airbox lid modification

[Zaddict]

Looking at the airbox lid on my 550 I see the inlet holes are pretty tiny - maybe a square inch of opening on either side. I'm thinking about enlarging them, and maybe installing Thunder Products TPI valves for precise adjustment. I've got some mods that may benefit from the increased airflow, and the bike is running a bit rich right now (air/fuel is something like 12:1 across the rpm range). I wonder if anybody has tried similar airbox modifications. Seems like it would be a nice compromise between the increased airflow of pods and the benefits of having an airbox. Only potential downside I can see is that the velocity of air entering the airbox might decrease with larger openings in the lid. Still trying to source an airbox lid for the experiment...

[Freddy]

My only advice would be that if you are going to make any irreversible changes, make sure you have sourced a second hand replacement part in advance so you can 'undo' the change if it proves necessary.

I once removed the rubber noise damper that sits in the throat of the 750 intake, for exactly the same reason (ZR7 forum sprooking this as a good idea). Bike ran like a complete 'dog'. I'm not talking subtle small problems, I'm talking you noticed a major loss of power the instant you went to take of, and the bike would just piss and fart and not rev out past half revs. Virtually un-ridable, all because of some seemingly minor change to the intake system.

At least in that case I was simple able to refit the damper which sits in a white plastic cage held in by a screw. Bike actually ran better than before because in refitting it I replaced the soft rubber 'wrapping' that goes around the cage the damper sits in which had complete disintegrated due to age. In effect reducing the size of the opening (returning it back to original) and the bike ran marginally better.

P.S. Your bike runs 4 30mm Keihin carburettors, which draw air one at a time. The area of a 30mm opening is 707mm2. The area of single a 'square inch' is 645mm2. With two openings you have an intake area of something like 1290mm2 feeding a 707mm2 opening, that's at WOT. And be aware that drilling holes in the air-box will also change or complete eliminate the air-boxs resonate effect. It will remove its ability to force i.e 'supercharge', the excess air in the air-box into the 707mm2 carby openings. If you want to understand how it does this read up on Helmholtz Resonators. A modern airbox is a Helmholtz resonator.

[Zaddict]

Wow, yeah, amazing what a small change can affect. I am going to wait until I can source a new lid to try the experiment, so I can just put the old one back if it's a disaster.

[Freddy]

Just in case you missed the edit I made to my original post, see my calculations that 2 'square inch' openings are way bigger than any carburetor even at WOT. They only pull one at a time. Plus a correctly designed and working airbox can force something like 110% of air into a corburettor in the design range compared to even just velocity stacks.

And don't let anyone tell you carbies with pods breath better. THE most inefficient intake system is an open throat carburetor e.g. a pod filter stuck straight on the end of the carburetors. This has the intake air moving in a stop/start fashion as the inlet valve opens/closes, and due to inertia efficiency is lost as there is a lag between when the intake valve opens and air can be drawn into the cylinder. At times air is actually going back out the carby due to the exhaust return pressure wave arriving back into the cylinder coinciding with the inlet/exhaust valve open overlap (the main reason for a mid range bog).

They discovered all this about 60 years ago, hence the development of tuned velocity stacks to capture the inertia of moving air. The next development was the airbox which not only has velocity stacks built into its design, it improves performance again because of its resonant effect. Even MotoGP bikes and F1 cars run airboxes. An open throat carburetor i.e pod filters does not 'flow air better', the exact opposite is actually the case.

[Zaddict]

Thanks Freddy. I did miss the edits the first time. Good points. I was trying to understand why only one carb would be pulling in air at a time given that the pistons move up and down in pairs. This video helped --

https://www.youtube.com/watch?v=M1h9eU9YH5o

I don't plan on messing with the plenum at all, just the lid of the airbox cleaner housing. Using something like these TPI valves I should be make fine adjustments.

https://thunderproducts.com/product/tot ... tpi-valve/

[Freddy]

Just be aware that statements like the following from the Thunder Products web page is more internet forum 'myth' than scientific fact........

Racers and tuners as well as many trail riders have known for many years that opening up the air box in order to flow more air makes more horse power. This is usually called “ventilating” or “gutting” the air box.

Fact would be something like 'modern race engineers have for many years known the value of a well tuned air-box, and spend a lot of time designing intake sizes, snorkel length, and airbox sizes to place the performance boost from the airbox in the designated rev range'. For a race engine this will obviously be toward the upper rev range.

