filter, in the audio range.

This is a technique used in electronics.... where you have to have air flow through the shielding you use to keep all the EMI inside the box, you can use a tube to flow the air you need.

As long as the dimensions of the tube are controlled, and the length of the tube exceeds the wavelength you want to exclude.... air can flow, but the wavelengths you want to control, cannot. When the tube is long enough, the waveform cannot ricochet through it. Shorter stuff will with no problem.... but shorter wave lengths do not carry as much energy as longer ones do.

The thickness of the airbox has always been interesting to me...... you could keep the air filter clean with a thin sheet metal box, much like the air filter housings on old american cars...... so why the thick plastic? Why not thin plastic? Surely, the suction isn't so great as to collapse lighter materials..... if it were, the filter element would get sucked into the engine.

Thick plastic is a pretty good sound insulator.

Overall, you get about 1/3 of the total engine noise, 'backwards' out the intake. Intake 'honk'.

With the OEM airbox, that 'honk' is contained.

 

[Spideyrex]

There is an article that was posted (By Wavex I believe) from Cycle World that describes how airboxes are tuned to help out midrange power, resonating frequencies and so on. It basically said airboxes are designed for both sound and power enhacement. The thinkness of the plastic is probably a factor in making sure the are not unwanted vibrations as the air goes to the throttle bodies.

 

[FZ6771]

Pic #1 is the 'after' shot, right? #2 shows the wrap on the pipe that replaced the cat?

Good work.

Yes that's correct, when you get on the gas now there is a giant sucking sound! It probably wouldn't work well with a 100% stock FZ .

 

[RJ2112]

Yes that's correct, when you get on the gas now there is a giant sucking sound! It probably wouldn't work well with a 100% stock FZ .

With more of the restriction removed from the exhaust, the intake can now suck in more air.... opening the snorkel on the intake to the air box will further reduce the system's restriction.

If the designers wanted to flow more air, they could have increased the cross section of the snorkel, and probably have kept the intake 'honk' inside the air box.

 

[RJ2112]

There is an article that was posted (By Wavex I believe) from Cycle World that describes how airboxes are tuned to help out midrange power, resonating frequencies and so on. It basically said airboxes are designed for both sound and power enhacement. The thinkness of the plastic is probably a factor in making sure the are not unwanted vibrations as the air goes to the throttle bodies.

A resonant cavity is going to be formed by the 6 sides of the box, rather (or not so much) by the size of the holes going in and out..... acoustic guitars use a resonant cavity to make the sounds they do, same as most stringed instruments.

What 'tone' it resonates at, will compliment the airflow through the space at some range of airflow, and subtract at others..... given the amount of fiddling around the factory people have done, to keep the noise below the CA requirements (specifically, that 'dip' right at 1/2 peak RPM.... where the sound measurements are made) I don't think the 'resonance' is as critical as it's described to be.

The cat is a major resonance in the OEM system.... first big impedance change, after the engine. (Upstream, it's the air filter)

Removing that should have all sorts of negative repercussions on engine tune..... yet the HP plots I've seen all seem to indicate that the exact same profile is produced, except you gain a few HP all across the board.

That tells me the 'monkey business' of keeping the engine noise controlled is more important to the mfg than the best engine performance.

 

[Maverick]

I remember trying this mod on my RZ350 back in the day (with Spec II pipes). I remember thinking that the new loud intake honk was awesome... I then went to bigger carbs with individual K&Ns. Has anyone here seen a dyno plot with the drilled airbox on the FZ? I'm curious if the intake honk and "wanting more power" are supported by dyno time (not just the butt dyno).

 

[SANGER_A2]

Yes that's correct, when you get on the gas now there is a giant sucking sound! It probably wouldn't work well with a 100% stock FZ .

I love that loud sucking sound! I posted a youtube clip of my bike doing it somewhere on here recently. The main advantage in doing it in my eyes is that you get rid of the ****ing annoying whine noise the air being sucked through the snorkel makes. The Yamaha designers did something wrong there. The engine now sounds a bit noisier, but much lower pitched.

 

[RJ2112]

I remember trying this mod on my RZ350 back in the day (with Spec II pipes). I remember thinking that the new loud intake honk was awesome... I then went to bigger carbs with individual K&Ns. Has anyone here seen a dyno plot with the drilled airbox on the FZ? I'm curious if the intake honk and "wanting more power" are supported by dyno time (not just the butt dyno).

There's a series of plots showing the dyno runs with at least 6 different aftermarket mfg's cans, on the same FZ6.... the only one showing a noticeable change being the one that removed the cat from the system. All the other systems stayed within 1 HP of the OEM plot, as I recall. (maybe 2 HP.)

