Drilling the airbox....is rejetting necessary?

[RED1978]

If you drill the airbox does this cause a jetting problem or will it
be ok with the originals?

Thanx

[James England]

Drilling the airbox allows air to enter it more easily, so it will weaken the mixture somewhat. I did something similar on my XJR1300 (removed snorkel, rain cover over airbox mouth, fitted free-flow air filter) and then I had it analysed on a Dynomometer last Monday. The mixture at higher throttle opening was on the weak side but no way dangerously so. The person who tested it does racing bikes etc and knows his stuff. He said that merely raising the main needle by one notch would richen it just enough, so I did that.

As you can see from this printout, my line (blue) is above the red dotted line (ideal mixture). He reckoned raising the main jet needle would richen it just enough and recommended NOT fitting a bigger main jet.... As you can see from the bottom part of the chart, the mixture is pretty constant, right up to 145mph. BTW, my bike has the OEM exhaust system.

I suspect that drilling your airbox and removing the snorkel will have much the same effect on your mixture as it did on mine.... maybe raise your main needle by a notch?



Here it is, compared to other XJR1300's that he'd tested. Mine's the blue one. He put the others on as a comparison,although he only took mine to 70mph, not 115mph like the two others. The top part of the chart doesn't really indicate anything accurate because of what gear he's in etc.:

[BA80]

So, what effect did it have on the engine other than leaning it out?

[James England]

So, what effect did it have on the engine other than leaning it out?

You mean removing the snorkel etc? It really made no noticeable difference to smoothness and the bike didn't have any problems whatsoever. I had it tested on the D/mometer just to check that I hadn't been a bit too clever and was risking leaning the mix to the point of burning a hole in the pistons or similar. I just wanted to ride safe in the knowledge that the engine is happy. He confirmed that point.....

Later that day, I raised the needles by a notch (by lowering the circlip on them). The engine felt a tiny bit easier when opening to full throttle from pilot jet levels. Nothing much but definitely there.

[RED1978]

removing snorkel sounds harsh

Awesome...

But if you completely remove the snorkel doesn't that cause the incomng air to bypass the filter element? I don't know what a free flow airfilter is.

I thought to just drill holes on the airbox bottom inside the filter element holding area that way the incoming air will still be filtered.....thought that was the purpose of the snorkel... to separate filtered air from non filtered inside the box.

[James England]

No. The snorkel just makes sure that the airbox takes air from just in front of the seat. It's the only source of air to the box, pre filter, apart from the tiny little drain hole under the airbox bottom (which has foam in it anyway). However, it's another hurdle for the air to get through on its journey to the cylinders and presumably causes turbulence, so removing it helps the engine 'breathe' better, as does drilling the airbox (in the right places, of course).

A free-flow filter is one with a cotton element, soaked very lightly in light oil. They filter well but allow more air to pass through than a paper element and they are also washable and good for 1,000,000 miles according to the manufacturer! (gotta be an estimate....) Here's one:

http://www.ebay.co.uk/itm/K-N-HIGH-F...item20c6573c87

Awesome...

But if you completely remove the snorkel doesn't that cause the incomng air to bypass the filter element? I don't know what a free flow airfilter is.

I thought to just drill holes on the airbox bottom inside the filter element holding area that way the incoming air will still be filtered.....thought that was the purpose of the snorkel... to separate filtered air from non filtered inside the box.

[crazy steve]

Some owners have cut down the snorkel to make getting the airbox in and out easier. You're right, you can't remove all of it or you'll draw unfiltered air. It really doesn't effect performance any. Even drilling the airbox won't gain you much....

You could try this.... http://www.xs11.com/forum/showthread...hlight=air+box

[James England]

you can't remove all of it or you'll draw unfiltered air.

How is that, Steve?

[RED1978]

The bottom of the snorkel

How is that, Steve?

The part of the snorkel inside the airbox separates the filered air from non-filtered air. I was going to completely remove it as well then I started looking at it and realized it's function. It's a wierd setup no doubt but it's a pretty sturdy airbox all things considered.....except maybe for the snorkel seems too small.

[motoman]

Drilling the airbox..........

...........is an exercise in futility, and distrupts velocity of airflow with more noise and no power gains. JMO, but to each their own...........

[sparks]

What were your net gains? Was there a measurable increase in either efficiency or horsepower? There is a difference between how well it can breath and how well it does breath.. My experience is with auto race engines and not motorcycles but I would guess that the principals are the same..Assuming that Yamaha had it dialed in fairly closely, I dont think you would get much gain without doing something with other parts of the induction system to take advantage of an increase in flow. (valve timing/cam profile, etc).. Of course, I could be just exposiing my ignorance.. Been wrong before.

Lee

[RED1978]

hmmm

...........is an exercise in futility, and distrupts velocity of airflow with more noise and no power gains. JMO, but to each their own...........

Hmm that's an interesting concept and probably true. But doesn't the velocity of the air change, slowing back down once inside the box? I didn't consider the noise change.