Fact would also be that the engineers designing a 'trail bike' will aim to place the performance boost from the airbox down relatively low in the rev range. Trail bikes aren't ridden at WOT, you want good 'ride-ability' and grunt from 1/4 to 1/2 throttle. The designer will spec out the airbox to give greatest benefit in this range. Yes, opening up the airbox when it has been designed for mid range performance may give some more top end HP, but at the expense of the way more important low/mid-range performance (because the intake boost provided by the airbox is no more). Nothing is for free (well other than all the increased induction noise the rider will assume means more power).

[Freddy]

Hi Zaddict,
A slight change of topic ......

I see from your posts that you have the the Nitron twin shocks on your bike. Did you get the R1's or R3's?

Fitted a set of R3's a few weeks back to see how they compared against the Wilbers I'd been running for the past few years. Have found them a bit tricky to really get firing and more 'fickle' and sensitive to adjustment than the Wilbers. Just got them working well, so happy to share some thoughts on setup if you want.

Freddy.

[Zaddict]

Hi Zaddict,
A slight change of topic ......

I see from your posts that you have the the Nitron twin shocks on your bike. Did you get the R1's or R3's?

Fitted a set of R3's a few weeks back to see how they compared against the Wilbers I'd been running for the past few years. Have found them a bit tricky to really get firing and more 'fickle' and sensitive to adjustment than the Wilbers. Just got them working well, so happy to share some thoughts on setup if you want.

Freddy.

I got the R3's. I didn't really like the way they came set up from the factory (even though they were theoretically tuned to my riding style and weight), and didn't have much success trying to dial them in myself.
Then I got them professionally adjusted during a track day and now I couldn't be more pleased. They feel plush yet precise - great control and comfortable and yet they communicate what's going on with the road well, if you know what I mean. Now I need to work on the front end -- I have progressive springs installed with adjustable spring preloaders but it's still not quite there. I'm thinking of installing cartridge emulators.

[Freddy]

Hi Zaddict,
A slight change of topic ......

I see from your posts that you have the the Nitron twin shocks on your bike. Did you get the R1's or R3's?

Fitted a set of R3's a few weeks back to see how they compared against the Wilbers I'd been running for the past few years. Have found them a bit tricky to really get firing and more 'fickle' and sensitive to adjustment than the Wilbers. Just got them working well, so happy to share some thoughts on setup if you want.

Freddy.

I got the R3's. I didn't really like the way they came set up from the factory (even though they were theoretically tuned to my riding style and weight), and didn't have much success trying to dial them in myself.
Then I got them professionally adjusted during a track day and now I couldn't be more pleased. They feel plush yet precise - great control and comfortable and yet they communicate what's going on with the road well, if you know what I mean. Now I need to work on the front end -- I have progressive springs installed with adjustable spring preloaders but it's still not quite there. I'm thinking of installing cartridge emulators.

Good to see you got the R3's working well. Agree they have both the rebound and compression damping set way to high for a shock specified as suitable for bad roads. Their idea of a 'bad road' seems to be a a billiard table smooth Autobahn.

Anyhow, easily correct, once I removed the stiction in the rear suspension suspension discussed in a separate thread. Near impossible to feel what was going on till that was fixed.

Regarding cartridge emulators, I have them fitted to the front. Just be aware they can be fiddly to really dial in, which means a messy job as you have to pull them out to do that. A lot of fork oil changing as it is the viscosity of the fork oil that controls rebound damping. An adjustment means heavier oil.

If you haven't already got a fork brace fitted, just do it. Best $100 you'll ever spend handling wise. Just be sure to get a 3 piece one so the distance between the forks can be fully adjusted, and any negatives you'll read about them is purely due to poor fitting. They do have to be put on precisely and with care so as not to introduce more stiction.

[Freddy]

Then I got them professionally adjusted during a track day and now I couldn't be more pleased. They feel plush yet precise - great control and comfortable and yet they communicate what's going on with the road well, if you know what I mean.

Just a further thought .... Don't be afraid to continue to experiment with slight adjustments from the current setting. That's the only way to be absolutely certain you've got them as good as your can for the range of conditions you ride and riding preference.

You have a solid base setting now. You can always return to this at any time you feel uncertain regarding any changes you've made. Just count the number of clicks in for the current settings for the rebound, hi and low speed damping settings, and write this down somewhere. Easy to return to those settings at any time.

Remember the first click back out from fully seated should be counted as Zero, not 1. It does matter. Count 10 clicks in, and then 10 back out starting with 1 and you'll be at a different setting to what you started (because you're starting position for counting in was also zero, not 1).

P.S. If I do have a gripe about the Nitrons it's how stiff the adjusters are to turn. Those tight small slow speed adjusters actually hurt my fingers. High speed compression is fine. The rebound is a bit tight, and this makes it difficult to turn being next to the hot exhaust on each side on a 750, plus a hot rear disk on the right hand side.