It's pretty reasonable to think that all those 'glass packs' are going to have some differences in design, that should in some way affect the overall tune of the exhaust..... but they don't. You take off that big auto style folded path muffler, and go to straight shot high flow glass packs, and there's no change in engine performance?

Taking the cat out, the rear wheel performance improved by 2-3 HP..... but the plot was otherwise nearly identical to the OEM setup.

I think that indicates the removal of the cat had more to do with increased performance than any of the 'cans did......

On that basis, I believe that opening up the air box is probably going to make a slight improvement in HP; probably less than the change made by the 'cat removal.

The guys who have added a PCIII or V to their bikes, and then dyno'd them... they'd see the actual change due to the most effective mapping for power, rather than the fiddling around to avoid the noise police.

Trying to correct for that dip centered on 6.5 K RPM, and the 'bounce' around 8K.... I don't think that's going to be corrected by cans, or intake mods.

 

[Bikebiz]

I'm planning a dyno run next week. My bike's engine and 'respiratory' system is completely stock right now.

I was hoping to have a 2nd airbox lid so I could instantly switch them, but to no avail (backorder at Yamaha is 2 weeks, please PM me if you have a spare one and are in Sydney).

Otherwise will do a dyno run with stock lid on the first day, remove the snorkel (inside and out) that night, then dyno again the next day. It should be close enough as back-to-back as I can get.

I can't see that anyone else has done a dyno comparison (surprisingly) without changing other variables at the same time. Hopefully this will put all question to rest.

Personally, I'm intruiged by all the turbulence theories circulating, but subscribe to the camp of it being irrelevant to our application. If power is unchanged then I'll leave the mod in place as I like the idea of an improved aural experience. Hopefully it's improved.

 

[Wolfman]

I got 3.5 more HP on the dyno after i modded my airbox (and the pipe, airfilter, fuel set up was identical, and both dyno reads were done by the same operator, on the same dyno)...

Have even thought of taking it away completely, and attaching pod filters to my velocity stacks!!! then getting the bike re-mapped again on the dyno..

:thumbup:

 

[Bikebiz]

Ah right, sorry, thought you changed the filter at the same time of the new read.

3.5hp, that's decent. It should be interesting to see if the same HP gain can be had in stock form, or whether having the other mods are what really exploits the intake mod.

I wonder about going for a wider opening. I remember when I had my DRZ that the aorbox mod was called the 3x3. You cut a 3" by 3" hole to remove the snorkel. A few gurus explained that this was the optimum opening. Going larger supposedly yielded no better results. 3x3 is certainly larger than simply the snorkel removal in our situation - have you expanded on that?

And now I'm wondering that, having an N, whether ram air could be experimented with.....?

 

[RJ2112]

I got 3.5 more HP on the dyno after i modded my airbox (and the pipe, airfilter, fuel set up was identical, and both dyno reads were done by the same operator, on the same dyno)...

Have even thought of taking it away completely, and attaching pod filters to my velocity stacks!!! then getting the bike re-mapped again on the dyno..

:thumbup:

So, after all the other mods were done, you cut open the air box? How much bigger is the hole into the box, compared to the previous dyno run?

I would think you could do the 'ultimate' run, just by taking the lid off the box, and running one run on the dyno without it...... that would be the least intake resistance you could expect......

 

[gusss]

I got 3.5 more HP on the dyno after i modded my airbox (and the pipe, airfilter, fuel set up was identical, and both dyno reads were done by the same operator, on the same dyno)...

Have even thought of taking it away completely, and attaching pod filters to my velocity stacks!!! then getting the bike re-mapped again on the dyno..

:thumbup:

how did you mod your air box?? what exactly did you do?
Can you please post some pics of the holes/hole?
Thanks

 

[Bikebiz]

I had some spare time today so have done my mod. Hopefully can find a stock one for my dyno comarison

Once off, I decided to go for a mild choppo. I left the outside as is, and just took the inner side of the 'snorkel' off. I can't imagine any further mod is required, and it means I retain the flanged edge on the outside.

Only started it briefly, haven't ridden yet. I cut it with a pneumatic air saw. Took me all of 30 secs. Then finished with a die grinder. Fingers crossed.

 

[Hellgate]

I would think you could do the 'ultimate' run, just by taking the lid off the box, and running one run on the dyno without it...... that would be the least intake resistance you could expect......

I've tried that on several vehicles (auto and bike) over the years and the net was zero. Remember that with an FI system you need the even pressure that the airbox provides for the system to work at peak performance, resistance typically isn't the issue. If the airbox is open you can loose charge velocity and charge traping capability. In modern bikes the airboxes a acoutically tuned to work with the overall engine package and are usually pretty good.