Air velocity through a passage is a function of the diameter of the passage ya know.

small diameter=fast air
large diameter = slow air

The density of the air changes as well. Through a small diameter passage air is rushing fast and it becomes a vacum, reducing the pressure and density of the air. The air actally get stretched apart as in a vacum.

[James England]

What were your net gains? Was there a measurable increase in either efficiency or horsepower? There is a difference between how well it can breath and how well it does breath.. My experience is with auto race engines and not motorcycles but I would guess that the principals are the same..Assuming that Yamaha had it dialed in fairly closely, I dont think you would get much gain without doing something with other parts of the induction system to take advantage of an increase in flow. (valve timing/cam profile, etc).. Of course, I could be just exposiing my ignorance.. Been wrong before.

Lee

Well, that and advancing the ignition 4 degrees gave the bike a measured 110bhp at the rear wheel, as opposed to Yamaha's 105bhp at the crank.....

I really don't think you can assume "that Yamaha had it dialed in fairly closely" actually. The XS1100, for example, launched in West Africa, was sold in all states of the USA, all countries in Europe, Australia, New Zealand, Norway, Finland, Denmark... and more. The OEM setup was a compromise to ensure that the bikes could roll off the production lines and meet varying emissions regulations, noise regulations and run on just about any quality of fuel...in all those locations, at various altitudes, without needing modifications when they unloaded them at the ports. So what they 'dialed' was something to get by everywhere but by no means the ideal setup for each location. eg the West generally has high quality fuel which means the ignition can be advanced, jet sizes, especially main needles, were compromised to meet strict emissions regs in some US states, exhaust systems choked up the engine etc... all of this can be rectified.

So, yes, I would agree, Yamaha dialed it in correctly for Yamaha but not for each bike. Increasing air flow, replacing a (comparatively) choking air filter, advancing ignition timing for consistently good fuel, removing turbulence creating things like small mouthed snorkels and the like, all these improve performance without any work done on the cams or valve timing. You can't really compare a standard production bike with a race machine, I think, because the race machines aren't compromised for global export to varying countries... quite the reverse, they are tuned to local parameters.

So, in the case of the XJR... Yamaha claim 105bhp at the crank. It's now producing an actual 110bhp at the rear wheel. And that's on a completely original machine with only 1800 miles on the clock (so effectively 'new). So, some minor tweaking by me (including Iridium plugs, I forgot those) has resulted in a significant power gain..... on a ready-dialed-in 'new' bike. I'd estimate an actual increase in BHP of 8-10%... if not slightly more. I'd say that is quite significant and it illustrates the inaccuracy of Yamaha's initial 'dailing' for this bike.

If I removed the OEM twin exhausts and replaced them with less 'choking' ones, the engine would breathe even more easily, without mods to other parts of the induction system. People have increased the actual bhp of this model to 125bhp. I've not done that because I like quiet bikes and I like the look of the OEM system.

[sparks]

Wow.. Actually your getting more than ten since the factory nr is at the crank. Did these changes move the peak power or was this an increase over the whole ropm spectrum? I had to spend a lot of time and effort to get ten percent on my engines, not to mention money. I dont supose you know how much of an improvement with only an initial timing change?

Lee

[James England]

Wow.. Actually your getting more than ten since the factory nr is at the crank. Did these changes move the peak power or was this an increase over the whole ropm spectrum? I had to spend a lot of time and effort to get ten percent on my engines, not to mention money. I dont supose you know how much of an improvement with only an initial timing change?

Lee

Hi Lee. The problem is that, at $60 a time, I couldn't afford to Dyno test the bike after each modification! I believe that improvements, however small, are worth doing because they all add up... "small drops fill the barrel" as they say!

If I had an XS1100 which I didn't want to maintain as completely original, I would fit the K&N air filter, remove the airbox snorkel, fit Iridium plugs, Dyna coils, remove the resistors from standard HT caps, replace the OEM HT leads with carbon-fibre silicone ones, fit a Dynojet stage 2 jet kit (which is meant to run with a non-OEM exhaust and OEM airbox with freeflow filter), replace the OEM exhaust system, if still on the bike, and possibly advance the ignition timing by up to 4 degrees depending on where it's at as standard (I don't know because I never tried it on the XS1100). Doing that lot is guaranteed to increase the BHP of the bike. Any one of those mods on its own would maybe not have such a great effect and would be therefore "hardly worth doing", as some people have pointed out (I agree) but, once you add them all up, you start gaining something worth having.

I really wish I'd had the bike Dyno tested before the mods!

People here in the UK that have achieved that measured 125bhp are gaining virtually 20% over the original setup. More, really, in that the BHP is measured at different points. And that's without any changes to valve timing or cam profiles or anything mechanical. Also, the bikes continue to run smoothly and tick over etc. Once you start messing with cams and putting high-lift ones in, it's a trade-off in terms of tickover smoothness etc.

According to the tester, the peak power is at the usual point... approx 5,000rpm. There's just more power at that point, rather than moving it. Without doubt, the bike is a LOT faster than pre-mods. It was noticeable immediately. The bike is as fast as I'm ever going to need it to go, so that's it now! No more mods until the pipes rot off (I'll have rotted off before then, methinks)