Proof of life! with a short video clip for verification...

[greg737]

Moved from Spokane to Denver almost a year ago, been pretty busy for most of that time. 

But today I got the GSF400 out for its first good ride in the Denver area (I've test-ridden it around my new neighborhood but no long rides until today).  Riding in Denver is very different from Spokane: In Spokane I had wonderful, twisty country roads available almost from my front door, but here in Denver it's a 20-30 minute ride to get a curvy road.  Also, the police presence is amped way up, you have to be careful around here.

But I enjoyed my ride, 100 miles total with some okay twisty canyon roads.  Probably would have been better if I'd gone out early in the morning but I didn't want to brave the colder temperatures.

Here's a 56 second-long video to celebrate getting the GSF out on the road again.
http://vid679.photobucket.com/albums/vv158/EWflyer/GSF400%20video%20library/GSF400%20in%20Colorado%20March%2017_zpsiparuopc.mp4

As other GSF400 owners have noted in the past, the Bandit does not like high altitudes.  Today I road up to a height of just under 8,000 feet and the Bandit's performance really fell off.  I've worked on its fueling with short rides around Denver but had never taken the bike any higher than that (for anyone who doesn't know, my GSF400 is a do-it-yourself Fuel Injection project).

[ventYl]

Hi Greg, glad to see that you managed to wake the bike up from winter sleep period.

Do you have any kind of altitute / ambient air pressure compensation attached to ECU? Also, is the third gauge lambda voltage? This looks pretty stable (wide-band?).

[greg737]

no, I don't have a constant baro correction hooked up to the Microsquirt ECU, it's an option that's very easy to add and implement with this system but I don't plan to do it because the problems are structural.  They're primarily caused by the B4's really small, fast-moving pistons trying to drag in a very thin atmosphere and they aren't something you can "tune" around without first making structural changes to the engine.  You would have to re-design the intake and exhaust of the bike because the B4's inability to breath at high altitude is simply an unavoidable manifestation of basic physics and is just part of a motorcycle that just wasn't designed to deal with those conditions.

Remember that these tiny-cylinder (100cc per) displacement bikes are really "sea level" designs.  The Suzuki engine designers gave us an airbox and intake system, valvetrain timing and the port-matching to the exhaust system all designed to function (to resonate properly) at sea level atmospheric pressure and density.

I'm pretty sure you could re-engineer the B4's engine for better operation at higher altitudes (would be more precise to say "at higher pressure altitudes/lower atmospheric densities").  This re-designed B4 would probably have a much smaller airbox, smaller intake valve diameter and smaller exhaust system diameter.

Proof/corroboration of the correctness of my analysis of the B4's high altitude performance problem can be found in the need for what is called "turbo normalization" in small, piston-engined aircraft.  Look up that term if you want more information/proof.

I understand that people always want to believe there's an across-the-board "one size fits all" solution to every problem, but in this case there's truly "no replacement for displacement" (from the old-school U.S.A. street-rod world of big-displacement engines).

[ventYl]

I am pretty much aware of small displacement to bore ratio problem at high altitudes. I personally didn't have a chance to experience it on my own as most probably the highest elevation I've ever been was somewhere around 1500 metres (roughly 4500 ft) above sea level. I was just curious if your problems were of standard nature or injection added additional issues.

Another little bit OT question which came up to my mind during reading the part about reasonance (and is haunting me for quite a time) is: I've read a lot about reasonant airboxes and stuff on how to perform a rough calculation of it. One particular note which almost every such article contains is: if you put foam inside the reasonator volume you will effectively cancel the reasonance. OEM GK75A/B airbox is equipped with foam-type filter. I expect that this filter effectively is cancelling the reasonance. I also know that 97-on B4s do have paper filters yet these are not exchangable with GK75s.

The only paper filter I know that exists for B4 is K&N which costs about $100 per unit. And probably has to be replaced every season. The question here is how much the foam filter affects airbox ability to reasonate or vice versa how big improvement paper filter would be? If any at all. I have one piece of that K&N filter on hand but it is of unknown age and state so I am not planning to try install it into my bike.

[greg737]

Forgot to answer one of your first questions: Yes, the third gauge is a wide-band O2 sensor readout (Innovate Motorsports LC-2)

[greg737]

Another little bit OT question which came up to my mind during reading the part about reasonance (and is haunting me for quite a time) is: I've read a lot about reasonant airboxes and stuff on how to perform a rough calculation of it. One particular note which almost every such article contains is: if you put foam inside the reasonator volume you will effectively cancel the reasonance. OEM GK75A/B airbox is equipped with foam-type filter. I expect that this filter effectively is cancelling the reasonance. I also know that 97-on B4s do have paper filters yet these are not exchangable with GK75s.

The only paper filter I know that exists for B4 is K&N which costs about $100 per unit. And probably has to be replaced every season. The question here is how much the foam filter affects airbox ability to reasonate or vice versa how big improvement paper filter would be? If any at all. I have one piece of that K&N filter on hand but it is of unknown age and state so I am not planning to try install it into my bike.

I've seen some pretty bizarre discussions of this subject (Resonance).  Like a lot of scientific issues, there's a lot of misunderstanding and crossed-up logic to be found on the internet (mostly in car and motorcycle enthusiast forums).  For example, I've seen a forum discussion thread run out to 3 or 4 pages of pure confusion before it was realized that the two main people posting on the thread were talking about 2 completely different types of resonance.  One guy was referring to resonant sound waves that an airbox tends to generate as an engine climbs up through its RPM range, and the other guy was referring to the physical nature of the airflow resonance (that difficult-to-engineer, complex, compounding fluid-dynamic of airflow that occurs when the volume+length of the intake tract perfectly matches and complements the open-closed-open-closed nature of a naturally aspirated engine's valvetrain).  The fact that these two items are interrelated was also adding to the confusion of an already very complex situation.

The design of the airbox (and other intake system parameters) of a naturally aspirated engine seems to exist at the border between Engineering Black Magic and Vehicle-Owner Wishful/Magical Thinking.  It's a zone where strange, under-informed, mis-informed thought processes are allowed (even encouraged) to run wild. 

On one hand, we all appreciate a good sounding engine (and to equate good sound with good performance) so we're inclined to install what is advertised as being a "less restrictive" air filter.  This less restrictive air filter probably allows more of the engine noise to escape from the air box which sounds good to the enthusiast's ear, but does this actually help or hurt the airflow resonance?  Quite often we really don't know the answer to this question, so we fall back on the old "more has to be better" argument that if the new filter "flows more air more easily" then it has to be an improvement. 

[ventYl]

Well ok, my background is electrical engineering and I am currently working in mechanical computation analysis field (how can EE work in that? he helps to develop it). So let's say I have quite good fundamental understanding what is one reasonance and what is the other.

I am talking about reasonant property of airbox which should ensure that at certain volumetric flow of air of certain density (e.g. certain engine RPM and load ratio) the airbox has the least resistance to air flow (classic property of reasonant circuit). With four valve-per-cylinder small displacement engines like are commonly used in bikes this point is set to be as close as valve overlap band-gap sits for that particular engine.

(I am not really interested in making more noise, I am okay with the amount it makes right now; actually if I hear that can is a lot more noisy than normal I know that something is wrong with my mixture)

Now; If you place foam into reasonant volume you will (partially) cancel this wave reasonance. This effect can be commonly observed in studios where foamy material is plated on walls to cancel reflections. Reasonance is effectively only wave "reflection" with least possible resistance.

So, given the fact that B4 is equipped with foam-type filter the question for me was how much this filter is affecting reasonance in the airbox. If it is even noticeable. Facelifted B4 model 97 onwards has paper filter insert too so naturally the question was if it helped mid-range power or the change was done for some other reason.

The reason why I mentioned K&N filter is that it is the only one I've found that has paper body and can be fitted into B4 airbox without doing mods. There are pod filters but these are mostly useful only if you want to make more noise and WOT power. Both mostly useless on the street. I also know that some K&N filters have quite poor performance in ISO filtering performance tests.

I also happen to have one piece of this filter I acquired with spare-parts bike. It is of unknown age which combined with their poor performance credit prevents me from mounting it into my bike. Another piece would cost me about $100 which is simply too much for learning that it has no effect (except of increased air-flow first few hundred kms which carbs need to be adjusted for). I am not seeking for ultimate cheapo power gainer. I am only trying to optimize / fix mid-range (without swapping cam / engine for 93-on type and/or VVT type which would probably not fit my frame).

The reason why I asked here is that you are probably one of very few people who did a fair amount of tuning on this engine for street and you had a chance to come across similar question and maybe to do some experimenting. Experience of circuit tuners are not usable here as they are usually tuning the engine for the most WOT power.

[Squishy]

Man your 400 sounds rough. Maybe it's just the exhaust....